More than 20 million Americans have diabetes, according to the U.S. Centers for Disease Control and Prevention, and at least 41 million are estimated to have prediabetes. The prevalence of both conditions is expected to grow as the population ages and rates of obesity continue to rise.

The Diabetes Prevention Program (DPP) was the first nationwide U.S. study to examine whether either diet and exercise or metformin, an antidiabetic agent, could prevent or delay the onset of type 2 diabetes in people with prediabetes. Prediabetes, also called impaired fasting glucose and/or impaired glucose tolerance, is a condition in which glucose (blood sugar) levels are higher than normal, but not high enough for a diagnosis of diabetes.

Sponsored by the federal government’s National Institutes of Health (NIH), the three-year study was launched in 1995. It was conducted on 3,234 people, at 27 medical centers around the country. The ages of the participants ranged from 25 to 85, with an average age of 51.

All of the participants were overweight or obese and had prediabetes. These conditions are risk factors for developing type 2 diabetes.

Nearly half of the participants were from minority populations that have an increased risk of developing type 2 diabetes. The racial and ethnic makeup was:

• White, 55 percent
• African American, 20 percent
• Hispanic/Latino, 16 percent
• American Indian, 5 percent
• Asian American/Pacific Islander, 4 percent

However, only 32 percent of the subjects were men. Men account for 53 percent of the estimated 20.8 million cases of diabetes in American adults, according to the NIDDK.

The participants were randomly divided into four groups.

The participants were then randomly divided into four groups:

• The first group was given intensive counseling on effective diet, exercise and behavior modification. By eating less fat and fewer calories and moderately exercising for 150 minutes a week, this group’s goal was to lose 7 percent of body weight and to maintain the loss. 
  
  
• The second group took an 850-milligram dose of metformin (see Biguanides) twice a day. Members also received information on diet and exercise but no intensive counseling.
  
  
• The third group took placebos (pills that have no effect) instead of the metformin. Like the second group, members also received information on diet and exercise but no intensive counseling.
  
  
• The fourth group was given the insulin-sensitizing medication troglitazone, a type of thiazolidinedione. This part of the study was discontinued in 1998 upon the discovery that troglitazone could seriously damage the liver.

Researchers continued to assess the 585 volunteers who had taken the medication. The NIH announced in 2005 that, according to a new analysis of data from the DPP, among those who had taken troglitazone - for an average time of less than 11 months – the rate of diabetes was 75 percent lower than among those who had taken a placebo. The scientists concluded that this development showed the value of treating insulin resistance to help prevent type 2 diabetes.