Does Fasting Make You Lose Muscle?

Fasting -- going extended periods without eating -- is often done for religious reasons, but some dieting approaches suggest that fasting can have health benefits. While fasting can help you reduce your weight simply because you consume fewer calories, fasting may also encourage the loss of muscle mass. Consult a doctor prior to starting any diet or new nutritional approach.


Muscle Maintenance Basics

Although working out at the gym is part of the process of building and keeping muscle, lifting weights alone is not sufficient to build or maintain muscle mass. In addition to providing the stimulus for growth via your workouts, you need to supply your body with adequate nutrients for repair, maintenance and new growth. According to the Institute of Medicine, you need to consume 0.8 grams of protein per kilogram of your body weight each day to maintain your muscle and other vital tissues. If you're fasting, you won't be supplying your body with those nutrients, which can lead to muscle loss.

Reduced Rate of Muscle Protein Synthesis

Your body retains and builds tissue through a process known as muscle protein synthesis. Several external and internal factors influence the rate of muscle protein synthesis, including the food you eat. According to research published in The Journal of Nutrition, fasting significantly reduces your body's rate of muscle protein synthesis. Thus, your body will be less able to repair and maintain muscle mass when you're in a fasting state.

Fasting and Testosterone

Testosterone is a hormone responsible for secondary sex characteristics, such as facial hair, in men. In addition, the hormone aids in improving body composition by encouraging muscle protein synthesis, muscle gain and fat loss. Levels of this vital hormone are not promoted by fasting; research from the August 1993 issue of the research journal Steroids found that fasting dramatically reduced testosterone levels. Thus, you may be more likely to lose muscle while fasting.

Fasting and IGF-I

Although growth hormone and testosterone are well known for their roles in the maintenance and accrual of muscle mass, other hormones aid in the process as well. Fasting is a traumatic event for your body, so it can have significant effects on physiological factors such as hormone release. According to research from The Journal of Clinical Endocrinology and Metabolism, fasting reduces levels of insulin-like growth factor-I, or IGF-I, a hormone that acts to promote muscle gain and fat reduction.


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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or