People who exercise on an empty stomach may have less motivation than their full-fed counterparts, but a new study shows it could be the way to go if want to burn more fat. Researchers at Nottingham Trent University in England found exercising on an empty stomach allowed people to burn 70 percent more fat than those who ate two hours before exercising.
Previous research conducted regarding exercising in a fasted state suggested working out first thing in the morning before eating. Researchers wanted to see if they could conduct a similar experiment later in the day during a more popular time for exercising for people who work or have other responsibilities during the day. They chose the window between 4 p.m. and 8 p.m. since that is when a large percentage of regular exercisers work out.
Nottingham Trent scientists partnered with colleagues from Manchester Metropolitan University and Loughborough University and published their findings in International Journal of Sport Nutrition and Exercise Metabolism.
Study participants started their workout with a 30-minute, moderate intensity session on an exercise bike at 6:30 p.m. They then completed a time trial on the exercise bike to see how far they could go in 15 minutes.
This was done twice during the study. One day it was completed with the study participants not having eaten within seven hours of their workout and the other day it was competed when they ate two hours before exercising.
Just like previous studies conducted first thing in the morning, the ones who did not eat within seven hours of their evening workout burned more fat during their workout. The increase in this case was 70 percent during the 30 minute session – from 4.5 grams to 7.7 grams.
Researchers also measured how much food the participants ate after their workout. The found those who fasted before working out ate a little more after their workout (100 calories) than those who ate two hours prior, but their overall calorie intake was down by 440 for the day when you factor in the fasting before the exercise.
The downside is the ones who exercised after fasting covered slightly less distance during the 15-minute time trial and the fully fed participants. They also had lower motivation to work out and also enjoyed their exercise experience less.
"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 in Nottingham Trent University's School of Science and Technology.
"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," Slater added. "If done regularly it may improve the way the body deals with spikes in blood sugar after eating. However, despite these benefits, fasting during the day does appear to reduce people's exercise performance, motivation and enjoyment, which may make it harder for some people to stick with it in the longer term."