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TYPE 2 PREVENTION IN SENIORS: Weight Loss, Exercise, Or Both?

Posted on: Tuesday, 2 November 2004, 03:00 CST

Bret Goodpaster, PhD, is studying the effects of weight loss and exercise on insulin sensitivity, both together and separately.

Weight loss and exercise are known to cut the risk of type 2 diabetes, mainly by decreasing insulin resistance, a condition in which the cells do not use insulin efficiently. The conventional wisdom is that weight loss and exercise go hand-inhand, and doctors usually recommend both for their patients who are at risk for type 2, including seniors, who are already at risk because of their age.

Exactly how weight loss and exercise work together is still a mystery, however, and one that Bret Goodpaster, PhD, assistant professor of medicine at the University of Pittsburgh, hopes to solve. Goodpaster and his team are studying the effects of weight loss and exercise, together and separately, in seniors at risk for type 2. Goodpaster hopes to learn how each works, and how they may work in tandem.

Using funds from an ADA Clinical Research Award, Goodpaster and his team are studying 60 to 75 sedentary seniors between the ages of 65 and 75 who are overweight. All participants have a condition called pre-diabetes in which their blood glucose is higher than normal, but not high enough to warrant a diagnosis of diabetes.

When the participants enroll in the study, they'll undergo a series of tests. They'll take an exercise test to reveal their level of physical fitness. The researchers will measure their body fat with a CT scan; record each participant's height, weight, and body mass index (BMI); and take a biopsy from each participant's thigh muscle. (The biopsy will be very useful in determining how efficiently their muscles store and use fat for energy.) Then the participants will stay overnight at the research center and undergo what is known as a glucose clamp. They will receive glucose through an IV so the researchers can measure their insulin sensitivity. (The less glucose their body uses, the more insulin-resistant their cells are.)

After the initial tests, the participants will be divided into three groups for 16 weeks. One group, the weight-loss group, will be assigned a diet that restricts calories enough to prompt weight loss. They will meet with a registered dietitian each week and receive nutrition information and individual counseling. They will not exercise.

The second group will start an exercise program consisting mostly of walking, with some stationary cycling. They'll also do some light resistance training. Because the participants have been sedentary up to this point, the exercise program will not be extremely strenuous. The participants in this group will not go on a calorie-restricted diet.

The third group will do it all. They'll go on a calorie- restricted diet, meet with a dietitian for counseling every week, and exercise.

"Dividing the participants like this will allow us to see the separate effects of each approach," says Goodpaster.

Practical Information

At the end of 16 weeks, the participants will undergo the same tests they did when they enrolled. Goodpaster's team will then compare the test results. What kind of changes occurred in the participants' weight, muscle mass, body fat, and insulin sensitivity?

Goodpaster has a few hunches.

First, he anticipates that the weight loss group will lose some body fat because of their calorie restriction. Body fat hinders insulin sensitivity, so the less body fat there is, the better the insulin sensitivity. In this group, the improved insulin sensitivity would come only from weight loss, and not from changes in muscles. There would be no changes in their muscles because these participants will remain sedentary for the duration of the study.

He doesn't expect to see much weight loss in the exercise-only group, however. Instead, he expects insulin sensitivity to improve for a different reason.

"The exercise-only group probably will not lose as much weight as the others, if they lose weight at all," he says. "However, I think exercise will have a more direct effect on muscle capacity to use insulin and blood glucose." Therefore, improved insulin sensitivity in this group would come from changes in their muscles themselves.

Finally, he anticipates that the third group-the group using both diet and exercise-will have the greatest improvement in insulin sensitivity. Fat loss from calorie restriction may remove an obstacle to insulin sensitivity, and changes in the muscle cells may make the cells more responsive to insulin.

While weight loss from calorie restriction may help, that's not the whole picture, according to Goodpaster. Calories are important, he says, but so is dietary fat and what the body does with it. In overweight people, the body tends to store dietary fat. That makes losing weight and keeping it off with diet alone difficult.

"There's pretty good evidence in other prevention studies to suggest that efficient use of fat calories is important. Exercise can help with that," Goodpaster says. "We anticipate that diet alone will not train the body to use fat efficiently."

Instead, he says, building muscle through exercise may help "train" the body to use dietary fat more efficiently. That will help keep the lost weight from returning.

"When it comes to weight loss, exercise is more for helping people maintain the loss and prevent regain," he says. When people regain lost weight, they tend to regain it as fat. That brings us back to body fat as an obstacle Io insulin sensitivity.

"The results of the study may have lots of implications for prevention," Goodpaster says. "The nice thing is that we'll get some practical information in terms of how these different interventions work, information that we can then use in practice."

BRET GOODPASTER, PHD

Occupation

Assistant Professor of Medicine

The University of Pittsburgh

Professional Focus

Type 2 prevention

Outside Interests

Cycling, family time

Research Funding ADA Clinical Research Award

To sponsor an ADA research project at the Research Foundation's Pinnacle Society level of $ 10,000 or more, call EIIy Brtva, MPH, managing director of Individual Giving, at (703) 253-4377, or e- mail her atebrtva@diabetes.org.

Weight loss from calorie restriction may help insulin sensitivity, but that's not the whole picture.

Copyright American Diabetes Association Nov 2004

Source: Diabetes Forecast

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