Should you eat before going running or heading to the gym? Many sports doctors recommend a meal rich in protein and carbohydrates at least three hours before intense exercise. However, a new study, published March 2017 in the journal of the American Physiological Society, could contradict this advice.
Researchers at the University of Bath studied a group of 10 young male volunteers all of whom were overweight. In a first test, they walked for 60 minutes at 60% maximum oxygen consumption on an empty stomach. In a second test, they walked for two hours after consuming a high-calorie carbohydrate-rich breakfast. The scientists took multiple blood samples from the volunteers after eating or fasting and after exercising. They also collected adipose tissue samples immediately before and one hour after the walking tests.
The scientists found that gene expression in adipose tissue was significantly different in the two trials. The expression of two genes in particular, PDK4 and HSL, increased when the volunteers fasted and exercised and decreased when they ate before exercising.
The researchers conclude that when fasting, the body uses stored fat to respond to energy needs during exercise and to provide the fuel required for physical activity. After eating, on the other hand, it was the carbohydrates from the recent meal that were used as fuel. In this specific case, adipose tissue is responding to a meal and to exercise at the same time and, as a result, does not stimulate the same beneficial changes.
According to the study, exercising in a fasted state could provoke more favorable changes in adipose tissue, which could be beneficial for health in the long term.
While the study’s sample size is relatively small, it is the first study of its kind to show the effects of eating versus fasting on gene expression in adipose tissue in response to exercise.
However, sports doctors recommend eating before all intense or long exercise sessions or endurance workouts.