Well this paper gave me pause for thought. I have always been rather nihilistic about dieting. The effect sizes in terms of actual weight loss seem nugatory and transient – a couple of kilograms after three years would be fairly typical. Well I was prompted to change my mind as a result of a recent meta-analysis of 54 RCTs of diet vs. no-diet. Most of the diets stressed saturated fat reduction as part of the diet, and most advocated exercise as well as a diet (although in only half of these trials were patients referred to a specific exercise programme). As I would have predicted weight loss was small in the intervention group vs. control – 3.4kg at one year, and 2.5kg at two years. Despite these small effect sizes, all-cause mortality was reduced by 18% (0.7-0.95) in the diet group. This finding held good, even when only the 34 best quality RCTs were retained in the analysis. There was a borderline significant reduction in cancer death in the diet groups among the eight trails that recorded this outcome. In an earlier study of abnormal liver function tests  we noted improvement in fatty livers in people who lost only small amounts of weight. My conclusion – it is worth persuading people to lose weight through diet and exercise. Even if the effects on weight are small they are not, after all, nugatory.
— Richard Lilford, CLAHRC WM Director
- Ma C, Avenell A, Bolland M, Hudson J, Stewart F, Robertson C, Sharma P, Fraser C, MacLennan G. Effects of weight loss interventions for adults who are obese on mortality, cardiovascular disease, and cancer: systematic review and meta-analysis. 2017; 359: j4849.
- Lilford RJ, Bentham L, Girling A, Litchfield I, Lancashire R, Armstrong D, Jones R, Marteau T, Neuberger J, Gill P, Cramb R, Olliff S, Arnold D, Khan K, Armstrong MJ, Houlihan DD, Newsome PN, Chilton PJ, Moons K, Altman D. Birmingham and Lambeth Liver Evaluation Testing Strategies (BALLETS): a prospective cohort study. Health Technol Assess. 2013; 17(28):1-307.