HIV can compromise your body’s ability to get the most out of food and nutrients in a number of ways, potentially leading to long-term nutritional deficiencies. These problems may be systemic (affecting whole systems of the body) or caused by specific factors or agents.

The systemic problems can include

• digestive and nutritional problems related to the course of HIV disease itself, and its effect on digestive organs (eg. HIV wasting syndrome);
• metabolic problems related to HIV or anti-HIV drugs (eg. the elevated blood fats, or diabetes, associated with the use of protease inhibitors and nucleoside analogues). The specific problems may include:

• opportunistic infections (eg. parasites, mycobacteria etc);
• ongoing drug side effects (eg. nelfinavir diarrhoea);
• food poisoning.

All of these factors can mean your body is not effectively absorbing all the nutrients and calories from your food. This can potentially put you at risk of developing either mild, moderate or even severe malnutrition. Malnutrition is a caused by an incorrect balance between what you eat, and what your body requires to maintain health and energy levels. This can occur through eating too little, but it can also be caused through eating an incorrect balance (too little or too much) of the basic foodstuffs: protein, fats, carbohydrates.

Most significantly, however, for people with HIV, is that deficiencies or excesses of one or more vitamins, minerals, or other essential food components can arise through the poor absorption or ineffective digestion of food, or through problems in the body’s metabolic organs and processes. Poor absorption of nutrients may be due to an infection (eg. a parasite or bacterial infection), systemic digestive or metabolic problems, or ongoing chronic side effects like diarrhoea or vomiting.

Many people with HIV may, over time, develop some form of weight loss or related nutritional problem. This sometimes manifests as "HIV wasting syndrome", in which a person may begin to lose weight — often for no apparent reason, and in the absence of the presence of an identifiable infection. If this happens unchecked over a period of time, the result can be malnutrition. Manifestations of this can include: extreme tiredness and lack of energy; continuing weight loss despite maintaining food at the same level; depression.

The causes of such nutritional deficiencies may be categorized as starvation or metabolic abnormality (American Dietetics Association). The "starvation" model does not mean a person has anorexia or is wilfully starving themselves (though depression may play some role here, diminishing the desire to eat). The starvation model more accurately refers to a lack of nutrients because of decreased intake or poor absorption (malabsorption) of food. Malabsorption is a common problem, and it can begin relatively early in the natural course of HIV infection.

The digestive system and HIV
The digestive system is the group of organs responsible for the absorbing, breaking down and eventually eliminating foods. If your digestive system is functioning well, the body will take all the necessary components of food and convert them into energy and nutrients for the body, excreting the rest as waste. Digestion begins in the mouth but mostly occurs in the stomach and intestine, which extends from the stomach to the anus, and is divided into two parts: the small intestine (where most of the processes of digestion and absorption take place), and the large intestine (which absorbs water from material once it has passed through the small intestine, and then propels waste out of the body).

The membrane of the small intestine is lined with numerous small, finger-like projections called villi. These increase the surface area of the small intestine. Glands in the mucous membrane of the small intestine also secrete the proteins and chemicals (enzymes) necessary for digestion. Each of these villi contain a network of blood capillaries and lymphatic materials called lacteals, which absorb digested fats. HIV, however, can interfere with the elements of the digestive process. This can cause a condition called villous atrophy, in which the villi waste away, due to the degeneration of intestinal cells.

An accompanying problem may be that the intestinal membrane can over time become thinner, with less surface area because of the reduced number of villi, so nutrients "leak through" the gut membranes before all the important components like vitamins and minerals be effectively absorbed. Nutritional abnormalities can be caused by HIV-related immune deficiency, or the action of the virus itself. Problems may also be related to drug side effects, or the presence of infections of the gut or intestine, like parasites or bacteria. The result can be that calories (energy), nutrients (vitamins and minerals) and other essential foodstuffs like fat are not be absorbed effectively, and so a person begins to "waste", or lose weight.

Emerging metabolic problems
You’ve probably recently heard quite a bit about metabolic problems related to HIV. Metabolism refers to the way in which the body processes energy: that is, how the body absorbs, makes use of and transforms foods, sugars, fats. Metabolism occurs through a series of processes in the body, involving a number of the body’s organs and systems and cells (for example, the pancreas, which is actually a large gland, and which plays a major role in carbohydrate metabolism).

