Even BMIs at the high end of normal conferred a substantially increased risk of diabetes A 16-year follow-up of 84,941 women (97% of whom were white) in the Nurses’ Health Study determined that 91% of cases of type 2 diabetes can be prevented by adhering to five lifestyle criteria: weight loss, regular exercise, diet modification, abstinence from smoking, and consumption of limited amounts of alcohol. Of these, weight control is the most effective.
Study subjects were free of diabetes, cardiovascular disease, and cancer at baseline. Sixteen years later, 3,300 new cases of type 2 diabetes were documented.
To assess the risk of diabetes, the investigators compiled a set of low-risk variables: 1) a body mass index (BMI) within the normal range (<25 kg/m2); 2) a diet high in cereal fiber and polyunsaturated fat and low in trans fat (formed during the partial hydrogenation of vegetable oils) and glycemic load (an indication of the effect of diet on the blood glucose level); 3) moderate-to-vigorous physical activity for at least 30 minutes a day; 4) no current smoking; and 5) the consumption, on average, of 5 g of alcohol a day (about half a drink).
The relative risk of diabetes was 0.09 in the 3.4% of women who adhered to the low-risk criteria throughout the study.
BMI was the most important predictor of diabetes. The relative risk was 38.8 in women with a BMI of > 35, 20.1 in those with a BMI of 30 to 34, 7.59 in women with a BMI of 25 to 29.9, 2.67 in women with a BMI of 23 to 24.9, and 1.0 in those with a BMI of <23.
Even BMIs at the high end of normal conferred a substantially increased risk of diabetes. In the group of women who were overweight (BMI, >25), 61% of diabetes cases were attributed to weight status.
When data on the other four behavioral variables were stratified according to BMI, the risk of diabetes associated with diet, physical activity, smoking status, and alcohol consumption were generally similar among normal-weight, overweight, and obese women. Nevertheless, each of the four factors was associated with a significantly increased risk of diabetes, even after adjustment for BMI. For example, the relative risk of diabetes was 1.34 for women who smoked 15 or more cigarettes a day. The other three risk ratios were expressed as inverse associations: for example, the relative risk of diabetes was 0.59 for women who drank more than 10 g of alcohol a day, 0.49 for women who most strictly adhered to the defined diet, and 0.71 for women who exercise more than 7 hours a week.
Stratification of data according to BMI also showed that almost 50% of the cases of diabetes among overweight and normal women might have been prevented had they adhered to the other four low-risk criteria. Among obese women, adherence to a healthy diet and regular exercise was associated with a 24% reduction in the risk of diabetes. It should be noted that the definition of diabetes used in this study was a fasting glucose of 140 mg/dL. Using current diagnostic criteria of a fasting glucose of 126 mg/dL, the number of identified cases is expected to be higher. Finally, this study demonstrates an association between weight, lifestyle, and development of diabetes. However, an intervention study is needed to prove causation between these risk factors and the ability to prevent diabetes.
Hu FB et al. Diet, lifestyle, and the risk of type 2 diabetes mellitus in women. N Engl J Med. 2001;345:790-797.