Introduction:
Obesity is a pandemic with potentially disastrous consequences forh ealth. More than 25% of adults in the UK are obese (BMI > 30), compared to 7% in 1980. Over two-thirds of UK adults are overweight (BMI > 25).The pandemic reflects changes in both energy intake and expenditure.
The estimated average global daily supply of food energy per person increased from ~2350 kcal in the 1960s to ~2800 kcal inthe 1990s. Portion sizes, particularly of sugary drinks and high-fat snacks, have increased. Corresponding changes in energy expenditure are important; obesity is correlated positively with hours spent watching television, and inversely with physical activity. Although obese people were ridiculed in the past when they bemoaned their inability to control their weight, it is likely that susceptibility does vary between individuals. Twin studies confirm a genetic pattern of inheritance, suggesting a polygenic disorder.
In a few cases, specific causal factors can be identified, such as hypothyroidism, Cushing’s syndrome or insulinoma.
Drugs implicated include: tricyclic antidepressants, sulphonylureas, sodium valproate and β-blockers.
Complications of obesity
Health consequences of obesity include:
● Metabolic syndrome.
● Non-alcoholic steatohepatitis.
● Cirrhosis.
● Sleep apnoea.
● Osteoarthritis.
● Psychosocial disadvantage.
Obesity has adverse effects on both mortality and morbidity; life expectancy is reduced by 13 yrs amongst obese smokers. Coronary artery disease (CAD) is the major cause of death but some cancer rates are also increased.
Clinical features and investigations
Obesity can be quantified using the body mass index (BMI = weight in kilograms divided by the height in metres squared (kg/m2) ):
● Normal 18.5–25.
● Overweight 25–30.
● Obese > 30.
Risk of complications rises steeply to very severe if BMI > 40. A dietary history may be helpful in guiding dietary advice but is susceptible to under-reporting of consumption. Alcohol consumption is an important source of energy intake. All obese patients should have TFTs performed, and an overnight dexamethasone suppression test or 24-hr urine free cortisol if Cushing’s syndrome is suspected. Assessment of other cardiovascular risk factors is important.
BP should be measured, and type 2 diabetes and dyslipidaemia detected by measuring blood glucose and serum lipids. Elevated transaminases suggest non-alcoholic fatty liver disease.
Management
The health risks of obesity are largely reversible. Interventions that reduce weight in studies in obese patients have also been shown to ameliorate cardiovascular risk factors. Lifestyle advice that lowers body weight and increases physical exercise reduces the incidence of type 2 diabetes.
Most patients seeking assistance will have attempted weight loss previously, sometimes repeatedly. An empathetic explanation of energy balance, recognising that some individuals are more susceptible to obesity, is important. Appropriate weight loss goals (e.g. 10% of body weight) should be agreed.
Lifestyle advice: All patients should be advised to maximise their physical activity by incorporating it into the daily routine (e.g. walking rather than driving to work). Changes in eating behaviour (including portion size control, avoidance of snacking, regular meals to encourage satiety, and use of artificial sweeteners) should be discussed.
Weight loss diets: In overweight people, the lifestyle advice given above may gradually succeed. In obese patients, more active intervention is usually required. Weight loss diets require a reduction in daily total energy intake of ~2.5 MJ (600 kcal) from the patient’s normal consumption. The goal is to lose ~0.5 kg/wk. Patient compliance is the major determinant of success. In some patients more rapid weight loss is required, e.g. in preparation for surgery. There is no role for starvation diets, which carry a risk of sudden death from heart disease. Very low calorie diets produce weight loss of 1.5–2.5 kg/wk but require the supervision of a physician and nutritionist.
Drugs:
Drug therapy is usually reserved for obese patients with a high risk of complications. Patients who continue to take anti-obesity drugs tend to regain weight with time. This has led to the recommendation that anti-obesity drugs are used short-term to maximise weight loss in patients who are demonstrating their adherence to a low-calorie diet by current weight loss. Several drugs have been withdrawn due to side-effects, and orlistat is the only drug currently licensed for long-term use. Orlistat inhibits pancreatic and gastric lipases, reducing dietary fat absorption by ~30%. Side-effects relate to the resultant fat malabsorption: namely, loose stools, oily spotting, faecal urgency, flatus and malabsorption of fat-soluble vitamins.
Surgery:
‘Bariatric’ surgery to reduce the size of the stomach is the most effective long-term treatment for obesity. It should be contemplated in motivated patients with a very high risk of developing the complications of obesity, in whom dietary and drug therapy has been ineffective. The mechanism of weight loss may not relate to limiting the stomach capacity per se, but rather in disrupting the release of ghrelin from the stomach, which signals hunger in the hypothalamus. Mortality is low in experienced centres but postoperative complications are common.
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