No foods need to be avoided specifically because you have A-positive blood. The popular “blood type diet,” introduced by naturopath Peter D’Adamo in the late 1990s, tells people with type A blood to eat a mostly vegetarian diet and steer clear of red meat, dairy, kidney beans, and wheat. But a 2013 systematic review in the American Journal of Clinical Nutrition found no evidence supporting the health claims behind blood type diets, and subsequent clinical trials have confirmed that any benefits from these eating patterns have nothing to do with the dieter’s blood group. The story behind why the idea persists, and what blood type actually does influence about your health, is more interesting than the diet itself.
What the Blood Type Diet Tells A+ People to Eat
D’Adamo’s framework assigns each ABO blood type a dietary identity. Type A is cast as “the agrarian,” meaning the diet leans heavily on fruits, vegetables, grains, tofu, and legumes while discouraging most animal proteins. The specific avoidance list for type A typically includes red meat, pork, most dairy products, kidney beans, lima beans, wheat, potatoes, tomatoes, peppers, bananas, and oranges. The rationale is that proteins called lectins in these foods react badly with type A blood antigens, causing agglutination (clumping) that supposedly leads to inflammation, weight gain, and chronic disease.
The diet became a bestseller and still circulates widely on wellness sites. For someone with A+ blood who searches this topic, the avoidance list above is what they will find repeated across dozens of health blogs. But the question worth asking is whether any of this holds up to testing.
What the Clinical Evidence Actually Shows
A systematic review published in 2013 searched the literature for any study that had tested whether following a blood-type-matched diet produced better health outcomes than a mismatched or standard diet. The result was straightforward: no such evidence existed at the time of publication. The authors noted that validating the concept would require studies comparing people who eat according to their blood type against people of the same blood type who do not, and those studies simply had not been done.1PubMed. Blood type diets lack supporting evidence: a systematic review
Since then, a few intervention studies have taken the question further. A large observational analysis found that people who followed the type A diet pattern did indeed have lower BMI, waist circumference, blood pressure, cholesterol, and triglyceride levels. That sounds like a win for the diet, but the same improvements showed up regardless of whether the person actually had type A blood. Someone with type O or type B blood who ate the type A diet got the same cardiometabolic benefits.2PLoS ONE. ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors A secondary analysis of a randomized clinical trial reached the same conclusion: participants eating a plant-rich diet had better cholesterol, lower BMI, and reduced insulin resistance, but blood type did not modify those effects in any meaningful way.3Journal of the Academy of Nutrition and Dietetics. Effect of ABO Blood Type on the Effects of a Plant-Based Dietary Intervention on Cardiometabolic Risk Factors: A Secondary Analysis of a Randomized Clinical Trial
Another study in overweight adults looked at adherence to each of the four blood type diets and measured cardiometabolic biomarkers. People who scored high on the type A diet had lower diastolic blood pressure compared to low-scorers, but again the benefit showed up across all blood types, not just type A individuals. Matching the diet to the blood group did not change the effect size for any biomarker tested.4The Journal of Nutrition. ABO Genotype Does Not Modify the Association between the “Blood-Type” Diet and Biomarkers of Cardiometabolic Disease in Overweight Adults
The pattern that emerges from these studies is consistent. Eating more fruits, vegetables, and whole grains while cutting back on processed foods and excess animal fat tends to improve metabolic health markers. That is well-established nutritional science. The blood type part is the ingredient that has never earned its seat at the table.
The Lectin Hypothesis and Why It Falls Short
The theoretical engine behind the blood type diet is lectins, which are carbohydrate-binding proteins found in many plants. The claim is that dietary lectins are blood-type-specific: a lectin in a kidney bean might clump the red blood cells of a type A person but leave a type O person unharmed, and this clumping supposedly causes systemic inflammation and disease when you eat the “wrong” food for your blood type.
