Thanks to Natasha, one of my regular readers, I was introduced this week to a whole new (for me) biome topic. (Thank you again for that, Natasha!) Absolutely fascinating stuff.
Like me, I’m sure most of you know that the best known way of categorizing blood type is the ABO system. That is, each of us has A, B, AB or O type blood. (For the sake of this post, I am not looking at other factors, like positive or negative.) These actually refer to the antigens (carbohydrates, also referred to as glycans) on the outside of the red blood cells. (The word antigen means any substance that evokes an immune response by the body (like the production of antibodies, for example).) Which antigen you express (or in the case of O blood, no antigen) is genetically determined.
News to me: those antigens are not just expressed on the red blood cells, but also, on platelets, many kinds of immune cells, certain tissues, in other bodily excretions, including saliva, tears, semen, breast milk, sweat, amniotic fluid, urine, etc.…and in the mucus lining of the gut. Research already exists in the literature that demonstrates that different ABO types are susceptible to different diseases. For example, a 2016 paper[i] on the subject contains a chart which shows diseases associated with blood types and the corresponding references to the medical literature. For example, those with A type blood are more prone to vascular disorders (like coronary artery disease and stroke) than those with other blood types, with O blood carrying the lowest risk. AB blood carries a higher risk than other types for dementia and cognitive impairment, while people with O blood type are more at risk for diseases like mumps, plague and tuberculosis.
Why would this be? Essentially, it’s because these carbohydrate structures “…can serve as receptors…for microbes, and may play a role in movement of normal and malignant cells throughout the body.” Relevant to this post: certain microbes, like bacteria, have a greater or lesser affinity for the different ABO antigens. A-type blood, for example, is particularly appealing to certain bacteria, versus B antigens, etc. Thus, it is now well documented that different blood types lead to different gut bacterial profiles. “Human blood group antigens can also be used as receptors by pathogens or mimicked by bacteria; even small variations in structure are recognized by the immune system, which produces antibodies in self-defense.”
Another factor to take into account, by the way, is secretor versus non-secretor status. Again, this was a wholly new concept to me. Determined genetically as well, 80% of the population are secretors, meaning that their bodies express these antigens in bodily excretions. Those who are non-secretors will have little to none of these antigens in their fluids and mucus. Secretors tend to have more stable microbiota over time and generally speaking, it is considered beneficial to health to be a secretor.
I made my way through two fascinating papers on the relationship of ABO blood type to the bacterial microbiome, and thought I’d share a few highlights.
The first paper[ii] was published in 2012, and to summarize their findings: “Our novel finding indicates that the ABO blood group is one of the genetically determined host factors modulating he composition of the human intestinal microbiota, thus enabling new applications in the field of personalized nutrition and medicine.” The paper reiterates what I stated above, that these ABO antigens are expressed in the intestinal mucosa and act as binding sites – and as a food source (after all, they are carbohydrates!) – for intestinal microbes, “…thereby providing a host-specific genetic agent affecting the microbiota composition.” This paper points out, for example, that H.pylori and other pathogenic bacteria and viruses use ABO blood group antigens as adhesion sites. Commensal bacteria, like certain strains of Lactobacillus, do as well. Some microbes, like bifidobacteria, specifically use blood group antigens as food.
These scientists studied the biomes of 64 adults with a mix of blood types and found, “…the microbial differences associated with the blood groups are large enough to affect the relative quantities of the major bacterial groups, thus impacting the overall microbial profile.” In particular, those with B blood showed the greatest variance.
The second paper[iii], published in 2017, had similar findings. These scientists too hypothesized that the microbiota composition would vary among those with different blood types, and tested this in 33 healthy adults. Summarizing their findings:
“This extends the previous findings by demonstrating that the impact of being a nonsecretor is higher than that of individual blood group antigens. Additionally, we demonstrate that both secretor status and blood group antigen expression especially affect the Lachnospiraceae family of bacteria within the gut microbiome, with lower abundances noted in nonsecretors and higher abundances in secretors of various blood groups. We further note specific differences in blood group A-secretors demonstrating that the genus Blautia is lower in the group A-secretors compared with the non-A-secretors and that this reduction is accompanied by higher abundances of members of the Rikenellaceae, Peptostreptococcaceae, Clostridiales, and Turicibacter.”
Why is this important? It can go a long way toward explaining individual variances in microbiota composition. More than that, it may soon help us determine what diet is best for someone, what probiotic is best, what donor for fecal transplant is best and so forth. Your secretor status and blood type may be genetically determined, but how you achieve optimal health regardless of this is not. Unfortunately, we don’t as yet know how to create that optimal dietary plan.* However, I can’t imagine, with the explosion of research into health the bacterial microbiome, that it will be long before we do know!
*Some of you may remember when, back in the 1990s, the book Eat Right 4 Your Type, by Peter D’Adamo became a best seller. I did some snooping around and as of now, there is no scientific evidence to support following his diet plan, even according to this Harvard Medical School physician.[iv] On the other hand, there’s also no evidence that it DOESN’T matter. I took a look at his website and while there is some great information on it, certainly, that appears to be factually correct based upon what I have been reading, the site also makes a broad claim on its home page that bothered me: “Throughout your life, you’ve probably observed that some people tend to lose weight more easily, while for others, their weight is an ongoing battle. Or wondered why some people are plagued by chronic illness while others stay healthy and vital well into their advanced years. Very simply, the answer is in your blood type.” Hmmm. Our blood type may well be a factor but to say categorically that it is THE answer, without the scientific evidence to back it up, is disturbing. I am not biased either for or against, and I very much appreciate that Dr. D’Adamo does provide a page on which he acknowledges his critics and responds to them. I see that he addresses one of the negative studies which the Harvard doctor mentions and was comforted by this statement: “The PLOS study effectively modeled only 13.7% of the total food values provided in Eat Right For Your Type; was performed on healthy volunteers for a only a short duration, and included numerous egregious errors in food valuations. That the Blood Type Diet theory has not been subjected to a rigorous scientific study is not argued. However, the methods used in the ‘debunking study’ in PLOS study by El-Sohemy, et al. and the errors that inevitably resulted with their conclusions, prove worse than no study at all.”[v] (I added the italics for emphasis.) Thus, I think it’s fair to say that there is very likely a place for adapting diet based upon blood type but we just don’t yet know exactly how it fits in to an individual’s optimal diet.
[i] Ewald, DR, Sumner, CJ. Blood type biochemistry and human disease. Wiley Interdiscip Rev Syst Biol Med. 2016 Nov; 8(6): 517–535.
[ii] Makivuokko, H, et. al. Association between the ABO blood group and the human intestinal microbiota composition. BMC Microbiology. 2012;12:94.
[iii] Gampa, A, Engen, PA, Rima, S, Mutlu, E. Relationships between gastrointestinal microbiota and blood group antigens. Physiological Genomics. 2017;49(9):473-483. doi: 10.1152/physiolgenomics.00043.2017