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The blood type diet

Clinical review pending

What the blood type diet recommends, what its studies show, and how food quality and nutritional needs compare with ABO-based rules.

Illustrated plate opening onto a sunlit landscape of leafy vegetables and carrots.

Can your blood type tell you which foods suit you best? That is the promise of the blood type diet, which assigns different foods to each ABO group. Naturopath Peter D’Adamo popularized the idea in Eat Right 4 Your Type. The studies discussed here provide no evidence that matching a diet to blood type improves health. Some people do lose weight on these plans. Changes in what and how much they eat offer a more plausible explanation than their blood type.

What is the blood type diet?

The blood type diet gives people with O, A, B and AB blood separate food lists. Its premise is that blood type determines which foods a person digests well, an idea that has not been established scientifically.

Blood type describes certain features on the surface of red blood cells. In the ABO system, the groups differ in their A and B antigens and in the antibodies normally present in plasma against the antigens a person lacks. These sugar structures and their corresponding antibodies do not, by themselves, describe a person’s nutritional needs.

The approach is also called “Eat Right for Your Type,” the “ABO diet” or “eating for your blood type.” A term such as “type O diet” refers to one of the four plans within the same system.

Where the blood type diet came from

The plan originated in the 1996 book Eat Right 4 Your Type, rather than in clinical trials. Claims about its reach include 7 million copies sold in more than 60 languages. Those publishing figures are not independently verified here. In any case, a book’s popularity cannot establish whether its biological explanation is right.

The book traces its food rules to human evolutionary history. It proposes that each blood group emerged in a different era and is particularly well adapted to that era’s foods: hunters should eat like hunters, farmers like farmers. The food lists follow from that story.

The genetic differences have a more specific explanation. ABO alleles differ through changes in a gene encoding a glycosyltransferase, including individual base changes. The gene supplies instructions for an enzyme that adds a sugar group to a structure on the cell surface. In the O variant described in this research, a deletion, or loss of part of the DNA sequence, prevents production of a functioning enzyme. This does not establish a digestive profile.

What each blood type is supposed to eat

The four lists differ mainly in how much animal protein, grain and dairy they allow. The descriptions below explain the diet’s rules; they are not dietary recommendations. Research on the blood type diet also distinguishes these four patterns.

Blood type Claimed evolutionary origin Foods emphasized Foods restricted
O Hunter Meat, fish, most vegetables Grains, dairy, legumes
A Farmer Vegetables, fruit, legumes, whole grains Red meat, most dairy
B Nomad Dairy, various meats, vegetables, fruit Certain grains and meats
AB “Enigma” A combination of the A and B lists Red meat, certain grains

Type O diet: the “hunter”

The type O plan emphasizes animal protein and substantially restricts grains, dairy and legumes. Its explanation is that people with type O inherited a capacity to digest meat from their supposed hunter ancestors, while being poorly suited to foods associated with farming.

A controlled dietary intervention tested a prediction that follows from this idea. On a plant-based diet, participants with type O lost a similar amount of weight to other participants. The measured weight changes did not show the difference predicted by the hunter model.

Type A diet: the “farmer”

The type A plan is largely vegetarian, emphasizing vegetables, fruit, legumes and whole grains while limiting red meat. According to the theory, people with type A should benefit especially from plant-based food because they supposedly descend from farmers.

In a study of a low-fat vegan diet, however, type A participants did not do better than the other participants. Average weight change was −5.7 kg for type A and −7.0 kg for everyone else. That result does not support the proposed special advantage for type A.

Type B diet: the “nomad”

The B list is the least restrictive of the four. It allows dairy and a range of animal and plant foods, while limiting certain grains. In the cited study, it also showed the fewest favorable associations: greater adherence to the B list was associated with no statistically significant differences in the cardiometabolic measures examined. These included body weight, blood pressure and insulin. A nonsignificant result alone does not rule out an effect.

Type AB diet: the “enigma”

For type AB, the plan combines the A and B lists: mostly plant foods, fish and seafood, some dairy and little red meat. AB is often described as the rarest of the four groups, although blood group frequencies vary among populations.

People who followed the AB pattern more closely had more favorable blood pressure, blood lipid and insulin measurements in the cited study. The association held regardless of their actual blood type. It therefore fits an explanation based on the food pattern better than one based on matching that pattern to blood type. As an observational finding, it establishes neither causation nor a guaranteed benefit for everyone.

