The carb cycling diet plan is a topic that comes up again and again when people talk about building muscle while losing fat. But is the success you see with this really due to carb cycling?
What Is The Carb Cycling Diet?
The whole idea behind the carb cycling diet and what its proponents believe in is that through this diet you can influence your body’s leptin level.
Leptin is a hormone that plays a key role in the regulation of hunger and energy expenditure. To put it simply: The more leptin in your body, the less hunger you have.
Very Little Calories
Will Brink, who advocates the idea in his book Fat Loss Revealed, cites this study as proof that it works. I had a close look at it and found that it examined men who were on a very low calorie diet and had leptin artificially administered.
The stress here truly being on a very low calorie diet, as the study itself says:
[...] Exogenous leptin resulted in additional weight loss only during severe energy restriction in the present study but failed to significantly affect weight loss during mild hypoenergetic conditions in the previous study [...]
This means that even when the leptin level was artificially raised through injections, it had no effect on those that had just a slight caloric deficit. You need to go way below your basal metabolic rate (BMR, the energy required for basic body processes) to make it work.
This is not healthy and for the study’s subjects also went hand-in-hand with a loss of fat-free mass (FFM), including muscle:
Conservation of FFM, which was observed in rodents treated with leptin, was not observed in the present study, in which both treatment groups lost equal amounts of FFM after 6 wk of severe energy restriction. The loss of FFM in both groups was within the normal physiologic range of ~25% of total body weight loss.
When via Facebook I asked Mr. Brink about this, he refused to answer.
No Scientific Proof
To make this short: It is very unlikely that by merely switching between low carb / high carb days you can influence your leptin level in a noticeable fashion. At least there is no scientific research that proves it.
The effect you see from doing carb cycling could very well be attributed to simply having a slight caloric deficit through a strict control of daily calories and providing enough protein and resistance training to preserve muscle. You can have that with much less trouble.