Chronic obstructive pulmonary disease (COPD) is the UK's fastest growing fatal disease and is estimated to cost the health service close to £1 billion every year. Around 80,000 people in Northern Ireland suffer from COPD. COPD is clinically defined as a slowly progressive condition characterised by airflow limitation, which is largely irreversible. Chronic inflammation and oxidative stress are key components of the underlying pathological process resulting in airflow limitation. Dietary factors and nutrients that have antioxidant or anti-inflammatory properties are therefore of interest with respect to the aetiology of COPD. The antioxidant vitamins C, E and beta-carotene are all present in the lung milieu. Such antioxidants represent the lung's first line of defence against oxygen free radicals. Observational studies indicate that a low dietary intake of antioxidant nutrients, or foods rich in antioxidants (e.g. fruit and vegetables), is associated with decreased lung function and increased risk of COPD. To date, there have been no food-based dietary interventions investigating the effect of increased fruit and vegetable intake on COPD. The investigators propose to recruit people with mild to moderate COPD and low fruit and vegetable intakes (<=2 portions daily) and randomise them to one of two study arms for 12 weeks - either to increase fruit and vegetable consumption to at least 5 portions a day, or to follow their normal diet. Airway and systemic oxidative stress and inflammation will be assessed at baseline and post-intervention in order to determine if fruit and vegetables have the potential to alleviate the oxidative stress and airway inflammation associated with COPD.