Protein, Gluconeogenesis, and Blood Sugar

Recently (for some conception of recent) we asked the question:
If You Eat Excess Protein, Does It Turn Into Excess Glucose?

One of the potentially confusing aspects of this question, is the difference between gluconeogenesis (GNG) — the creation of new glucose that didn’t exist before, and increases in blood sugar.
In response to our post, several people made comments that indicated an implicit assumption that changes in blood sugar can be used as a measurement of GNG, but as we will explain below, this is not the case.
However, it brought to our attention an important distinction.

There are several reasons people might care about excess GNG.
One we have already addressed:
It is not the case that GNG requires excess cortisol.

In terms of the effect of the glucose itself that results from GNG, there are two distinct concerns:

  • How does excess GNG affect blood sugar levels?
    Blood sugar levels are important because too much sugar in the blood at a given time can cause damage to cells&nbsp.
  • Does producing more glucose via GNG ultimately lead to either using more glucose for fuel, or storing it as fat?

So when people worry about protein causing excess GNG, what they are really worrying about is that protein will adversely affect their blood sugar levels, or that they are going to use more glucose for fuel than they intended, or that they will store it as unwanted fat.

While it would be interesting to understand the effect of eating excess protein on GNG, it doesn’t directly address those underlying questions, because there are many other mechanisms in play.
We want to know whether for ketogenic dieters eating excess protein adversely affects blood sugar levels, whether it leads to higher consumption of glucose for fuel, and whether it increases the tendency to store fat.

In this article, we will directly approach the first of these questions.

In Brief:

  • Because the level of sugar in your blood depends on how much is coming in (and there is more than one source), and how much is going out, changes in blood sugar cannot by themselves tell us about the rate of GNG.
  • Nonetheless, when we wrote the original article suggesting that eating excess protein was unlikely to result in an increased rate of GNG, one of the assumptions we made was that eating protein does not raise blood sugar.
    We made this assumption because it is true in non-diabetic, non-ketogenic dieters.
    However, we have recently learned that this is not true in ketogenic dieters.
  • In response to protein, blood sugar rises on a keto diet, even though I/G — the ratio of insulin to glucagon, stays constant, whereas on a glycolytic diet, I/G rises, but blood sugar stays constant.
    There is evidence that I/G is tightly correlated with glucose production, so this is suggestive that in keto dieters glucose production is not affected by eating protein.
    However, we lack direct experimental evidence.
  • Although blood sugar rises in keto dieters eating protein, it stays within safe bounds, at least in our experience, and in the experiment we looked at.

What affects blood sugar?

Fundamentally, the amount of sugar in the blood at any given time depends on two things: how much is coming in, and how much is going out.
On the input side, blood sugar can come from three sources:

  • We can eat carbohydrates, and have sugar enter the blood through digestion.
  • We can make glucose out of glycogen (the limited amount of glucose stored in persistent form in the liver).
    This process is called glycogenolysis.
  • Thirdly, we can produce new glucose by GNG.

Note that because of glycogen storage, it is possible for sugar to enter the blood that has not come directly from GNG.
Even on a keto diet, there is still a substantial proportion of glucose production from glycogenolysis.
Ultimately, of course, the glycogen in keto dieters also comes from GNG that happened previously.

On the outgoing side, the rate of sugar leaving the blood can also change depending on the uptake by cells.
It can be used for fuel, stored as fat, or turned into glycogen for storage (glycogenesis).

This means that changes in blood sugar can happen in either direction, without us being able to conclude anything about the rate of GNG.
Therefore, observations about increases in blood sugar in response to protein are not conclusive evidence about GNG.

The effect of protein on blood sugar

It is well established that under typical test conditions protein ingestion does not significantly effect blood sugar levels, either alone&nbsp¹ or in combination with other foods&nbsp².
This graph shows the typical response to glucose (solid line) and protein (dashed line) ingestion in two non-diabetics after an overnight fast&nbsp³:

Of course, the “typical conditions” in those experiments did not include keto dieters.

However, there was an experiment in 1971 that did test the blood glucose response to protein in people who had restricted carbohydrates to ketogenic levels for one week, and compared it to the values after reintroducing carbohydrates for a week&nbsp.
The group size was small, and the keto-adaptation time was short, but nonetheless, the results showed that blood glucose did in fact rise in the keto dieters ingesting protein.
The experimenters also measured the blood levels of the blood sugar regulating hormones insulin and glucagon and their ratio, I/G.

There is evidence that it is I/G, and not the absolute levels of either hormone, that ultimately regulates glucose production&nbsp,,,.

Interestingly, in the keto dieters, although the levels of these hormones significantly changed, their ratio did not.

Here is a summary of the results:

Diet type Fasting After Protein
glucose insulin glucagon I/G molar ratio glucose insulin glucagon I/G molar ratio
Ketogenic 78 +/- 3 8 +/- 2 128 +/- 17 1.7 +/- 0.3 90 +/- 3 15 +/- 4 218 +/- 10 1.83 +/- 0.4
Glycolytic 94 +/- 5 17 +/- 4 87 +/- 15 4.35 +/- 1.38 “baseline or lower” 28 +/- 14 167 +/- 13 8.2 +/- 4.66

In response to protein, blood sugar rises on a keto diet, even though I/G stays constant, whereas on a glycolytic diet, I/G rises, but blood sugar stays constant.

Because the number of subjects was small, the authors emphasize that this study cannot give us precise estimates of the numerical values of blood sugar (or hormones) in response to protein.
It can only tell us that this rise in blood sugar happens qualitatively.
In other words, they’ve shown that a rise in blood sugar happens, but we can’t be sure that the average rise is going to be 10 mg/dL if we tested a lot more people.

It is important to understand that this is not a very complete picture.
For example, it doesn’t show whether there is a relationship between how much protein is eaten and blood sugar.
It could be, for example, that any amount of protein results in the same increase in blood sugar.
It could be that protein ingestion results in a small rise in blood sugar with a duration that depends on the amount of protein.
It could be that eating protein on a keto diet causes your blood sugar to rise steadily according to the amount of protein eaten until it reaches some maximum value, such as a 20 point rise, after which no further amount of protein has an effect.
What is very unlikely is that the amount of protein has an unlimited effect: we would not expect, for example that if eating 50g of protein caused a 10 point rise, then eating 300g of protein would cause a 60 point rise.
There is still a lot to learn here.







Note: Incidentally, these experiments would be easy for any of us to do at home. For example, you could get up after an overnight fast and measure your blood sugar.
Then ingest 25g of protein, and measure your blood sugar every half hour until it returns to baseline to see how your blood sugar changes and for how long.
Do that for three days, and then try it with 50g for three days.
Then try 100g and then 200g.
Use the same kind of protein in each case, like lean beef or egg whites (save the yolks for later!).
Tell us what you find out.

