Eating a Mediterranean diet rich in fruit and vegetables halves the chances of developing lung disease, researchers have found.
Anti-oxidant vitamins in the foods help to counteract inflammatory processes that damage the lungs, a study shows.
By contrast, nitrites in processed meats, part of the typical Western diet, may contribute to progressive deterioration in lung function with age. Refined foods with a high glycaemic index (such as desserts and sweets) may also promote inflammation.
Serious lung disease is principally caused by smoking and is set to become the third leading cause of death worldwide by 2020, as a result of the rise in smoking in developing nations. It is known by the umbrella term Chronic Obstructive Pulmonary Disease (COPD), which includes bronchitis, emphysema and related conditions. Not all smokers develop the disease, which has led researchers to look for the genetic and environmental factors that offer protection. One of these is diet.
In the first study to examine the link between diet and COPD, scientists from the Harvard School of Public Health in Boston monitored 43,000 men taking part in the US Health Professionals Follow-up Study. Of these, 111 were diagnosed with the condition in the 12 years from 1986 to 1998.
They found eating patterns fell into two distinct groups, with some of the men eating plenty of fruit, vegetables, whole grains and fish (a Mediterranean diet) and others eating processed food, refined sugars, cured and red meats (the Western diet). The men who ate the Mediterranean diet had a 50 per cent reduced risk of developing COPD even after other risk factors, including smoking and age, were taken into account.
The more closely the men stuck to a Mediterranean diet over the 12-year duration of the study, the lower their risk. Conversely, the more Western foods they ate, the higher their risk.
However, there was no effect of diet on the risk of developing adult-onset asthma, the study found.
The researchers, led by Dr Raphaelle Varraso, say in the journal Thorax that there is "no clear association between one particular food and COPD". They add that trials of vitamin supplements had no effect, and it may be the cumulative effect of anti-oxidants in a range of foods that provides protection.
The study says: "Although the effect of any individual nutrient in reducing the risk of COPD may be too small to detect, as suggested by these negative results, when several nutrients are consumed together the cumulative effect may be sufficient for detection."
The authors conclude: "Temporal changes in dietary patterns may contribute to ongoing increases in COPD."
Last month, researchers from the UK's National Heart and Lung Institute, the University of Crete, Venezelio General Hospital in Crete and the Centre for Research in Environmental Epidemiology in Barcelona found that a Mediterranean diet helped prevent the development of asthma and respiratory allergies in children.
And last year, US researchers found that eating a Mediterranean diet could reduce the risk of developing Alzheimer's. Other researchers have shown that people live longer, are less likely to suffer heart disease and have fewer digestive conditions if they follow the diet.
Benefits of eating fruit, vegetables and fish
A Mediterranean diet rich in olive oil, fruit, vegetables and fish has been proved repeatedly to be good for people's health.
In addition to high levels of anti-oxidants, which mop up free radicals in the blood which can block arteries, the diet contains low levels of meat, dairy products and saturated fats. It reduces cholesterol and blood pressure which are both risk factors for heart disease. People who eat a Mediterranean diet are less likely to be overweight or obese, or to suffer from Type 2 diabetes or metabolic syndrome (a condition which precedes diabetes). They have a lower risk of breast and bowel cancer, and a lower incidence of gall stones. A high intake of leafy vegetables which are high in folic acid is believed to contribute to a reduced incidence of birth defects. A major study on the impact of the diet on mental decline has shown it also reduces the risk of Alzheimer's disease by 40 per cent.Reuse content