As we learn more about the fat redistribution syndrome known as lipodystrophy (which was first identified in people with HIV about two years ago, largely on the basis of the characteristic physical changes it caused), it is becoming increasingly clear that HIV drugs, or even HIV itself, may be causing a number of complex metabolic disorders, of which lipodystrophy may only be one example. In many people with HIV, something is causing the processes by which the body absorbs and utilizes energy to go haywire. The body becomes ‘confused,’ and unable to normally deal with things like fat and sugar. Why this happens is a matter of speculation and some disagreement among doctors and specialists.

One of the main areas of research is looking at a problem known as mitochondrial dysfunction, in which the energy centres of the body’s cells (called mitochondria) become damaged (possibly due to the effects of HIV itself, or to long-term use of some anti-HIV drugs), so the cells cannot perform their usual functions. If this happens, it is thought, a whole range of the body’s organs and bodily processes could be thrown into a state of confusion and will not function effectively. So fats and sugars, among other things, may not be properly handled and converted into energy. Some doctors believe mitochondrial damage is the cause of some common problems in HIV, including fat redistribution and wasting, pancreatitis, (in which the pancreas becomes inflamed) diabetes, and damage to the peripheral nervous system (neuropathy).

Diarrhoea and other drug side effects
As well as the systemic problems outlined above, there are some other specific factors which can contribute to weight loss and poor nutrition in people with HIV. Some of these problems and symptoms can be addressed through changes to your diet. Because you may not be effectively receiving all the nutrients and energy you need, supplementation may be useful to compensate for any vitamin or mineral deficiencies, but this needs to be done with the advice of a qualified dietician or naturopath. One of the most common and distressing of these ongoing problems is diarrhoea.

Ongoing diarrhoea is associated with a number of anti-HIV drugs. It is particularly reported among people using the protease inhibitors, especially nelfinavir and ritonavir. Some people using these drugs also report vomiting, nausea and gastrointestinal pain. Diarrhoea over a long period of time can be serious. It can cause weight loss, exhaustion, malnutrition and depression. It is extremely important, if you do have this problem, to consult your doctor and find out what is causing it. It could be a drug side effect, but you can’t necessarily assume this is the case. It could also be caused by other agents, like infections.

Infections and opportunistic infections
There are many bugs, viruses or organisms, which can lead to diarrhoea. Acute bouts of diarrhoea may be caused by a simple and common viral infection. This can affect anyone, regardless of HIV status, and the gastrointestinal symptoms will generally clear up after a couple of days.

Ongoing diarrhoea in HIV positive people, however, needs further investigation. You can’t manage the symptom properly until you know what the cause is, and the cause might be serious, especially of you have a low CD4 cell count (roughly, under 300).

Diarrhoea and vomiting in people with low CD4 counts could very well be caused by an opportunistic infection: that is, a bug or germ which specifically attacks people with little or no natural immunity. Infections which can cause this problem include:

• mycobacteria (a group of bugs, one of which is responsible for the infection known as MAC or mycobacterium avium complex);
• cryptosporidia (a protozoal infection, found in the environment in things from water to animal faeces);
• intestinal parasites or worms.

If you have ongoing diarrhoea and gastrointestinal disturbance, you may need to have a test for the presence of any of these or other infections. Usually, they can be treated with antibiotics or other drugs, but they can be dangerous and cause serious weight loss, energy depletion and malnutrition if they are not diagnosed and managed. Some people with low CD4 counts opt to take medication, which can prevent the onset of these infections (prophylaxis).

Food poisoning
Finally, a note on food poisoning, which is often more common in people with poor immune function. The most common agents causing food poisoning are the bugs: listeria, salmonella and staphylococcus. More rare are botulism poisoning and poisoning from e. coli. There are simple ways to avoid food poisoning, which you may wish to discuss in further detail with a doctor or dietician, especially if you have a low CD4 count, are considering pregnancy, or have had significant damage to your immune system. In general, you should observe the following safeguards.