There is a strong link between microbiota and poor mental health.

In recent years, there has been an increased focus on mental disorders such as anxiety or depression in the media. For example, a report published in 2023 found that 17% of young Spanish university students were taking medication to relieve symptoms of anxiety or depression they were suffering from.

It is clear that the fear, uncertainty and saturation caused by the Covid-19 pandemic in health centers and hospitals has caused chaos. In these cases, the reason that can provoke it is clearly defined. But what if I told you that diet may also be associated with an increase in these pathologies?

Since the advent of movements such as real nutrition or plant-based diets (veganism, flexitarianism, etc.), the reputation of ultra-processed foods has plummeted. And one of the latest arguments in favor of reducing its consumption is the numerous data showing a connection between its excessive consumption and the appearance of mental problems.

This is, for example, the conclusion of a recent review of studies linking high consumption of these foods to the risk of symptoms associated with depressive or anxiety disorders, although it is not yet clear why this occurs.

The evidence is overwhelming. If we look at the analyzes one by one, we are struck, for example, by a study conducted in South Korea that found a 1.4 times greater likelihood of developing depression if a diet rich in ultra-processed foods was mediated, with a greater impact among women. Another study conducted in the US provided similar data: the population that exercised less and ate these types of foods regularly were also more likely to develop this disorder.

The microorganisms that inhabit our digestive system are divided into types, which, in turn, consist of different genera. The most common phyla are Firmicutes and Bacteroidetes, but there are other important phyla such as Actinobacteria, Fusobacteria, Proteobacteria and Verrucomicrobia. Among the numerous genera, the most famous is Bifidobacterium.

In both animal and human studies, Firmicutes bacteria have been shown to decrease in anxiety symptoms, while Bacteridetes and Fusobacteria populations proliferate. In the context of depression, Prevotella, Klebsiella and Clostridium are the genera most associated with the gut microbiota.

Ideally, the microbiota should have a balanced ratio of phyla and genera, known as eubiosis. When harmony is disturbed, the opposite effect appears: dysbiosis, associated not only with depression or anxiety, but also with a number of chronic pathologies. For example, genres that might be considered pro-inflammatory are found to be more common in individuals with depression or anxiety.

If we want to reverse dysbiosis, one option is to resort to probiotics, although changing dietary habits seems to produce better results. This is because the microbiota obtains most of its energy through food, so changes in intake have a direct impact on the phylum and genera ratios.

In this sense, Western eating patterns, characterized by an abundance of animal products, overconsumption of ultra-processed foods and unhealthy culinary practices, are associated with higher rates of anxiety and depression, in contrast to diets such as the Mediterranean, Nordic and Scandinavian diets. or the Japanese. High intake of polyunsaturated fatty acids from fish, fruits, vegetables, whole grains and fermented foods may contribute to the eubiosis state.