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Persons who are naturally very fat are apt to die earlier than those who are slender.


Obesity is the most common nutrition-related disorder in the Western world; as Tunnessen puts it, ‘Obesity is the most common form of malnutrition in the United States’.1 Most overweight adults and children who are obese have exogenous obesity, which tends to imply that ‘they ate too much’, but the problem is more complex than relative food input. Physical activity and environmental and genetic influences must also be taken into account. However, only a small percentage (4–6%) of human obesity is thought to be due to a single gene mutation.2 There is still a persisting tendency of affected families to blame ‘glandular’ problems as a cause of obesity. It is now considered that there is a strong genetic basis to obesity and that attributing it to overeating and lack of exercise is an overly simplistic viewpoint.

Key facts and figures

  • Two-thirds of the Australian population are overweight or obese and only 2–4% underweight.3

  • Abdominal obesity gives a higher cardiovascular risk at any weight.

  • The onset of obesity can occur at any age.

  • Secondary or pathologic causes are rare.

  • Less than 1% of obese patients have an identifiable secondary cause of obesity.2

  • Two conditions causing unexplained weight gain that can be diagnosed by the physical examination are Cushing syndrome and hypothyroidism.

  • After pregnancy, obesity may result from a failure to return to prepartum energy requirements.

  • Even small weight losses are effective in preventing diabetes and improving the cardiovascular risk profile.4


A summary of the diagnostic strategy model is presented in TABLE 78.1.

Table 78.1Weight gain: diagnostic strategy model

Probability diagnosis

The outstanding cause of weight gain in exogenous obesity is excessive calorie intake coupled with lack of exercise. This is determined largely by environmental influences. Overweight people often deny overeating but the true situation can be determined by recording actual food intake and energy expenditure, and by interviewing reliable witnesses.

Serious causes not to be missed

It is important not to misdiagnose hypothalamic disorders, which may result in hyperphagia and obesity. Injury to the hypothalamus may occur ...

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