Exercise enthusiasts often wonder whether it's better to eat or fast before a workout. A new study is the first of its kind to show the effects of eating versus fasting on gene expression in adipose (fat) tissue in response to exercise. The study highlights the different roles fat plays in powering and responding to exercise.
For the study, researchers from the University of Bath in the U.K. studied a group of overweight males. The volunteers walked for 60 minutes at 60 percent maximum oxygen consumption on an empty stomach and, on another occasion, two hours after eating a high-calorie carbohydrate-rich breakfast.
The research team took multiple blood samples after eating or fasting and after exercising. The researchers also collected adipose tissue samples immediately before and one hour after walking.
Gene expression in the adipose tissue differed significantly in the two trials. The expression of two genes, PDK4 and HSL, increased when the men fasted and exercised and decreased when they ate before exercising.
The rise in PDK4 likely indicates that body fat stores was used to fuel metabolism during exercise instead of carbohydrates from the recent meal.
HSL typically increases when adipose tissue uses stored energy to support increased activity, such as during exercise.
These results reinforce the view that after eating, adipose tissue "is busy responding to the meal and a bout of exercise at this time will not stimulate the same beneficial changes in adipose tissue. Exercise in a fasted state may bring about more favorable changes in fat tissue, which could be beneficial for health in the long term.
Earlier research findings in agreement
This isn’t the first study to suggest that you burn more body fat if you workout before instead of after eating breakfast, for instance. But it is the first to show the effects of eating versus fasting on gene expression in adipose (fat) tissue in response to exercise.
A 2013 study published in the British Journal of Nutrition found that healthy men who ran on the treadmill for 60 minutes at a moderate intensity before eating breakfast burned 20 per cent more body fat afterwards than when they ran the same distance two hours after eating a morning meal.
Research conducted at Glasgow University in 2012 found that among non-exercising, overweight men, those who walked briskly for an hour before breakfast burned more body fat over the next eight-hour period than they did when they ate before exercising.
It’s thought that working out before eating breakfast increases the proportion of body fat burned during exercise. Research also suggests that exercising in a fasted state increases levels of proteins that help insulin move glucose into muscle cells.
Source: American Journal of Physiology - Endocrinology and Metabolism, March 14 2017.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.