One important conclusion from all of this, though, is that, at least at these protein levels, blood sugar stays in a safe range&nbsp.
There is good reason to be concerned about the level of sugar in your blood over the long term.
We will write more about that in subsequent posts.
For now we can simply note that the fasting level of blood sugar in this experiment was at the low end of the range considered optimal, and the rise in response to protein was well below the amount considered dangerous.

Acknowledgements:

This article was most spurred by a comment on the original article by Anna K. Thank you, Anna.

Once again, we are indebted to friendly correspondents for access to relevant scientific papers.
This article was supported by friends in Windy City, Orlando, and Edinburgh.
We couldn’t have written it without you!

References:

Evidence type: summary of experiments


Campos C.
Chronic hyperglycemia and glucose toxicity: pathology and clinical sequelae.
Postgrad Med. 2012 Nov;124(6):90-7. doi: 10.3810/pgm.2012.11.2615.

(Emphasis ours)

Abstract

Type 2 diabetes mellitus (DM) is a progressive disease characterized by elevated plasma glucose levels. Type 2 DM results from a combination of factors affecting both peripheral tissue insulin sensitivity and β-cell function. A survey of the scientific literature on DM, glucose toxicity, hyperglycemia, nephropathy, neuropathy, reactive oxygen species, and retinopathy cited on PubMed/Medline from January 1975 to May 2011 was conducted. The relevant publications, chosen at the author’s discretion, were used to synthesize this narrative review article. Chronic hyperglycemia imposes damage (glucose toxicity) on a number of cell types and is strongly correlated with the myriad of DM-related complications. Tissues most vulnerable to the effects of prolonged elevated plasma glucose levels include pancreatic β cells and vascular endothelial cells. The ensuing β-cell dysfunction promotes decreased insulin synthesis and secretion, further perpetuating the associated hyperglycemia. As for the vascular endothelium, chronic hyperglycemia is strongly correlated with many DM-related microvascular complications, including retinopathy, nephropathy, and neuropathy. The role of hyperglycemia in macrovascular complications is not well defined. Pathophysiologic modifications that arise in response to chronic hyperglycemia persist and may promote DM-related complications that manifest years later, even if plasma glucose levels have been brought under control. Increasing awareness of the mechanisms by which even modest hyperglycemia promotes long-lasting tissue damage highlights the need to achieve early tight glycemic control in patients with DM before substantial disease progression.

¹ Evidence type: review of experiments


Franz MJ.
Protein: metabolism and effect on blood glucose levels.
Diabetes Educ. 1997 Nov-Dec;23(6):643-6, 648, 650-1.

“Protein has a minimal effect on blood glucose levels with adequate insulin. However, with insulin deficiency, gluconeogenesis proceeds rapidly and contributes to an elevated blood glucose level. With adequate insulin, the blood glucose response in persons with diabetes would be expected to be similar to the blood glucose response in persons without diabetes. The reason why protein does not increase blood glucose levels is unclear. Several possibilities might explain the response: a slow conversion of protein to glucose, less protein being converted to glucose and released than previously thought, glucose from protein being incorporated into hepatic glycogen stores but not increasing the rate of hepatic glucose release, or because the process of gluconeogenesis from protein occurs over a period of hours and glucose can be disposed of if presented for utilization slowly and evenly over a long time period.”

² Evidence type: experiment


José Galgani, Carolina Aguirre and Erik Díaz.
Acute effect of meal glycemic index and glycemic load on blood glucose and insulin responses in humans
Nutrition Journal 2006, 5:22 doi:10.1186/1475-2891-5-22

“When mixed meals are consumed, other food and macronutrients will be present. In this study, the results were similar to those observed in studies using isolated carbohydrates [6] and imply that other macronutrients had a negligible effect on the differential serum glucose and insulin responses. It has, in fact, been reported elsewhere that the amount and type of carbohydrate account for about 90% of the total variability in blood glucose response, whereas protein and fat in mixed meals scarcely contribute to the variance in blood glucose and insulin responses [1,2].”

³ Evidence type: experiment


Jerome W. Conn and L. H. Newburgh
THE GLYCEMIC RESPONSE TO ISOGLUCOGENIC QUANTITIES OF PROTEIN AND CARBOHYDRATE
J Clin Invest. 1936;15(6):665–671. doi:10.1172/JCI100818.

Evidence type: experiment


Walter A. Muller, M.D., Gerald R. Faloona, Ph.D., and Roger H. Unger, M.D.
The Influence of the Antecedent Diet upon Glucagon and Insulin Secretion.
N Engl J Med 1971; 285:1450-1454December 23, 1971DOI: 10.1056/NEJM197112232852603

Evidence type: experiment (non-human animal)


H.J. Seitz,
M.J. Müller,
W. Krone,
W. Tarnowski
Coordinate control of intermediary metabolism in rat liver by the insulin/glucagon ratio during starvation and after glucose refeeding: Regulatory significance of long-chain acyl-CoA and cyclic AMP.
Archives of Biochemistry and Biophysics.
Volume 183, Issue 2, October 1977, Pages 647–663

(Emphasis ours)

