How The Keto Diet Affects Testosterone And Cortisol

A ketogenic diet is characterized by limiting daily carbohydrate intake to no more than 50 grams, or 5% of total daily calorie intake, while maintaining a moderate to high protein intake (e.g., 1.2 to 1.5 g/kg/d). While this is done primarily through the food consumed in your diet, many also rely on carb free & stimulant free keto fat burners.

The majority of the remaining 80% of energy consumption comes from fats, with the relative amount of fat consumed dependent on how much protein and carbs have been replaced. [1]

At a state of physiological ketosis, where ketone body concentrations in the plasma are higher than on a mixed diet, this type of macronutrient distribution causes an increase in the production of ketone bodies such acetoacetate, -hydroxybutyrate, and acetone. [2]

The main male sex hormone, testosterone, is essential for the growth and operation of the reproductive system.

An increased risk of chronic diseases, such as type 2 diabetes [3] and cardiovascular disease, is linked to low endogenous testosterone. [4]

Because exogenous cortisol decreases testosterone, it differs biochemically from testosterone in several ways. The interaction between testosterone and cortisol is most likely caused by each hormone’s unique anabolic and catabolic characteristics.

What are the advantages of a low-carb diet?

For many years, low-carb diets have been divisive. Others claim that these diets’ high fat content raises cholesterol and contributes to heart disease. Low-carb diets, however, consistently demonstrate their value as healthy and advantageous diets in scientific investigations.

These are 10 substantiated advantages of low-carb and ketogenic diets for health:

Lower “bad” LDL cholesterol levels: A low-carb diet causes your “bad” LDL particles’ size to expand, which lessens their negative effects. Reducing your carb intake may also result in fewer total LDL particles in your blood. [5] Effective against metabolic syndrome: Good low-carb diets successfully correct all five of the dangerous condition’s symptoms, which include an elevated risk of heart disease and type 2 diabetes. Metabolic syndrome is a serious condition. [6]

May lower blood pressure: Reducing your carb intake significantly lowers your blood pressure, which should minimize your risk of developing several common ailments. [7]

Decreased blood sugar and insulin levels: Cutting back on carbs is the greatest approach to lower blood sugar and insulin levels, which may help treat and even reverse type 2 diabetes. [ 

Increases in “good” HDL cholesterol levels: [8] Higher blood levels of “good” HDL cholesterol: Low-carb diets are frequently heavy in fat, which causes remarkable  

Reduces blood triglyceride levels: [9] Triglycerides are fat molecules that raise the risk of heart disease. Low-carb diets are extremely effective at reducing blood triglycerides. [5]

An abdominal cavity-centric approach to weight loss: A significant majority of the fat shed on low-carb diets is typically unhealthy abdominal fat, which is known to cause serious metabolic issues. [10] 

The effects of a ketogenic or low-carb diet on testosterone

According to a recent systematic review and meta-analysis, high protein, low carb diets resulted in a significant decrease (37%) in resting total testosterone, whereas diets with moderate protein and carbs had no discernible impact. [11]

This is due to the possibility that protein intake beyond 35% may exceed the ability of the urea cycle to convert nitrogen from amino acid catabolism into urea, which might result in hyperammonaemia and associated deleterious repercussions [12].

The urea cycle has been demonstrated to be suppressed by testosterone while being stimulated by glucocorticoids [13]. Also, the longest high protein, low carb diet research showed the most noticeable reduction in resting cortisol.

Hence, the upregulation of the urea cycle and increased nitrogen excretion on high protein diets may aid to reduce the negative consequences of excessive protein consumption by counteracting the decrease in testosterone and increase in cortisol.

Moreover, studies show that long-term moderate protein, low carb diets resulted in higher post-exercise total testosterone levels than short-term high protein, low carb diets.

The fact that long-term low-carb diets had no effect on resting total testosterone and that high protein, low-carb diets significantly reduced it suggests that protein consumption, rather than diet duration, may be responsible for the observed subgroup effects in post-exercise total testosterone. Even with this knowledge, some men will still proceed with this diet and supplement with a good testosterone booster.

To sustain activation of the urea cycle and increased nitrogen excretion, as previously indicated, high protein consumption may lower post-exercise total testosterone.

The increase in blood cholesterol on low carb diets may have contributed to the result that long-term moderate protein, low carb diets boosted post-exercise total testosterone. Testosterone is produced when there is an increase in anabolic signaling, which occurs during exercise. [14]

The greater anabolic response to exercise suggested by the higher post-exercise total testosterone on moderate protein, low carb diets may be favorable, especially in people aiming for strength, power, or hypertrophy.

The limited sample size in these trials should be taken into consideration when interpreting the finding that low carb diets boost post-exercise testosterone. Further studies should validate this result.

Effects of a ketogenic or low-carb diet on cortisol

The role of glucocorticoids in glucose homeostasis is probably the cause of the rise in resting cortisol on short-term low carb diets, but not on long-term ones. Short-term low carb diets cause a rise in cortisol, glucagon, and gluconeogenesis (i.e., the production of glucose from certain non-carbohydrate carbon substrates, such as amino acids), but not long-term low carb diets [15].

On brief low carb diets, the initial spike in cortisol may be partially to blame for a transitory increase in gluconeogenesis because glucocorticoids stimulate gluconeogenesis.

