Part of the weight lost during wasting is fat. More important is the loss of muscle mass. This is also called "lean body mass," or "body cell mass." Lean body mass can be measured by bio electrical impedance analysis (BIA) or by a full body x-ray (DEXA) scan. These are simple, painless office procedures.
AIDS wasting and lipoatrophy can both cause some body shape changes. Wasting is the loss of weight and muscle. Lipoatrophy can cause a loss of fat under the skin. Wasting is not the same as fat loss caused by lipodystrophy. However, wasting in women can start with a loss of fat.
Several factors contribute to AIDS wasting:
Low food intake: Low appetite is common with HIV. Also, some AIDS drugs have to be taken with an empty stomach, or with a meal. It can be difficult for some people with AIDS to eat when they're hungry. Drug side effects such as nausea, changes in the sense of taste, or tingling around the mouth also decrease appetite. Opportunistic infections in the mouth or throat can make it painful to eat. Infections in the gut can make people feel full after eating just a little food. Depression can also lower appetite. Finally, lack of money or energy may make it difficult to shop for food or prepare meals.
Poor nutrient absorption: Healthy people absorb nutrients through the small intestine. In people with HIV disease, several infections (including parasites) can interfere with this process. HIV may directly affect the intestinal lining and reduce nutrient absorption. Diarrhea causes loss of calories and nutrients.
Altered metabolism: Food processing and protein building are affected by HIV disease. Even before any symptoms show up, you need more energy. This might be caused by the increased activity of the immune system. People with HIV need more calories just to maintain their body weight.
Hormone levels can affect the metabolism. HIV seems to change some hormone levels including testosterone and thyroid. Also, cytokines play a role in wasting. Cytokines are proteins that produce inflammation to help the body fight infections. People with HIV have very high levels of cytokines. This makes the body produce more fats and sugars, but less protein.
Unfortunately, these factors can work together to create a "downward spiral." For example, infections may increase the body's energy requirements. At the same time, they can interfere with nutrient absorption and cause fatigue. This can reduce appetite and make people less able to shop for or cook their meals. They eat less, which accelerates the process.