Exercise Makes Fasting Easier

This article presents a study that shows that exercise suppresses the release of the hunger hormone to delay hunger while fasting.

The study was presented at the International Journal of Exercise Science conference in 2021.

The researchers were from Brigham Young University. Brigham Young is the second president of The Church of Jesus Christ of Latter-day Saints (LDS).

Members of the LDS are commonly called the Mormons, and they fast at least 24 hours every month.

Study background

Many people exercise and do intermittent fasting or time-restricted eating to get healthy. A common question is, will exercise make me more hungry and shorten my fast?

Ghrelin is a hormone that signals hunger to the brain. Whenever we feel hunger, ghrelin levels are up.

In contrast, increased levels of satiety hormones give a sensation of fullness. They are GLP-1, Leptin, PP, and PYY

In this study, exercise and fasting were coupled to know the effect of exercise on the hunger and satiety hormones.

Research Design

The researchers measured the hunger and satiety hormones every 12 hours during a 36-hour water-only fast with and without an initial bout of intense exercise. 

Additionally, they measured subjective ratings of hunger and mood change using the Brunel Mood Scale every two hours and compared them with what is expected with the hormonal changes. 

The eleven men and nine women stayed hydrated throughout the fast with water only. Noncaloric, electrolyte, or caffeinated additives were not allowed. Gum chewing was also prohibited. 

The group exercised thirty minutes after the start of the fasting period. The exercise consisted of a treadmill running at a grade and speed to increase their estimated heart rate reserve (HRR) to 70%. 

Results

Ghrelin

The hunger hormone ghrelin remained constant for the first 24 hours of the fast and decreased from 24 to 36 hours.

In addition, ghrelin was higher during the fasting-only condition but lower when exercise was added to fasting.  

GLP-1

The satiety hormone GLP-1 was higher in the exercise and fasting conditions but lower in the fasting-only condition.

Exercise Makes Fasting Easier
Source: The Effects Of Exercise On Hunger And Satiety Hormone Concentrations Over A 36-Hour Fast: A Randomized Crossover Study

Leptin, PP, and PYY

Levels of leptin, PP, and PYY remained constant during the exercise and non-exercise conditions.

Subjective measures of hunger

The subjects’ sensation of hunger increased throughout the study in both conditions (p<0.01). However, there was no difference in the feeling of hunger, thirst, or stomach discomfort between fasting only and fasting plus exercise conditions. 

The authors considered the possibility that their subjects were not able to accurately assess their subjective feelings of hunger and satiety during an acute fast.

Application of results

According to the authors,

Since, higher levels of circulating ghrelin has a powerful impact on hunger, these results indicate that starting a fast with exercise does not make fasting more challenging but may actually make it easier.

This finding is strengthened when combined with the results of GLP-1, which was higher in the exercise condition.

GLP-1 has been shown to signal fullness and has a satiating property that can reduce food seeking behavior.

The same authors also published a study that showed that ketosis happens 3.5 hours faster when exercise is combined with fasting.[2] 

In ketosis, ketone levels are elevated and are used by the body, including the brain, for fuel instead of glucose.

In the same research, glucagon levels also increased with exercise and fasting.

Glucagon is a hormone that increases glucose levels even in the absence of food. The mobilization of endogenous glucose can prolong the fast by making it more sustainable.

Take away message

Fasting and exercise have many benefits. Based on hundreds of medical research I have read, I believe that doing both can spare the vast majority of people from a variety of common medical problems, including heart attacks, strokes, and cancer, that cause the highest mortality rates.

Depending on the individual conditions, longer fasting produces more health benefits. Doing exercise with fasting can make it easier.

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References:

  1. Coleman, Jacob L.; Deru, Landon; Chamberlain, Hunter; and Bailey, Bruce W. (2021) “The Effects of Exercise on Hunger and Satiety Hormone Concentrations Over a 36-Hour Fast: A Randomized Crossover Study,” International Journal of Exercise Science: Conference Proceedings: Vol. 14: Iss. 1, Article 2.
  2. Deru LS, Bikman BT, Davidson LE, Tucker LA, Fellingham G, Bartholomew CL, Yuan HL, Bailey BW. The Effects of Exercise on β-Hydroxybutyrate Concentrations over a 36-h Fast: A Randomized Crossover Study. Med Sci Sports Exerc. 2021 Sep 1;53(9):1987-1998. doi: 10.1249/MSS.0000000000002655. PMID: 33731648.

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