In 2000, 46% of women and 33% of men in the United States were trying to lose weight1; they spent an estimated $34.7bn (£18.5bn; €27bn) on weight loss products and programmes.2 Did they get their money's worth? Unfortunately, the answer is probably no. The prevalence of obesity increased from 30.5% to 32.2% between 1999 and 2004 in the United States,3 and expenditures on health care associated with excess body weight exceeded $56bn.4 Further, the Federal Trade Commission found four years ago that 40% of all advertisements for weight loss products made false or misleading claims.2

There has been little rigorous scientific research on the efficacy and safety of commercial products and programmes5—but in this week's BMJ Truby and colleagues report their findings from such a study (p 1309).6 Participants were recruited by national advertisements to take part in …