—Obesity is widely regarded as a pandemic with potentially disastrous consequences for human health

—More than 20% of adults in the UK, and more than 30% in USA, are obese (i.e. body mass index, BMI ≥ 30 kg/m2)

—The prevalence of obesity has increased ∼threefold within the last 20 years and continues to rise

—In developing countries, average national rates of obesity are not nearly so high, but these figures disguise alarmingly high rates of obesity in many urban communities

Body fat distribution

—For some complications of obesity, the distribution rather than the absolute amount of excess adipose tissue appears to be important

—‘Central' ('abdominal', 'visceral', 'android' or 'apple-shaped') obesity-Increased intra-abdominal fat

—more common in men, more closely associated with type 2 diabetes, the metabolic syndrome and cardiovascular disease

—'generalised' ('gynoid' or 'pear-shaped') obesity- subcutaneous fat accumulation the former is and is

Consequences of abnormal body fat distribution

—The key difference between these depots of fat probably lies in their vascular anatomy, with intra-abdominal fat draining into the portal vein and thence directly to the liver

—Many factors which are released from adipose tissue

—free fatty acids;

—'adipokines' such as adiponectin, resistin and tumour necrosis factor alpha (TNF-α), ; and

—steroid hormones including cortisol

—They are at higher concentration in the liver and hence induce insulin resistance and promote type 2 diabetes

Aetiology

—Accumulation of fat results from a discrepancy between energy consumption and expenditure over and above that which can be compensated for by hypothalamic regulation of basal metabolic rate (BMR)

—A small daily excess consumption of only 0.2-0.8 MJ (50-200 kcal; < 10% of intake) can lead to a weight gain of 2-20 kg over a period of 4-10 years

—Given the cumulative effects of subtle energy excess, body fat content shows 'tracking' with age, such that individuals are likely to maintain their rank in the age-adjusted population distribution throughout their lives

—Thus obese children are very likely to become obese adults

—Weight tends to increase throughout adult life, as BMR and physical activity decrease

Susceptibility to obesity

—Although obese people were ridiculed in the past when they bemoaned their inability to control their weight, today there is little doubt that susceptibility to obesity, and to its adverse consequences, varies between individuals

—The pattern of inheritance suggests a polygenic disorder, with small contributions from a number of different genes, together accounting for 25-70% of variation in weight.

—A few rare single gene disorders cause severe childhood obesity. These include

—mutations of the melanocortin-4 receptor (MC4R) that accounts for approximately 5% of severe early-onset obesity,

—defects in the enzymes processing POMC in the hypothalamus, and

— mutations in the leptin gene -can be effectively treated by leptin injections.

—Additional genetic conditions in which obesity is a feature include the Prader-Willi  and Lawrence-Moon-Biedl syndromes

Clinical assessment

—In assessing an individual presenting with obesity, the aims are to

—quantify the problem,

—exclude an underlying cause,

—identify complications, and

—reach a management plan.

Quantifying the problem

—Obesity can be quantified conveniently using the body mass index (BMI)

—BMI is calculated as the person's weight in kilograms divided by the square of his or her height in meters (kg/m2)

—For example, an adult weighing 70 kg with a height of 1.75 meters has a BMI of 70/1.752 = 22.9

—A simple measure which reflects the degree of abdominal obesity is the waist circumference, measured at the level of the umbilicus.

—A waist circumference of > 102 cm in men or > 88 cm in women indicates that the risk of metabolic and cardiovascular complications of obesity is high

—Bioimpedance or dual energy X-ray absorptiometry (DEXA) scanning

Reversible causes of obesity and weight gain

—Endocrine factors

—Hypothyroidism

—Hypothalamic tumours or injury

—Cushing's syndrome

—Insulinoma

—Drug treatments

—Tricyclic antidepressants

—Corticosteroids

—Sulphonylureas

—Sodium valproate

—Oestrogen-containing contraceptive pill

—β-blockers

Complications of obesity

—Obesity has adverse effects on both mortality and morbidity

—Lowest mortality rates are seen in individuals with a BMI of 18.5-24

—Data from population studies, such as that in Framingham, USA, show that for individuals aged between 30 and 42 years, the risk of death increases by 1% per annum for each 0.5 kg increase in weight; for those aged 50-62, this figure is 2%

—Obesity reduces life expectancy by 7.1 years in men and 5.8 years in women amongst non-smokers, and by 13.7 and 13.3 years respectively amongst smokers

—Coronary heart disease is the major cause of death

—Cancer rates are increased in the overweight, especially

— colorectal cancer in males and

—cancer of the gallbladder, biliary tract, breast, endometrium and cervix in females

—Epidemic obesity is accompanied by an epidemic of type 2 diabetes

—Obesity may lead to profound psychological consequences for individuals

—Society also suffers from the effects of obesity-related disability and early retirement

The only medical benefit of obesity is seen in osteoporosis, where bone density increases in response to increased mechanical stress.


OBESITY-2:http://obesitypart2inhuman.blogspot.com/

—

—

—