Our research on the human microbiome, the next health frontier
Obesity as a public health threat
Obesity is characterized by an excess of adipose tissue. According to the World Health Organization, today it is a public health problem with >39% of people suffering from obesity around the world, becoming a global pandemic. In addition, obesity is associated with many health problems such as type II diabetes, cardiovascular disease or cancer, among others, which have been the cause of >70% of premature deaths from 2015 to date.
The relationship of obesity with the microbiome
Obesity is a multifactorial disease that includes genetic, environmental, and personal/ behavioral factors. A study by Jeffrey Gordon in 2006 sparked curiosity about the relationship between the microbiome and obesity. In 2004 it had already been shown that when the microbiome of normal mice was transplanted into sterile mice, the latter gained 60% body fat without increasing caloric intake. This happens because the gut bacteria that make up the microbiome feed on the non-absorbable polysaccharides (especially fibers) in our diet and as a by-product they generate short-chain fatty acids (SCFA), especially acetate, propionate and butyrate in a 60:20:20 M ratio, and monosaccharides, increasing energy to the host by up to 10%.
Types of bacteria in our microbiome
In short, there are different enterotypes and genus that have been traditionally reported:
Enterotype 1- Bacteroides which ferment carbohydrates and proteins to produce B vitamins and vitamin C.
Enterotype 2 - Prevotella which degrade mucins (glycoproteins) and synthesize vitamins and minerals such as folic acid or B1.
Entereotype 3- Firimictues, specifically the Ruminococcus, which have a great capacity to degrade cellulose and other fibers and produce monosaccharides and SCFAs.
SCFAs passively diffuse and act as signaling molecules. Butyrate is an important energy source for colonocytes. Propionate and acetate bind to the G-protein Gpr41 and Gpr42 receptors of GLP-1-producing enteroendocrine cells that stimulate insulin secretion from the intestinal epithelium. The stimulation of G proteins, specifically Gpr41, produces an increase in the expression of leptin in adipocytes in mice, inhibiting the expression of peptide YY, which is responsible for accelerating intestinal transit and reducing energy extraction from the diet. In addition, acetate, one of the fatty acids produced by the fermentation of fiber by Firmicutes, is associated with being a cholesterol precursor.
On the other hand, absorbed monosaccharides also increase transcription factors such as carbohydrate response element-binding protein, and hepatic lipogenesis is stimulated. Another mechanism produced by the increase in Firmicutes and its metabolism is the decrease in fasting-induced adipose factor (Fiaf). Fiaf is an inhibitor of lipoprotein lipase (LPL). If Fiaf decreases, the concentration of LPL increases, which contributes to insulin resistance and adipocyte hyperplasia, therefore, to a higher concentration of fatty acids in the cell and accumulation of triglycerides. In diets rich in fat and sugar, the CB1 receptor that controls the concentration of LPL is usually affected.
Effect of fat the diet in our microbiome
Diets rich in fats and sugars produce higher Firmicutes/Bacteroides ratio leading to a series of consequences for the host. Obese individuals usually have an entereotype 3 microbiome, causing consequences such as those mentioned above.
How to improve our microbiome
Tactics to influence bacterial diversity to reduce the Firmicutes ratio would be supplementation with fructooligosaccharide-type inulin, or lactulose, among other fibers that stimulate the growth of bifidobacteria and lactobacilli. The increase in bifidobacteria is associated with a decrease in LPS and therefore an increase in glucose tolerance, weight loss and increased satiety. Another strategy would be the direct supplementation of lactobacillus that favors Fiaf and decreases fatty acids. However, the best strategy is to follow a balanced diet low in saturated fat and high in legumes, fruits and vegetables that contains a high content of fiber and polyphenols and a greater diversity of bacteria.
Authored by Patricia Jurado, MsC Nutrition and public health
