The new study demonstrates the effects of eating versus fasting on gene expression in adipose (fat) tissue in response to exercise. The research indicates the different roles fat plays in powering and responding to exercise. Adipose tissue refers to a loose connective tissue composed mostly of adipocytes. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body. Adipose tissue also produces hormones.
There are two types of adipose tissue: white adipose tissue, which stores energy, and brown adipose tissue which generates body heat. Sometimes the terms ‘bad fat’ and ‘good fat’ are used, especially with those concerned about losing weight.
The study into the exercise, diet and fat relationship comes from the University of Bath. The researchers studied a group of overweight males in England. The subjects were required to for 60 minutes at 60 percent maximum oxygen consumption on an empty stomach. The experiment was later repeated, over the same distance. This time the volunteer subjects carried out the physical activity two hours after consuming a high-calorie carbohydrate-rich breakfast.
For both tests the scientists took various blood samples. In addition, the scientists collected adipose tissue samples immediately before and one hour after walking. The analysis of the results showed that gene expression in the adipose tissue differed significantly in the two trials.
Looking specifically for the expression of two genes: PDK4 and HSL, the study found the expression of these genes increased when the men fasted and exercised. Conversely the genes decreased when the men ate before exercising. Interpreting this, the rise in PDK4 indicates that stored fat was used to fuel metabolism during exercise instead of the carbohydrates from the recent meal. The other gene, HSL typically increases when adipose tissue uses stored energy to support increased activity (as with exercise).
This means adipose tissue often faces competing challenges. After a person has eaten a meal adipose tissue functions to respond to the meal and any exercise taken at this time will not stimulate the same changes in adipose tissue.
So the answer to the exercise before or after the meal conundrum means that exercise in a fasted state should provoke more favorable changes in adipose tissue: that is, if you want to lose weight then exercise on an empty stomach and eat a meal afterwards.
The findings have been published in the American Journal of Physiology – Endocrinology And Metabolism. The research paper is titled “Feeding influences adipose tissue responses to exercise in men.”
