The type of carbohydrates you eat before a workout may influence how much fat you burn during your exercise session, new research suggests.
Women who ate a breakfast rich in carbohydrates that do not cause a spike in blood sugar -- think muesli, yogurt, skimmed milk -- burned 50% more fat during a post-breakfast workout than did those who ate a breakfast rich in the kind of carbohydrates known to make blood sugar rise sharply, such as cornflakes and white bread.
Carbs that cause a sharp blood sugar rise are known as high-glycemic index carbs, while those that don't are called low-glycemic index carbs.
While other researchers have also found that a low-glycemic menu is beneficial to fat-burning, the new study has some unique points, noted lead author Emma Stevenson, a senior lecturer at Northumbria University, Newcastle Upon Tyne, U.K. She conducted the study while at the University of Nottingham.
"Most of the research in the effects of the glycemic load of pre-exercise feeding has been carried out in male subjects," Stevenson said. Most of it also has focused on endurance athletes, which doesn't describe the bulk of the population.
Instead, the new study included eight women of a typical healthy weight who averaged 24 years of age. On two different occasions, the women ate either a high- or the low-glycemic index breakfast, then walked on a treadmill for 60 minutes three hours later. Stevenson's group drew blood samples before the breakfast and also during and after the exercise to measure parameters such as free fatty acids, which are a marker for fat burning.
The average amount of fat oxidized during the exercise was 7.4 grams after the low-glycemic meal but just 3.7 grams the higher glycemic index meal, a nearly 50% difference.
Why the disparity? High-glycemic index carbs are known to spur a big spike in blood sugar, and the researchers believe that a meal rich in low-glycemic carbs, which elicit a lower blood sugar response, may boost the body's use of body fat for burning rather than for blood sugar.
Each breakfast totaled about 265 calories, but the low-glycemic meal had more fiber, the team noted.
The study was funded by Mars UK, the food and candy company. It is published in the May issue of The Journal of Nutrition.
The take-home message, according to Stevenson: To burn more fat, focus on the low-glycemic foods. "LGI foods tend to be whole grains, porridge, some whole grain cereals, soy and linseed bread," she said.
The new study makes sense and builds on previous research, said Barry Braun, director of the Energy Metabolism Laboratory at the University of Massachusetts, Amherst, who has done his own research on post-workout eating.
While Stevenson's study findings are limited to healthy-weight women, Braun said he suspects it will also hold true for those hoping to shed excess pounds. "Eating large amounts of high-glycemic carbs right before exercise is probably as detrimental for overweight people as it is for normal-weight," he said.
Like Stevenson, he said he is talking about pre-exercise meals for those who work out at less than triathlon intensity. "There may be a place for these high-glycemic carbs" when an athlete needs high energy immediately, such as before running a marathon, Braun said.
Last year, Braun's own research found that the type of food eaten after exercise can make a difference in weight control for everyday exercisers.
Based on his studies, Braun suggests that eating a meal low in carbohydrates after working out at moderate intensity, is potentially better for weight control than eating a meal high in carbs.