Abstract

The levels of serum insulin, glucagon, and free fatty acids (FFA) and the tissue concentrations of hepatic cyclic AMP, long-chain acyl-CoA (LCA), adenine nucleotides, inorganic phosphate, the intermediates of the Embden-Meyerhof pathway, the citric acid cycle (including acetyl-CoA and free CoA), and the cytoplasmic and mitochondrial redox couples were determined in the rat 12, 24, and 48 h after food withdrawal and 5, 10, 20, 40, 60, and 120 min after the refeeding of glucose. Using the measured metabolite contents in the liver, the alterations in the concentration of malate, oxaloacetate, citrate, and α-ketoglutarate and the changes in the energy state of the adenine nucleotide system and the redox state of the NAD system were attributed to the cytoplasmic and mitochondrial compartments by applying established calculation methods. Glucose refeeding provoked significant alterations in all parameters investigated. These changes occurred within minutes, reversing the hormone and metabolite pattern which had developed within 24 h in response to food withdrawal. Particularly, glucose refeeding resulted in a drastic increase in the insulin/glucagon ratio. Simultaneously, the level of serum FFA and the concentration of LCA in the liver declined. The latter alteration was accompanied by an increase in the cytoplasmic and a decrease in the mitochondrial ATP/ADP x P ratios. Moreover, the redox state of the cytoplasmic NAD system was shifted toward the oxidized state. When the appropriate data were plotted against each other, highly significant correlations were obtained (i) between the insulin/glucagon ratio and the serum FFA concentration, (ii) between the serum FFA concentration and the concentration of hepatic LCA, (iii) between the hepatic LCA concentration and the cytoplasmic energy state, and (iv) between the cytoplasmic energy state and the redox state of the cytoplasmic NAD system. These findings are interpreted to support the hypothesis derived from experiments carried out in vitro that the insulin/glucagon ratio via the FFA-dependent concentration of hepatic LCA might affect the translocation of adenine nucleotides between the cytoplasmic and the mitochondrial compartment, thereby regulating the cytoplasmic energy state and the redox state of the cytoplasmic NAD system, consequently. Glucose refeeding provoked rapid coordinate changes in the concentration of the intermediates of both the citric acid cycle and the Embden-Meyerhof chain, indicating the altered substrate flow through these pathways. Those metabolites, known to modulate the activity of key regulatory enzymes in vitro, were analyzed with respect to their suggested regulatory function. As to the established shift from pyruvate carboxylation to pyruvate decarboxylation after glucose refeeding, the data revealed that the decrease in pyruvate carboxylase activity can be attributed to the decrease in the intramitochondrial ATP/ADP ratio and the simultaneous fall in acetyl-CoA concentration, while the coordinate increase in pyruvate dehydrogenase activity can be ascribed to the decline in the concentration of LCA and, consequently, in the ratios of ATP/ADP , NADH/NAD, and acetyl-CoA/CoA within the mitochondria. As for the citric acid cycle, increased citrate synthesis from acetyl-CoA and oxaloacetate was supported by the rapid drop in the concentration of the established inhibitor of citrate synthesis, LCA. In contrast, the concentration of succinyl-CoA, an inhibitor of the enzyme in vitro, remained practically constant, questioning its regulatory function under the present experimental conditions. In addition to the activation of citrate synthase, the coordinate activation of isocitrate dehydrogenase was indicated by the LCA-mediated decline in both the mitochondrial ATP/ADP and the NADH/NAD ratios. Glucose refeeding immediately reduced urea excretion to basal values. This alteration was preceded by a drastic fall in the tissue concentration of cyclic AMP, supporting the physiological role of the nucleotide in the control of hepatic gluconeogenesis. In contrast, the observed changes in the concentration of the effectory acting metabolites (ATP, AMP, fructose 1,6-diphosphate, citrate, and alanine) were incompatible with the suggested function of these intermediates in switching over the substrate flow through the Embden-Meyerhof pathway from gluconeogenesis to glycolysis. The results are discussed in reference to the known rapid stimulation of fatty acid biosynthesis in the liver and to the transfer of reducing equivalents by the different shuttles of the inner mitochondrial membrane. In summary, it can be concluded that the insulin/glucagon ratio in a moment-to-moment fashion controls the glucose balance across the liver by regulating hepatic intermediary metabolism via the concentration of both LCA and cyclic AMP.

Evidence type: experiment (non-human animal)


Peret J, Foustock S, Chanez M, Bois-Joyeux B, Assan R.
Plasma glucagon and insulin concentrations and hepatic phosphoenolpyruvate carboxykinase and pyruvate kinase activities during and upon adaptation of rats to a high protein diet.
J Nutr. 1981 Jul;111(7):1173-84.

(Emphasis ours)

Abstract

Plasma hormones, glucose and free fatty acids, liver glycogen and two key enzymes of glycolysis and gluconeogenesis were examined in adult rats during a 40-day period of high protein feeding. Plasma insulin fell within 1 day but returned to normal after 4 days. Glucagon changed more slowly, reaching a maximum on day 4 and declined to near the control value within 24 days. Consequently, the insulin to glucagon ratio was lower on days 1, 4 and 8 and was nearly normal on day 24. With respect to hepatic enzymes, phosphoenolpyruvate carboxykinase activity rose sharply on the 1st day and remained elevated for 40-day period; the L-isozyme of pyruvate kinase, although unchanged on the 1st day, decreased thereafter and from day 8 on represented 15–20% of control. Circadian variations in these parameters were also measured in rats adapted to the high protein diet. In such animals, the diurnal change in plasma hormones was less marked but tended to be inverted with respect to controls; the insulin/glucagon ratio was highest during daylight on high protein and in late night on the control diet. Over 24 hours, pyruvate kinase activity was related directly and phosphoenolpyruvate carboxykinase inversely to the hormone ratio. We concluded that in rats adapted to high protein, as in controls, the diurnal balance between glycolysis and gluconeogenesis is probably regulated by the same factor, namely the insulin/glucagon ratio.

Evidence type: authority


Eric C. Westman, John Mavropoulos, William S. Yancy and Jeff S. Volek
A review of low-carbohydrate ketogenic diets.
Current Atherosclerosis Reports
Volume 5, Number 6 (2003), 476-483, DOI: 10.1007/s11883-003-0038-6

The insulin/glucagon (I/G) ratio is a key determinant of lipolysis, glycogenolysis, and gluconeogenesis [14,15].

(We followed the references given for this assertion, and did not understand how they supported it, so we consider this evidence as authority-based, at least for us.)

Evidence type: in vitro experiment


S.R. Wagle.
Interrelationship of insulin and glucagon ratios on carbohydrate metabolism in isolated hepatocytes containing high glycogen.
Biochemical and Biophysical Research Communications.
Volume 67, Issue 3, 1 December 1975, Pages 1019–1027

Abstract

The effect of physiological concentrations of glucagon and insulin on glycogenolysis was studied in the presence and absence of substrates in isolated hepatocytes containing high glycogen. In the absence of substrates glucagon stimulated glycogenolysis at 10−14M concentration, and addition of 100 μunits of insulin partially inhibited glucagon stimulated glycogenolysis (10−14M to 10−11M). However, in the presence of substrates, insulin completely inhibited glucagon stimulated glycogenolysis (10−14M to 10−11M), indicating that molar glucagon and insulin ratios control carbohydrate metabolism in liver. Additional studies showed incorporation of amino acid into protein was linear for only 3 to 4 hr in cells containing low glycogen, whereas in cells containing high glycogen, incorporation was linear for 8 to 10 hr.

Evidence type: authority


Postprandial Blood Glucose.
doi: 10.2337/diacare.24.4.775 Diabetes Care April 2001 vol. 24 no. 4 775-778

Dissatisfying as it is, for now we will talk about safe as meaning not identified as correlating with current or subsequent development of diabetes.
We will talk more about blood sugar in a subsequent post.

(Emphasis ours)

The word postprandial means after a meal; therefore, PPG concentrations refer to plasma glucose concentrations after eating. Many factors determine the PPG profile. In nondiabetic individuals, fasting plasma glucose concentrations (i.e., following an overnight 8- to 10-h fast) generally range from 70 to 110 mg/dl. Glucose concentrations begin to rise ∼10 min after the start of a meal as a result of the absorption of dietary carbohydrates. The PPG profile is determined by carbohydrate absorption, insulin and glucagon secretion, and their coordinated effects on glucose metabolism in the liver and peripheral tissues.