The theory about lectins

Lectins are proteins found in plant foods that bind to sugar structures and can make red blood cells clump together in laboratory tests. Their hemagglutinating activity can be measured in commonly eaten plant foods. The blood type diet uses this as its proposed mechanism: each group is said to react badly to lectins in foods assigned to the other groups.

The claim that ordinary foods make the blood cells of the “wrong” blood type clump inside the body goes beyond the findings cited here. Measurable lectin activity is particularly common in legumes. Soaking and cooking change the amount of active lectin. How far activity falls, and whether normal preparation removes much of it, depends on the food and the method. Soaking alone is not a reliable way to make raw beans safe.

A documented outbreak shows the risk from undercooked beans. Investigators reported 200 cases of gastroenteritis, a 12% attack rate and a median incubation period of 3.3 hours after a meal containing chili con carne made with inadequately cooked red kidney beans. The 12% figure used the dining population of 1,700 as its denominator. Phytohemagglutinin activity in the chili exceeded 400 HAU/g, a level the investigators described as potentially toxic. That is an assay-based activity measurement, not a universal safe serving size or a blood-type-specific threshold.

This was acute poisoning associated with undercooked beans. The risk is not confined to a particular blood type. Nor does a risk that is independent of blood type mean that everyone who eats the food will become ill: 200 cases were reported in the population of 1,700.

Does the blood type diet work? What the research shows

The studies discussed here have not demonstrated a health advantage from matching food choices to blood type. A systematic review found no suitable evidence for the claimed benefits. Studies that genetically determined blood group, including Wang et al. (2014) and Wang et al. (2018), also measured how closely people followed the different food patterns. Favorable associations appeared whether or not a pattern matched the person’s blood type.

The studies address different parts of the question:

The results point in the same direction: observed advantages tracked the eating patterns, without an additional advantage from having the “matching” blood type. The researchers behind the largest intervention discussed here concluded that their findings did not support the theory behind the blood type diet.

Why people may still lose weight

People can lose weight while following a blood type diet. All four plans remove substantial categories of food. If that means eating fewer readily available processed foods that are easy to consume in large amounts, calorie intake may fall. That would be an explanation independent of blood type. A study of ultra-processed food offers evidence for a general mechanism, although it did not directly test the four blood type diets.

In that inpatient study, all meals were provided and the diets offered were matched for macronutrients. Participants consumed 508 kcal more per day on the ultra-processed diet. Weight changes were related to energy intake. This describes one possible general mechanism; it does not establish that the mechanism explains every blood type plan.

Weight loss also occurs with different named diet programs. An analysis of 48 randomized trials involving 7,286 participants estimated 8.73 kg more weight loss with low-carbohydrate diets and 7.99 kg more with low-fat diets at six months, each compared with no diet. Differences between individual named programs were small and likely to matter less than whether a person could keep following the plan. Losing weight after changing food habits does not, on its own, validate a blood-type mechanism.

Risks and possible nutrient gaps

The main practical risks come from narrowing the choice of foods. Each plan excludes whole food groups. Depending on the resulting meals, this can leave nutrient gaps that deserve attention when planning the diet and deciding whether any testing is needed.

The nutrient and fracture findings below come from studies of vegetarian or vegan diets, not direct studies of the blood type diet. Their prevalence estimates and risk figures do not apply to everyone eating this way, or transfer unchanged to blood type plans. They do highlight nutrients worth considering when food choices are restricted:

How it compares with better-studied eating patterns

Some blood type food lists resemble Mediterranean or DASH eating patterns. Their evidence bases differ, though. Mediterranean and DASH diets have been studied in randomized trials measuring health outcomes. The cited systematic review found no adequate evidence for a benefit from matching food choices to blood type.

Eating pattern Evidence base Degree of restriction Nutritional coverage
Blood type diet The cited studies do not demonstrate a benefit from matching diet to blood type High; whole food groups are excluded depending on blood type Variable; possible gaps depend on the list followed
Mediterranean diet Randomized research with cardiovascular outcomes Low; the emphasis is generally on adding favorable foods Broad food choices, with few excluded food groups
DASH Pooled randomized trials measuring blood pressure Low to moderate; sodium is limited A broad range of foods designed to meet everyday nutritional needs

In people at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil was associated with fewer major cardiovascular events, with a hazard ratio of 0.69, compared with the control diet in the corrected PREDIMED analysis. Across 30 randomized trials involving 5,545 participants, DASH reduced systolic blood pressure by 3.2 mmHg and diastolic pressure by 2.5 mmHg relative to control diets.

