Many people believe organic food to be healthier, as well as more ethical and sustainable. We review the evidence

What is organic food?

  • The criteria for organic agriculture differ from one country or region to another, but in general it involves respect for the environment and animals, and the production of high-quality foodstuffs
  • Organic farming does not use (or strictly limits the use of) chemical pesticides and does not allow chemical fertilisers, growth hormones, antibiotics or genetically modified organisms (GMOs)
  • Organic farmers also adopt other practices to compensate for the prohibited use of artificial chemicals. For example, they often use longer crop rotations and frequent mechanical weeding.

What are the benefits of organic food?

A meta-analysis of available evidence, led by researchers at Newcastle University School of Agriculture, revealed statistically significant and meaningful differences in composition between organic and non-organic products. Most importantly, the combined results of the 343 peer-reviewed studies they examined show the concentrations of a range of antioxidants such as polyphenolics and carotenoids to be substantially higher in organic crops and crop-based foods. Many of these compounds have previously been linked to a reduced risk of chronic diseases.

Significant differences were also detected for some other compounds, including higher levels in organic crops of vitamin C and trace minerals such as zinc. Non-organic crops, on the other hand, had significantly higher concentrations of the toxic metal cadmium, and pesticide residues occurred four times more often in conventional than organic crops.

There is also evidence that not using inorganic nitrogen and phosphorus fertilisers, as in organic farming systems, is linked with higher antioxidant concentrations and lower cadmium concentrations. Other studies in a wide variety of foods support the view that organic foods tend to have superior nutrient contents:

The beneficial effects of organic farming on nutritional quality are not confined to vegetable foods. Meat fat in sirloin steaks from organically raised and summer-finished cattle has been found to contain higher concentrations of health-promoting conjugated linoleic acid, vaccenic acid and individual omega-3 fatty acids, and to have a lower ratio of omega-6 to omega-3 fatty acids compared with non-organic and winter-finished cattle respectively.

Summer-finished cattle feed outdoors on grass for the last few months before slaughter, whereas winter-finished cattle are usually housed indoors and are fed a grain-based diet.

Is eating organic food better for us?

There is some evidence from animal trials and human epidemiological studies that suggests eating organic food might make us healthier.

When rats were given otherwise identical diets made from crops grown with or without synthetic pesticides and using either manure or mineral fertilisers, significant effects on their physiology became apparent. In particular, the immune status of rats fed a diet made from organically fertilised crops was greatly affected — for instance, spontaneous lymphocyte proliferation was seen to increase (multiplication of white blood cells) — compared with those fed with conventionally fertilised crops.

Human epidemiological studies can only show associations, not cause and effect, but have yielded some interesting results. A recent study from Norway of 28,192 pregnant women reviewed the prevalence of pre-eclampsia, a disorder of pregnancy characterised by high blood pressure and high levels of protein in the urine. Women who reported to have eaten organic vegetables ‘often’ or ‘mostly’ had a 21 per cent lower risk of pre-eclampsia than those who reported eating them ‘never/rarely’ or ‘sometimes’.

Possible explanations for an association between organic vegetables and preeclampsia could involve lower exposure to pesticides, greater intake of secondary plant metabolites such as polyphenols and terpenoids and changes in the composition of the gut microbiota.

Another large, case-controlled study looked into possible associations between a mother’s diet during pregnancy and the incidence of hypospadia, a birth defect of the urinary tract in male babies. The results suggested a link between hypospadias in the offspring and mothers eating certain food items that were conventionally, rather than organically produced. There was a particularly strong association with high consumption of nonorganic butter and cheese, a finding that was thought to be due to chemical contamination of high-fat dairy products.

When should you buy organic?

The current trade-off is that organic foods are generally more expensive and many consumers are unsure which organic foods are best to buy on a limited budget.

Given that most UK citizens need to increase the quantities of fruit and vegetables in their diet, the most useful advice would be to start with these categories along with any dairy products (organic milk has higher amounts of healthy fatty acids than conventional milk, including omega-3 fatty acids and conjugated linoleic acid).

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