The magnitude and time of the peak plasma glucose concentration depend on a variety of factors, including the timing, quantity, and composition of the meal. In nondiabetic individuals, plasma glucose concentrations peak ∼60 min after the start of a meal, rarely exceed 140 mg/dl, and return to preprandial levels within 2–3 h. Even though glucose concentrations have returned to preprandial levels by 3 h, absorption of the ingested carbohydrate continues for at least 5–6 h after a meal.

We were talking about gluconeogenesis, not ketogenesis.

Our last post described the evidence that the rate of gluconeogenesis (GNG) is stable under a variety of metabolic conditions.
We also described several experiments in which large amounts of protein were ingested or infused and did not increase the rate.
We concluded that eating more protein than your body needs probably doesn’t increase GNG.

Many of our readers expressed confusion about the implications of this finding, and our purpose in posting it.

The reason we investigated this was to address the following concern. One of the reasons keto dieters want to minimize the amount of carbohydrate they eat is so that their bodies don’t have to deal with excess glucose in the blood.
Whenever we ingest carbohydrate, it becomes sugar in the blood&nbsp¹.
Since blood sugar must be kept within a narrow range for safety&nbsp², eating carbs then causes the body to release insulin in order to draw sugar quickly and safely out of the blood and into storage (as fat tissue)&nbsp³.

In our opinion, the ideal situation is to introduce no significant amount of sugar into the blood by eating, and instead allow the body to supply the blood with just the amount of glucose it needs by producing it at a slow and steady rate through GNG.
This is achieved by keto dieters who carefully count any carbohydrates they eat, with the goal of keeping them below a certain level, for example, 25g per day.

Because some people have said that when you eat protein above basic requirements it turns into sugar, the question some dieters have is whether they need to count excess protein toward their carb counts&nbsp.
They want to know if eating an extra 30 grams of protein means that they have added some 20 grams of sugar into their bloodstreams that now has to be dealt with just as if they had eaten 20 more grams of carbohydrate.
This is the conclusion we were setting out to deny.
Protein you eat in excess of your needs does not become extra blood sugar, unless you are severely diabetic.

However, this does not mean that eating too much protein has no adverse effects, or that keto dieters should be unconcerned about excess protein intake!
In particular, there is another important reason that keto dieters minimize the carbohydrate they eat — to increase the levels of ketones in the blood.
So a second question, and one that we did not address in the last post, is whether excess protein inhibits ketogenesis, the production of ketone bodies.
In contrast to the situation with gluconeogenesis, we suspect protein does inhibit ketogenesis.
If so, that’s a valid reason for not eating more than you need.

References:

¹ Evidence type: authority


Marks’ Basic Medical Biochemistry: A Clinical Approach. Michael
A. Lieberman, Allan Marks. Lippincott Williams & Wilkins, Apr 21, 2008.
p. 479

The major carbohydrates of the diet (starch, lactose, and sucrose) are digested to produce monosaccharides (glucose, fructose, and galactose), which enter the blood.

² Evidence type: authority


Marks’ Basic Medical Biochemistry: A Clinical Approach. Michael
A. Lieberman, Allan Marks. Lippincott Williams & Wilkins, Apr 21, 2008.
p. 483

(Emphasis in original)

[I]nsulin and glucagon maintain blood glucose levels near 80 to 100 mg/dL, (90 mg/dL is the same as 5mM), despite the fact that carbohydrate intake varies considerably over the course of the day.

³ Evidence type: authority


Human Biochemistry and Disease. Gerald Litwack. Academic Press, Jan 4,
2008. p. 583

The anabolic effects of released insulin, after glucose is sensed by glucoreceptors of beta cells, are to cause the uptake of glucose and amino acids from the blood into muscle, and the uptake of glucose from the blood to form triglycerides in fat cells.

Evidence type: observation


Protein turns into glucose if you eat too much?!!

So I am trying to research a bit over the interwebs about just how much protein is to much and at what point your body will convert protein into glucose but there are so many different opinions on this… *pulls her hair out* This is where i think Calories in vs. calories out makes more sense… what yall think?

Is there a rule of thumb to what the bodies tipping point is for when it will convert protein into glucose?


How much protein can you eat before it turns to glucose?

muffin_maiden: I’ve read before that eating too much protein at once can cause it to turn to glucose, but how much protein can you eat before that happens?
I tend to eat two larger meals (or one big one) during the day with between 10 and 16 ounces of protein at a time.
Would that amount turn to glucose or are we talking that you’d have to eat a LOT of meat before that happens?

[…]

redtoile: Thanks for this post. I worry about this all the time.

[…]

CarolynF: According to Dr. Atkins, it is around 52 percent of protein gets converted to glucose.

So, if you overeat protein at each meal, it will act like carbs.

If You Eat Excess Protein, Does It Turn Into Excess Glucose?

Gluconeogenesis is Demand-Driven, not Supply-Driven

We have seen the claim that any protein you eat in excess of your immediate needs will be turned into glucose by spontaneous gluconeogenesis ¹.
(Gluconeogenesis (GNG) is the process by which glucose is made out of protein in the liver and kidneys.) Some people think that because protein can be turned into glucose, it will, once other needs are taken care of, and that therefore keto dieters should be careful not to eat too much protein.

While we believe there are valid reasons for limiting protein intake, experimental evidence does not support this one.
In our opinion, it makes sense physiologically for GNG to be a demand-driven rather than supply-driven process, because of the need to keep blood glucose within tight bounds.

In brief

  • Gluconeogenesis is a slow process and the rate doesn’t change much even under a wide range of conditions.
  • The hypothesis that the rate of gluconeogenesis is primarily regulated by the amount of available material, e.g. amino acids, has not been supported by experiment.
    Having insufficient material available for gluconeogenesis will obviously limit the rate, but in the experiments we reviewed, having excess material did not increase the rate.
  • We haven’t found any solid evidence to support the idea that excess protein is turned into glucose.
  • More experiments are needed to confirm that this still holds true in keto dieters.

Gluconeogenesis has a Stable Rate

Gluconeogenesis (GNG) is a carefully regulated process for increasing blood sugar.
It is stimulated by different hormones, including glucagon — the primary hormone responsible for preventing low blood sugar.
GNG produces glucose slowly and evenly ².
It was once thought that the main determination of the rate of GNG was how much glucogenic substrate, that is, raw materials for it, was available, but further experiments have shown that this is not the case ³.
Instead, it now appears that GNG is relatively constant over a large variety of conditions .

As an example of this stability, a study by Bisschop et al.
in 2000  showed that subjects following a keto diet for 11 days had only a small (14%) increase in glucose production from GNG after overnight fasting, as shown in this graph.
This works out to a difference of less than a gram of glucose per hour.

Note that 11 days might be too little time for all of the subjects to keto-adapt, and it is possible that the rate of GNG would change in subsequent weeks.

