Page 512 - Medicine and Surgery

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508 Chapter 13: Nutritional and metabolic disorders

Pathophysiology BMI should be calculated and the fat distribution doc-
The mechanisms of obesity are poorly understood. At umented by measurements of skin fold thickness, and
a simplistic level weight gain results when the energy waist and hip circumference ratio calculated.
intake exceeds expenditure; however, both intake and
expenditure are controlled in complex physiological sys- Management
tems. Women tend to gain excess weight after puberty, It is important to use goal setting in the management
precipitated by events such as pregnancy, use of the oral of obesity. Initially the aim is to maintain weight prior
contraceptive therapy and the menopause. Changes in to establishing a realistic weight loss (average of 0.5–
lifestyle in men during the third and fourth decade lead 1 kg/week). Patients should be aware that weight loss
toreducedphysicalactivityandhenceweightgain,which induces a reduction in energy expenditure and there-
continues until the sixth decade. The quantity, type and foremakesfurtherweightlossmoredifficult.Techniques
pattern of food intake have all been implicated in the used include the following:
development of obesity. Both the appetite and the sensa- Behaviour modification including examining the
tionofsatiety(fullness)areimplicated.Centraladiposity background of the individual, the eating behaviour
(waist-to-hipratiomeasurements>0.9inmenand>0.84 and the consequences of the behaviour, usually con-
in women) increases the risk of many health problems ducted by psychologists.
such as diabetes and hyperinsulinaemia. Dietary manipulation: Reducing the calorie intake
The control system is complex, it is regulated by a con- to below expenditure results in weight loss; how-
trol centre thought to be located in the hypothalamus. ever, food diaries are recognised to be inaccurate as
Afferent signals to the control centre may include nerves, all patients underestimate their intake. Diets include
hormones and nutrients: balanced low-calorie diets, low-fat diets and low-
Leptin production correlates with body fat mass; a carbohydrate diets, which are ketogenic possibly in-

leptin receptor has been identified in the ventromedial ducing calcium loss and tend to be high in saturated
region of the hypothalamus. fat.
Gastric distention signals satiety. Medications have a limited role in the treatment of

Hormonal signals including cholecystokinin and obesity. Their use falls under guidelines issued by

glucagon-related peptides inhibit food intake; neu- NICE.
ropeptideYisapotent stimulus for appetite. Mono- 1 Sibutramine is a noradrenaline and serotonin re-
amines, including noradrenaline and serotonin, also uptake inhibitor and promotes a feeling of satiety. It
modulate the hypothalamic control centre. should be prescribed only as part of an overall treat-
The efferent of the control is energy expenditure. Ap- ment plan for management of obesity in patients
2
proximately 70% of energy expenditure is for resting aged 18–65 years who have a BMI of 27.0 kg/m or
metabolic processes such as temperature control and more in the presence of significant co-morbidities
2
physiological function. A further 10% of energy ex- or a BMI of 30.0 kg/m .
penditure is related to the thermic responses to food. 2 Orlistat inhibits pancreatic lipases so that ingested
fat is not completely hydrolysed or absorbed. NICE
Catecholamine-stimulated lipolysis is mediated via β 3
receptors, and low receptor activity decreases thermoge- guidelines dictate that Orlistat should only be pre-
nesis. The remaining 20% of energy expenditure is due scribed for patients aged 18–75 years who have lost
to physical activity and exercise. at least 2.5 kg in weight by dietary control and
increased physical activity in the month prior to
Clinical features the first prescription. They must have a BMI of
2
Evaluation of obese or overweight patients requires ae- 28 kg/m or more in the presence of significant co-
2
tiological factors and co-morbid conditions to be iden- morbidities or a BMI of 30 kg/m .Treatment is re-
tified. Blood pressure, cardiovascular risk factors and viewed at 4 and 6 months to confirm that weight
diabetes should all be reviewed. Smoking cessation may continues to be lost and should stop at 12 months.
lead to increase in weight; however, the health benefits The use of surgery is also covered by guidelines is-
of smoking cessation override the weight increase. The sued by NICE. Its use is confined to patients with