High-salt diet reduces good gut bacteria

A German study has found that a high salt intake may reduce levels of Lactobacillus bacteria in the gut, therefore causing blood pressure to rise.

With the Western diet containing very salty foods including processed snacks and ready meals, it is no surprise that this is a contributing factor in poor health conditions including hypertension and cardiovascular problems. High salt intake may also cause autoimmune diseases by increasing the activity of pro-inflammatory T helper 17 (TH17).

Published in Nature, Dominik Müller and colleagues studied the effects of high salt intake on gut microbiota using faecal samples from mice fed a normal salt diet (NSD) and a high salt diet (HSD).

The researchers found that by day 14, several microbial species were significantly decreased in HSD-fed mice. They then used a machine-learning algorithm and DNA sequencing to establish bacterial groups that decreased when mice were fed a HSD, and genus Lactobacillus (Lactobacillus murinus) had the strongest connection to HSD.

Researchers found that administering L. murinus to mice reduced TH17 cells and prevented salt-induced exacerbation of actively induced experimental autoimmune encephalomyelitis — a mouse model of brain inflammation — and salt-sensitive hypertension.

To see if these results could be translated to humans, Wilck’s team carried out a small pilot study in which healthy people were given 6 g of supplemental sodium chloride on top of their normal diet for 14 days. They found that blood pressure increased and so did the number of TH17 cells in their blood.

Lactobacillus is not highly abundant in the human gut (if present at all) and for those who did have the species in their gut before treatment, most or all of it had been lost by the end. Overall, the amount of Lactobacillus species decreased as a result of a high consumption of salt.

Known as good bacteria, Lactobacillus can be found in foods such as yoghurt and some types of cheese, and both the study on mice and humans suggested that increasing this bacteria may have positive health implications. This raised the question whether probiotics could be used to increase gut bacteria and prevent or reverse the effects of salt-related health conditions.

“People with a healthy traditional diet have high Lactobacillus in their gut, but the high salt diet of people in more affluent countries probably explains why they have low Lactobacillus levels and an epidemic of hypertension, as well as various autoimmune diseases,” explained Brian J Morris, Professor Emeritus of the School of Medical Sciences and Bosch Institute at the University of Sydney. “Studies have shown that taking probiotics rich in Lactobacillus can lower blood pressure in people with hypertension.”

However, there are a number of differences between mice and humans that means further investigation in humans is required.

Dr Francine Marques, National Heart Foundation Future Leader Fellow and Baker Fellow at Baker Heart & Diabetes Institute, praised the study for contributing to the research surrounding the connection between the gut and health conditions, noting that there is still much to be done.

“We are still in our baby steps to fully understand the role of the gut microbiota in complex diseases such as hypertension.

“The study by Wilck and colleagues adds to this important puzzle by characterising the changes in the gut microbiome after the intake of a high salt diet, which is known to increase blood pressure.”

Gut microbiota is becoming increasingly researched, and this study could have important implications on future preventative measures. As Hannah Wardill, PhD student in the Cancer Treatment Toxicities Group at the University of Adelaide, stated, “This exciting research is the first to suggest that gut bacteria might act as the middleman between salt and heart health, and provides a new therapeutic target to counteract salt-sensitive diseases.”