Negative Results

In another experiment (this time in subjects on a glycolytic, or carb-based, rather than a ketogenic diet), ingesting 50g of protein resulted in the same amount of glucose production as drinking water .
In other words, the amount of glucose that was made after ingesting that protein wasn’t any more than would have been produced without it.
While it’s possible that this protein doesn’t count as “excess”, it was likely to be nearly half of their daily required protein intake, and eaten in one sitting, and so it is enough to cast serious doubt on the idea.

There are other experiments in which increasing the available material for GNG to high levels didn’t increase GNG ³.
In these experiments GNG substrates were infused directly into the blood rather than eaten.

The problem with applying the results of these experiments to the question of excess protein consumption is that infusion might bypass some mechanism that increases GNG when the protein is actually eaten.
For instance, it is known that protein consumption stimulates a great deal of glucagon (along with insulin) , and it might be suggested that this glucagon would thereby increase GNG.
A counterargument to that possibility is that although glucagon stimulates GNG in many conditions, its action appears to always be overridden by insulin .
This means that the insulin that is produced when eating protein will counteract the glucagon and GNG will not be affected (except in the case of insulin-dependent diabetes, where insulin is neither created nor responded to in the normal fashion).

Both the argument from infused substrates and the counter-arguments outlined here are plausible mechanism arguments — taking physiological processes known to occur in one context and arguing that they will occur in another context.
Plausible mechanism arguments should be used with caution.

Summary

In sum, then, there is no evidence that we could find that consuming excess protein will increase glucose production from GNG.
On the other hand, there is much suggestive evidence that it does not.

Further experiments need to be carried out to answer the question completely.
In particular, we would like to see a comparison of the rate of GNG in keto-adapted dieters consuming no protein, adequate protein, or a large quantity of protein, with and without dietary fat.

Follow-up posts

For clarification and further discussion of this topic, please see:

References

(We owe a debt of gratitude to a special friend from Windy City for helping us access full texts, as our previous access has expired.
Thank you!)

¹ Evidence type: observation
Please note
We have cited some people here as making what we believe to be an unsupported assertion.
This does not imply any disrespect for the authors!
To the contrary, we believe that writers such as these contribute to scientific knowledge even when they make mistakes.
By writing specific and falsifiable statements and by posting them publicly where others can cite them, they give others a chance to learn from both their accurate statements and their mistakes.

We, too are fallible, and we expect that errors of our own will come to light sooner or later; such is the nature of science.
There is no shame in this, and we intend none.
Please see Apologia for our philosophy about this.

Scientific progress is made in large part through discovering errors and correcting them.
We sincerely hope that those we have quoted will be glad to either learn from this post, or conversely, to point out to us where we have erred.
In either case, an issue that was obscure will have been clarified for everyone.

Nora Gedgaudas

Also, keep in mind that a significant percentage of protein consumed that is in excess of what you actually need for your daily maintenance and repair will convert to sugar and get used exactly the same way.

Mark Sisson

As I’ve said before, I’m trying to minimize my use of glucose, whether exogenous or endogenously produced.
If I’m eating so much protein that the excess is being converted to glucose, I’m not really minimizing it, am I?

Eric Westman in an interview with Jimmy Moore

34:37

JM: Well, and I would think that if you’re sensitive to carbohydrate then you would be sensitive to eating too much protein as well, because you want to stave off the effects of gluconeogenesis from happening, which would provide too much glucose in your body, tantamount to eating a lot of carbs.

EW: That’s a good point, that some of the protein that we eat can be turned into the glucose through gluconeogenesis, and that may be a reason why someone is not able to get to ketosis — that too much protein is being converted to glucose.

(Update 2012-08-21)

The Rosedale Diet, p82.

When you eat more protein than your body needs to replace and repair body parts, excess protein is largely converted into glucose and burned as fuel.

² Evidence type: experimental

Jerome W. Conn, L. H. Newburgh. The Glycemic Response to Isoglucogenic Quantities of Protein and Carbohydrate. J Clin Invest. 1936; 15(6):665–671 doi:10.1172/JCI100818

(Emphasis ours)

In the process of protein metabolism, the complex protein molecule is split in the intestinal tract to amino-acids. These are absorbed into the blood stream and transported to the liver where oxidative deamination occurs. Here the glycogenic amino-acids are split to form urea and glucose. That this process is a slow one is shown in the charts by the slowly rising blood urea nitrogen. Glucose is, therefore, liberated into the blood stream in this process at a slow and even rate over a prolonged period of time. Under these conditions the diabetic is able to utilize a greater total amount of glucose without glycosuria in the eight hour period. Therefore, the inability of a diabetic to dispose of large quantities of glucose is partially compensated if the glucose is presented for utilization slowly and evenly. There appears, then, to be some advantage to the diabetic of this slow liberation of glucose from protein foods.

³ Evidence type: review of experiments

F. Jahoor, E. J. Peters, and R. R. Wolfe. The relationship between gluconeogenic substrate supply and glucose production in humans. AJP – Endo February 1, 1990 vol. 258 no. 2 E288-E296
(Emphasis ours)

Gluconeogenesis plays an integral role in the maintenance of glucose homeostasis in humans, contributing about one-third of glucose produced in the postabsorptive state and all glucose produced when hepatic glycogen is depleted by starvation (6, 23-25). Because the results of in vivo experiments in humans and animals (12-15, 20) and in vitro perfused rat liver studies (11, 27) have demonstrated a close correlation between the rate of glucose production and the flux of gluconeogenic substrates, it is believed that gluconeogenic precursor supply plays a major role in the regulation of glucose production (12,13,20). Several studies in vivo support this concept. For example, we and others have demonstrated that the hyperglycemic response to severe burn injury and sepsis is a direct result of an increased rate of glucose production, which is associated with a concomitant increase in the fluxes of alanine and lactate, major gluconeogenic substrates (15, 39). The proposed regulatory role of precursor supply received further support in the quest to rationally explain the paradox of a reduced glucose production rate (and hypoglycemia) in starvation, despite a hormonal-substrate milieu that would normally favor stimulation of gluconeogenesis (2, 7, 12, 13, 28), thus glucose production. After prolonged starvation (3-4 wk), human subjects had low levels of gluconeogenic precursors associated with hypoglycemia and a reduced glucose production rate (6, 7, 12, 25). Infusion of unlabeled alanine caused hyperglycemia and an increased incorporation of [ 14C]label from alanine into glucose in this circumstance (12,13). It was therefore proposed by Cahill, Felig, and Marliss and their associates (7, 12, 13, 20) that the reduced glucose production rate in starvation was due to the reduced availability of gluconeogenic substrates; hence, gluconeogenic precursor supply was rate-limiting for glucose production rate.

