Positive Health Online

Of all the claims made for the benefits of organically grown food, the most controversial is the claim that it is healthier than food grown conventionally. To proponents, the vitality and healthfulness of organic food is a basic tenet of organic farming. To skeptics, it is wishful thinking. Unfortunately there is as yet no definitive answer. Despite decades of research and more than 200 papers published on the subject, the claim remains unsubstantiated.

Food is undoubtedly healthier if it is not contaminated by pesticides, nitrates, and other agrochemicals. But the main health promoting properties of food lie in its ability to provide us with the vitamins, minerals, proteins, fats, carbohydrates, fibre and protective factors we need for our growth, repair, reproduction, energy and good health. Plants produce these complex nutrients from water, air, soil and sunlight. How well they do this is under the influence of many environmental and genetic factors, of which the type of agriculture is but one.

The type of agriculture which is the norm in Britain developed since the second World War. It is an industrial process with a linear flow of nutrients and characterised by its use of synthetic chemicals such as pesticides. Inorganic fertilisers of the three main plant nutrients (nitrogen, phosphorous, potassium) are added to the soil with little attention to micronutrients such as selenium. When the crop is harvested, the nutrients accumulated by the plant and eaten by humans and animals are not returned to the soil but are eliminated as waste. The soil is viewed as nothing more than an inert container. High yield is the goal.

Organic farming is based on ecological principles of the cyclical flow of nutrients and does not involve synthetic chemicals. The soil is viewed as an essential part of the process. Microorganisms in the soil feed on the soil organic matter and make the inorganic part available to plants. The fertility of the soil is maintained by returning nutrients removed by the plant in the form of compost and manure and by a system of crop rotation in which crops which remove more nutrients alternate with crops such as legumes which remove less and add some.

There are clear differences between the two systems of agriculture in philosophy, sustainability, effect on the environment and wildlife, and amount and type of pollution they generate. But neither system is precisely defined and clear-cut in its practices. Some conventional farmers use compost and manure and crop rotations. All are affected by the soil type and climate of their region. There may or may not be differences in the varieties they choose to grow. Even when all these variables are carefully controlled, the studies either demonstrate no differences in nutrient levels or give inconsistent and unreproducible results.

It is extremely difficult to rule out all the possible environmental and genetic factors which might influence nutrient content. Many research studies on organic food do not manage to achieve controlled conditions, in which case it's impossible to say what might have caused any difference which is revealed. Before certification of organic food was widespread, unscrupulous producers capitalised on the higher prices they could obtain for organically labelled food. There was no way of verifying that the food had been grown organically. This may explain why a number of studies found no differences in nutritional value or in pesticide residues between so-called organic and conventional food.

Even where the studies are designed well, results are often uninterpretable, as in these two examples. Organically grown tomatoes in a Vermont (USA) study had significantly less vitamin C and carotene than the conventional ones. But when the trial was repeated the following year, the organic tomatoes had significantly more vitamin C and carotene. In a Canadian study on apples, the organic apples had a significantly higher content of potassium and phosphorous but no difference in calcium and magnesium levels.

Consistent results from one study to another and within each study would be more convincing of a real nutritional difference between organic and conventional food. But there is a bigger question about nutrition and that is whether people are getting all the nutrients they need from their overall diet, rather than from individual foods. Once the crops leave the fields, the loss of nutrients during storage, food processing and food preparation is of much greater significance than anything done by farmers.

Our health does not depend on whether we eat organic or conventionally grown food but on how much fruit and vegetables we eat in our diet. For a healthy diet, five portions a day are recommended (about 400g). The average British person eats only half this amount and the poorest tenth of the population eat next to none. The issue for the organic movement should be the same as that for the public health movement – how to make the consumption of fruit and vegetables easier, cheaper and more attractive than a diet of refined, highly processed, unhealthy food.