Diabetes Prevention Program: lifestyle change versus metformin

Why this study matters

The Diabetes Prevention Program, often called the DPP, is one of the most cited trials in diabetes care. It asked a simple question: if people at high risk of type 2 diabetes change how they eat and move, or take the medicine metformin, can diabetes be prevented or delayed? The answer shaped diabetes prevention programs around the world, including in Canada. For readers who have been told they have prediabetes or a higher body weight with raised blood sugar, this is the trial behind much of the advice they hear. It is also the starting point for later follow-up reports covered elsewhere on this site.

Who was in the study

The trial enrolled 3234 adults who did not have diabetes but had raised blood glucose both when fasting and after a glucose drink. That pattern marks a high risk of developing diabetes. The average age was 51 years, and the average BMI was 34.0. BMI, or body mass index, is weight in kilograms divided by height in metres squared. Of the participants, 68% were women and 45% were members of minority groups. The average follow-up was 2.8 years. The published summary we reviewed does not name the countries or sites.

What the researchers did

This was a randomized trial. Randomized means people were assigned to a group by chance. There were three groups. One received placebo, an inactive pill that looks like the real one. One received metformin at 850 mg twice a day. Metformin is a long-established diabetes medicine. The third group joined a lifestyle-modification program with two goals: losing at least 7% of body weight and doing at least 150 minutes of physical activity a week.

The main outcome was the development of type 2 diabetes. The published summary we reviewed does not say whether the placebo and metformin groups also received lifestyle advice, or whether the trial was blinded.

What they found

Diabetes developed at a rate of 11.0 cases per 100 person-years in the placebo group, 7.8 in the metformin group and 4.8 in the lifestyle group (R32-C99). "Person-years" adds up the time every participant was followed, so 100 person-years could mean 100 people followed for one year or 50 people followed for two years.

Compared with placebo, the lifestyle program reduced the incidence of diabetes by 58% (95% confidence interval 48 to 66%). Metformin reduced it by 31% (95% CI 17 to 43%). A confidence interval is the range of values the data are reasonably consistent with. The authors report that the lifestyle program was significantly more effective than metformin.

The authors also estimated how many people would need to take part to prevent one case of diabetes over three years: 6.9 people in the lifestyle program, or 13.9 people taking metformin. This is sometimes called the number needed to treat.

The published summary we reviewed does not report how much weight each group lost, so this page cannot give a weight figure.

Side effects and people who stopped

The published summary we reviewed does not report side effects, dropout rates, or how many people stopped metformin or left the lifestyle program. Later papers from the same program, covered elsewhere on this site, add some of this detail.

What this study does not tell you

• Everyone in the trial was chosen because of raised blood glucose. The results describe people at high risk of diabetes, not people with a higher body weight and normal blood sugar.
• Preventing or delaying a diabetes diagnosis over 2.8 years is not the same as preventing heart attacks, strokes or early death. The trial did not show those benefits, and later follow-up reports address that question separately.
• The summary does not report weight change, so it cannot tell you how much of the benefit came from weight loss versus activity or other changes.
• The trial did not test any of the weight-management medicines used today. Metformin was the only medicine studied.
• The lifestyle program was intensive and delivered within a research trial. Community programs may differ in what they offer and achieve.
• Later reports from this program have had published corrections. This page covers only the original 2002 results.
• The summary we reviewed does not state the funding source.

What it means in Canada

Diabetes prevention programs in Canada draw heavily on this trial. Its lifestyle goals of about 7% weight loss and 150 minutes of weekly activity are the ones many clinicians still quote. It says nothing about the newer weight-management medicines, and comparing its numbers with medicine trials would be a mistake because the people, the outcomes and the time frames are all different. If you are curious about how the lifestyle results held up over time, see the follow-up pages linked below. For an overview of the medicines available in Canada, see semaglutide in Canada and tirzepatide in Canada, and for how care is paid for see public drug coverage by province and compare services.

Related reading

Other studies in this library that bear on the same question.

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