Organic agriculture got a big boost Monday from a study proving that fruit grown without chemical inputs contains significantly larger quantities of at least three compounds associated with improved health.

Scientists at the University of California in Davis grew two otherwise identical plots of kiwis side-by-side, one organically and the other with a standard mix of herbicides, pesticides and chemical fertilizer.

Upon reaching maturity, and after different periods of storage, the organic fruit showed 18 and 27 percent higher levels, respectively, of polyphenols and antioxidant activity, both widely linked with health benefits.

A raging scientific debate over whether eating organic makes a difference has not prevented organic food sales from soaring 20 percent a year, reaching some 28 billion dollars in 2006, according to the Bonn-based International Federation of Agriculture Movements.

This is one of the first studies, the authors contend, that factors out all other possible influences in comparing conventionally grown and chemical-free food plants.

Polyphenols -- found in red wine, red berries, peaches and pears -- have been shown in other studies to reduce cholesterol and improve blood circulation.

Some research has indicated that they may help prevent some forms of cancer.

The authors of the study, published in the peer-reviewed British journal of the Society of Chemical Industry, conjecture that the difference in polyphenol levels may be due to the negative impact of chemical farming.

"It is possible that conventional growing practices utilize levels of pesticides that can result in a disruption of phenolic metabolites in the plant that have a protective role in plant defence mechanisms," wrote Maria Amodio and three co-authors.

Antioxidants are found in plant substances and are thought to help protect the body by neutralizing free radicals, or unstable oxygen molecules, which can damage cells and are linked to poor health and disease. Green tea has especially high concentrates of one kind of antioxidant.

The study also reported higher levels of ascorbic acid, better known as vitamin C.

While not all scientists agree that these factors promote health, the study proves that they are more present in chemical-free produce.

The study suggests that the organic plants, thrown onto their own defences against disease and predators, are more "stressed" and therefore produce more of these beneficial compounds.

In terms of flavour, the scientists said, the organic and non-organic fruits were virtually the same, though the chemical-free kiwis had thicker skin and slightly less fleshly fruit.

Organic yields were also smaller, averaging 22.5 tonnes per hectare (nine tonees per acre) as opposed to 26.9 tonnes per hectare (10.75 per acre) for the conventionally grown fruit.

The market for organic foods has developed mainly in rich countries among wealthier consumers willing to pay a premium price. Supporters of conventional farming contend that chemical inputs are essential for providing nutrition at affordable prices for the bulk of the world's population.

mh/ri/smc

Health-science-food-organic

AFP 261327 GMT 03 07