There is a kernel of biological reality here. Certain plant lectins do interact with ABO blood group antigens in test-tube settings. Research on Malaysian fruit extracts has shown that some plant lectins can agglutinate red blood cells and could theoretically irritate the gut lining in susceptible individuals.5JOURNAL OF SUSTAINABILITY SCIENCE AND MANAGEMENT. EFFECT OF LECTINS FROM SELECTED MALAYSIAN LOCAL FRUITS ON HUMAN BLOOD GROUP ANTIGENS Thai vegetable extracts have been tested against blood group antigens, and some (like those from certain seed and bean extracts) do show specific agglutination against group A.6Progress in Applied Science and Technology. Thai Vegetable Extracts Affecting Human Red Blood Cell Surface Antigens in the ABO Blood Group System
But the leap from “a purified lectin can clump red blood cells in a laboratory dish” to “you should avoid tomatoes because you’re type A” is enormous, and the evidence does not bridge it. Cooking destroys most dietary lectins. The lectins that survive digestion are present in tiny concentrations compared to what is used in lab assays. And the clinical trials described above tested the real-world version of this hypothesis by looking at actual health outcomes in real people eating real food, and found no blood-type-specific effect. The lectin mechanism is real at a biochemical level but has not been shown to matter at a dietary level for any blood type.
Genuine Biological Differences Tied to Blood Type A
While the blood type diet does not hold up, blood type A is not biologically irrelevant. There are some real, well-documented health associations that have nothing to do with what you eat but may be useful to know about.
Heart disease risk is one area where blood type has been studied extensively. A combined analysis of two large prospective cohort studies found that people with blood group A had a modestly higher risk of coronary heart disease compared to type O, with an adjusted hazard ratio of about 1.08. Types B and AB showed similar or slightly larger elevations.7PubMed Central. ABO Blood Group and Risk of Coronary Heart Disease in Two Prospective Cohort Studies The difference is real but small in absolute terms, and it is driven by mechanisms involving clotting factors and inflammatory pathways, not by what foods you ate for breakfast.
Gastric cancer is another association. A large genetic study combined with a meta-analysis of 40 studies covering over 33,000 cancer cases found that blood group A was associated with roughly a 19% higher odds of gastric cancer compared to group O.8PubMed Central. Blood groups A and AB are associated with increased gastric cancer risk: evidence from a large genetic study and systematic review A separate study from Pakistan confirmed that the frequency of blood group A was significantly increased among gastric cancer patients compared to the general population.9PubMed. Association of ABO Blood Groups and Risk of Gastric Cancer These are statistical risk increases across large populations. They do not mean that having type A blood causes stomach cancer, and the absolute risk remains low for any individual.
On the other hand, a study examining blood groups and type 2 diabetes found no significant association between blood groups A or AB and the disease.10PubMed Central. The Correlation Between Blood Group Type and Diabetes Mellitus Type II: A Case-Control Observational Study From Pakistan So the disease risks associated with type A are selective, not across-the-board.
How Blood Type Affects Your Gut at a Deeper Level
One of the more intriguing and still-developing areas of research involves the gut microbiome. If you are a “secretor” (and about 80% of people are), your ABO antigens are expressed not just on your red blood cells but also on the mucus lining of your intestinal tract. These sugar molecules can serve as attachment points and food sources for certain gut bacteria, which means your blood type may subtly influence which microbial communities thrive in your digestive system.11PubMed. Intersections of ABO blood group, secretor status, and the gut microbiome: implications for disease susceptibility and therapeutics
A study of fecal microbiomes from healthy subjects found that blood group A secretors showed distinct shifts in gut bacterial populations. Specifically, the genus Blautia was lower in type A secretors compared to non-A secretors, and this was accompanied by higher levels of several other bacterial families. The researchers also found that secretor status itself had a larger overall impact on the microbiome than the specific blood group antigen.12PubMed Central. Relationships between gastrointestinal microbiota and blood group antigens
This does not mean type A people digest food differently in a way that would require them to avoid specific foods. A much larger study analyzing fecal samples from 1,500 twins found no robust associations between ABO or secretor status and gut microbiome composition when measured rigorously. Overall community structure, diversity, and the relative abundances of individual bacterial species were not significantly tied to blood type in that dataset.13BMC Genomics. ABO antigen and secretor statuses are not associated with gut microbiota composition in 1,500 twins The evidence, in other words, is conflicting. Smaller studies find differences; larger ones wash them out. If ABO antigens do influence gut bacteria, the effect is likely modest enough to be overwhelmed by factors like diet, medications, and individual variation.
A Lesser-Known Enzyme Connection
There is one genuinely interesting digestive difference tied to blood type A that rarely makes it into popular discussions. Intestinal alkaline phosphatase is an enzyme involved in fat digestion and gut barrier function. Research has shown that type A red blood cells bind almost all available intestinal alkaline phosphatase to their membranes, whereas type O and type B red blood cells do so to a much lesser degree. As a result, intestinal alkaline phosphatase is found more frequently in the serum of people with blood group O or B than in those with blood group A.14Clinica Chimica Acta. Intestinal alkaline phosphatase and the abo blood group system — a new aspect
This is a real biochemical difference, and it could theoretically influence how your gut processes dietary fat. But “could theoretically influence” is doing a lot of heavy lifting. No clinical study has shown that this enzyme difference changes what foods type A individuals should or should not eat. It is the kind of finding that researchers note and file for further investigation, not the kind that should drive your grocery shopping.
