Diet and Exercise Delay Diabetes and Normalize Blood Glucose
Millions of overweight Americans at high risk for type 2 diabetes can delay and possibly prevent the disease with moderate diet and exercise, a major clinical trial has found. The same study found that the oral diabetes drug metformin also reduces type 2 diabetes risk, although not as effectively as lifestyle changes. Researchers announced results of the trial, called the Diabetes Prevention Program (Diabetes Prevention Program), last August after ending the study a year early. The study results are reported in the February 7 issue of the New England Journal of Medicine.
"This research conveys a powerful message of hope to individuals at risk for type 2 diabetes, a painful, life-threatening disease that has been increasing in this country along with obesity," said HHS Secretary Tommy G. Thompson. "By adopting a moderate, consistent diet and exercise program, many people with one or more of the risk factors for type 2 diabetes can stop the disease before it becomes irreversible."
The Diabetes Prevention Program compared three approaches—lifestyle modification, treatment with metformin, and standard medical advice—in 3,234 overweight people with impaired glucose tolerance (IGT), a condition in which blood glucose levels are higher than normal but not yet diabetic. About 20 million people in the United States have IGT, which raises the risk of developing type 2 diabetes and cardiovascular disease. Once a person has type 2 diabetes, the risk of heart and blood vessel disease is even greater—two to four times that of people without diabetes.
Diet and exercise that achieved a 5- to 7-percent weight loss reduced diabetes incidence by 58 percent in participants randomized to the study's lifestyle intervention group. Participants in this group exercised at moderate intensity, usually by walking an average of 30 minutes a day five days a week, and lowered their intake of fat and calories. Volunteers randomly assigned to treatment with metformin had a 31 percent lower incidence of type 2 diabetes. Metformin lowers blood glucose mainly by decreasing the liver's production of glucose.
"Lifestyle intervention worked equally well in men and women and in all the ethnic groups. It was most effective in people age 60 and older, who lowered the risk of developing diabetes by 71 percent. Metformin was also effective in both sexes and in all the ethnic groups, but it was relatively ineffective in older volunteers and in those who were less overweight," said study chair Dr. David Nathan of Massachusetts General Hospital, Boston.
Both interventions lowered fasting blood glucose levels, but lifestyle changes more effectively lowered blood glucose levels 2 hours after a glucose drink. Also, about twice as many people in the lifestyle group compared to placebo regained normal glucose tolerance, showing that diet and exercise can reverse IGT.
"Not only did changes in diet and physical activity prevent or delay the development of diabetes, they actually restored normal glucose levels in many people who had impaired glucose tolerance," said Dr. Allen Spiegel, director of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the part of the National Institutes of Health (NIH) that sponsored the study. "These findings bring us closer to the goal of containing and ultimately reversing the epidemic of type 2 diabetes in this country."
Diabetes Prevention Program volunteers were randomly assigned to one of the following groups:
The latter two groups also received information on diet and exercise.
A fourth arm of the study, treatment with the drug troglitazone (Rezulin) combined with standard diet and exercise recommendations, was discontinued in June 1998 due to the potential for liver toxicity.
Diabetes Prevention Program participants ranged from age 25 to 85, with an average age of 51. Upon entering the study, all had impaired glucose tolerance as measured by an oral glucose tolerance test, and all were overweight, with an average body mass index (BMI) of 34. About 29 percent of the Diabetes Prevention Program standard group developed diabetes during the average follow-up period of 3 years. In contrast, 14 percent of the diet and exercise arm and 22 percent of the metformin group developed diabetes. Volunteers in the diet and exercise arm met the study goal, on average a 7 percent—or 15-pound—weight loss, in the first year and generally sustained a 5 percent total loss for the study's duration. Participants in the lifestyle intervention arm received training in diet, exercise (most chose walking), and behavior modification skills.
Forty-five percent of Diabetes Prevention Program participants were from minority groups that suffer disproportionately from type 2 diabetes: African Americans, Hispanic Americans, Asian Americans and Pacific Islanders, and American Indians. The trial also recruited other groups at higher risk for type 2 diabetes, including individuals age 60 and older, women with a history of gestational diabetes, and people with a first-degree relative with type 2 diabetes.
Can the interventions prevent diabetes completely? "We simply don't know how long, beyond the 3-year period studied, diabetes can be delayed," says Dr. Nathan. "We hope to follow the Diabetes Prevention Program volunteers to learn how long the interventions are effective." The researchers will analyze the data to determine whether the interventions reduced cardiovascular disease and atherosclerosis, major causes of death in people with type 2 diabetes.
Other studies have shown that diet and exercise delay type 2 diabetes in at-risk people. However, the Diabetes Prevention Program, conducted at 27 centers nationwide, is the first major trial to show that lifestyle changes can effectively delay diabetes in a diverse population of overweight American adults with impaired glucose tolerance.
About 16 million people in the United States have diabetes. It is the main cause of kidney failure, limb amputations, and new onset blindness in adults and a major cause of heart disease and stroke. Type 2 diabetes accounts for up to 95 percent of all diabetes cases. Most common in adults over age 40, type 2 diabetes affects 8 percent of the U.S. population age 20 and older. It is strongly associated with obesity (more than 80 percent of people with type 2 diabetes are overweight), inactivity, family history of diabetes, and racial or ethnic background. The prevalence of type 2 diabetes has tripled in the last 30 years, due in large part to the upsurge in obesity. People with a BMI of 30 or greater have a five-fold greater risk of diabetes than those with a normal BMI of 25 or less.
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