A typical severely obese patient will have about 50 kg excess weight to lose, which is equivalent to a store of 350,000 kcal. The optimum rate of weight loss in such a patient is about 1 kg/week, which involves an energy deficit of 1000 kcal/day for about a year. It is difficult to maintain this degree of dietary restriction over such a long period, and procedures such as jaw wiring or stomach stapling may help in some cases. Maintenance of weight loss is difficult to achieve and may be helped by fitting a nylon waist cord after weight loss. On theoretical grounds, patients who do not lose weight despite keeping to a properly-designed reducing diet would not benefit from surgery, but in practice this problem does not arise. It is dangerous to resort to surgery for the treatment of severely obese patients who cannot diet by reason of psychiatric disorder.