In contrast, the findings of several kinetic studies performed in human and dog do not support this proposal (1, 30, 34, 38). These studies in postabsorptive subjects employed either the isotope dilution or hepatic vein catheterization techniques and failed to show any significant change in glucose production rate in response to infusions of substantial quantities of alanine, lactate, and glycerol even when there was a fivefold increase in the hepatic uptake of the infused substrate (1, 30, 34, 38)

These conflicting findings suggest that the relationship between gluconeogenic substrate supply and gluconeogenic enzyme activity in prolonged starvation may be different from that of the postabsorptive state. Alternatively, it is possible that the response to an increase in precursor supply is different from the response to a decrease. This latter possibility could occur if the endogenous supply of gluconeogenic precursors is just sufficient to maximally satisfy the capacity of the gluconeogenis enzyme system or of a particular key-limiting enzyme.

[…]

Our data so far indicate that under almost any physiological situation, an increase in gluconeogenic precursor supply alone will not drive glucose production to a higher level, suggesting that factors directly regulating the activity of the rate-limiting enzyme(s) of glucose production normally are the sole determinants of the rate of production; hence, there will be no increase in glucose production if the increase in gluconeogenic precursor supply occurred in the absence of stimulation of the gluconeogenic system. On the other hand, results of the DCA experiments suggest a coupling between precursor supply and gluconeogenic enzyme capacity. In this light, if there is a stimulation in gluconeogenic enzyme capacity (for example because of hyperglucagonemia of severe trauma), then there will have to be an increased rate of uptake of gluconeogenic precursors to meet the requirements of such a stimulated system. Thus the rate of uptake of gluconeogenic substrates and the rate of glucose production will be closely related, but the increased uptake of gluconeogenic precursors will be a consequence of a stimulated gluconeogenic enzyme system rather than the cause of an increased rate of gluconeogenesis.

Evidence type: review of experiments

Frank Q. Nuttall, Angela Ngo, Mary C. Gannon. Regulation of hepatic glucose production and the role of gluconeogenesis in humans: is the rate of gluconeogenesis constant? Diabetes Metab Res Rev 2008; 24: 438–458.

(Emphasis ours)

Current data support the hypothesis that the rate of glucose appearance changes but the rate of gluconeogenesis remains remarkably stable in widely varying metabolic conditions in people without diabetes. In people with diabetes, whether gluconeogenesis remains unchanged is at present uncertain. Available data are very limited. The mechanism by which gluconeogenesis remains relatively constant, even in the setting of excess substrates, is not known. One interesting speculation is that gluconeogenic substrates substitute for each other depending on availability. Thus, the overall rate is either unaffected or only modestly changed. This requires further confirmation.

Evidence type: experimental

P. H. Bisschop, A. M. Pereira Arias, M. T. Ackermans, E. Endert, H. Pijl, F. Kuipers, A. J. Meijer, H. P. Sauerwein and J. A. Romijn. The Effects of Carbohydrate Variation in Isocaloric Diets on Glycogenolysis and Gluconeogenesis in Healthy Men. The Journal of Clinical Endocrinology & Metabolism May 1, 2000 vol. 85 no. 5 1963-1967

(Emphasis ours)

Abstract

To evaluate the effect of dietary carbohydrate content on postabsorptive glucose metabolism, we quantified gluconeogenesis and glycogenolysis after 11 days of high carbohydrate (85% carbohydrate), control (44% carbohydrate), and very low carbohydrate (2% carbohydrate) diets in six healthy men. Diets were eucaloric and provided 15% of energy as protein. Postabsorptive glucose production was measured by infusion of [6,6-2H2]glucose, and fractional gluconeogenesis was measured by ingestion of 2H2O. Postabsorptive glucose production rates were 13.0 ± 0.7, 11.4 ± 0.4, and 9.7 ± 0.4μ mol/kg·min after high carbohydrate, control, and very low carbohydrate diets, respectively (P < 0.001 among the three diets). Gluconeogenesis was about 14% higher after the very low carbohydrate diet (6.3 ± 0.2 μmol/kg·min; P = 0.001) compared to the control diet, but was not different between the high carbohydrate and control diets (5.5± 0.3 vs. 5.5 ± 0.2 μmol/kg·min). The rates of glycogenolysis were 7.5 ± 0.5, 5.9 ± 0.3, and 3.4± 0.3 μmol/kg·min, respectively (P < 0.001 among the three diets).

Evidence type: experimental
M A Khan, M C Gannon and F Q Nuttall. Glucose appearance rate following protein ingestion in normal subjects. J Am Coll Nutr December 1992 vol. 11 no. 6 701-706

Unfortunately, we have been unable to access the full text of this paper.
However, the results are described by the authors in the paper above () in text and in the table in the line marked [108]:

[T]here was no change in glucose production after ingestion of 50 g of protein in the form of cottage cheese.

If anyone having access to this paper would like to share it with us, we would be grateful, because it is the most relevant experiment we could find on the topic, and further details may be important.

Evidence type: experimental

Richard D. Carr, Marianne O. Larsen, Maria Sörhede Winzell, Katarina Jelic, Ola Lindgren, Carolyn F. Deacon, and Bo Ahrén. Incretin and islet hormonal responses to fat and protein ingestion in healthy men. AJP – Endo October 2008 vol. 295 no. 4 E779-E784

(Emphasis ours)

Fasting glucose levels were 4.6 ± 0.2 mmol/l, and glucose levels did not change significantly during any of the tests. Fasting insulin levels were 55 ± 3 pmol/l. Insulin levels were unaltered after water ingestion, whereas they increased after fat and protein ingestion. The increased plasma insulin concentrations were seen between 30 and 240 min after fat ingestion (P = 0.031 vs. water) and between 15 and 240 min after protein ingestion (P = 0.018 vs. water). When compared with water ingestion, fat and protein ingestion both significantly increased early and late insulin responses (Table 1). These responses were more pronounced after protein than after fat ingestion (P < 0.001 for all). Fasting glucagon levels were 65 ± 3.7 ng/l. Glucagon levels were unaltered after water ingestion. In contrast, glucagon levels were increased by both fat and protein ingestion, with significant elevations from minute 120 and onward after fat ingestion (P = 0.019 vs. water) and from minute 30 and onward after protein ingestion (P = 0.005 vs. water). The late glucagon response was increased by fat ingestion, whereas, after protein ingestion, both early and late responses were significantly increased. As for insulin, early and late glucagon responses were higher after protein ingestion than after fat ingestion (both P < 0.001; Fig. 1).

Evidence type: review of experiments

Hua V. Lin and Domenico Accili. Hormonal Regulation Of Hepatic Glucose Production In Health And Disease. Cell Metab. 2011 July 6; 14(1): 9–19

(Emphasis ours)

Tracer studies in dogs have defined hormonal regulation of HGP [Hepatic Glucose Production] in detail. As in the isolated rodent liver, HGP is exquisitely sensitive to glucagon and insulin. Glucagon sets the basal tone, but insulin trumps glucagon at any concentration–just as it does in vitro. Both hormones affect primarily glycogenolysis by reciprocal changes of glycogen synthase and glycogen phosphorylase, and by modulating glycolysis through glucokinase, fructose-bisphosphatase and pyruvate kinase (see below) (Cherrington, 1999). Hormonal regulation of gluconeogenesis has proven difficult to demonstrate.

