Endurance Exercise without Weight Loss May Reduce Body Fat

High-volume cycling over one week reduced liver fat, increased lean muscle

Rockville, Md. (September 18, 2024)-Participating in a high volume of exercise over a short period of time, such as cycling hundreds of miles in a few days, could reduce body fat levels without weight loss. The first-of-its-kind study is published ahead of print in the American Journal of Physiology-Endocrinology and Metabolism and has been chosen as an APSselect article for September.

The benefits of exercise are well known. Studies have shown that even without losing weight, if a person gains lean muscle through exercise, they may also lose body fat. This change in body composition is particularly important in relation to the visceral fat located in the abdominal cavity and the fat accumulated in normally lean organs such as the heart and the liver. In a new study, researchers explored how a "very large energy turnover produced by an extreme exercise protocol over a short period of time" could lead to significant body composition changes with minimal to no weight loss.

A small group of middle-aged male recreational cyclists participated in a seven-day ride. The men cycled approximately 710 miles (1,144 kilometers) over the course of the week. The research team recorded the volunteers' blood pressure, resting heart rate, cholesterol and blood sugar levels, as well as levels of inflammatory markers and body fat content throughout the trial.

The participants were asked to try to maintain a stable body weight. To do so, they had unlimited access to a buffet breakfast and lunch on each cycling day and took home a boxed dinner and snacks. Each day, the research team measured the volunteers' waist circumference, body composition, how many calories the volunteers ate and how much energy they expended. Any food the men ate that was not provided through the study was identified and nutritional information accounted for by their packaging. Based on these measurements, the cyclists were directed to eat and drink more to prevent significant weight loss and dehydration.

Compared to a control group of men in the same age range who did not perform the road cycling ride, the cycling group had significantly lower levels of liver fat (as shown through magnetic resonance imaging) before the weeklong ride. They also had less fat under the skin (subcutaneous). Surprisingly, these recreational cyclists had similar levels of visceral fat compared to controls. In addition, the cycling group had lower HbA1C levels, a long-term measure of blood sugar.

Despite attempts to consume enough calories to prevent weight loss during the trial, the volunteer group lost about 1% of their body weight and dropped an average of 1.26 inches off their waist size. They also lost just over 9% of their overall body fat mass (including a 14.6% reduction in visceral fat) and gained 1.2% lean muscle from their week of cycling. The cycling group saw a more than 20% reduction in their total cholesterol and a decrease of almost 40% in their triglyceride levels in addition to a substantial reduction in their blood pressure.

These findings "support the importance of promoting a physically active lifestyle rather than caloric restriction in obesity prevention, the latter being quite difficult to follow in the current socio-economic environment where highly processed, energy-dense foods are omnipresent," the researchers wrote. The study "provides evidence that humans were designed to be physically active rather than eat as little as possible."

Read the full article, "Effects of 1,144 km of road cycling performed in seven days: a cardiometabolic imaging study." It is highlighted as one of this month's "best of the best" as part of the American Physiological Society's APSselect program. Read this month's selected research articles.

NOTE TO JOURNALISTS: To schedule an interview with a member of the research team, please contact APS Media Relations or call 301.634.7314. Find more research highlights in our Newsroom.

Physiology is a broad area of scientific inquiry that focuses on how molecules, cells, tissues and organs function in health and disease. The American Physiological Society connects a global, multidisciplinary community of more than 10,000 biomedical scientists and educators as part of its mission to advance scientific discovery, understand life and improve health. The Society drives collaboration and spotlights scientific discoveries through its 16 scholarly journals and programming that support researchers and educators in their work.

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