I recently read a comment in a newspaper by obesity researcher Professor Lau from the University of Calgary. He made the point that “muscle protein breakdown occurs in the first 24 hours of starvation,” and expressed concern that people who fast may be losing crucial muscle mass.
My response to this is that he is really talking about long term fasting, ie fasting for days or weeks at a time. With intermittent fasting you are not fasting for 24 hours or longer. In the version that I practice, I never go more than 12 hours without eating. If your protein intake is adequate, and we actually recommend an increased protein intake on fasting days, then you are not going to get “muscle protein breakdown”. In fact the evidence from human studies clearly point towards intermittent fasting being better than standard diets when it comes to muscle preservation.
Dr Krista Varady of the University of Illinois at Chicago has done a number of human trials using intermittent fasting. Her most recent paper was in, Metabolism, Volume 62, Issue 1, Pages 137-143, January 2013. In this study thirty-two overweight volunteers, average age 42, were put on an ADF (alternate day) intermittent fast for 8 weeks. At the end of 8 weeks the volunteers had lost an average of 4kg and seen significant improvements in biomarkers related to the risks of diabetes and coronary heart disease. Interestingly, the weight loss was all fat, not muscle. As she points out “A similar preservation of lean mass was noted in a previous ADF study conducted by our group.” This retention of lean mass, ie muscle, is not seen with standard calorie restricted diets. “The reason why ADF may assist with the preservation of lean mass is not known at present, but will undoubtedly be of interest in future studies in this field”
In another study of intermittent fasting (Int J Obes . 2011 May;35(5):714-27), 107 young overweight women were randomly allocated to either a standard low calorie diet or a diet where for two days a week they ate 650 calories a day. At the end of 6 months the intermittent fasting group had lost an average of 6 kg of fat and 3 inches from their waists compared to 4.9 kg of fat and 2 inches from waist for the normal dieters.
Doing the diet, I have now lost just over 22lbs and my body fat is down from 28% to under 20%. I walk everywhere and do 30 press ups each morning. Keeping muscle mass is important, not just because it looks better but also because muscle is more metabolically active than fat; it burns calories even when you are asleep. Rest assured, the diet will keep you healthy as well as help you lose weight.