Low-carb diets, cortisol & testosterone

Executive summary

* A systematic review (look at all evidence) and meta-analysis (pool it together to see the overall effect) has been published reviewing the effect of low-carb diets on cortisol and testosterone in young, healthy, active, men.

* As a general principle, findings of higher cortisol and/or lower testosterone, resulting from a diet, would be seen as bad outcomes.

* The review examined 27 studies involving 309 men with an average age of 27.

* Various permutations of resting and post-exercise, cortisol and testosterone, exercise duration and whether the low-carb diet was high or moderate protein were examined in separate sub-groups.

* Half the sub-group analyses did not achieve significant results; the other half did. Non-findings are important as well as findings.

* The most important non-findings were that nothing significant was found – for either cortisol or testosterone – in diets lasting longer than three weeks.

* The most important findings were that low-carb diets resulted in higher cortisol after exercise lasting 20 minutes or longer. This may have been the result of gluconeogenesis. Also, high-protein low-carb diets decreased resting testosterone, but moderate-protein low-carb diets didn't, so don't blame the low carb for what the high protein did.

* This was a thorough and impressive study with some interesting findings. Anyone following a low-carb diet for longer than three weeks should not be concerned by the results.