He's a fascinating article on the importance of gut flora: Human nutrition, the gut microbiome and the immune system. I saw a link to this gem on Paul Whiteley's blog Feed Me Research. It's been said they you can't fully discuss nutrition without the role of the gut flora. This article discusses some of the nuts and bolts of this, and for the most part it is easy to follow for us laypersons. The article makes several points worth mentioning:
"During the past 30 or so years, the North American diet has also shifted in terms of the relative contributions of different foods to total energy intake. Since 1970, two dietary 'epochs' can be distinguished based on the contribution of grains to overall calories (the mean increase in daily carbohydrate intake for men and women during this period was 62.4 g and 67.7 g, respectively). The consumption of other food items has also changed: Spearman's rank correlations between food availability and time, followed by adjustments of P values to reflect false discovery rates, show that the representation of 177 out of 214 items tracked by the USDA has increased or decreased significantly in US diets since 1970. For example, Americans now eat less beef and more chicken, and corn-derived sweeteners have increased at the expense of cane and beet sugars. Furthermore, methods of food modification and preparation have changed."
I find this interesting because chronic autoimmune and digestive diseases are on the rise. As a SCD'er I can't help but wonder if the drastic uptake of grains and sugar are a factor. A fun look at this change can be seen by Tom Naughton here and here.
"The intestinal microbiota can synthesize several vitamins involved in myriad aspects of microbial and host metabolism, including cobalamin (vitamin B12), pyridoxal phosphate (the active form of vitamin B6), which is involved in several enzymatic interconversions in amino-acid metabolism, pantothenic acid (vitamin B5), niacin (vitamin B3), biotin, tetrahydrofolate and vitamin K. In addition to vitamin B12, gut microbes produce a range of related molecules (corrinoids) with altered 'lower ligands', including analogues such as methyladenine and p-cresol. More than 80% of non-absorbed dietary vitamin B12 is converted to these alternative corrinoids. There is preliminary evidence to suggest that syntrophic relationships among members of the human microbiota, and the fitness of some taxa, may be based on the ability to generate, use or further transform various corrinoids."
I found this one interesting because those of us with gi issues also tend to be lacking in these vitamins. Vitamin B6 has also been found to help in autism, again pointing to a possible gut issue. As well as anemia in both populations:
"Likewise, iron is an essential micronutrient for bacteria. Given the low solubility of Fe3+, microbes have evolved the capacity to produce several high-affinity iron-binding siderophores. Microbes take up soluble Fe3+–siderophore complexes by several active transporters. Early studies in gnotobiotic animals showed a link between the gut microbiota and the development of iron deficiency. Germ-free but not conventionally raised rats become anaemic when fed a low-iron diet. The germ-free rats also show increased loss of iron in their faeces compared with their conventionally raised counterparts54. The iron balance that exists between host and microbiota is disturbed in a mouse model of Crohn's disease in which tumour-necrosis factor-α (TNF-α) expression is dysregulated: oral (but not parenteral) iron supplementation in these animals causes a shift in the gut microbial community composition, as defined by 16S ribosomal-RNA-based surveys, and exacerbates their ileitis."
This article also discusses the role of gut flora in obesity and diabetes. I was curious about which type of fat they used in this study reference: "Mice fed a high-fat diet have increased serum levels of lipopolysaccharide".
It turns out the researchers used corn and lard for the 72 percent fat diet for the mice. (I suspect a lot of corn and corn oil in the modern diet may not be a good thing).