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Intermittent dietary restriction may boost physical endurance

Animal studies show that intermittent fasting can improve overall health and prevent certain diseases. Whether the same applies to people is a subject for future study. ThitareeSarmkasat/iStock/Thinkstock

Most people in modern society eat three meals a day, plus snacks in between. Athletes typically consume multiple meals every day during training. Many load up on carbohydrates on the assumption that fueling their muscles with glucose will enhance performance.

For most of human history, however, people needed to be capable of high levels of physical performance even during periods of food deprivation. Studies in rodents have found that intermittent fasting can have positive health effects. These include extending lifespan and protecting against diabetes, heart disease, certain cancers, and other conditions. Emerging evidence from human studies suggests there may be benefits for some people.

Researchers have been working to understand the biological mechanisms involved in the potential benefits of fasting. When energy intake is restricted for more than 12 to 16 hours, glycogen stores in the liver become depleted. The body then switches from glucose to fats as a source of energy. Extended exercise can cause a similar shift. Fatty acids are metabolized to compounds called ketones. This metabolic state, called ketosis, brings a host of changes throughout the body.

A team led by Dr. Mark P. Mattson at NIH’s National Institute of Aging (NIA) used mice to study the effects of food deprivation on metabolism during endurance training. Thirty-five male mice were randomly assigned to four groups: a sedentary control group that could eat whenever they wanted; a sedentary group that was deprived of food every other day; a daily treadmill exercise group that could eat whenever they wanted; and a daily treadmill exercise group fed on alternate days. The study was published online on February 27, 2018, in the FASEB Journal.

After two months, the mice that had daily treadmill training ran significantly farther and for longer in a test of endurance than sedentary mice, no matter their eating patterns. Mice that had alternate-day food deprivation during training were able to run significantly farther and longer than the trained mice who were free to eat. Food deprivation itself, however, didn’t affect the performance of the untrained mice.

Food deprivation caused ketosis, as expected. These mice switched from glucose to fats as their energy source and had better metabolic efficiency. An analysis of gene expression in liver and muscle tissues and metabolites in blood showed that food deprivation during training strongly affected molecular pathways involved in production of mitochondria (which make the cell’s energy), energy metabolism, and others. Food deprivation also affected fatty acid metabolism and cell growth pathways. Despite all these differences, body weight among the mouse groups was similar.

“Emerging evidence suggests that intermittent dietary energy restriction might improve overall health and reduce risk factors for diabetes and cardiovascular disease in humans,” Mattson says. “Our new findings in laboratory animals provide evidence that similar intermittent eating patterns can enhance the beneficial effects of aerobic exercise on endurance performance.”

These effects could vary by the type of exercise and type of muscle under study. They may also differ in humans. Further research will be required to answer these questions.

—by Harrison Wein, Ph.D.