Formula food-reducing diets:A new evidence-based addition to the weight management tool box.

The changing pattern of obesity-related disease has created a need for a greater range of weight management options for the increasing number of people for whom weight loss and maintenance cannot be addressed by conventional dietary methods. Formula diet weight loss programmes [very low-calorie diets (VLCDs) (400-800 kcal/day) and low-calorie diets (LCDs) (800-1200 kcal/day)] can deliver weight loss at rates of 1-2 kg/week. This rate of weight loss can result in 10-20 kg weight loss in 8-12 weeks. Many health benefits associated with weight reduction seem to require between 10 and 20 kg weight loss. Formula diet programmes can result in weight loss, reduction of liver volume and reduction of visceral fat before bariatric surgery; weight loss before knee joint replacement surgery has also been shown. The benefit of pre-operative weight loss is still under investigation and such practices before bariatric surgery are variable in surgical units across the UK. Weight loss with formula diet in obesity-associated conditions where inflammation is an important component, such as osteoarthritis and psoriasis, has been demonstrated. Maintenance of about 10% of initial bodyweight loss, with symptom improvement in elderly obese people with knee osteoarthritis, has been shown over a period of 4 years. In obese people with psoriasis, weight loss with skin improvement has been maintained for 1 year. Clinical trials are currently underway to examine the merits of an initial weight loss with formula diet in pre-diabetes, in early type 2 diabetes and in insulin-treated type 2 diabetes. Rapid initial weight loss can result in rapid symptom improvement, such as reduced joint pain in osteoarthritis, improved sleep quality in obstructive sleep apnoea, reduced shortness of breath on exertion, reduced peripheral oedema and rapid improvement in metabolic control in diabetes, all changes that are highly motivating and conducive towards compliance. There is also some evidence for improved vitamin D status and maintained bone health in elderly obese people with osteoarthritis but more research is needed. Rapid initial weight loss was feared to be followed by rapid weight regain. However, provided initial weight loss is delivered in parallel with an intense education programme about nutrition, cooking, shopping and lifestyle for long-term maintenance; and where long-term support is provided, subsequent weight maintenance after VLCDs and LCDs has been shown to be possible. A recent literature review identified high-protein diets, obesity drugs and partial use of formula meal replacements as methods which can result in statistically significantly greater weight maintenance after initial weight loss with VLCDs or LCDs. Anxiety about serious adverse side effects seems to be unfounded although users need to be aware of both minor and more serious, though very infrequent, adverse events, such as gallstones and gallbladder disease.