Abstract
No-one is immune to obesity, but those with a family history of obesity, or those who have in the past lost weight, are particularly liable to excessive weight gain. There is no useful way of identifying that portion of the population which is at particularly high risk of obesity so that preventive measures can be focussed on that subgroup. Prevention of obesity therefore requires early detection and treatment of excessive weight gain. For various reasons the age range 5–12 years is particularly advantageous for correcting obesity in children, since normal weight-for-height can be achieved without actual weight loss. Obesity in adults is to a small extent genetically determined, but weight loss is always possible with the appropriate dietary treatment. The most difficult problem in preventing adult obesity is to ensure that excess weight which has been lost is not regained. Reasons are given for believing that a waist cord provides a necessary cognitive clue to this weight regain, and thus assists in maintaining normal weight in formerly obese people.