The study said this is because men, who tend to be more muscular than women, will use carbohydrates as fuel. So when men eat before exercising, the exercise only uses the energy from the carbohydrates, which doesn't allow them to burn fat, Daily Mail reported.
Meanwhile, whatever a man eats after exercising will only be used to store more energy for the next workout, the study said.
"Men get a better effect if they exercise fast [as in don't eat] as they're putting more stress on the muscle to burn more fuel, so the muscles burn more fat," Dr. Adam Collins, lead researcher of the study, told Daily Mail.
But women will more often burn fat as a way to conserve carbs, Daily Mail reported. When women eat carbs, the energy is stored in the body, unlike a man's. So a workout immediately targets their fat, not the energy and muscle produced by the carbs, Daily Mail reported.
"Women have more fat around hips, bums and tums, better release of fatty acids into the blood, hormonal differences which mean they can be better and more frugal at conserving glucose [sugar from carbohydrates] and burning fat," Collins said. "This is probably an evolutionary advantage to do with pregnancy. If women are better at managing their fuels they have glucose to spare for the foetus."
Though this study offers a guiding light for people on when and when not to exercise, it's not a solid answer. After all, there's been an ongoing debate for years about when is the best time to work out and eat.
But there's also been some suggestions about eating before a workout, mostly to provide energy for physical activities. Rebecca Scritchfield, a sports nutritionist, said food often acts as energy to give people the push they need to perform a workout.
"It's this simple," she wrote. "Cars don't go far without adequate gas. Planes don't fly without jet fuel. Why would our body 'machine' operate without food fuel?"
Even though there seems to be a divide, the best method may be eating before and after a workout.
For example, she said it might be a good idea to pack in some carbs, especially complex ones, like whole grains and vegetables, before hitting the gym, since they will act as fuel to increase your workout potential. Other carbs, like cookies and processed foods, will only increase your weight and not your energy, Time reported.
"In general, you'll want to eat a meal high in carbs and protein and low in fat roughly three to four hours before you exercise," Cohen told Time.
After your workout, eating is also recommended, depending on what you're trying to accomplish.
Cohen suggests eating or drinking some protein to help build muscles. Though it's also important to limit the amount of protein you consume, as too much can lead to kidney damage and weak bones, Time reported.