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Ben Bikman - Does Low Carb Spike Cortisol? with Dr. Ben Bikman

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Author: Ben Bikman
Categories: Nutrition Education
Tags: nutrition, education
Views: 2 · Last viewed: 2026-10-14 23:14 UTC

Short Summary

Main recommendation: Based on the two studies discussed, the speaker argues that a low-carb ketogenic diet does not appear to spike cortisol or reduce muscle mass over the long term, and that people should not fear protein on such a diet. The first study (six weeks, volunteers) showed no significant cortisol rise and gains in lean mass, while a second study in obese humans found only a brief, marginal rise in cortisol in women at week two that disappeared by week eight.

Key Points

  • Cortisol is a glucose-raising hormone (alongside growth hormone, epinephrine, and glucagon) that can break down muscle and bone protein to make glucose, which is why it is a concern on low-carb diets.
  • In the first study, a low-carb ketogenic group cut carbohydrate from about 50 percent to 8 percent of calories, and cortisol did not significantly change; it tended to go down, though variability was very large.
  • Despite eating about twice as much protein as the control group, insulin in the low-carb group dropped significantly, from about 23 to 15 picomoles, while the control group's insulin stayed flat.
  • Over six weeks, the low-carb group lost about 2 kilograms of body mass, with fat mass falling by over 3 kilograms and lean mass rising by over 1 kilogram, showing that the scale alone can hide body composition changes.
  • The speaker says the cortisol concern is rarely raised by clients who come from physicians with type 2 diabetes, and that if blood sugar doesn't improve as expected, a stress response (not the diet itself) may be the cause.

Details Worth Noting

  • Concrete instructions: The speaker gives no step-by-step protocol for patients. The only actionable guidance is: do not fear protein on a low-carb diet, since insulin fell even with roughly doubled protein intake (about 170 g protein and 160 g fat in the study diet, roughly 60 percent fat and 30 percent protein by calories); and, if cortisol or blood sugar behaves unexpectedly while cutting carbohydrates, consider it may be a stress response and not caused by the diet itself.
  • The first study was not randomized: the diet group was self-selected volunteers, which the speaker says is a scientific weakness but more realistic for adherence. The study used DEXA scanning, a gold-standard body composition measure.
  • Bone mineral content did not change in the first study, which the speaker says matters for people beyond middle age, especially women, who worry that weight loss will cost bone.
  • The second study (published 2019 in Nutrition Research, PubMed ID 30803508) involved obese participants; cortisol rose slightly in women at week two (statistically significant but marginal) and was gone by week eight, with no significant change in men.
  • The speaker notes the first study included no women, and the second study's female results are the only suggestion of a cortisol effect, which the speaker calls debatable in meaning.
  • The speaker mentions the 80-15-5 macronutrient split was once taught in keto but is no longer emphasized, with a roughly 60-30 fat-to-protein split by calories being more common in low-carb research.

Bottom Line

The evidence discussed suggests a low-carb diet is unlikely to cause lasting cortisol elevation or muscle loss, but the speaker frames this as a view from limited, short-term studies rather than settled fact.