How do processed foods affect the gut-brain axis?

There has been a lot of discussion around processed foods and their effects on our health.

Processed foods can include those high in sugar, salt, and saturated fat such as ready meals, fast-foods, sausages, biscuits, and cakes. But processed foods can also include foods which are high in fibre and nutrients including wholegrain bread.

Food is complex, and how it influences our health is even more complicated to understand, so it’s important we consider both the nutritional content of food and how it has been processed to fully understand the impact of food on our health.

One major area of interest is the effect of processed foods on the microbiota-gut-brain axis.

What is the microbiota-gut-brain axis?

The microbiota-gut-brain axis is a web of connections that allows communication both ways between the gut microorganisms, our gut cells, and the brain. The communication is facilitated by a network of nerves, in both the gut and the brain, and hormones.

The gut microbiota is influenced by the food we consume. A varied diet that is rich in fibres, fruits, and vegetables has been seen to promote the diversity and abundance of  beneficial microbes.

On the other hand, a restricted diet, high in refined sugars and lacking fibre can lead to disparities in diversity and lead to reduction in the growth of helpful microbes.

There is also increasing evidence indicating that microbial changes in the gut can lead to changes in cognitive and mental health. When fibres from the diet are scarce, gut bacteria can switch to forage on sugars naturally produced by the gut.

How changes in the gut’s lining affect the brain?

Researchers are exploring the link between the sugars decorating the lining of the gut and the brain.

Quadram Institute scientists are studying whether alterations of the intestinal epithelial in mucin glycosylation cause changes to the gut-brain axis. Cells lining the gut produce proteins rich in sugars, called mucins, that make up the mucus gel which provides a habitat for the gut bacteria.

Quadram Institute researchers have found that alterations in mucin glycosylation are associated with a leaky gut and changes in brain function and cognition.

So, do microbes causing glycosylation changes to the gut also affect the brain? This is what the researchers found in another study where they identified some of the cells and processes involved.

We don’t yet know how findings in mice relate to humans, but these two studies points to how intestinal mucus, glycosylation and microbes link to brain function.

How do low-fat processed foods change the gut environment and cause changes to the brain?

A new study published this year, by researchers at the University of East Anglia and the Quadram Institute, has explored the impact of low-fat processed diets on the relationship between our gut, brain, and overall health.

The researchers found that mice fed a low-fat processed diet had changes in their gut that affected their brain functions; specifically changes to bile acid concentrations. Bile acids are a key regulator of inflammatory signalling in the gut, so this may suggest one mechanism of how foods could be influencing our gut-brain axis.

The high sugar and fibre-poor refined diet in the study disrupted the gut microbiota, and this affected how the body was processing bile acid. The disturbance was linked to changes in genes related to inflammation in the brain, that in turn caused a decline in brain function. The study suggests that certain foods can have a cascade of affects, leading to the decline in brain health.

The research was carried out on mice, so caution is needed extrapolating these results into humans, but this has provided valuable new insights on the connection between low-fat processed foods, the gut, and brain health. It also draws attention to the important role of bile acid concentrations on inflammation in the brain.

With a better understanding of the associations between processed foods and the microbiota-gut-brain axis, we can start to unpick the complexity of how different foods affect health. Understanding this complexity will help lead to an evidence-based approach to changing our diets to benefit health and wellbeing.

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This blog was written by Keni Duguma, an intern with the Microbiology Society supporting the Centre for Microbial Interactions in Norwich with Dr Sam Rowe.