Weight loss diets

Weight loss diets - In overweight people, adherence to the lifestyle advice above may gradually induce weight loss. In obese patients, more active intervention is usually required to lose weight before conversion to ‘weight maintenance’ advice above. A significant industry has developed in marketing diets for weight loss. These vary substantially in their balance of macronutrients (Box 5.27), but there is little evidence that they vary in their medium-term (1 year) efficacy.

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They all involve a reduction of daily total energy intake of ∼2.5 MJ (600 kcal) from the patient’s normal consumption. The goal is to lose ∼0.5 kg/week. Weight loss is highly variable, with patient compliance being the major determinant of success. There is some evidence that weight loss diets are most effective in their early weeks, and that compliance is improved by novelty of the diet; this provides some justification for switching to a different dietary regime when weight loss slows on the first diet. Vitamin supplementation is wise in those diets in which macronutrient balance is markedly disturbed.

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In some patients more rapid weight loss is required, e.g. in preparation for surgery. There is no role for starvation diets, which risk profound loss of muscle mass and the development of arrhythmias (and even sudden death) secondary to elevated free fatty acids, ketosis and deranged electrolytes. Very low calorie diets (VLCDs) are recommended for short-term rapid weight loss, producing losses of 1.5–2.5 kg/week compared to 0.5 kg/ week on conventional regimes, but require the supervision of an experienced physician and nutritionist. The composition of the diet should ensure a minimum of 50 g of protein each day for men and 40 g for women to minimise muscle degradation. Energy content should be a minimum of 1.65 MJ (400 kcal) for women of height < 1.73 m, and 2.1 MJ (500 kcal) for all men and for women taller than 1.73 m. Side-effects are a problem in the early stages and include orthostatic hypotension, headache, diarrhoea and nausea.

Drugs A huge investment has been made by the pharmaceutical industry in finding drugs for obesity. The side-effect profile has limited the use of many agents, but a few drugs are currently licensed (Box 5.28). There is no role for diuretics, or for thyroxine therapy without biochemical evidence of hypothyroidism. Orlistat inhibits pancreatic and gastric lipases and thereby decreases the hydrolysis of ingested triglycerides, reducing dietary fat absorption by ∼30%. The drug is not absorbed and adverse side-effects relate to the effect of the resultant fat malabsorption on the gut: namely, loose stools, oily spotting, faecal urgency, flatus and the potential for malabsorption of fat-soluble vitamins.

Orlistat is taken with each of the three main meals of the day and the dose can be adjusted (60–120 mg) to minimise side-effects. Its efficacy is shown in Box 5.29 and Figure 5.13; these effects may be explained because patients taking orlistat adhere better to low-fat diets in order to avoid unpleasant gastrointestinal side-effects.