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To Fast or Not to Fast on Your Rest Day from Running: The Benefits of Fasting for 24-Hours

Posted by George Parker on
Peter Attia Fasting Runner Fasting 24-Hour Fast

I have a rest day from running, usually once per week. I decided to experiment with fasting on my rest day. Who knows where I got the idea. The idea of fasting or intermittent fasting seems all over the health literature. My latest exposure to fasting comes from Dr. Peter Attia on the Disney+ series Limitless featuring Chris Hemsworth.

The idea behind a 24-hour fast is simple: You abstain from food for a full day. You can drink water, black coffee, and other liquids that do not contain calories. During this time, your body shifts from burning glucose as a primary fuel source to burning fat. You give your digestive system a rest day, allowing your body to focus on repairing and growing. Dr. Attia highlights several repair and growth benefits from fasting, but autophagy piqued my interest first.

Autophagy (from the Greek words “phagy” meaning eat, and “auto” meaning self) is a natural cellular process that plays a critical role in maintaining cellular health and preventing diseases. During autophagy, your body breaks down and recycles old, damaged, or dysfunctional cellular components, such as proteins, mitochondria, and other organelles. This process allows your cells to dispose of waste and build new, healthy components, which can help improve cellular function and longevity

Exercise (e.g., running) and fasting are the two methods to induce autophagy. In a 2012 paper summarizing clinical research with mice, researchers discovered that running “is even faster than starvation” at inducing autophagy. “If you just exercise the mice for 30 minutes on a treadmill, autophagosomes start to form. Thirty minutes of running induces autophagy 40 to 50 percent.” As mice extended their running to 80 minutes, autophagy was induced to 100 percent. Researchers then compared the normal mice with a mutant with normal background autophagy levels but could not induce higher levels. After training on the treadmill, the normal mice could run longer, but the mutant mice got no increased endurance from the training. Rest-day fasting can continue cellular housekeeping from autophagy without the stress of exercise.

Another benefit from fasting is increased human growth hormone (HGH) levels, which can help build and maintain muscle mass and aid recovery after a workout. Studies have shown fasting can increase HGH levels in both men and women. For example, a study published in the Journal of Clinical Endocrinology and Metabolism in 1988 found that a 24-hour fast increased HGH levels by up to 2,000% in men and up to 1,300% in women. The increase in HGH during fasting is thought to be due to a combination of factors. For example, fasting-induced stress may stimulate the release of HGH from the pituitary gland. Additionally, fasting can lower insulin levels, increasing the pituitary gland's sensitivity to signals that promote HGH release.

I am unsure if rest-day fasting will become part of my regular routine, but I will try it a handful of times.

Lastly, you can technically continue taking your Runner Multivitamin during a fast, but I would not. You need to take your multivitamin with food to absorb the nutrients best.

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