[Chris Graham is a graduate student at The University of Texas at Tyler and is currently studying Kinesiology. He is currently a sport performance intern at Athletic Lab.]

Intermittent fasting (IF) has been popularized in the recent years as a method of weight loss and there are many people who claim to have found success using this method. What exactly is IF, and is it an effective and sustainable method to achieve weight loss?

First off, IF is the practice of not consuming food for an extended period of time (typically 12+ hours) which is called your “fasting” time. This is followed by a “feast” time where you can eat ad libitum. There are a variety of ways to accomplish this, but one of the most common is to alternate fast and feast days for an extended period (3-8 weeks).

In a recent review comparing IF and caloric restriction in overweight and obese individuals, Varaday (2011) found that both diets had similar results on weight loss 4-8% from IF and 5-8% from caloric restriction. However, in the IF studies 10% of the weight loss was from fat free mass compared to 25% in the caloric restriction studies (Varaday, p. e599). This retention of more fat free mass compared to regular caloric restriction proved to be more beneficial in improving body composition, and may be a result of average HGH increases of 1,300% in women, and nearly 2,000% in men during a 24-hour fast (Intermountain Medical Center, 2011). This spike of HGH protects your current muscle mass while also stimulating the breakdown of fat cells.

In a separate study examining the effects of IF in resistance trained individuals, one group was assigned a “time restricted feeding window” (TRF) while a second group was assigned a standard diet. Both groups had similar total calories in their diets, but at the end of the eight-week period, the TRF group lost 16.4% of their total fat mass compared to 2.8% in the standard diet group while also making similar gains in total strength and muscle mass (Moro, 2016). This may be due to a promotion of autophagy (how your body breaks down damaged organelles) “which is important for optimal muscle health” (Moro, 2016, p. 8) and is contrary to the thought that your body will convert the protein in your muscle tissue to glucose for energy.

In a second study published in the American Journal of Clinical Nutrition, Heilbronn Et Al (2005) found that non-obese subjects lost an average of 2.5% of their initial body weight (p.70) while on a three-week alternate day fasting program. In addition, Heilbronn (2005) found that “fat oxidation increased from 64 g/24h at baseline to 101 g/24h” (p.71) over this time. This is partly due to a drop in fasting blood insulin levels and an increase in adiponectin (Moro, 2016) (which helps stimulate the breakdown of fat molecules (Saleem, 2016)). This combination of blood level changes may be what primarily stimulates the adipose tissues to release fat molecules to be used as an energy source for the body while calories are not being consumed through the diet.

Intermittent fasting has proven to be just as effective at weight loss as calorie restriction, but even more so when it comes to improving body composition and losing fat weight. Intermittent fasting has also proven to be better than caloric restriction at improving health-related biomarkers (Moro, 2016, p. 8) and has been shown to be a feasible method of weight loss (Stote, 2007, p. 987).

References:

Heilbronn, L. K., Smith, S. R., Martin, C. K., Anton, S. D., Ravussin. E. (2005).  Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. American Society for Clinical Nutrition, (81), 69-73.

Intermountain Medical Center. (2011, May 20). Routine periodic fasting is good for your health, and your heart, study suggests. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2011/04/110403090259.htm

Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q. F., Battaglia, G., …(2016). Effects of eight weeks of time‑restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance‑trained males. Journal of Translational Medicine, 14:290. DOI 10.1186/s12967-016-1044-0

Saleem, W. (2016). Adiponectin and Diet. Retrieved from http://www.livestrong.com/article/313879-adiponectin-and-diet/.

Stote, K. S., Baer, D. J., Spears, K., Paul, D. R., Harris, G. K., Rumpler, W. V., … (2007). A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. American Journal of Clinical Nutrition, (85), 981-988.

Varaday, K. A., (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?, Obesity Reviews, 12, e593-3601. doi: 10.1111/j.1467-789X.2011.00873.x