However, Dr Haby said more research was needed before the link between polyunsaturated fats and asthma could be proved.

BBC: Margarine 'may increase asthma risk'

Liquid oils are usually unsaturated fats, including monounsaturated fats in olive and canola oils and polyunsaturated fats in safflower, corn, soybean and fish oils.

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Lead researcher Dr Michelle Haby, from the Centre for Community Child Health, Royal Children's Hospital, Melbourne, told BBC News Online why polyunsaturated fats might be linked to asthma.

BBC: Margarine 'may increase asthma risk'

Polyunsaturated fats, contained in walnuts and soy oil, are good.

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The authors suggest that the increase in the number of children developing asthma could be significantly reduced if more were breastfed or given a diet lower in polyunsaturated fats.

BBC: Margarine 'may increase asthma risk'