Our immune system protects us against bacteria, viruses, and other disease-causing organisms. It is an efficient, complex defence system. Does the way we eat affect the immune system?

The immune system is our shield against disease. Due to the complexity of the immune system, it is extremely difficult to assess the effects of diet on our immune function. However, research results have identified some die-tary factors that affect the human immune response.

Energy intake seems to have an important influence on immune activity. Undernourished people are at greater risk from infections. Weight reduction schemes using diets with less than 1200 kcal per day can also reduce immune function, an excellent reason to avoid unhealthy "crash diets". Excessive energy intake may also compromise the immune system's ability to fight infection. Obesity is linked to an increased rate of infectious disease. Furthermore, obese people are more likely to develop coronary heart disease, which has been linked to alterations in the immune function.

Reducing fat in the diet is important for weight control but it also seems to influence how well the immune system works. Diets that are high in fat seem to depress the immune response and thus increase the risk of infections. Reducing fat content in the diet can increase immune activity. This might not just affect infections but could also strengthen the type of immune cells, which can fight tumour cells. However, it is not just the amount of fat that is important but also its origin. It is important to include oily fish, nuts, soy or linseed oil in your diet because we need the right balance of different fatty acids.

Regular consumption of fermented dairy products such as yoghurt or kefir may enhance the immune defences in the gut. Recent research results suggest that yoghurts made with certain bacteria (called probiotics) may have a beneficial effect on the immune system. For example, human volunteers who ate yoghurt every day made with specific probiotic bacteria showed a higher resistance to microorganisms that cause food poisoning. More research is needed.

Immune system maintenance requires a steady intake of all the necessary vitamins and minerals. This can be accomplished by eating a well-balanced diet including plenty of fruit and vegetables, yoghurt products on a regular basis. To date, most studies show that supplements do not stimulate immune response in healthy, well-nourished individuals. However, a recent study among elderly people showed that a multivitamin and mineral supplement can boost their immunity.

ILSI Europe Concise Monographs, 1999 International Life Sciences Institute