NEW YORK (Reuters Health) - Intensive lifestyle changes can help people at risk of developing diabetes to ward off the disease, according to a report. But more modest efforts to boost exercise and improve diet may not be successful.
    Insulin resistance occurs when a person begins to lose the ability to respond to the effects of this blood sugar-regulating hormone. People with insulin resistance are at risk of going on to develop full-fledged diabetes.
    "Although increased physical activity and dietary modification have been shown to improve insulin sensitivity, there are no data that clearly show the extent of lifestyle change required," Dr. Kirsten A. McAuley of Otago University in Dunedin, New Zealand, and colleagues note in the March issue of Diabetes Care.
    To investigate, the researchers randomly assigned 79 non-diabetic, insulin-resistant individuals to either a no-intervention "control" group or one of two lifestyle intervention groups.
    In the "modest" intervention group, designed to reflect present dietary and exercise advice, participants aimed to consume less than 32% of total energy from fat, more than 25 grams of fiber per day, and incorporated 30 minutes of physical activity into their lives 5 days per week. Importantly, the level of intensity of this activity was not specified.
    In the "intensive" intervention group, participants tried to consume less than 26% of total energy from fat, more than 35 grams of fiber per day, and to exercise to an intensity of 80% to 90% of their age-adjusted maximum heart rate for 20 minutes 5 times per week. This level of exercise meets American College of Sports Medicine guidelines for developing and maintaining cardiorespiratory and muscular fitness.
    At the end of the 4-month study period, the intensive group posted a 23% increase in insulin sensitivity compared with only a 9% increase in the modest group, which was not much better than the control group.
    The authors believe improved aerobic fitness is one of the main factors accounting for the improved insulin sensitivity. Aerobic fitness improved 11% in the intensive exercise group versus 1% in the modest exercise group.
    These findings have "profound implications for public health, because it appears that current advice, even when vigorously implemented, did not significantly influence a major underlying abnormality of type 2 diabetes," they write.
    "The prevention of diabetes requires substantial rather than modest changes in lifestyle habits," co-author Dr. Jim I. Mann told Reuters Health. "Our research has shown that to achieve the maximum benefit of exercise, it is necessary to exercise at least five times per week to an extent that appreciably increases heart rate."
    Weight loss, increased consumption of dietary fiber, whole grain cereals and replacing a high proportion of saturated fat with unsaturated fat are the dietary measures that have the potential to reduce risk, he added.

SOURCE: Diabetes Care 2002;25:445-452.

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