The idea that diet could have a role to play in preventing the signs of asthma is starting to gain ground, with studies highlighting certain deficiencies in patients or warning against the consumption of certain foods. On World Asthma Day, May 2, Relaxnews spoke to Dr. Bertrand Delaisi, a pediatric pulmonologist at Clinique Marcel Sembat in Boulogne-Billancourt, France, for an overview of what's currently known on the subject.

The prevalence of asthma has increased considerably in recent decades, in parallel with changes in lifestyles and dietary habits, tending towards diets rich in carbohydrates and fat, and low in fiber.

As well as pollutants, allergens, passive smoking and air pollution, allergy specialists are increasingly interested in how diet can promote or modify the development of asthma on a physiopathological level.

Eating ham, cured sausage or smoked meats at least four times a week could aggravate the symptoms of asthma over time, concludes a study carried out by researchers at Inserm, the French National Institute of Health and Medical Research, published in January in the medical journal Thorax.

On the contrary, consuming fiber may influence the gut flora and could reduce inflammation in the bronchial tubes. A diet rich in fruit and vegetables and vitamin C -- and especially vitamin D (calf's liver, soy, egg yolks) -- could, therefore, help limit the risks of asthma, according to Dr. Bertrand Delaisi, a pediatric pulmonologist at Clinique Marcel Sembat in Boulogne-Billancourt, France.

The same goes for omega-3 fatty acids, present in oily fish and other foods (walnuts, canola oil), which can relieve inflammation, including in the respiratory airways. People whose diets are rich in omega-3 have a lower risk of suffering from asthma than those whose intake is limited. They could also be beneficial to people who already suffer from the condition.

Foods containing quercetin could reduce the frequency of asthma attacks, as this antioxidant flavonoid is an anti-inflammatory. Studies carried out in vitro found that quercetin inhibited the liberation of inflammatory substances by mast cells, which play a role in allergic reactions, mirroring certain anti-asthma medications. This antioxidant is found in onions, mustard oil, tea and apples.

An estimated 300 million people worldwide suffer from asthma.