Diet therapy

Immune system

Our immune system is constantly challenged.

Particularly by the environment in which we live, stress, drugs, smoking, alcohol, disease processes, dietary practices and ageing.

Along with lifestyle change there are several dietary factors that can protect the body against infecting organisms and help the body overcome an infection once established.

Fish oil

Fish oil contains essential fatty acids particularly the n-3 polyunsaturated fatty acids- eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which even at low levels are helpful in combating acute and chronic inflammation, such as rheumatoid arthritis and multiple sclerosis. Sources of n-3 polyunsaturated fatty acids include salmon, tuna, sardines, herrings and mackerel.

Protein and Energy

Protein and energy are essential for body repair, muscle growth and immunity. Groups most at risk of low levels are children and the elderly, particularly if they find chewing difficult and their food intake is limited.

Athletes of all ages can also be at risk, particularly those that limit or alter their diets in order to make a particular weight category for their sport. With prolonged exercise depletion of glycogen stores can lead to competition between the muscles and immune cells for key amino acids. This has lead sports nutritionists to develop the concept of “periodised nutrition” which seeks to provide sufficient carbohydrate during the pre-event, event and the recovery phase to replenish glycogen stores.

Iron, Zinc, Copper, selenium, Vitamin B6, C, E and A

These nutrients are often lacking when protein and energy food sources are low, which reduces cell-mediated immunity and increases the risk of infection.

Good food sources of protein, iron and zinc include lean red meat, fish, poultry, eggs, dairy products, lentils and legumes. Although there has been concern about the lack of selenium (and iodine) in New Zealand soils this is now less of a problem as more grains and breakfast cereals are imported from other countries with naturally higher selenium (and iodine) soil levels than our own.

There are some instances when athletes may be deficient in these nutrients, particularly if they over train, compete in ultra- endurance exercise or during times of excess weight loss. They should see a sport Dietitian for dietary analysis and advice.


Vitamins A, D, E, C, beta-carotene and selenium.
These occur naturally in fresh fruit and vegetables and promote immunity by reducing the activity of free radicals and oxidants that cause cellular damage. In particular the allium vegetable family, onion, garlic, leeks and chives- has been associated with a reduction in stomach cancers and calciferous vegetables such as broccoli, cauliflower and brussel sprouts have been found to protect against oestrogen-related cancers such as breast and endometrial cancers.

Soybeans and legumes are a rich source of dietary fibre and saponins that protect against colon cancer. Soy has also been found to aid immune recovery after extreme exercise.

Dietary Supplements

While it may be tempting to take dietary supplements there is no conclusive evidence that these will benefit immunity and in fact excessive intakes can often produce negative effects.


Good hydration is essential, particularly for athletes competing in extreme temperatures and altitudes. Most sports drinks contain electrolytes such as sodium which increases glucose absorption in the small intestines for transport to muscle cells and for maintaining cellular processes.

Drinking water also helps to maintain saliva levels in the mouth; Saliva contains IgA important for mucosal immune defence. During exercise such as cycling or swimming athletes may be exposed to micro-organisms present in the swimming water or open air. A decreased IgA mediated immunity during exercise may increase risk of infections such as supper respiratory tract infections (URTI). More on fluids in Cricket Question


Studies have shown that regular exercise, adequate sleep, less stress, and satisfying relationships all benefit the immune system.
The family environment is particularly important for children. Irrespective of household income, land ownership, diet, workloads and access to private health care, it has been found that diminished immunity and frequent illness in children may be associated with unstable relationships.

If you would like a wellness check to consider how adequate your intake of nutrients that protect your immunity are then contact us for an appointment

About the author View all

Lea Stening

Lea is one of New Zealand’s leading paediatric dietitians and also specialises in Sports Nutrition. She has specialised in Paediatric Nutrition for 31 years and in 1985 was the first paediatric dietitian to enter private practice in New Zealand. Lea helps families through her private consultations, public lectures, newspaper and magazine articles as well as television and radio interviews. Read more »

View all posts by Lea Stening »


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