Treatment and prevention of obesity—are there critical periods for intervention?

Both professionals and the public view obesity, increasingly apparent in childhood, and already highly prevalent in adults in the Western world, as one of, if not, the most important public health problem of our times. The considerable effort expended on researching risk factors for obesity (a Medline search for studies examining risk factors for obesity conducted at the time of writing this editorial (November 2005) resulted in 264 326 hits) contrasts starkly with the simplicity of the key underlying problem, that obesity is largely a consequence of over-nutrition and under-activity. Despite the clarity of this message, there is little evidence-based guidance on successful, viable long-term strategies to prevent or treat obesity.We believe there is a need to develop findings from epidemiological research into coherent decisions regarding prevention and treatment interventions and ultimately appropriate polices for the improvement of public health. Our intention was that a themed issue on obesity in the International Journal of Epidemiology would contribute towards this aim. In the first half of this editorial we review the current evidence for the treatment of adult obesity and conclude that to date there is no strong evidence that such treatments have long-term benefits in terms of health gain. Clearly, lack of evidence does not equate to lack of effect and there is no doubt that most trials to date have not been large enough or had sufficiently long-term follow-up to answer these questions. On the other hand treating established obesity in adulthood may be ‘shutting the gate after the horse has bolted’. Further, epidemiology tells us that obesity is socially patterned, varies between countries, but in recent years has shown marked increases in all countries, and that what we eat and the exercise we take is largely determined by the food industry, transport policy, and the built environment (see for example the piece by Cummins and Macintyre in this issue 1 ). Thus, a population approach to the primary prevention of obesity and to the prevention of its associated diseases is more likely to be beneficial than an individual or small group level approach such as treating established obesity. Animal studies suggest that brief interventions during critical or sensitive periods of development can have lasting effects in terms of disease prevention. This seems such an exciting prospect to us that we spend the second half of this editorial considering whether there is sufficient evidence relating critical/sensitive periods of development to the risk of later obesity and its associated diseases to warrant trials in humans of such interventions.