Running on empty miles better for slimming
Published 04/06/2010 | 05:00
RUNNING on empty may not be such a bad idea after all.
Though many athletes eat before training, some scientists say that if you really want to get rid of more fat, you should skip the pre-workout snack.
Several studies suggest exercising while your body is low on food may be a good way to trim excess fat. In a recent paper, European researchers found that cyclists who trained without eating burned significantly more fat than their counterparts who ate.
Muscles usually get their energy from carbohydrates, which is why athletes like Lance Armstrong and Michael Phelps scarf down enormous amounts of food before a race. But if you haven't eaten before exercising, your body doesn't have many carbohydrates in reserve. That forces it to burn fat instead, scientists say.
"When you exercise (after fasting), your adrenaline is high and your insulin is low," said Peter Hespel, a professor of exercise physiology at the University of Leuven in Belgium. "That ratio is favourable for your muscles to oxidise (break down) more fatty acids."
In a study published in April, researchers at the University of Birmingham and elsewhere assigned seven people to cycle three days a week, followed by an intense session an hour later without eating. Another seven people followed the same regime, without fasting.
Though members of the group that didn't eat performed worse on the intensive training, they burned a higher proportion of fat to carbohydrates than the group that ate.
The results were published in 'Sports & Exercise', the journal of the American College of Sports Medicine.
In a 2008 study, Hespel and colleagues tested the effects on men who did endurance training without eating versus those who ate. In the athletes who hadn't eaten, the researchers found a spike in the amount of proteins needed to process fat, meaning their bodies had been primed to burn more fat.
Though Hespel and colleagues have primarily studied the effects of exercising without eating in young, healthy people, he thinks the method could also help people with problems like diabetes.
Because exercising without eating produces muscles that are better at absorbing glucose -- which is important for preventing diabetes -- Hespel theorised the strategy would also help diabetics control their insulin levels.
For recreational athletes interested in maximising their exercise regimen, some experts recommend a regular training session where you deliberately do not eat beforehand.
Others are more sceptical and say people shouldn't exercise without having at least a small snack first.
"I think it's actually a pretty bad idea," said Dr Alexis Chang Colvin, a sports medicine expert at Mount Sinai Hospital in New York who has worked with professional football and hockey teams.
"If your blood sugar is low, you could wind up getting dizzy and you might not be able to exercise as well as if you were well-nourished," she said.
Colvin recommended having something small like a banana before training.
She also warned the strategy might make people more prone to injury and that eating was important so the body would have enough nutrients to recover from a bout of exercise.