Why exercise on empty stomach may be better for your health

The study analysed effects of eating versus fasting on gene expression in adipose (fat) tissue in response to exercise. 

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", explained corresponding author of the study Dylan Thompson from University of Bath in Britain.

"This means that exercise in a fasted state might provoke more favourable changes in adipose tissue, and this could be beneficial for health in the long term," Thompson added.

"We propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise," the researchers noted in the study published in the American Journal of Physiology -- Endocrinology and Metabolism.

The study participants were a group of overweight males who walked for 60 minutes at 60 per cent maximum oxygen consumption on an empty stomach and, on another occasion, two hours after consuming a high-calorie carbohydrate-rich breakfast. 

The research team took multiple blood samples after eating or fasting and after exercising.

The researchers also collected fat 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 stored fat 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, Thompson said.

These results reinforce the view that "adipose tissue often faces competing challenges," Thompson wrote. 

"This is the first study to show that feeding prior to acute exercise affects post-exercise adipose tissue gene expression," the study said.