Topic 3 The influence of diet on intestinal microbiota

  • Role of the intestinal microbiota in the development of metabolic disorders
  • Possibility of modulating the microbial flora for the treatment of obesity and related disorders, such as insulin resistance, diabetes and hepatic steatosis.

Many bacterial genes have been identified that have no correspondent in the human genome: mainly related to the metabolism of carbohydrates and amino acids and the biosynthesis of vitamins.

Symbiotic relationship between the intestinal microbiota and the human being:

a superorganism

The secret of a “healthy” (rich and varied) microbiota is:

  • Natural childbirth and breastfeeding
  • Physical activity
  • Wash infrequently and greater relationship with land, animals and natural food
  • Do not wash fruits and vegetables too much and eat them as raw as possible
  • Do not use antibiotics (especially in the first 2-3 years of life)

Two groups of beneficial bacteria are dominant in the human gut: Bacteroidetes and  Firmicutes.


  • Reduced bacterial biodiversity
  • ↑ Firmicutes/Bacteroidetes
  • Enrichment in genes involved in the recovery of energy from food
  • Low-grade inflammation

⮚The Westernization of the diet may reduce gut microbial diversity leading to dysbiosis, alteration of barrier function and permeability, and abnormal activation of immune cells, leading to high incidences of chronic diseases.

Impact of diet on gut microbiota

Children from rural Africa

Children from Europe

  • BF children showed a significant enrichment in Bacteroidetes and depletion in Firmicutes.
  • Significantly more short-chain fatty acids were found in BF than in EU children.
  • Gut microbiota coevolved with the polysaccharide-rich diet of BF individuals, allowing them to maximize energy intake from fibers while also protecting them from inflammations and noninfectious colonic diseases.

Food components have a key impact on the gut microbiota, influencing its composition in terms of richness and diversity:

  • High intake of animal proteins, saturated fat, sugar, and salt could stimulate the growth of pathogenic bacteria
  • The consumption of complex polysaccharides and plant protein could be associated with an increase of beneficial bacteria quantity, stimulating SCFA production.
  • Omega-3, polyphenols, and micronutrients appear to confer health benefits via modulation of the gut microbiota.

🡪 A varied diet with abundant fiber and vegetable fats is linked to greater bacterial diversity, a lower concentration of pro-inflammatory molecules in the blood and increased synthesis of SCFAs. 

The next step consists in modifying the bacterial flora for therapeutic purposes, through diet (prebiotic substances) and lifestyle or the administration of specific bacterial strains (probiotics).