The DaQing Study Pan et al

Another important study was carried out in Da-Qing, China based on a large population-based screening programme to identify people with IGT. The 33 participating clinics were randomized to carry out the intervention according to one of the four specified intervention protocols (diet alone, exercise alone, diet-exercise combined or none). Data on the preventive effect of a diet and exercise intervention have been reported from this cluster-randomized clinical trial on 577 subjects with IGT in 1986. The cumulative 6-year incidence of type 2 diabetes was lower in the three (diet alone, exercise alone, diet-exercise combined) intervention groups (41-46 per cent) compared with the control group (68 per cent). Because no individual allocation of study subjects to the intervention and control groups was done, but the participating clinics were allocated, the results based on individual data analysis must be interpreted with caution. Furthermore, the study subjects were relatively lean, the mean BMI 25.8 kg/m2 making inferences for other ethnic groups, where IGT subjects are usually obese, difficult. The mean BMI was 25.8 kg/m2. Also, the progression from IGT to diabetes was high, more than 10 per cent per year in the control group, which is more than usually reported by observational studies. In this study the relative risk reduction was approximately 40 per cent while the absolute risk reduction was 22-26 per cent during the 6-year period.

In clinics assigned to dietary intervention, the participants were encouraged to reduce weight if BMI was >25 kg/m2, aiming at <24kg/m2, otherwise a high-carbohydrate and low-fat diet was recommended. Counselling was done by physicians and also group sessions were organized weekly for the first month, monthly for 3 months and every 3 months thereafter. In clinics assigned to physical exercise, counselling sessions were arranged at a similar frequency. In addition, the participants were encouraged to increase their level of leisure-time physical activity by at least 1-2 'units' per day. One unit would correspond, for instance, to 30min slow walking, 10min slow running or 5min swimming.

The overall changes in risk factor patterns were relatively small. Body weight did not change in lean subjects, and there was a modest, less than 1 kg reduction in subjects with baseline BMI > 25 kg/m2. Also, the estimated changes in habitual dietary nutrient intakes were small and non-significant between groups. Exercise intervention seemed to produce best effects. Thus, it is not easy to determine the factors responsible for the beneficial effects on the risk of type 2 diabetes. It is nevertheless obvious that weight control was not the key issue. Thus, physical activity and qualitative changes in diet that are difficult to measure on individual level probably played a key role.

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