Moreover, since the brain cannot significantly utilize fatty acids as fuel, cortisol may increase to save glucose for brain function.

In order to preserve glucose for brain function, glucocorticoids prevent glucose uptake and oxidation in adipose tissue and skeletal muscle.

On the other hand, during the first three weeks of a very low carb diet, endogenous ketone synthesis increases significantly [16], and ketones can be used as brain fuel. Since cortisol’s glucose-sparing actions are no longer necessary when ketones dominate over glucose as the primary source of brain fuel, levels may drop back to normal.

Research also suggests that low carb diets resulted in a larger rise in cortisol during exercise.

Furthermore, even after adaption to a low-carb diet, this impact still seems to be present, albeit significantly diminished. Intriguingly, studies employing carbohydrate supplements during exercise on high carb diets found that the increase in post-exercise cortisol was decreased [17].

It would seem that reduced carbohydrate availability increases the cortisol spike that occurs during exercise.

Three plausible, complimentary explanations are available for this. First off, because low-carb diets partially deplete glycogen stores, cortisol levels may rise more quickly to support greater gluconeogenesis during exercise.

Second, low-carb diets promote greater fat oxidation during exercise compared to high-carb diets [15], and cortisol may rise to promote greater fat oxidation by stimulating lipolysis in adipose tissue.

Thirdly, as exercise increases skeletal muscle glucose uptake [18], cortisol levels may rise to protect brain glucose levels.

Following adaption, there is still a larger cortisol rise during exercise on reduced carb diets compared to high carb diets. Several immunological markers suggest that low carb diets are not overtly immunosuppressive, despite higher post-exercise cortisol, contrary to the conventional wisdom that cortisol has immunosuppressive effects [19].

A little care may be advised until more research is done because the possible immunosuppressive effects of greater post-exercise cortisol may be intensified in athletes doing high volume training.


The majority of the research in the literature shows that short-term low carb diets (3 weeks) raise resting and post-exercise cortisol levels. Also, studies suggest that while post-exercise cortisol levels stay increased, resting cortisol levels return to baseline after around 3 weeks on a reduced carb diet.

However, further study is required to establish the latter effects due to the small number of trials and unexplained inconsistency in long-term low carb diets.

Although the decrease in resting total testosterone observed in randomized moderate protein, low carb studies highlights the need for additional randomized controlled trials, moderate protein, low carb diets do not appear to affect resting total testosterone.

Last but not least, high protein, low carb diets significantly decreased resting total testosterone, suggesting that those who follow these diets may need to be on the lookout for potentially harmful endocrine repercussions.

I advise a low-carb diet if it is something you can follow, control your calorie intake, and lose weight with. Although it won’t be significant, it’s possible that you could lose some lean body mass.

However, a low-carb diet is not advised if your objective is to preserve or increase your muscle mass as much as possible. Find out more about this and supplementation at Simply Supplements.

1.    Aragon, A.A., et al., International society of sports nutrition position stand: diets and body composition. J Int Soc Sports Nutr, 2017. 14: p. 16.
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3.    Yao, Q.M., et al., Testosterone level and risk of type 2 diabetes in men: a systematic review and meta-analysis. Endocr Connect, 2018. 7(1): p. 220-231.
4.    Corona, G., et al., Endogenous Testosterone Levels and Cardiovascular Risk: Meta-Analysis of Observational Studies. J Sex Med, 2018. 15(9): p. 1260-1271.
5.    Wood, R.J., et al., Carbohydrate restriction alters lipoprotein metabolism by modifying VLDL, LDL, and HDL subfraction distribution and size in overweight men. J Nutr, 2006. 136(2): p. 384-9.
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10.    Volek, J., et al., Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women. Nutr Metab (Lond), 2004. 1(1): p. 13.
11.    Whittaker, J. and M. Harris, Low-carbohydrate diets and men’s cortisol and testosterone: Systematic review and meta-analysis. Nutr Health, 2022: p. 2601060221083079.
12.    Bilsborough, S. and N. Mann, A review of issues of dietary protein intake in humans. Int J Sport Nutr Exerc Metab, 2006. 16(2): p. 129-52.
13.    Lam, T., et al., Testosterone prevents protein loss via the hepatic urea cycle in human. Eur J Endocrinol, 2017. 176(4): p. 489-496.
14.    Pasiakos, S.M., Exercise and amino acid anabolic cell signaling and the regulation of skeletal muscle mass. Nutrients, 2012. 4(7): p. 740-58.
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16.    Vidic, V., et al., Effects of calorie restricted low carbohydrate high fat ketogenic vs. non-ketogenic diet on strength, body-composition, hormonal and lipid profile in trained middle-aged men. Clin Nutr, 2021. 40(4): p. 1495-1502.
17.    Moreira, A., et al., Nutritional modulation of exercise-induced immunodepression in athletes: a systematic review and meta-analysis. Eur J Clin Nutr, 2007. 61(4): p. 443-60.
18.    Evans, P.L., et al., Regulation of Skeletal Muscle Glucose Transport and Glucose Metabolism by Exercise Training. Nutrients, 2019. 11(10).
19.    Shaw, D.M., et al., Adaptation to a ketogenic diet modulates adaptive and mucosal immune markers in trained male endurance athletes. Scand J Med Sci Sports, 2021. 31(1): p. 140-152.

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Lee Clarke
Lee Clarke
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