Is It Better to Exercise on a Full or Empty Stomach?

Many sports enthusiasts grapple with this question: they want to maximize their running, aerobics class, or any physical activity they engage in, but they are unsure whether eating beforehand will enhance their performance or the opposite.

A new study sought to determine once and for all how food intake before physical activity affects gene expression in fat tissue post-exercise. Researchers from the University of Bath in the UK examined a group of overweight men who, on certain days, walked briskly for sixty minutes on an empty stomach, and on other days, performed the same walk two hours after a carbohydrate- and calorie-rich breakfast. The researchers took numerous blood samples both after exercising on an empty stomach and after exercising on a full stomach. They also collected samples from the participants' fat tissue before the walk and an hour after it.

The results: there is indeed a clear difference between exercising on an empty or full stomach. When exercising on an empty stomach, there was an increase in the expression of genes that use the body's fat stores instead of carbohydrates from a meal (since participants, as mentioned, skipped breakfast). After a rich breakfast, however, the fat tissues were primarily dealing with the new intake rather than contributing to the benefits of the exercise.

In other words, to optimize changes in fat tissue, it is best to go for a run when you are hungry.