Will Fasting Make My Muscles Shrink?

This article was first released on March 13, 2019. It is republished with new information.

One concern with intermittent fasting is lean muscle may shrink. This article presents two studies that showed that lean mass or muscles are preserved with intermittent fasting.

The first study showed that after eight weeks of alternate-day fasting, the muscles did not change over eight weeks. [1]

The second research published in 2016, A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity., compared intermittent fasting to a regular three times per-day reduced-calorie diet. [2]

Alternate daily fasting (ADF) is when regular meals are taken between days when no calories are taken. A caloric restrictions diet involves daily meals but with lower calories.

The result is that the group on ADF lost more fat mass than the group in the caloric restriction diet. In addition, the loss of muscle mass is more significant in the caloric restriction, while the ADF group gained more muscle.

Growth Hormone with Intermittent Fasting

Moller and colleagues showed that growth hormone (GH) increases during fasting due to a decrease in growth hormone clearance. The persistent rise in growth hormones results in the burning of fat.[3]

GH is essential for the maintenance of all tissues in the body. GH reaches its peak during rapid growth in puberty and decreases as we get older, which explains the loss of muscle mass in older people.

Skeletal muscles burn glucose for energy. Fewer muscles and inactivity lead to higher circulating glucose because there are fewer muscles and physical activity to use the glucose. That is why the risk of developing diabetes goes up with age.

Fasting is an excellent way to increase the GH level, limit muscle loss and prevent diabetes.

In addition, growth hormones also mobilize fat storage from the visceral fat and decreases the waist circumference. A large waist circumference significantly contributes to the development of metabolic syndrome that can lead to severe illnesses.

Growth hormone is needed for muscle and bone growth. Source: Häggström, Mikael (2014) used with permission

If I don’t eat carbs, where will I get energy?

Glycogen is stored in the liver and skeletal muscles after we eat carbohydrates. During activity and the fasted state, glycogen is broken down into glucose and used for energy.

The body will switch its energy source to fatty acids depending on your physical activity. The visceral fat, the intraabdominal fat inside the abdomen, is the first to be mobilized.

The fat is broken down into smaller molecules called ketones and used by the skeletal muscles and the brain.

Ketones “burn cleaner” because less oxidation is produced compared to glucose. Ketosis is a state when you are burning more ketones rather than glucose as a fuel source for the body. Ketosis differs from ketoacidosis, a complication of Type 1 diabetes.

Update July 19, 2022: A systematic review of eight studies about intermittent fasting and resistance training showed that lean body mass (LBM) was generally maintained. Lean body mass is the total body weight minus the total fat weight.

There were 219 participants across all groups, including 153 males and 66 females. The study periods ranged from four to eight weeks.

One study reported a significant increase in LBM. Body fat mass or percentage was significantly reduced in five of eight studies.

Overall, the review suggests intermittent fasting paired with resistance training generally maintains LBM and promotes fat loss.

So there you go. Fasting is an inexpensive way to lose fat, decrease your risk for other diseases by improving the fatty liver, insulin resistance, metabolic syndrome, and make you look younger.

Thanks to Dr. Willie N. for the blog topic idea.

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Growth Hormone with Intermittent Fasting

If I don’t eat carbs, where will I get energy?

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