Intermittent fasting: Fat loss and better health?

Intermittent fasting, also known as interval fasting, is eating according to the clock and is said to be particularly effective for weight loss and improving health parameters. Especially trendy is the ‘5:2 diet’, where for five days food is eaten to your heart’s content within the normal calorie intake and on two (non-consecutive) days the calorie intake is strongly reduced. Intermittent fasting is generally divided into 3 categories (1):

  • Alternate-day fasting’: on one or several (non- consecutive) days per week nothing is eaten, or at most 25% of the required calories (typically in just one meal) are consumed. 
  • Whole-day fasting’: Fasting periods for once or twice a week for 24 hours.
  • Time-restricted feeding’: With intermittent fasting through time restricted food intake, for 16-20 hours no food is eaten alternated by a time window of 4-8 hours of eating. This includes, for example the fasting month Ramadan, during which no food is eaten from sunrise until sunset.

Fundamentally with intermittent fasting, calories are “saved” on one or several non-consecutive days during the week and it is a well-known fact, that the only magic key to weight loss is energy deficit. If the calories saved during fasting are not subsequently compensated, then body fat is lost. Therefore, intermittent fasting can be a useful method to reduce overall calorie intake for some of us. However, those who balance fasting periods with binge eating days or simply do not achieve an overall calorie deficit will have no success with fat loss.

Dr. Brad Schoenfeld, one of the internationally most renowned strength and fitness experts explains whether intermittent fasting is a useful and appropriate diet for weight loss and improvements in health compared to a continuous calorie reduced diet.

Is intermittent fasting a suitable method for weight loss in Fitness enthusiasts and Bodybuilders?

Dr. Schoenfeld: “The weight loss benefits of intermittent fasting appear to be solely a function of restricting caloric consumption. By limiting the window in which food is eaten, intermittent fasting helps to control caloric consumption and thus facilitate fat loss. It should be noted that the same results can be achieved simply by controlling calories via portion control in a standard dietary approach. Therefore, the best practice dietary approach for weight loss depends on the individual.”

Through intermittent fasting body fat level can be reduced via energy deficit. But how about the maintenance of valuable muscle mass in athletes?

Dr. Schoenfeld: “Food, dietary protein in particular, is anabolic. Intermittent fasting will put an individual in a state of catabolism for a majority of the fasting day – not an ideal muscle-building environment. Based on applied logic it would be prudent to consume protein more frequently throughout the day to maximize the training-induced hypertrophic response and to support muscle maintenance/growth.”

Starving the body during fasting kick-starts positive health benefits for the immune system - True or false?

Dr. Schoenfeld: “I have seen no compelling evidence to support that hypothesis.”

It is often claimed that intermittent fasting is superior in improving health parameters, such as improved cholesterol levels compared to traditional continuous energy-restricted diets - True or false?

Dr. Schoenfeld: “This is an area that is still not well explored. Based on what I can derive from the current literature, I do not feel there is sufficient evidence to infer that intermittent fasting is superior to a traditional energy-restricted diet from a health standpoint. That said, the topic remains under-researched so we should be open to the possibility that an intermittent fasting strategy may confer additional health-related benefits, but that is purely speculative at this time.”

Author: Corinne Mäder Reinhard, International Sports Nutrition Lead Active Nutrition International. She holds an International Olympic Committee postgraduate Diploma in Sports Nutrition and is a certified Sports Nutritionist from the International Society of Sports Nutrition.

The exercises, training and/or nutritional information and recommendations presented in this article/video are to be followed at your own risk and do not substitute personal and/or individual advice. Medical advice should be obtained beforehand by anyone under 18 years of age, by individuals with health restrictions (especially orthopaedic or internal complaints/conditions), and by women who are pregnant or breastfeeding. If problems are encountered when applying the training and nutritional methods, a doctor should always be consulted immediately. No liability is assumed by Active Nutrition International GmbH.

Tinsley, G.M. & La Bounty, P.M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev, 73(10):661-74.