Does the Rh Factor Matter for Diet
The “+” in A+ refers to the Rh factor, a protein on red blood cells that is separate from the ABO system. Most dietary advice about blood types ignores the Rh factor entirely, focusing only on A, B, AB, or O. There is limited research on whether Rh status influences nutritional needs. One study found that Rh-positive individuals had higher consumption of alcohol, caffeine, and certain vitamins (C, D, E, and K) compared to Rh-negative individuals, and that cholesterol intake was also higher in the Rh-positive group. However, no significant differences were found for fat intake, fiber, sugar, or omega fatty acids.15PubMed Central. The Potential Impact of Blood System on Dietary Habits and Smoking
These findings describe what people with different Rh types happened to eat, not what they should eat. The study is observational and cannot tell us whether Rh-positive people need more of these nutrients or simply happen to consume them for unrelated reasons. For practical purposes, the “+” in your blood type does not add a meaningful layer to dietary planning.
Why the Blood Type Diet Feels Like It Works
People who follow the type A blood type diet and feel better are not imagining the improvement. They are just misidentifying the cause. The type A diet is essentially a plant-forward eating pattern: more vegetables, fruits, legumes, whole grains, and soy; less red meat, processed food, and dairy. That description overlaps substantially with dietary patterns that decades of nutritional research have linked to lower rates of heart disease, better blood sugar control, and healthier body weight. If you shift from a standard Western diet to a mostly plant-based one, you will probably feel better and see improvements in your bloodwork regardless of whether you are type A, O, B, or AB.
The clinical trials bear this out clearly. In multiple studies, people of every blood type who scored high on adherence to the type A diet showed improvements in BMI, cholesterol, blood pressure, and insulin resistance.3Journal of the Academy of Nutrition and Dietetics. Effect of ABO Blood Type on the Effects of a Plant-Based Dietary Intervention on Cardiometabolic Risk Factors: A Secondary Analysis of a Randomized Clinical Trial The diet works. The blood type matching does not.
This creates a strange situation where the blood type diet “succeeds” for type A individuals specifically because it happens to recommend a dietary pattern that is healthy for everyone. If D’Adamo had assigned type A the type O diet (heavy on red meat), the story would have played out very differently.
Blood Type A in Evolutionary Perspective
Part of the appeal of the blood type diet is its evolutionary narrative: type O is cast as the “ancient hunter,” type A as the “farmer” who emerged with the development of agriculture, and so on. The implied logic is that different blood types evolved to thrive on different diets. The actual evolutionary history of ABO blood groups does not support this timeline. The same ABO genetic variants have been maintained in primates for at least 20 million years, long before anything resembling agriculture, animal husbandry, or even modern humans existed.16PubMed Central. Ancestry runs deeper than blood: the evolutionary history of ABO points to cryptic variation of functional importance
The persistence of multiple ABO variants for millions of years across species suggests that maintaining blood type diversity is itself advantageous, probably because different blood group antigens offer varying levels of resistance to different infectious diseases. This “balancing selection” is a well-understood evolutionary mechanism, and it has nothing to do with humans adapting to specific agricultural diets over the past 10,000 years. The evolutionary backstory that makes the blood type diet feel scientific is the part that most clearly contradicts what we know about ABO genetics.
What You Should Actually Focus On
If you have A+ blood and are looking for dietary guidance tailored to your real health profile, the honest answer is that your blood type does not meaningfully narrow or expand your food options. The modest associations between type A and conditions like gastric cancer and coronary heart disease are worth being aware of, but they are best addressed through general strategies like regular screenings, not smoking, staying physically active, and eating a diet rich in whole foods. The slightly elevated gastric cancer risk associated with type A, for instance, is better addressed by limiting processed meat and excessive salt than by avoiding tomatoes because a blood type book said to.
If you enjoy the type A diet’s plant-forward approach, there is no reason to stop. It is a healthy eating pattern. Just know that it is healthy because of its nutritional composition, not because it matches some biochemical key to your red blood cells. And if you have been anxiously avoiding a food you love because a blood type chart told you to, the peer-reviewed evidence says you can relax.