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Updated 10:00 AM November 21, 2005




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Exercise nearly as successful as drugs at lowering blood sugar

Exercising before eating can regulate blood sugar levels almost as well as two common glucose-lowering drugs, U-M research shows.

"For people who would rather exercise than be dependent on taking medication for the rest of their lives, this could be very good news," says Katarina Borer, professor of kinesiology and a member of the Center for Exercise Research.

Borer studied the body's response to exercising on an empty versus a full stomach. A group of post-menopausal women participated in two exercise studies. In one, they walked on a treadmill for two hours in the morning, then ate breakfast, and exercised the same length of time again in the afternoon just before dinner. In the other, they reversed the order, eating breakfast before their first round with the treadmill and having dinner before working out a second time.

Blood sugar naturally rises and falls as we eat and the body processes food for fuel. When the participants exercised before eating, their blood glucose rose significantly higher after their meals than when they exercised following eating. Between meals and during the following night, however, blood glucose was about 18 percent lower than when they ate first then exercised.

Borer compares the effects of exercising on an empty stomach to two common glucose-lowering medications, Metformin and Pioglitazone. Metformin lowers blood sugar about 19 percent after four months of use, while Pioglitazone lowers glucose about 22 percent after the same period.

The benefit of exercise comes the same day as the workout and lasts for 24 hours.

Borer says her research focuses on post-menopausal women in part because women are understudied, and hormone fluctuations of the menstrual cycle are not involved. Further studies are needed to see whether the results also apply to men and type II diabetics.

The preliminary study involved a high level of exercise—four hours in one day—so she wants to do follow-up research to look at whether less exercise gives the same sort of benefits.

Additionally, the level of insulin in the blood of the participants who exercised hungry was almost twice as high after they ate. With these kinds of benefits, perhaps people with mild diabetes would have the motivation to try even a demanding exercise regimen, rather than having to take medication, Borer says. She wants to see if pre-diabetic or type II diabetic patients respond the same way.

Borer surmises the liver is at work in generating these results. The liver provides sugar for the body's use. First thing in the morning when subjects have not eaten all night, the liver's sugar supply is lower. A demanding bout of exercise might clear out whatever glycogen is left in the liver, prompting it to signal the brain to lower its demand for sugar because this fuel is in short supply.

Borer describes this as the liver being wise with the body's fuel supply, rationing in case it might be a while before the next meal.

Borer recently presented her results at the Society for Neuroscience's annual meeting.

Her collaborators on the research were Elizabeth Wuorinen, formerly a graduate student at U-M and now an assistant professor at Norwich University, and Charles Burant, an associate professor of internal medicine at U-M.

The researchers also collaborated on a paper published earlier this year in the journal Appetite looking at exercise as an appetite suppressant. They concluded that the body does not consciously detect the need to replace calories burned in exercise, but hunger is instead controlled by factors such as volume of food in the stomach.

Borer and Wuorinen have another study under way to follow up, looking at how participants rate their hunger after doing 10 small bouts of exercise in one day. Participants either eat 400 calories less a day or burn 400 more calories. Borer will compare how the 400 calorie deficit affects the perception of hunger.

"There are a lot of reasons that we eat and it's not all caloric," Borer says. She is looking to see if exertion or volume of food consumed triggers a desire to eat, for example.

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