While Americans' increasing waistlines and the associated health problems have been making headlines, US researchers have been examining how adopting a healthful diet and physical activity plan can prevent type 2 diabetes.

Multi-center study

The Diabetes Prevention Program Research Group included more than 3,200 US adults. All had a Body Mass Index of at least 24 (22 or higher in Asians), and a fasting blood glucose level of 95 to 125 mg/dL (5.3 to 6.9 mmol/L) and 140 to 199 mg/dL (7.8 to 11.0 mmol/L) two hours after a 75-gram oral glucose load. According to the 1997 American Diabetes Association standard, these glucose levels are considered elevated, but not diagnostic of diabetes.

The volunteers were randomly assigned to one of three treatment groups: standard lifestyle recommendations (diet and exercise) plus metformin (Glucophage®) at a dose of 850 mg twice daily; the standard lifestyle recommendations plus a placebo; or, an intensive lifestyle modification program.

The standard lifestyle recommendations consisted of written handouts and an annual 30-minute individual session that emphasized healthful eating, weight reduction, and the importance of physical activity.

The intensive lifestyle modification program was a 16-lesson curriculum designed to help participants achieve a 7% weight loss through a healthful low-fat, low-calorie diet and at least 150 minutes each week of moderate physical activity. This program was designed to be flexible and culturally sensitive, and was taught individually to each participant during the first 24 weeks, with subsequent group sessions for support. While some subjects were studied for 4 years, the average follow-up period was 2.8 years.

The primary outcome measure was a diagnosis of diabetes, determined by either an oral glucose-tolerance test or a fasting plasma glucose test. Values diagnostic of diabetes were based on the American Diabetes Association guidelines: fasting plasma glucose at least 126 mg/dL (7.0 mmol/L), or at least 200 mg/dL (11.1 mmol/L) two hours after a 75-gram oral glucose load.

Positive changes

Participants assigned to the intensive lifestyle intervention group were more successful in making healthful changes than those in the other groups. On average, they decreased their daily food intake by 450 calories, and fat intake by almost 7%. Over half met the goal of at least 150 minutes of physical activity each week. These changes resulted in a mean weight loss of 12 lbs, significantly more than the other two groups.

As expected, health benefits accompanied these lifestyle changes. The incidence of diabetes was 58% lower in the intensive lifestyle intervention group than the placebo group, while those taking metformin had a 31% lower diabetes incidence compared with the placebo. The overall incidence of diabetes was 11.0, 7.8, and 4.8 cases per 100 person-years in the placebo, metformin, and lifestyle groups, respectively.

Metformin is typically used for the treatment of diabetes, not prevention. This study indicates that it may be an effective preventive measure as well, although less so than diet and exercise.

Weight loss as preventive medicine

Healthful lifestyle changes benefited all age and racial and ethnic groups -- African Americans, Hispanics, American Indians, and Asians, some of whom are at particularly high risk of developing type 2 diabetes. An estimated 10 million people in the United States, similar to the volunteers in this study in terms of age, weight, and blood sugar measurements, and therefore at risk for developing diabetes, could benefit from a lifestyle intervention.

For patients who fit this common profile for diabetes risk, a healthful, low-fat, low-calorie diet and at least 20 minutes each day of moderate activity seems to be effective preventive medicine. Health care providers need to be aware that most patients will require assistance implementing lifestyle changes. By familiarizing themselves with weight loss programs or fitness centers that can offer this component, health professionals can direct patients to resources that will benefit their health.