Dietary aspects of obesity.

A new FAO report on how to estimate the energy and protein requirements of individuals is imminent and has direct application to the management of obese patients. Energy needs, although variable form individual to individual, are reasonably stable unless gross overfeeding or prolonged semi-starvation occurs; unconscious appetite control is surprisingly important. No longer will energy needs be expressed per kg body weight, a reference point difficult to apply to obese subjects anyway. There are now equations for estimating basal metabolic rate (BMR) these can be appled to obese subjects to give BMR in MJ per day; for kcal from kJ divide by 4.184. The equations apply to all races although north Europeans and Americans tend to have high values and Indians low. An obese patient has a higher BMR than a normal person of the same height. Lean body mass is increased in obesity so some long term loss is inevitable with slimming and accounts for the persistent fall in BMR on weight loss. Energy and protein needs are just the beginning of dietary management. Obese patients are prone to cardiovascular and gall bladder disease. A low fat diet is important and a polyunsaturated: saturated ratio (P:S) of 0.5 to 1.0 is appropriate: higher ratios will exacerbate cholestasis in the biliary tract which can be precipitated by weight loss. New evidence suggests that cereal fibre intake is important for preventing secondary bile salt recycling from the colon with its effect on biliary cholesterol saturation. Therefore long term high cereal (not bran) fibre intakes are as important in obese patients as is a low fat diet. High carbohydrate diets produce a slightly higher metabolism rate than iso-energetic diets. Low sugar diets lead to slightly lower energy intakes. Trace element deficient diets can lead to obesity so the obese patient and his family should be advised and shown how to permanently adjust to a 'prudent' diet. The short term approach to management is usually a waste of time.