As doctors, we all know that the classical features of a patient suffering from cancer include progressive loss of appetite, loss of weight and energy, and a severely wasted terminal stage. Significant weight loss is usual. However, a small minority may die with a normal weight.

How does cancer cause cachexia-anorexia? Can anorexia be treated? How do the nutritional requirements of a cancer patient change as the disease progresses? What are the appropriate guidelines for food and fluid administration in the terminal phase?

These are some of the questions confronted by doctors managing patients with cancer.

Answering such questions requires not only the application of pathophysiology and pharmacology but also a good knowledge of cultural and ethical issues.

Is cachexia the same as starvation?

Since time immemorial human beings have struggled to adapt to wide fluctuations in food supply. Research information on the adaptive physiological response has been obtained from the studies of obese patients seeking weight reduction, as well as those in a situation of food deprivation.

The following physiological changes occur:

1. Protein catabolism diminishes over about 10 days.

2. Fat becomes the chief source of energy.

3.The brain energy source switches from glucose to ketones

4. A daily intake of 30-45 grams of glucose meets the brain energy requirements, suppresses ketosis and reduces protein catabolism.

5. Weight loss is about 200 grams per day

The metabolic changes leading to cachexia are far more complicated than simple fasting or starvation.  The cancer itself utilises  energy  at a wasteful rate. In cancer cachexia there are widespread metabolic disturbances. Hepatic gluconeogenesis is increased. The ability of skeletal muscle to process glucose into glucogen is impaired. There is significant loss of host adipose tissue.

These metabolic disturbances are partly due to normal physiological adaptation to fasting, but also aggravated by changes in lipid metabolism.