Ketogenic Diets, Cortisol, and Stress: Part I — Gluconeogenesis

One recent myth, prevalent in the Paleo Diet community, is that the keto diet is stressful to the body ¹. This idea arises from misunderstandings about cortisol — “the stress hormone”. There are two different arguments we know of, and this post will address the first one, the “gluconeogenesis requires cortisol” myth.

This myth comes from a mistaken chain of reasoning with three steps in it, only one of which is correct:

  1. On a keto diet, because you get very little glucose from carbohydrate in your diet, your body makes its own glucose on demand, in a process called gluconeogenesis. (This is correct.)
  2. Gluconeogenesis requires elevated cortisol. (This is not correct.)
  3. Chronically elevated cortisol damages the body. (This is not precisely true. In a subsequent article in this series, we will explore the relationship between cortisol levels and health. Nonetheless, it makes no difference for this argument — because gluconeogenesis does not in fact require excess cortisol.)

In Brief:

  • Gluconeogenesis does not require high levels of cortisol.
  • When blood sugar begins to get low, glucagon — the primary hormone responsible for ensuring adequate blood sugar — is produced. This promotes gluconeogenesis, and it happens before blood sugar gets low enough to trigger increases in cortisol.
  • When blood sugar gets so low that excess cortisol is produced, it is also low enough that symptoms of hypoglycemia (“low blood sugar”) appear — anxiety, palpitations, hunger, sweating, irritability, tremor; or in more extreme cases, dizziness, tingling, blurred vision, difficulty in thinking, and faintness. So hypoglycemic signs are a good way to judge if cortisol is involved.
  • Since keto dieters do not normally appear to suffer from hypoglycemic episodes, especially when eating enough protein and not fasting for long periods (indeed, hypoglycemic episodes appear to be reduced by keto diets), it is unlikely that cortisol comes into play to regulate blood sugar for normal keto dieters.
  • If you are concerned about your blood sugar, and whether cortisol is being called upon to regulate it, we recommend you measure your blood sugar levels with a glucometer such as this one (but any drug store should offer several models). If your blood sugar is sometimes too low, then we recommend that you experiment with increasing your protein or how frequently you eat.

Gluconeogenesis

On a keto diet, your body makes the modest amount of glucose it needs out of protein in a process called gluconeogenesis (GNG). There is a widely-held misconception that for GNG to occur, there must be high levels of the stress hormone cortisol in the blood. This mistake comes out of the fact that cortisol stimulates GNG. Therefore, it is reasoned, whenever you rely on GNG, your body has to produce and circulate more cortisol. This, however, is like arguing that since a reliable way to make people laugh is to tickle them, that every time you hear someone laughing it means they are being tickled. It turns out there are other ways to make people laugh, and there are other hormones that induce GNG.

The usual hormone to stimulate GNG is glucagon. Glucagon is produced when blood sugar gets low, and its primary function is to restore blood sugar to optimal levels. Cortisol levels rise when blood sugar reaches an even lower level. That is, the blood sugar threshold for cortisol production (55 mg/dL) is lower than the threshold for glucagon (65 mg/dL) ². This lower threshold could be reached if GNG was somehow obstructed. There are some rare disorders that prevent GNG, such as Fructose 1,6-Diphosphatase Deficiency or Glycogen Storage Disease, but in most people, GNG is a straightforward, unimpeded process.

In fact, it turns out that the level of blood sugar that has to be reached to significantly increase cortisol is so low that clinical symptoms of hypoglycemia also start to appear at that level ³. Not only are reports of hypoglycemic episodes in studies of keto dieters rare, it has been known since at least 1936 that keto diets with adequate protein help prevent hypoglycemia. (It is reported in that paper that keto diets with lower protein help somewhat, but not enough.) A more recent paper from 1975 asserts that the best treatment for hypoglycemia is a low carbohydrate diet with frequent small meals, though they note that this worsens the condition in occasional cases where the patient has one of the above-mentioned or similar disorders. The only other examples of hypoglycemia we could find referred to the initial fasting or severely calorie-restricted phases of ketogenic diets for epilepsy.

Based on this collection of observations, it appears that in keto dieters, the glucagon response is enough stimulate adequate GNG to restore blood sugar, unless they have rare GNG disorders, are eating insufficient protein, or have been engaging in extended fasting.

What you can do

If you experience symptoms that could indicate hypoglycemia, and you are concerned about the possibility that cortisol is being activated to regulate your blood sugar, we recommend you purchase a blood glucometer. It is an inexpensive device that measures the sugar in a drop of blood you get from your finger. Excess cortisol is not deployed for blood sugar regulation unless your blood sugar drops below about 55 mg/dL. If you notice this happening, you could experiment with increasing your protein intake or the frequency of eating.

Summary:

  • GNG is stimulated by glucagon, and as long as the GNG response to glucagon is enough to restore blood sugar before it goes down to about 55mg/dL, cortisol will not be called upon to regulate blood sugar.
  • By the time blood sugar levels have gotten so low that cortisol is deployed to help fix it, hypoglycemic symptoms also appear.
  • Keto dieters don’t appear to experience hypoglycemic symptoms (except in some cases involving inadequate protein or prolonged fasting). In fact keto diets, especially protein-adequate keto diets, have been used to reduce the occurrence of hypoglycemic episodes in susceptible people.
  • Therefore it is not true that because keto diets use GNG for blood sugar regulation, they cause stress to the body.
  • Since blood sugar is easily measured, you can indirectly test for whether cortisol is being used to regulate your blood sugar yourself. If you find it to be low, there are other strategies you can try to alleviate it that don’t involve giving up your keto diet.

References:

¹ Statements that imply this argument can be found in quotes like these:

That latter one seems to be a mistaken generalization that came from taking Mat Lalonde’s comments out of context. Lalonde was describing his experience of severe hypoglycemia that happened after extremely intense exercise. He said: “Gluconeogenesis gets turned on by cortisol and other hormones and it’s not that fast. In order for gluconeogenesis to ramp up, cortisol has to ramp up.” By “ramp up”, we infer he means ramp up enough to keep up with the excessive intensity he had induced — a situation unlikely to occur in most keto dieters. We hope to return to the subject of keto diets and athletics another time.

² Evidence type: repeated experimental evidence.
Ober, K. Patrick (Ed.) Endocrinology of Critical Disease. 1997 Humana Press.

(Emphasis ours.)

