In their article Nutrition key to cutting infection rates, Andrew Thorne-Lyman and Wafaie Fawzi highlight the links between malnutrition and infectious disease. I agree with their assessment that micronutrient interventions offer a low-cost, yet underfunded, strategy for preventing and treating infectious disease, and that it is "time to turn knowledge into action".

The underlying problem is that people have moved away from their traditional diets, while a combination of environmental degradation, modern agricultural practices and food processing remove essential nutrients from people's diets. The malnourished are being fed refined foods, fortified with vitamins and minerals in the form of chemical isolates.

In southern Africa, people are moving away from traditional nutrient-rich diets. These would normally include home-grown millet and sorghum, hand-gathered herbs, roots and fruits, as well as groundnuts, sweet potato, pumpkin, cabbage and a moderate intake of free range meat, eggs and milk.

The staple foods today are refined maize meal, bread (mostly refined) and white sugar — all of which provide 'empty calories' (i.e. they are high in calories but are nutritionally poor) — together with cooking oil and traditional margarine packed with extremely unhealthy trans-fats.

The consequences for nutrition are severe. In Mozambique, 95 per cent of children under five suffer from iron deficiency. And a National Food Consumption Survey in 1999 found that South African children were deficient in iron, zinc, vitamin A and most of the B vitamins.

Is it any wonder that immunity is impaired and there is an escalating prevalence of infectious disease?

To address micronutrient deficiencies, especially in the most vulnerable, South Africa began a food fortification programme in 2004, adding iron, zinc, vitamin A, B vitamins and folic acid to all maize and wheat flour.

But, five years on, the project was judged a resounding failure. The prevalence of vitamin A, zinc and iron deficiencies in children have all increased. Why is this?

Part of the problem is that the recommended daily allowances are based on adult, not child, food portions. Children, who are more vulnerable, eat less and so need more highly fortified food. Partly, the problem is that cooking can destroy the vitamins. But, most importantly, it is because chemical isolates have a significantly lower bioavailability — the extent to which someone's body can absorb the micronutrient — than whole foods. The iron used in the South African fortification programme, for example, has a bioavailability of less than two per cent.

Fortifying or supplementing a defective diet with micronutrients in the form of chemical isolates is now commonplace, despite a plethora of scientific evidence that they are poorly absorbed, rarely act in the body in the way intended and, in some cases, can even be toxic.

Take, for example, the essential mineral and antioxidant, selenium. Where there is deficiency, bread or salt is often fortified with sodium selenate or selenite. But this is unlikely to have the desired benefit because these salts are toxic and poorly absorbed — and the little that is absorbed does not act as an antioxidant. It is a mad world that bans mineral water contaminated with sodium selenite — an industrial pollutant — and then puts it in bread!

Nor is it appropriate to cite improvement in Body Mass Index (BMI) as evidence of improved nutrition. You can raise your BMI by eating just carbohydrate and fat, which does not equate to good nutrition.

The key to success in micronutrient fortification or supplementation lies in the form of micronutrient used. For the past 15 months, my organisation — Health Empowerment Through Nutrition (HETN) — has been working with the South African National Tuberculosis Association to provide tuberculosis patients and their families with an inexpensive and effective daily nutritional supplement.

The supplement, e'Pap, costs just 18 South African Rand (US$2.33) per person per month. It is wholegrain (based on maize and soya), pre-cooked, and contains the recommended daily allowance of 28 important micronutrients, in a bio-available form, all in a small meal portion.

Recipients' general health and wellbeing have improved dramatically. Tuberculosis cure rates have risen by 39 per cent. Now HETN is embarking on a longitudinal study with the University of the Witwatersrand to confirm these anecdotal findings and evaluate other non-invasive indicators of nutritional status.

Micronutrient supplements can and do make a real contribution to alleviating the burden of infectious disease but only if they are formulated to ensure bioavailability and bioefficacy.