Most people have never heard of secretor status, yet it changes what your gut lining offers to the bacteria that live on it. About 1 in 5 people of European ancestry are non-secretors. Here is what that means, what the research shows, and what it does not.
What is a non-secretor?
Your body can put sugars from the ABO blood-group system, rich in a sugar called fucose, into your saliva, mucus and the lining of your gut. Whether it does depends on one gene, FUT2. With at least one working copy you are a secretor. With two non-working copies you are a non-secretor. In people of European ancestry this is almost always the same variant, W143X (rs601338), which raw DNA files from 23andMe and AncestryDNA contain.
Secretor status is a different gene from your blood group. You can be blood group O and a secretor, or blood group A and a non-secretor.
What changes for your gut bacteria
Many gut bacteria use the fucose sugars on the gut lining as food or as a place to anchor. When those sugars are missing, the bacterial community adapts:
- Bifidobacteria. In a 2011 study, non-secretors had lower diversity and abundance of bifidobacteria than secretors, and some bifidobacterial groups were rarely found in them (Wacklin et al., PLoS One). The study was small (14 non-secretors), but later work pointed the same way.
- Other bacteria. In a German study of 8,956 people (Rühlemann et al., Nature Genetics 2021), secretor status was linked with Roseburia, and together with blood group with some Bacteroides and Faecalibacterium.
These are differences between groups of people, not a diagnosis of your own gut. What you eat shapes your gut bacteria far more than FUT2 does.
Vitamin B12: the opposite of what many sites say
You will often read that non-secretors absorb less vitamin B12. The large genetic study on the subject found the opposite: non-secretors had higher blood B12 on average (Hazra et al., Nature Genetics 2008). The difference is small. Your real B12 status depends far more on your diet (B12 comes only from animal foods, fortified foods or supplements), your age and some medicines, such as stomach-acid reducers and metformin. A blood test measures it; your FUT2 result does not.
Norovirus and other infections
The most common norovirus strains attach to these same fucose sugars to infect gut cells. Non-secretors are therefore much less likely to catch them. Large genetic studies have also linked secretor status with small shifts in the risk of some other conditions, in both directions. These are population averages, not predictions for one person.
Breast milk and babies
Secretor mothers make a milk sugar called 2'-fucosyllactose; non-secretor mothers do not. In a study of 44 mother-baby pairs, bifidobacteria appeared later and less often in breastfed babies of non-secretor mothers (Lewis et al., Microbiome 2015). A later study found no measurable effect in babies born vaginally, so the effect may matter mostly when a baby's gut bacteria are otherwise disturbed, for instance after a cesarean birth. Some infant formulas now add 2'-fucosyllactose.
Is there a non-secretor diet?
No specific diet has been tested and proven for non-secretors. Secretor status is popular with followers of the blood type diet, but a study of 1,455 people found that the benefits of blood type diets had nothing to do with the person's blood group (Wang et al., PLoS One 2014). A reasonable, evidence-based approach for everyone, and especially for non-secretors, is to feed bifidobacteria with fiber they ferment: oats, legumes, onions, leeks, garlic, asparagus, chicory and slightly green bananas, alongside a wide variety of plants.
How to find out if you are a non-secretor
If you have tested with 23andMe, AncestryDNA, MyHeritage, FamilyTreeDNA or Living DNA, you already have the answer in your raw data file. Our free secretor status test reads it in your browser, without sending the file anywhere, and also shows your lactase persistence and gut histamine clearance. MyHeritage files lack rs601338, so we read rs492602, which is inherited with it: on the real files we checked, the two always agreed (49 of 49).
For the bigger picture, read what your DNA can and cannot tell you about your gut microbiome.
Sources: Wacklin et al., PLoS One 2011; Hazra et al., Nature Genetics 2008; Rühlemann et al., Nature Genetics 2021; Lewis et al., Microbiome 2015; Wang et al., PLoS One 2014. Educational information, not medical advice.