Food before exercise boosts blood sugars, giving the body fuel to increase the intensity and length of a workout. It also keeps you from being fatigued or dizzy.
A 2017 study from the University of Bath, also co-authored by Gonzalez, looked at 10 men and found the same results — because of lower blood sugar levels after fasting, the men burned more fat.
However, this time the men burned more calories if they ate breakfast first.
A 2010 study found similar results, this time in a group of 28 healthy, physically active men. One group did no exercise. Two other groups were put through grueling morning exercise of running and cycling four times a week; one group ate before exercise and the other after.
It’s likely no surprise that the group who didn’t exercise gained weight. But contrary to the 2017 study the group who ate breakfast before exercise also gained weight. It was the group who exercised on water and an empty stomach that maintained their weight, lost fat, and kept their blood sugars in good shape.