HIGH-FAT food provokes the same defence reaction in the body as a bacterial invasion.

The airways become inflamed as protective cells are deployed, says Associate Professor Lisa Wood, a speaker at a meeting of the Thoracic Society of Australia and New Zealand.

She studied how people responded to a meal of two breakfast burgers and two hash browns, in what she calls an acute fat challenge.

"The fat activates the same defence mechanism that responds to bacteria," says Prof Wood, a nutrition expert at the University of Newcastle's Centre for Asthma and Respiratory Diseases.

"The fat in the blood peaks after about four hours. If this inflammation happens after every meal it becomes a chronic problem."

Prof Wood's acute fat challenge shows people with asthma should avoid fatty food before using ventolin, a drug that increases air flow to the lungs.

They get the same initial benefit as other people, but the effectiveness wears off as the fat content of the blood increases.

"By four hours we've got this inflammation occurring and lung function returns to pre-treatment levels.

"That's pretty important. It suggests that if people are eating these types of meals their bronchodilator is not going to work effectively."

Another study by Prof Wood shows significant benefits for asthmatic people who eat lots of vegetables and fruit.

The three-month study shows people on a diet that includes five serves of vegetables and two of fruit a day have fewer asthma attacks than those who eat two serves of fruit and one of vegetables.

There is increasing evidence that diet is important for asthma management, she says.

"Low fruit and vegetable intake increases inflammation and increases your risk having an attack."

Prof Wood presented research at the meeting that shows poor quality diets could be contributing to increased asthma prevalence.

Her team studied 99 people with stable asthma and 61 healthy controls.

They found those with asthma were more likely to eat higher volumes of processed food, fat and refined sugar than the controls.

"The usual diet consumed by asthmatics in this study was pro-inflammatory relative to the diet consumed by the healthy controls."

This could contribute to an increased incidence of asthma.

Originally published as Fatty food fires up body's defences: study