For Insulin Sensitive Overweight Patients, One Session Of Exercise Improves Metabolic Health, New Research Suggests

Obesity-related complications are associated with an abnormal fat metabolism in the muscle.  As a result, accumulated fat by-products inside the muscle affect insulin resistance. To avoid the build up of fat by-products, fat must either be oxidized (burned, as in exercise) or stored (as benign fat) in muscle.

A team of researchers has examined the effect of exercise on fat accumulation in a new study involving five obese women. In one session the women overate and did not exercise; in a follow-on session they overate and did exercise. The researchers found that:

• the body’s fat-burning oxidation rate was reduced after one day of overeating;
• conversely, just one session of exercise increased the rate of fat-burning oxidation; and
• exercise increased the amount of fat that would eventually be stored in the muscle. 

The findings indicate that even one bout of exercise helps to reduce the fat by-products inside the muscle, which affects the insulin sensitivity. The findings also suggest that a single session of exercise “steers” muscle fat towards oxidation, thereby avoiding the accumulation of fat by-products.

The study was conducted by Andrea Cornford, Minghua Li, Simon Schenk, Matthew Harber and Jeffrey Horowitz, Division of Kinesiology, University of Michigan, Ann Arbor. Their research is entitled "Alteration in Lipid Metabolism After One Day of Overeating Are Reversed by a Single Session of Exercise.” They will present their findings at a meeting sponsored by the American Physiological Society. The conference, The Integrative Biology of Exercise V, will be held September 24-27, 2008 in Hilton Head, SC. 

Study Summary

The aim of the study was to assess changes in fatty acid (FA) metabolism in response to acute overeating and exercise. Five obese women performed three separate two-day trials in which they consumed (1) a weight-maintaining diet [Control]; (2) a hypercaloric diet (700 calories above normal); and (3) the same hypercaloric diet, but exercised to the point where they expended the 700 excess calories.

The morning after each trial, researchers measured whole-body FA oxidation [FAO] and calculated non-oxidative FA disposal as the difference between FA uptake and FAO.

A muscle biopsy was performed to measure the presences of triglycerides that are involved in fat storage.

The morning after the trials, the researchers observed that overeating suppressed fatty acid oxidation below the control levels, while exercising increased oxidation. Non-oxidative FA disposal was the same in each trial and a direct correlation between FA uptake and muscle GPAT activity were found.

Conclusions

According to Andrea Cornford, a member of the research team, “Exercise decreases everyone’s insulin resistance and therefore reduces the chances of developing diseases such as type 2 diabetes. This study shows that even a single bout of exercise helps obese individuals increase their body’s fat-burning rate and improve their metabolic health.”