Eating fatty foods during stressful periods can impair the body's 'recovery' from the effects of stress, new research suggests.

The study, published recently in Frontiers in Nutrition and Nutrients, showed that consuming foods high in fat before a mentally stressful episode can reduce brain oxygenation and cause poorer vascular function in adults.

Researchers from the University of Birmingham took a group of young, healthy adults and gave them two butter croissants as breakfast.

They then asked them to do mental math, increasing in speed for eight minutes, alerting them when they got an answer wrong.

They could also see themselves on a screen while they did the exercise. The experiment was designed to simulate everyday stress that we might have to deal with at work or at home.

The team found that eating high-fat foods attenuated cerebral oxygenation in the pre-frontal cortex, with lower oxygen delivery (39 per cent reduction in oxygenated haemoglobin) during stress compared to when participants consumed a low-fat meal.

Furthermore, fat consumption had a negative effect on mood both during and after the stress episode.

The scientists were also still able to detect reduced arterial elasticity -- which is a measure of vascular function -- in participants up to 90 minutes after the stressful event was over.

"When we get stressed, different things happen in the body: our heart rate and blood pressure go up, our blood vessels dilate, and blood flow to the brain increases. We also know that the elasticity of our blood vessels declines following mental stress," explained Rosalind Baynham, a doctoral researcher at the University.

"We found that consuming fatty foods when mentally stressed reduced vascular function by 1.74 per cent (as measured by Brachial Flow-mediated dilatation, FMD)."

"Previous studies have shown that a 1 per cent reduction in vascular function leads to a 13 per cent increase in cardiovascular disease risk. Importantly we show that this impairment in vascular function persisted for even longer when our participants had eaten the croissants," Baynham said.

For people who already have an increased risk of cardiovascular disease, the impacts could be even more serious, the researchers said.

"We all deal with stress all the time, but especially for those of us in high-stress jobs and at risk of cardiovascular disease, these findings should be taken seriously," said Jet Veldhuijzen van Zanten, Professor of Biological Psychology at the University.

The research also suggested that by consuming low-fat food and drinks, people's recovery from stress is less affected.

After eating a low-fat meal, stress still had a negative effect on vascular function (1.18 per cent decrease in FMD), but this decline returned to normal 90 minutes after the stressful event.

Further research has shown that by consuming 'healthier' foods, particularly those rich in polyphenols, such as cocoa, berries, grapes, apples and other fruits and vegetables, this impairment in vascular function can be completely prevented.