Abstract
Animals and humans have very different gut microbiota, and the human microbiota is unique to each individual. For these reasons, it is difficult to find a diet that provides all the nutrients according to individual requirements. In this study, we investigated the possibility of using simple in vitro fecal fermentation of digested food to evaluate fundamental differences in the gut metabolism of individuals with different microbiomes in response to specific dietary interventions. We fermented beef using six human fecal microbiotas, analyzed shifts in these microbiomes, and quantified short-chain fatty acid (SCFA) production in each system. Our results demonstrate that each microbiome responds with a unique shift in composition, SCFA production, and metabolic activity following 90 min of fecal fermentation of beef. Differentially abundant genera and metabolic activities varied among subjects. Only two subjects’ fecal microbiome showed no significant changes in their metabolic activity, while the other subjects’ microbial metagenome showed anywhere between 17 and 60 differences in their metabolism, including several changes associated with heart disease (i.e., depletion of oleate and palmitoleate biosynthesis). This study revealed the varying responses of each microbiome when exposed to digested beef, suggesting that this method could provide fundamental information in understanding personal nutrient requirements and the impact of changes in the individual gut microbiota on human health. Although further studies using larger study populations are required, this study describes a simple and cost-effective protocol for evaluating the interactions between specific dietary interventions and individual gut microbiota differences.
Highlights
The human gut harbors around 1014 microbes, comprising a genome size almost 150 times larger than that of the host itself [1,2]
Previous studies have shown that a protein diet can be metabolized by the gut microbiota to produce beneficial substances such as short-chain fatty acid (SCFA) and toxic substances, such as sulfur metabolites, depending on the type of microbes found in the gut [5,6,7]
We observed a significant increase in acetic acid in all of the samples following the addition of digested beef powders to the fermentation broth (p < 0.05), while propionic acid did not increase in subject 4 and butyric acid did not increase in subjects 3, 4, and 6 (Figure 2)
Summary
The human gut harbors around 1014 microbes, comprising a genome size almost 150 times larger than that of the host itself [1,2]. These microbes interact with each other through various metabolites, such as short-chain fatty acids (SCFAs) and amines, to create a microenvironment inside the gut, which affects the host. Amino acids produced by the enzymatic digestion of proteins can be used by gut microbes as an energy source and facilitate SCFA production [5]. Previous studies have shown that a protein diet can be metabolized by the gut microbiota to produce beneficial substances such as SCFAs and toxic substances, such as sulfur metabolites, depending on the type of microbes found in the gut [5,6,7]
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