Importance of fibre-rich diets to support healthy gut bacteria

High protein or high fat diets have become increasingly popular over the last few years, especially as a means to lose weight. However this may lead to increased levels of fatty and protein-dense foods such as meat, eggs and cheese being consumed in large quantities on a daily basis. Whilst there is no doubt fish, meat and eggs are rich in essential nutrients, consuming too much protein at the expense of fibre rich vegetables is not beneficial for our health.

A recent study has shown that stool samples from 144 vegetarians (including dietary dairy and eggs) and 105 vegans (no animal protein in their diets) have different profiles of gut microflora compared to an omnivore diet (i.e. a diet containing mixed plant and animal foods). Major differences included lower levels of pathogenic bacteria such as E. coli and lower stool pH in the vegetarian and vegan diets.

One explanation for these findings includes fermentation of soluble and insoluble fibre, found in vegetables and certain grains, pulses and legumes, by beneficial gut bacteria leads to an increase in short chain fatty acid production. These types of fatty acids, including acetate, butyrate and propionate, create a slightly acidic (pH 5.5-6.5) environment in the gut. This in turn allows further growth of beneficial gut bacteria such as Lactobacilli, which produce natural acids so enhancing the optimal slightly acidic gut pH. Bifidobacteria, which suppress levels of pathogenic bacteria growth, also thrive in this environment.

Coupled to theses findings, diets high in animal protein may also lead to increased protein fermentation in the gut by certain bacteria species. This type of putrefactive fermentation leads to increased levels of harmful metabolites, such as amines, which increase stool pH and may also damage the gut lining. This means that the pH within our guts, measurable via the stools and heavily influenced by diet, is vital to maintaining levels of beneficial bacteria and therefore good health.

Of particular interest in the study was the finding that women have a slightly higher pH stool value compared to men on the same omnivore diet with similar amounts of fibre. However, when men and women followed a strict vegan diet during the study the women’s stool pH decreased to similar levels compared to the male cohort. This indicates that some women may benefit from a more vegan-based diet compared to men.

Alongside the diet, supplementing with a good quality, scientifically proven probiotic supports growth of beneficial gut bacteria. Probiotic strains include Lactobacilli, which belong to the lactic acid bacteria family that produces natural acids to support a slightly acidic gut pH, and Bifidobacteria, which ferment fibre into short chain fatty acids that also help maintain acidic gut pH.