After an awful day, a big chocolate cake can feel like your best friend. Or a plate of sausage rolls might be your go-to comfort food.

Until now, science has supported the idea that naughty foods, can serve as a balm when you’re stressed or upset.

They might make you fat, but at least they make you feel better.

This is because carbohydrates increase brain levels of serotonin,  a chemical messenger that helps regulate mood.

People low in serotonin tend to withdraw socially, ridden with sadness, and suffer low self-esteem. Under these circumstances, cake can be an emotional essential.

However, two new studies suggest the comfort benefits of fats and carbs is awfully compromised.

They slow recovery from stress

New research from the University of Birmingham found that eating fatty treats when dealing with everyday stress “can impair the body’s recovery from the effects of stress”.

How so?

Because these foods, when consumed before “a mentally stressful episode can reduce brain oxygenation and cause poorer vascular function in adults”.

First author Rosalind Baynham, a PhD researcher, in a prepared statement explained: “We took a group of young, healthy adults and gave them two butter croissants as breakfast. We then asked them to do mental math, increasing in speed for eight minutes, alerting them when they got an answer wrong.”

The participants could see themselves on a screen while they did the exercise.

The experiment, she said, “was designed to simulate everyday stress that we might have to deal with at work or at home”.

The thinking behind the experiment was this: 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.

It’s known that the elasticity of our blood vessels, a measure of vascular function, declines following mental stress.

So what happened with the croissant eaters?

Baynham said: “We found that consuming fatty foods when mentally stressed reduced vascular function by 1.74 per cent.”

Doesn’t seem like much?

Previous studies have shown that a one per cent reduction in vascular function leads to a 13 per cent increase in cardiovascular disease risk.

“Importantly,” Baynham said, “we show that this impairment in vascular function persisted for even longer when our participants had eaten the croissants.”

The scientists were able to detect reduced arterial elasticity in participants up to 90 minutes after the stressful event was over.

The good news?

The Birmingham team, in other research, found that consuming healthier foods – particularly those rich in polyphenols, such as cocoa, berries, grapes, apples and other fruits and vegetables – prevents this impairment in vascular function.

Dr Catarina Rendeiro, Assistant Professor in Nutritional Sciences,  said: “The impact of these foods during stressful periods cannot be understated. For example, reduced oxygenation to the brain could potentially impact mood and mental health, making people even more stressed.”

Other signs of trouble

Turning to junk food for solace, according to new University of Colorado Boulder research, may backfire cause you anxiety.

In a study with animals, a high-fat diet disrupted resident gut bacteria, altered behavior and, through a complex pathway connecting the gut to the brain, influenced brain chemicals in ways that fuel anxiety.

Adolescent rats given a high-fat diet showed higher expression of three genes (tph2, htr1a, and slc6a4) involved in production and signaling of the serotonin – the transmitter we think of as a feel-good brain chemical”.

But it’s not as simple as that.

The Colorado scientists say that certain subsets of serotonin neurons “can, when activated, prompt anxiety-like responses in animals”.

Worse, “heightened expression of tph2, or tryptophan hydroxylase… has been associated with mood disorders and suicide risk in humans”.

The potential link between comfort foods and anxiety needs a lot more research. For the moment, the study is food for thought.