|Image 1: You better feed them right, or your gut bacteria could will disbehave just like the Alien in Ellen Ripley (Sigourney Weaver) in Alien 3 (20th Century Fox).|
Scientists estimate that the genome of the sum of our gut microbia is about 100x more complex than our own gene-sequence and the type and ratio of the 300-1000 different species within your intestinal tract have a major impact not only on how you digest your food, but also on how you look, feel and perform. It is therefore particularly interesting that Gary D. Wu and his colleagues established (for the first time) the existence of a stable microbiome composition that appears to be specialize to strive on a specific diet.
Note: Currently, the data is still too scarce and the variety of gut microbia, as well as their interactions too complex, for any reliable conclusions on whether it is "optimal" to eat according to your current gut biome or whether and in which way it would benefit your health, performance or body composition to modify / tweak the composition of the latter by dietary strategies and/or supplements or even medications. Even the idea of "optimizing" the microbial composition of our guts for "optimal" macro-nutrient usage is illusive, as it could well be that the specialization of our gut bacteria, i.e. their efficiency in using only little of the dietary energy for themselves and redirecting the rest to us, could theoretically be among the reasons for the obesity epidemic, as well.In a preliminary analysis Wu et al. had established that in 98 healthy volunteers, whose stool they had analyzed for its individual microbiome composition there was a high correlation between habitual diets (measured by dietary questionnaires; data cf. figure 1, below) and the predominant type of bacteria.
Bacteroide enterotype was highly associated with animal protein, a variety of amino acids, and saturated fats, suggesting that meat consumption as in a Western diet characterized this enterotype. [...] The Prevotella enterotype, [...] was associated with [...] high values for carbohydrates and simple sugars, indicating association with a carbohydrate-based diet more typical of agrarian societies.As one would expect, "self-reported vegetarians (n = 11) showed enrichment in the Prevotella
enterotype (27% Prevotella enterotype vs. 10% Bacteriodes enterotype; p = 0.13)" and the one self-reported vegan was in the Prevotella enterotype group, as well.
|Image 2: Prevotella histicola is a major driving force of tooth decay (King's College). Its relatives in the gut, on the other hand, have been found to be implicated in insulin resistance and infertility due to endotoxin-related inflammation.|
|Figure 1: Associations (Spearman correlation; -1: max neg. / +1 max pos.) between habitual dietary intake of sugars, vitamins & minerals, fats, amino acids, proteins and micronutrients and bacterial composition, where enterotype 1 is bacteriode dominant, and enterotype 2 is prevotella dominant (data adapted from Wu. 2011)|
The bacteria maintain a complex and generally beneficial relationship with the host when retained in the gut, but when they escape this environment they can cause significant pathology, including bacteremia and abscess formation in multiple body sites.Based on the results of Wu's study, which also showed that a short-term dietary intevention (10 days) could not change the Bacteriode dominance of the 10 subjects who had been randomly assigned to high fat/low or a low fat/high fiber diets, we can thus only say that we probably are "optimized" for a certain macronutrient composition. Whether this is a beneficial or detrimental adaptation has still to be determined. What has however been established (in a rat model) is that chronic treatment with the probiotic bacteria Lactobacillus rhamnosus
[...] induced region-dependent alterations in GABAB1b mRNA in the brain [, ...] reduced GABAAα2 mRNA expression in the prefrontal cortex and amygdala, but increased GABAAα2 in the hippocampus [and] reduced stress-induced corticosterone and anxiety- and depression-related behavior.Bravo et al. ascribe these beneficial psycho-physiological effects to the "modulatory constitutive communication pathway between the bacteria exposed to the gut and the brain". And highlight the "bidirectional communication of the gut–brain axis" as a possible target to treat stress-related disorders.
|Image 3: The antibiotic vancomycin could potentially induce obesity month after treatment.|
In defense of "antibiotics" and as a word of caution against exuberant enthusiasm for all bacteria it should yet be mentioned that alternative antibiotics did not exhibit the same profound effects in the Thuny study. Moreover, observations in germ-free mice suggest that (Bäckhed. 2006)
[germ-free] animals are protected from diet-induced obesity by two complementary but independent mechanisms that result in increased fatty acid metabolism: (i) elevated levels of Fiaf, which induces Pgc-1α; and (ii) increased AMPK activity.In view of the ever increasing resistance towards antibiotics, it is however unrealistic to assume that we will see similar effects in humans after the administration of individual or even combined high-dose antibiotics.
We will see what future research will bring. Yet, while you are waiting for me to keep you on par with the results, I suggest you better stay away from growth or non-growth promoting antibiotics if you want to stay healthy, sane and slim.