Evidence for a role of diet in asthma and chronic obstructive pulmonary disease (COPD) has been accumulating rapidly over the past decade. Associations have been reported between the intake of fruit, fish, antioxidant vitamins, fatty acids, sodium or magnesium, and indicators of asthma and COPD. Several issues need to be addressed before causality of these associations can be established. The role of diet in the development of disease and the induction time and reversibility of the effect needs further investigation. The role of smoking habits in the relation of diet and respiratory disease also needs to be elucidated. Nevertheless, based on the available evidence, dietary guidelines could be proposed for the primary and secondary prevention of asthma and COPD that are in line with existing dietary guidelines for the prevention of coronary heart disease and cancer.