High-fat diets have an ‘extraordinary’ effect on anxiety

When feeling stressed, many of us may turn to junk food to help. Perhaps some chocolate for a mid-afternoon boost, or a donut on the way home to reward surviving another 9 to 5.

However, scientists at the University of Colorado Boulder have discovered that eating fatty foods may actually make our anxiety worse.

Which, let’s face it, isn’t ideal.

The team found that when animals were given a high-fat diet, it disrupted their gut bacteria – which in turn altered the brain chemicals that fuel anxiety.

Lead author Professor Christopher Lowry said: ‘Everyone knows that these [high-fat items] are not healthy foods, but we tend to think about them strictly in terms of a little weight gain. 

‘If you understand that they also impact your brain in a way that can promote anxiety, that makes the stakes even higher.’

The government recommends men should not eat more than 30g of saturated fat a day, and women 20g – roughly about 11% of our total energy intake from food.

However, in the UK, many people exceed this, and in the US, the Centers for Disease Control says the typical diet is about 36% fat.

To investigate the effects of this on mental health, the researchers studied adolescent rats, which were divided into two groups. One ate a standard diet of 11% fat for nine weeks, the other a high-fat diet of 45%.

During the study, published in Biological Research, the team collected faecal samples to assess gut bacteria, and at the end of the study used tests to determine what effects, if any, the diet had on their behaviour.

Unsurprisingly, the rats on the high-fat diet were heavier than those in the other group, but they also showed a significantly less diverse gut microbiome. In particular, they hosted far more of a bacteria in the category known as Firmicutes, and fewer in the group called Bacteroidetes.

In addition, three genes associated with the production of serotonin were more active in the high-fat group.

While serotonin is often thought of as a ‘feel-good’ hormone, some neurons, or nerve cells, have been shown to generate an anxiety-like response when activated by it. One of the three genes, called tryptophan hydroxylase, or tph2, is also associated with mood disorders and suicide risk in humans.

‘To think that just a high-fat diet could alter expression of these genes in the brain is extraordinary,’ said Professor Lowry. ‘The high-fat group essentially had the molecular signature of a high anxiety state in their brain.’

Although not yet confirmed, Professor Lowry suspects the reason high-fat diets cause anxiety is because an unhealthy microbiome compromises the lining of the gut. This can allow bacteria to make their way into the blood, and eventually communicate with the brain through the vagus nerve, a pathway from the gastrointestinal tract to the brain.

‘If you think about human evolution, it makes sense,’ he said. ‘We are hard-wired to really notice things that make us sick so we can avoid those things in the future.’

He added that not all fats are bad, and that some research shows good fats, such as from avocado, can counteract the bad, such as from a burger.

In addition, healthy fats like those found in fish, olive oil, nuts and seeds can be anti-inflammatory and good for the brain.