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Everything in excess is opposed to nature.


In Australia, as in most other developed nations, the population health issue of having too much body weight has far outstripped the health issue of being underweight. The vexing problem of obesity is covered in the chronic disease section (see CHAPTER 80). However, the relatively short-term gain or loss of weight presents a significant diagnostic challenge in general practice, particularly as so many underlying conditions can result in weight change.


Key facts and figures

  • Two-thirds of the Australian population are overweight or obese and only 2–4% underweight.1

  • Less than 1% of obese people 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.3


A summary of the diagnostic strategy model is presented in TABLE 67.1.

Table 67.1Weight gain: diagnostic strategy model

Probability diagnosis

The outstanding cause of weight gain in exogenous obesity is excessive calorie intake coupled with lack of exercise, and influenced heavily by socio-environmental factors (see CHAPTER 80).

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 following trauma and encephalitis and with a variety of tumours, including craniopharyngiomas, optic gliomas and pituitary neoplasms. Some of these tumours may cause headaches and visual disturbances.

It is also important not to overlook major organ failure and kidney disorders as a cause of increased body weight, especially cardiac failure, liver failure and the nephrotic syndrome. The associated increase in body water needs to be distinguished from increased body fat. Consider the obesity hypoventilation syndrome (Pickwickian syndrome) in those with BMI >40 kg/m2.


Endocrine disorders

The endocrine disorders that cause obesity include Cushing ...

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