Conducting large-scale, communitywide trials to address the prevention of obesity is a very expensive and difficult process; consequently, evidence of this nature is very limited. However, a number of large CVD and diabetes prevention trials have included weight as an intermediary outcome, which can also provide useful information about effective strategies to address obesity, and have demonstrated that it may be possible to prevent weight gain if not reduce weight at a population level.
The results of early large-scale community CVD prevention trials, such as the Stanford Three Community and Five Community studies as well as the Minnesota Heart Health Program, had limited impact on weight status and reinforced the difficulty of preventing weight gain in the community. However, later programs, such as the Pawtucket Heart Health Program, were able to make a modest impact on weight gain in the intervention community after 10 years. These programs demonstrate the time lag that can be expected between the implementation of a truly community-wide program and the extent of behavior change likely to be required to impact upon the weight status of the community. It has been suggested that unless weight is the primary outcome of the intervention, it is unlikely that sufficient focus will be placed on achieving the level of change required to impact on energy balance and community weight status.
Strong and consistent evidence of the success of large-scale weight gain prevention initiatives has been obtained from diabetes prevention trials that have addressed the progression to diabetes in people identified as glucose intolerant. Four large-scale trials have produced significant reductions in the rate of diabetes by focusing on exercise and diet, which resulted in small weight losses of approximately 3 or 4 kg on average. The largest trial conducted in the United States found that advice to reduce the energy and fat in the diet together with modest increases in physical activity, which was reinforced with regular follow-up from a 'coach,' led to an average weight loss of 5.6 kg and 58% reduction in the number of people progressing from impaired glucose tolerance to diabetes.
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