A LIFESTYLE INTERVENTION OR METFORMIN PREVENTED OR DELAYED THE ONSET OF TYPE 2 DIABETES IN PEOPLE AT RISK
Diabetes Prevention Program Research Group Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin N Engl J Med 2002 Feb 7;346:393-403.

QUESTION: In overweight people with increased fasting and postload plasma glucose concentrations, does an intensive lifestyle intervention or treatment with metformin plus standard lifestyle recommendations prevent or delay the onset of type 2 diabetes mellitus?
A  DESIGN
Randomised (allocation concealed*), blinded clinicians and participants for metformin and placebo),* placebo controlled trial with mean follow up of 2.8 years.
B  SETTING 
27 centres in the US.
C  PARTICIPANTS
3234 participants (mean age 51 y, 68% women) without diabetes who had a body mass index ≥ 24 (≥ 22 for Asians) and a plasma glucose concentration of 5.3 to 6.9 mmol/l in the fasting state and 7.8 to 11.0 mmol/l 2 hours after a 75 g oral glucose load. Exclusion criteria included medications known to alter glucose tolerance and illnesses that could seriously reduce life expectancy or ability to participate in the trial. Follow up was 93%.
D  INTERVENTION
Participants were allocated to an intensive programme of lifestyle modification (n=1079), standard lifestyle recommendations plus glucose control with metformin (850 mg twice daily) (n=1073), or placebo (n=1082). The intensive lifestyle intervention consisted of a 16 lesson curriculum aimed at achieving and maintaining a weight reduction of ≥7% of initial body weight through a low calorie, low fat diet and physical activity of moderate intensity. Standard lifestyle recommendations emphasised the importance of reducing weight and increasing physical activity.
E  MAIN OUTCOME MEASURES
Incidence of type 2 diabetes mellitus.
F  MAIN RESULTS
Analysis was by intention to treat. At 3 years, the cumulative incidence of diabetes was lower in the intensive lifestyle intervention and metformin groups than in the placebo group (table). The incidence rates of diabetes were 4.8, 7.8, and 11.0 patients per 100 person years for the intensive lifestyle intervention, metformin, and placebo groups, respectively.
G  CONCLUSION
In overweight people with increased fasting and postload plasma glucose concentrations, an intensive lifestyle intervention or treatment with metformin plus standard lifestyle recommendations was more effective than standard lifestyle recommendations alone for preventing or delaying the onset of type 2 diabetes mellitus.
H  Intensive lifestyle intervention (ILI) or metformin plus standard lifestyle v placebo plus standard lifestyle for prevention of type 2 diabetes at 3 years †

Outcome                      Comparisons                    Event rates               RRR (95% CI)       NNT (CI)
Incidence of diabetes     ILI v placebo                    14% v 29%               50% (41 to 58)     7 (6 to 10)
Metformin v placebo         22% v 29%               25% (13 to35)      14 (9 to 34)
† Abbreviations defined in glossary; RRR, NNT, and CI calculated from data in article.