Sorry low carbers, your microbiome is just not that into you. I recently posted a scatter plot (below) on Facebook/Twitter of preliminary metadata that we are accumulating as part of the American Gut project . ![]() Plotting participants self- reported height, weight, and 7 days of dietary info (recorded using an online calorie counter), we can plot percentage of daily calories from fat (all sources) against body mass index (BMI) . While the data is of the dreaded self- reported kind, the lack of any significant correlation between % of daily calories from fat and BMI, is still very interesting (note even if you remove the various obvious outliers, the correlation – or lack of – is the same). In other words, as fat goes up in the diet, BMI does not per se. Will be able to see how the metadata correlates with the microbial data in a few months – stay tuned). As I look at the preliminary generic metadata (below) and follow the conversation around the benefits of a low carb diet, I continue to be concerned about the low- carbers gut microbiota (note I eat meat daily, so my diet is high in fat, animal protein – but also dietary fiber – as I eat a large diversity and qty of plants. Though I don’t consume many grains in any form). While there is no denying the wonderful results many people enjoy on a low (and even lower) carb diet . ![]() Low-Fiber Diet Promotes Extinction of Gut Bacteria. Lack of bile can kill bacteria. It seems you are eating a low-fiber. I strongly believe this was because I deprived the healthy bacteria of their food supply so. As we can see from our accumulating metadata (ultimate goal is 2. This data will allow us to compare the gut microbial communities of this population against other dietary strategies. The following discussion is based on some general observations based on the existing literature about fermentation, p. H, and its impact on the gut microbiome). Please note the data in the plot above is self- reported and preliminary. As with all self- reported data, its not ideal. As data points are added over the coming months, will be interesting to see if the (lack) correlation holds. The average age of the persons in the plot is 4. The point of showing this particular plot is that “these particular data” do not show any correlation with fat intake as a % of calories and BMI. Again, this has NOTHING to do with gut bacteria – at the moment – just an interesting “lack” of correlation (and should be interesting/useful for those following a HF diet). ![]()
![]() ![]() Depending on whom you talk with, a low carb diet is many different things to many people. I think most misinterpret a Paleo or Primal lifestyle as somehow low carb. It can be, but most folks eat a diversity and quantity of whole plants that exceed that of the average American . It can sometimes be a little low carb- like due the absence of high caloric foods made from grains. But I often find people who skip grains, sugar and the like as really paying attention to whole plants in their diet . But a bona fide low, low carb eater is another animal all together. ![]() Whether you draw that line at 2. I. Especially if those carbs contain a limited amount of resistant starch and other dietary fibers . As the rules/tenants of basic microbial ecology go, a reduction in fermentable substrates derived from carbohydrates means less energy sources for the microbes . As fermentation drops, so to does the byproducts of fermentation which include short chain fatty acids (primarily acetate, butyrate, propionate), organic acids, and gases like hydrogen. All of this can and will dramatically shift the p. H of the colonic environment. As it stands in a healthy or normal gut, the p. H of the colon changes from proximal to distal end, being more acidic in the proximal (front) end than the tail end . As the p. H shifts to being more alkaline from less fermentation, a number of shoes begin to drop (or can). A less acidic environment means acid sensitive groups of bacteria, like those in the Phylum Proteobacteria, which includes a who. Coli, Salmonella, Vibrio, Helicobacter, might bloom . You see the same blooms following antibiotic treatment. In addition, as p. H shifts away from acidic, the genus Bacteroides can also bloom as well, gaining an ecological niche in this less acidic environment courtesy of a low carb diet. For those of you keeping score, many talk about the American gut in general being dominated by Bacteroides as a function of our high fat, high sugar diet. The reality is, it might have to do with what we are not eating . The all- important butyrate producers Roseburia spp. A drop in fecal butyrate and butyrate producing bacteria was demonstrated in an elegant study comparing diets of varying amounts of carbs. Given the importance of butyrate in colonic health, any dietary strategy that potentially shifts p. H away from acidity as a function of reduced fermentation, might contribute to various forms of IBD. So, low carb equals a less acidic colonic environment due to the drop in fermentation (and I presume harder, and less frequent stools as a function of reduced biomass from bacteria – or maybe not). As p. H shifts, prospects for opportunistic pathogens increase, as does opportunities for gram- negative bacteria like Bacteroides and Enterobacter. When you add this up . This dysbiosis can lead to issues associated with IBD, autoimmune disease, metabolic disorders and so on. But again, a large cohort of low, low carb dieters has never been looked at using 1. S r. RNA methods. So the jury is still out – but will be fascinating to see. A bit of a paradox in all of this is the increased likelihood that a low carb microbial community will most certainly lead to increased gut permeability . So it is a paradox that a leaky gut that can be triggered from a low carb (high fat) diet . Weird. I hope people do not take this as some kind of attack on low carb diets – couldn’t be farther from the truth. Just wanted to point out some obvious concerns (maybe unfounded) and that if we get a large enough sample of low carb folks in American Gut, we might be able to provide some interesting insight – or not. Who knows, maybe low carb folks have super healthy gut microbiota (whatever that is). So to my low carb brothers and sisters out there, try and eat a little more fibrous material if you can . The more people we have for each dietary group, the more we will hopefully learn.
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