Researchers at Nottingham University, UK, have found that exercising on an empty stomach can help people burn 70 percent more fat than exercising two hours after eating. They discovered study participants who exercised on both fed and empty stomachs did not overcompensate for the calories skipped earlier in the day. Some studies have suggested that exercise can benefit more in the morning followed by overnight fasting.
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The science behind fat burning
Our body converts food into fuel to keep it functioning properly. After a meal, our metabolism converts carbohydrates from food into energy, and the excess carbohydrate turns into glycogen and is stored as fat in the liver. Weight loss works on the concept of managing calories. If you want to lose weight, you have to burn more calories than you consume. Hence, weight loss methods like fasting and exercising on an empty stomach can help. During such processes, the stored fat is consumed to meet energy requirements for daily activities leading to fat burn. However, people must first consult with professionals before following such practices as every body type is different and may require a different approach to weight loss.
Back to the research
While experimenting, researchers found that evening exercise between 4 pm to 8 pm is more popular among people than morning workouts due to their busy schedules. Hence, they designed the study so participants could cycle an exercise bike at 6:30 pm at moderate intensity for 30 minutes. And then, cycle fast for 15 minutes as per their strength. Participants did this exercise twice on different days, once after a 7-hour fast and once after eating food two hours before the trial. They also measured how much food the participants ate after exercising.
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The outcomes showed that fasted exercise in the evening increased fat burn during exercise similar to exercising after an overnight fast. The amount of fat burned increased by up to 70 percent from 4.5g to 7.7g after 30 minutes of cycling. Also, the overall calorie intake per day of those doing fasted exercises was reduced to 440 Kcal.
“We wanted to explore the impact of fasted exercise in the early evening which we’d found was the most popular time for people to exercise during the week,” said Tommy Slater, a sports science researcher at Nottingham University and study author. “Fasting before evening exercise might benefit some elements of health due to increasing the amount of fat burned during exercise, or by reducing the number of calories that are eaten during the day. If done regularly it may improve the way the body deals with spikes in blood sugar after eating.”
The researchers concluded that despite the benefits, fasting during the day affects people’s motivation, performance and enjoyment which makes it difficult for them to stick with it for the long term.
The research was published in the journal International Journal of Sport Nutrition and Exercise Metabolism.