Biology of Disease

Anorexia Nervosa and Bulimia Nervosa

Anorexia nervosa (AN) and bulimia nervosa (BN) are both disorders of eating

behavior and body weight regulation. Anorexia is simply a lack of appetite;

bulimia is derived, in part, from the Greek word limos meaning hunger. Both

have received considerable publicity in recent years although they were reported

many centuries ago. The prevalence rate for AN in young females is estimated to

be 0.3% and for BN 1% and 0.1% in young women and young men respectively.

The incidence in the general population is much lower with the incidences of

AN and BN being approximately 8 and 12 cases per 100 000 respectively.

Anorexia nervosa is an extreme refusal or reluctance to eat and associated

psychological problems, leading to a severe weight loss. Compulsive exercising

and the abuse of laxatives and diuretics often compound the reduced input

of dietary energy. Patients are therefore normally extremely hungry and are

obsessed with food but they avoid eating, especially carbohydrates. The

signs and symptoms of AN include a body weight at least 15% below the

recommended weight, a ‘wasted’ appearance with reduced muscle mass,

and swelling of the joints. In younger females, puberty is delayed; an older

female is likely to become amenorrhetic and infertile because her body

weight reduces to less than 45 kg and/or fat content becomes less than 22% of

body weight. The skin is dry, hair thin and the nails brittle. Constipation and

decreased heart rate and blood pressure are common. If left untreated, long-

term damage to the skeleton and cardiac systems are likely and death can

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BOX 10.3 continued

Glucose

1-phosphate

Glucose

6-phosphate

UDP-Glucose

Glycogen

Oxaloacetate

Alanine Alanine Alanine

Pyruvate

Pyruvate

Glutamate

Glutamate

2-oxoglutarate 2-oxoglutarate

Liver Blood Small intestine

Glucose

Food Protein

turnover

Phosphoenolpyruvate

Figure 10.28 An overview of how dietary

proteins can be metabolized to support

gluconeogenesis to provide glucose during a low

dietary intake of carbohydrates.