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The composition of the gut bacteria  is, to a large extent, a reflection of diet. Studies show, for example, changes in the bacteria composition of young children with the introduction of solid food. One well cited study, examined gut microbiota in health children between the ages of one and six either living in Europe (Italy) or rural Africa (Burkina Faso). One of the biggest differences in the diet was the fiber content. It was almost twice as high in the children from Burkina Faso as compared to the Italian children. As a result the composition of bacteria was seen to be different in the two groups, (particularly the ratio of the two largest populations of bacteria, the Firmicutes and Bacteriodetes).

A number of studies have extended this research of comparing children and adults from different geographical locations. The findings are consistent and show significantly different microbial communities, which, in part, are as a result of differences diets in these locations.

In another study it was shown that those who eat protein and animal fats typical of Western diet have predominantly Bacteroides bacteria, while in those who consume more carbohydrates, especially fibre, have a prevalence of the Prevotella species of bacteria.

More recent studies have shown dietary changes can rapidly change the composition of the bacteria in the human gut days. Extreme diets either made entirely of animal or plant products . The animal-based diet consisted of bacon and eggs for breakfast, spare ribs and brisket for lunch, and salami and cheese for dinner pork rinds and string cheese for snacks. This diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii). The increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease.

The plant group feasted on high-fiber group got fruits, vegetables, grains, and beans, FreeFire. Plant-eaters had fewer bile-resisting bacteria and higher expression levels of gene associated with carbohydrate digestion.

This study changes our view of how rapidly the microbiome can change.

In a large Danish study the genomes of gut bacteria from 123 non-obese and 169 obese Danish individuals were analyzed. The results revealed that the group of individuals with a more diverse composition of gut bacteria were healthier than those that had a less diverse composition who tended to be more obese with increased resistance to insulin and higher levels of inflammation.

All of these studies confirm that diet shapes the microbial community and that this core community remains relatively stable during the individual’s life span, until finally in old age the diversity of the population declines.



Conlon, MA, and Bird AR, The Impact of Diet and Lifestyle on Gut Microbiota and Human Health. Nutrients 2015; 7, 17-44

O’Sullivan, A et al., The Influence of Early Infant-Feeding Practices on the Intestinal Microbiome and Body Composition in Infants. Nutrition and Metabolic Insights 2015;8(S1) 1–9

Clarke, SF et al., Exercise and associated dietary extremes impact on gut microbial diversity. Gut Dec 2014; 63(12):1913-20

Bonder, MJ et al., The influence of a short-term gluten-free diet on the human gut microbiome. Genome Medicine 2016; 8:45

Le Chatelier, E et al., Richness of human gut microbiome correlates with metabolic markers. Nature 500(7464):541-6