Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates

Abstract

The gut microbiota of a healthy person may not be equivalent to a healthy microbiota. It is possible that the Western microbiota is actually dysbiotic and predisposes individuals to a variety of diseases. The asymmetric plasticity between the relatively stable human genome and the more malleable gut microbiome suggests that incompatibilities between the two could rapidly arise. The Western lifestyle, which includes a diet low in microbiota-accessible carbohydrates (MACs), has selected for a microbiota with altered membership and functionality compared to those of groups living traditional lifestyles. Interactions between resident microbes and host leading to immune dysregulation may explain several diseases that share inflammation as a common basis. The low-MAC Western diet results in poor production of gut microbiota-generated short-chain fatty acids (SCFAs), which attenuate inflammation through a variety of mechanisms in mouse models. Studies focused on modern and traditional societies, combined with animal models, are needed to characterize the connection between diet, microbiota composition, and function. Differentiating between an optimal microbiota, one that increases disease risk, and one that is causative or potentiates disease will be required to further understand both the etiology and possible treatments for health problems related to microbiota dysbiosis.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1. The Divergent Metabolic Scenarios of a High-MAC versus a Low-MAC Diet

Two scenarios represent a trade-off in how calories are absorbed by the host. In the first scenario, a high-MAC diet that has few simple sugars, the major contribution of carbohydrates to host metabolism is in the form of the SCFA fermentation end-products of the microbiota. In addition to calories, these molecules play diverse regulatory roles in human physiology, including protection from many Western diseases. In the second scenario, the low-MAC Western diet results not only in a loss of beneficial microbial metabolites such as SCFA, but also in selection of a distinct microbiota that may seem foreign to the host. Increased representation of mucus-utilizing microbes, decreased gut motility, and increased calories in the form of sugar and fat may synergize to cause Western diseases. MACs include carbohydrates from diet, host secretion (e.g., mucin glycans), or other resident microbes that serve as a metabolic input for members of the microbiota.

Figure 2. The Western Microbiota Diverges from That of Non-Western Populations

(A) Principle coordinate plot of gut microbiota composition in individuals (each dot represents one person's microbiota) from three populations based on Unifrac distances of the bacterial 16S rRNA profile. Distance between dots represents extent of compositional difference. (B) Average number of bacterial phylotypes detected within the gut microbiota from three populations; error bars indicate SEM. Data reprinted with permission (Yatsunenko et al., 2012).

Figure 3. The Multiple-Hit Hypothesis for How the Microbiota of Industrialized Societies Has Lost Diversity over Time

(A) Microbiota diversity was likely altered at multiple stages of human evolution. As diversity and quantity of dietary MACs decreased with agriculture, industrialized food production, and processed food, the model reflects data that indicate a corresponding decrease in microbiota diversity. (B) While diet is likely a key mediator of microbiota diversity, additional technological and medical leaps, while providing solutions for important problems such as infectious disease, have likely served as insults to the microbiota. These multiple hits have prevented the maintenance of microbiota diversity over recent generations.