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Why do the different blood groups have different gut flora?

Q: Why do the different blood groups have different gut flora? Can you explain this for all blood groups?

Krishna: Sure!

In humans, the gut microbiota has the highest numbers and species of bacteria compared to other areas of the body. The complex communities of microbes that constitute the human microbiome are influenced by host and environmental factors.

Image source: iStock

Gut microbiota, gut microbiome, or gut flora are the microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals.

They need food to survive. Right?

The bacteria in our gut not only extract energy from the food we eat, but also from our blood sugars.

People with different blood groups have different metabolic sugars (called glycans) attached to the surfaces of their red blood cells. These surface sugars determine whether your blood type is A, B, AB, or O.

Type A: The final sugar is N-acetylgalactosamine.
Type B: The final sugar is D-galactose.
Type AB: Has both types of sugars.
Type O: Has neither of these extra sugars. It acts as a blank slate (or sugar-free base).

For many microbes, success in the host begins with the ability to adhere, and host glycans are ideal receptors. The diversity of blood glycan structures likely arose as a means to inhibit the binding of pathogens to host cells, but these molecules also present a scaffold for commensals.

The secretion of these glycans also evolved as a strategy to bind up pathogens before they encounter infectable cells . These evolutionary skirmishes have resulted in differential disease risk based on host blood type.

Think of your blood cells like houses, and these sugars as decorations on the front door. Type A puts a star on its door, Type B puts a circle, AB has both, and O leaves the door plain.

How Does This Affect Your Diet and Metabolism?

While these sugars define your blood type, your body breaks down all the sugars and carbohydrates you eat into standard energy (glucose) in the exact same way. However, scientists have discovered some interesting metabolic links.

Gut Health: Your gut bacteria use different carbohydrates for energy. Certain bacteria thrive on Type A sugars, creating a unique gut microbiome for those with Type A blood.

Disease Risk: Some studies show that people with Type B blood may have a higher risk of developing type 2 diabetes. Conversely, Type O blood is often linked to a slightly lower risk.

Different blood groups have different gut flora (the bacteria living in your intestines) because your blood type genes create specific sugars in your body. These sugars line your digestive tract and act as an all-you-can-eat buffet. Certain bacteria are really good at eating specific blood sugars, so they thrive in that blood type.

It is like a restaurant menu. The body puts out different sugars (menus) depending on the blood type. Bacteria that like that specific menu will move in and grow. This causes different bacterial communities in each blood type:

Type A: The body secretes a specific sugar called the A-antigen. Bacteria like Ruminococcus gnavus have special tools to break down and eat this sugar, giving them an advantage to grow.

Type B: The body secretes the B-antigen in the gut mucus. This creates a unique environment where the overall clustering and amount of certain bacterial families differ from non-B types.

Type AB: These individuals produce both A and B antigens. Because they have both food sources available, their gut often hosts a blended mix of the bacteria typically found in both Type A and Type B people.

Type O: These individuals do not produce A or B antigens. Instead, they produce an "H antigen." Without A or B sugars to feed on, their gut often harbours a higher abundance of generalist bacteria like Bacteroides, which are very good at digesting a wide variety of plant fibres and starches.

Our genetic makeup itself determines which bacteria are in our gut, this seems to help explain variations we see in how people respond to nutrition and therapy.

Enterotoxigenic Escherichia coli expresses an adhesion molecule that specifically targets the A blood glycan which results in children with type A or AB blood being disproportionately affected by the diarrheal disease caused by this pathogen. Helicobacter pylori binds to fucosylated blood antigens on the gastric epithelium and while H. pylori can be found in healthy individuals of all blood types, it can better access this receptor in type O individuals, putting them at greater risk for the overgrowth and pathogenesis of H. pylori . The commensal Lactobacilli have diversified and target A, B, and H antigens in a strain specific manner; with L. gasseri OLL2827 targeting the H-antigen, L. gasseri OLL2755, OLL2877 the B-antigen, and L. brevis OLL2772 the A antigen. An indirect benefit of our commensal bacteria adhering to these receptors is that they prevent pathogens from getting a foothold via adhesion exclusion. (1)

Certain microbes thrive on specific blood groups because your blood type sugars exist in your digestive tract and mucus. Bacteria use these sugars as food or docking sites to enter your cells. The most common bacterial preferences and disease risks include (2,3,):

Blood Type A

Preferred by: Certain strains of beneficial Lactobacillus and Escherichia coli (specifically those that cause stomach issues).
Disease Risk: Higher susceptibility to Pseudomonas aeruginosa (a serious hospital infection) and Plasmodium falciparum (the parasite that causes malaria).

Blood Type B

Preferred by: Neisseria gonorrhoeae (causes gonorrhea), E. coli, and Group B Streptococcus. People with Type B blood naturally have a wider variety of these gut microbes.
Disease Risk: Higher risk for skin and soft-tissue infections.

Blood Type O

Preferred by: Helicobacter pylori (a stomach bacteria that causes ulcers and cancer).
Disease Risk: Higher risk for Vibrio cholerae (causes cholera), severe rotavirus, and Staphylococcus infections.