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Poor diet can increase asthma risk


Eating a poor quality diet high in saturated fats and refined sugar can increase the risk of symptoms in asthmatics, according to a new study.

University of Newcastle researchers studied the diets of a group of subjects using the Dietary Inflammatory Index (DII), based on their potential to either cause inflammation linked to overactivity in the immune system, or to protect against it.

Inflammatory foods included those high in saturated fats and refined sugar, while anti-inflammatory foods included fruit and vegetables and those high in soluble fibre, such as oat bran and lentils.

Lead researcher Associate Professor Lisa Wood said that, after studying the diets of 99 asthmatics and 61 people without asthma symptoms, asthmatics who participated in the study were more likely to eat inflammatory diets, increasing their risk of asthma attacks.

For every one unit increase in the DII score, the odds of having asthma increased 62 per cent.

The researchers also found that lung function was significantly associated with DII score.

Lung function was found to reduce by about 10 per cent in the third of patients with the highest DII score compared with the third of patients with the lowest. Levels of the inflammatory marker interleukin-6 were also positively associated with the DII score.

Associate Professor Woods said the usual diet consumed by asthmatics in the study was pro-inflammatory relative to the diet consumed by healthy controls, and that eating a single high-fat meal could cause inflammation in the airways of people with asthma.

She explained that the body responds to excess dietary fat the same way as it would an invading pathogen, so that those who regularly ate fatty food had a chronically activated immune system.

In addition, researchers found that the effectiveness of ventolin – the most common inhaler-based treatment for asthma, also known as salbutamol – can become compromised by the consumption of fast food or sugary drinks.

Associate Professor Woods, with Dr Mehra Haghi, found that the amount of salbutamol transported through the cell membrane was significantly higher in the presence of polyunsaturated fatty acids compared with saturated fatty acids or no fats at all.

“Incubation with polyunsaturated fatty acids appeared to reduce the stiffness of the cell membrane,” Dr Haghi said. “Our findings suggest that the presence of polyunsaturated fatty acids is essential for membrane fluidity.

“Our findings also demonstrate that, if saturated fatty acids are present, then this effect is lost and drug transport is prohibited.”

She said it was particularly important for people who already had asthma to eat a diet high in fruit and vegetables.

The studies were presented at the Thoracic Society of Australia and New Zealand’s annual meeting.

Kirsty Waterford