Is it better to eat before or after exercise?

Exercise fanatics have as many opinions about their routines and diets as there are exercisers. No two agree with what is the best timing of meals to exercise. Some feel that meals would occur before exercise to provide you with fuel to burn. Others feel that that you should exercise on an empty stomach to allow yourself to lean up.

A new study is the first of its kind to show the effects of eating versus fasting on gene expression in adipose or fat tissue in response to exercise​[1]​. This study highlights the different roles fat plays in powering and responding to exercise. We know that feeding profoundly affects metabolic responses to exercise in various tissues, but the effect of feeding status on human adipose tissue responses to exercise has never been studied.

The study enrolled ten healthy overweight men that were overweight and trying to lose weight. The subjects walked at 60% of maximum oxygen uptake under either fasted or fed conditions in a randomized, counterbalanced design. Feeding comprised 648 Calories two hours before exercise. Blood samples were collected at regular intervals to examine changes in metabolic parameters.

The researchers found that feeding status did not impact serum and ex vivo adipose secretion or metabolic markers in response to exercise. 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. These results clearly indicate that feeding after exercise is the best strategy.

The bottom line: Exercise prior to meals is a better strategy. You burn calories prior to eating and this magnifies weight loss. This is the first study to show that feeding before acute exercise affects post-exercise adipose tissue gene expression, and we propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise. More research is needed.