The importance of maintaining a fairly constant level of serum glucose is reflected in the elaborate system for defending against falling glucose concentrations. Four major counterregulatory hormones are of varying importance and effectiveness in counteracting a hypoglycemic threat, and there is a hierarchy of response of the factors that counterbalance the threat of hypoglycemia. Each factor has a somewhat different threshold for activation (39 ³, 40) and the physiological importance of each component in the system of defense against hypoglycemia tends to be reflected by its position in the hierarchy. Small decreases in the plasma glucose concentration to the threshold of 65 mg/dL (3.6 mM/L) are usually sufficient to trigger the secretion of glucagon and epinephrine (40,41), the hormones that are of greater counterregulatory importance. Cortisol levels do not increase until the blood glucose falls below 55 mg/dL.

The single most important counteregulatory hormone is glucagon, which enhances hepatic glycogenolysis and gluconeogenesis; without glucagon, full recovery from hypoglycemia does not occur (1). Epinephrine, which has an additional action of inhibiting insulin secretion, is not necessary for counterregulation of hypoglycemia when glucagon is present, but it becomes essential in the absence of glucagon (a common occurrence in the patient with insulin-dependent diabetes). Growth hormone and cortisol are slower to act as counterregulatory agents, and these hormones do not make any substantial contribution to glucose counterregulation during acute insulin-induced hypoglycemia (42); since growth hormone and cortisol cannot compensate effectively for hypoglycemia in the absence of glucagon and epinephrine, they are of secondary importance in the counterregulatory scheme (34).

The relevant references from that passage are:

³(Ober’s 39.) Evidence type: experimental.
Schwartz NS, Clutter WE, Shah SD, Cryer PE. Glycemic threshold for activation of glucose counterregulatory systems are higher than the threshold for symptoms. J Clin Invest 1987;79:777-781.
(Emphasis ours.)

Arterialized venous plasma glucose concentrations were used to calculate glycemic thresholds of 69 +/- 2 mg/dl for epinephrine secretion, 68 +/- 2 mg/dl for glucagon secretion, 66 +/- 2 mg/dl for growth hormone secretion, and 58 +/- 3 mg/dl for cortisol secretion. In contrast, the glycemic threshold for symptoms was 53 +/- 2 mg/dl, significantly lower than the thresholds for epinephrine (P less than 0.001), glucagon (P less than 0.001), and growth hormone (P less than 0.01) secretion.

(Ober’s 40.) Evidence type: experimental.
Mitrakou A, Ryan C, Veneman T, et al. Hierarchy of glycemic thresholds for counterregulatory hormone secretion, symptoms, and cerebral dysfunction. Am J Physiol 1991;260:E67-E74.

The glycemic thresholds for increases in plasma growth hormone, glucagon, epinephrine, and norepinephrine were not significantly different from one another (-67 mg/dl) but were significantly higher than that for cortisol (55 t 2 mg/dl, P < 0.004-0.0003) and for the appearance of autonomic symptoms (58 t 2 mg/ dl, P c 0.039-0.001).

(Ober’s 41.) Evidence type: experimental.
Bolli GB, Fanelli CG. Unawareness of hypoglycemia. N Engl J Med 1995;333:1771-1772.

In normal humans, small decreases in the plasma glucose concentration to the threshold of 65 mg per deciliter (3.6 mmol per liter) elicit the secretion of the rapid-acting counterregulatory hormones glucagon and epinephrine, which oppose the glucose-lowering effects of insulin in plasma within minutes. Should plasma glucose levels decrease further, to about 55 mg per deciliter (3.1 mmol per liter), the secretion of counterregulatory hormones increases, and autonomic symptoms (anxiety, palpitations, hunger, sweating, irritability, and tremor) appear, as well as neuroglycopenic symptoms (dizziness, tingling, blurred vision, difficulty in thinking, and faintness).

Evidence type: case studies
Jerome W. Conn. THE ADVANTAGE OF A HIGH PROTEIN DIET IN THE TREATMENT OF SPONTANEOUS HYPOGLYCEMIA: Preliminary Report. Published in Volume 15, Issue 6, J Clin Invest. 1936; 15(6):673 doi:10.1172/JCI100819

Waters(5) in 1931 advised strict curtailment of the carbohydrate in the diet, most of the calories being derived from fat. Following this a high fat, low carbohydrate diet with feedings divided into six daily meals was generally adopted. On this regime there was often prompt improvement; but while hypoglycemic attacks were diminished in number, they still occurred with alarming frequency.

It was realized, then, that the ingestion of large amounts of protein would supply glucose to the blood stream at a constant, slow rate, without the production of a hyperglycemia.

Conclusions

1. The slow rate at which glucose is liberated into the blood stream during the metabolism of protein is of advantage in the treatment of spontaneous hypoglycemia because —

(a) It causes no hyperglycemia and thus avoids excessive production of insulin and secondary hypoglycemia.

(b) It provides a source of glucose over a prolonged period of time.

(c) It allows in severe cases further restriction in carbohydrate than could otherwise be effected.

2. These facts justify the use of a diet high in protein and low in carbohydrate in the treatment of this condition.

Evidence type: experiment.
Hofeldt FD. Reactive hypoglycemia. Metabolism. 1975 Oct;24(10):1193-208.
(Emphasis ours)

The backbone of successful management of reactive hypoglycemia is the diet. A 100-g carbohydrate diet, isocaloric (25 calories per kilogram body weight) with six equal feedings with avoidance of refined carbohydrates will be successful in the majority of cases. Some authors report a beneficial effect by the restriction of caffeine-containing beverages(33,39,53,60,32-134) and alcohol.(33,35) Alcohol utilizes important gluconeogenic NAD substrate (17,136,137) for its metabolism, depresses the activity of important gluconeogenic enzymes,(138,139) limits alanine and substrate availability.(140)

An occasional case may show worsening on the low-carbohydrate, high-protein diet. Since there is an aminogenic influence on insulin secretion, this could potentially aggravate the reactive hypoglycemia in some patients. However, the concurrent protein stimulation of glucagon release could offset the effects of insulin.(18,23,145) Our studies on hepatic gluconeogenesis have shown that in patients with the fructose 1-6 diphosphatase deficiency there is characteristically a worsening of symptoms when stressed with a low-carbohydrate (ketogenic) diet. These patients, in order to maintain blood-glucose levels early in the fasting state, must call on adrenergic mechanisms to release glycogen stores. Similarly, an occasional patient will develop intolerant symptoms while on the low-carbohydrate, weight reduction Stillman or Atkins diet. These patients may well show similar hepatic enzyme defects. In this special low-carbohydrate intolerant subgroup, the stress of any ketotic diet is avoided and dietary carbohydrates are increased to 150 g or greater. We are presently conducting studies on the therapeutic effectiveness of folic acid (15 mg/day) in these patients with beneficial results.