Many dietary patterns have been associated with cardiometabolic risk reduction. A commonality between these dietary patterns is the emphasis on plant-based foods. Studies in individuals who consume vegetarian and vegan diets have shown a reduced risk of cardiovascular events and incidence of diabetes. Plant-based dietary patterns may promote a more favorable gut microbial profile. Such diets are high in dietary fiber and fermentable substrate (ie, nondigestible or undigested carbohydrates), which are sources of metabolic fuel for gut microbial fermentation and, in turn, result in end products that may be used by the host (eg, short-chain fatty acids). These end products may have direct or indirect effects on modulating the health of their host. Modulation of the gut microbiota is an area of growing interest, and it has been suggested to have the potential to reduce risk factors associated with chronic diseases. Examples of dietary components that alter the gut microbial composition include prebiotics and resistant starches. Emerging evidence also suggests a potential link between interindividual differences in the gut microbiota and variations in physiology or predisposition to certain chronic disease risk factors. Alterations in the gut microbiota may also stimulate certain populations and may assist in biotransformation of bioactive components found in plant foods. Strategies to modify microbial communities may therefore provide a novel approach in the treatment and management of chronic diseases.
Alex’s Notes: Last week we looked at a review about the health effects of dietary fiber, and as mentioned there, most of fiber’s extensive benefits come from the manipulation of the gut microbiome. No doubt many dietary patterns have benefits for cardiometabolic risk, but the one common theme between them is a focus on whole-foods with plenty of vegetables and fruits. Unfortunately, the majority of Americans don’t meet the recommended intake for these food groups, which becomes clearly evident in the low estimated average fiber intake of about 16 grams per day. Their loss, I suppose, because the gut microbiome is a tremendous health advantage when taken care of.
A lot of progress has been made in decoding the composition of the gut microbiome and the relationship between it and the health of the host (i.e. us). Bacteroidetes and Firmicutes appear to dominate the adult gut microbiota, but the proportion and species of each varies greatly between individuals. Having greater diversity appears to be beneficial, as it may ensure that key metabolic functions are unaffected by changes in the microbial composition. In other words, different microbes with similar functions can substitute for one another when the microbial composition is more diverse resulting in the host potentially being more resilient to stress or change. In fact, lower levels of diversity have been observed in obesity.
So how does diet play a role? Variations in dietary patterns appear to be a key contributing factor to the diversity of the human gut microbiome, and this diversity is likely to have evolved in parallel with the dietary pattern of our evolutionary ancestors. Analysis of “healthy” human poop shows a microbial composition similar to other mammalian omnivores. But the type of omnivorous diet also plays a role. The Bacteroides enterotype was associated with animal protein, amino acids, and saturated fats, while the Prevotella enterotype was associated with higher carbohydrate and sugar intake. It is likely that many environmental factors also play a role, as US adults show the least diversity of the gut microbiome when compared to more “ancestral” communities. What still needs further investigation is the understanding of the health effects of these enterotypes and whether we can modulate them via dietary modifications.
A growing interest in the differences of the microbiome composition between healthy and diseased individuals has also emerged recently. Obesity, for example, is associated with a shift in the ratio of the two main phyla mentioned earlier, Bacteroidetes and Firmicutes, with obese persons having much more of the latter and less of the former. The importance of the microbiome in obesity is exemplified in mice who don’t have any gut microbes and are protected against diet-induced obesity. It is suggested that the obese microbiome is more capable of extracting energy from the diet, and it is shown that transplantation of lean and obese mice with the opposing gut bacteria results in a metabolic shift. These observations were also demonstrated in one fascinating year-long study of 12 obese persons assigned to one of two low-calorie diets (low-carb or low-fat). Regardless of which diet the obese person was assigned, weight-loss was accompanied with an increased abundance of Bacteroidetes and reduced amount of Firmicutes, and the increased abundance of Bacteroidetes correlated with the percentage loss of body-weight and not with the caloric content of the diet.
Hippocrates once said "all disease begins in the gut." Given the recent advances into the relationship between the microbiome and cardiometabolic diseases, he was dead on. It is prudent we take care of our gut, and the number one way to do that is to consume fiber. These non-digestible carbohydrates are the primary source of energy for our gut microbes, and can be classified as prebiotics. Examples include oligosaccharides (inulin & oligofructose), resistant starch, beta-glucan, pectin, and so on. I’m sure many have heard of fecal transplants. That will cause an immediate shift in the type of gut microbes present, but why not just stimulate the growth of the good guys from the beginning?