Benefits can also fade over time with well-studied eating programs. Across 121 trials with 21,942 participants, low-carbohydrate and low-fat programs produced similar additional weight loss at six months compared with usual diet: 4.63 kg and 4.37 kg, respectively. Most advantages were substantially smaller by 12 months. Choosing an eating pattern therefore involves both the evidence and whether it can fit into everyday life for the long term.

What blood type actually tells us about health

Blood groups matter in medical care and are associated with certain disease risks at the population level. Research describes associations with a range of health outcomes, although the mechanisms are not fully understood. Those associations do not produce blood-type-specific food rules.

There are concrete uses in transfusions, pregnancy and newborn care:

For disease-risk associations, both the size of an estimate and its comparison group matter. A blood-donor cohort analyzed 1,112,072 people over 13.6 million person-years of follow-up; the paper’s title refers to 1.5 million donors. Non-O groups had more venous thromboembolic events than group O. For deep vein thrombosis, the reported incidence rate ratio was 1.92.

Type A was associated with a slightly higher risk of stomach cancer, with a pooled odds ratio of 1.11. In two prospective cohorts totaling 107,503 participants, pancreatic cancer incidence ranged from 27 to 46 cases per 100,000 person-years, depending on blood group. Registry data from 1.6 million blood donors also identified associations between ABO groups and cancer at 13 anatomical sites.

A meta-analysis of infection risk reported a pooled odds ratio of 2.13 for SARS-CoV-2 infection when non-O groups were compared with O across 22 case-control studies (95% CI 1.49–3.04). The corresponding estimate from 15 cohort studies was 1.89 (95% CI 1.56–2.29). Differences between studies were substantial. These estimates describe associations in the populations studied, not a fixed personal risk or a reason to change foods by blood type.

These are population averages. Different relative measures cannot all be described as “small” or “moderate”; their practical meaning also depends on the underlying absolute risk. They neither predict what will happen to an individual nor dictate what that person should eat.

What can help personalize nutrition

Family medical history, current health and, where relevant, laboratory measurements can inform nutrition planning. Family history cannot be changed, but it can help put individual risks into context. Blood type is also a largely fixed inherited trait, unaffected by changing diet. In simplified terms, ABO differences arise from differences in an enzyme. That genetic basis does not establish a personalized food list.

Personalization using measured characteristics has been studied in a dietary intervention. One randomized trial enrolled 347 adults aged 41–70 and compared an 18-week program with standard dietary advice. The program used individual glucose and triglyceride responses after meals, the gut microbiome and health history. Triglycerides fell significantly relative to the control group, while LDL cholesterol did not differ significantly. Some secondary outcomes, including weight, waist circumference and HbA1c, also improved; blood pressure and several other markers did not differ between groups. These results concern a specific program and do not validate every form of personalized nutrition. Several authors had financial relationships with the company behind the program. The background article on berberine and the gut microbiome concerns a different topic and is not evidence that this program works.

Depending on the situation, a clinical discussion might consider blood lipids, HbA1c, fasting glucose or vitamin D. Restrictive food choices may also warrant attention to iron and vitamin B12. Serum ferritin is one part of assessing iron status, while reviewing vitamin B12 intake and status may be useful with little or no meat intake. The cited research does not show that these two markers are invariably the first to change on a restrictive diet.

This is not a standard laboratory panel for everyone. The person’s circumstances should guide which measurements, if any, are useful before or after a dietary change. Together with medical history, diet-related measurements can offer more concrete guidance than blood type alone.

Frequently asked questions

Does the blood type diet actually work?

The studies discussed here have not shown a health benefit from matching diet to blood group. A systematic search of Cochrane, MEDLINE and Embase screened 1,415 records and found one eligible study that did not answer the underlying question. That finding applies to the review’s search period. In a six-month intervention involving 973 adults with overweight, greater adherence to A, B or O patterns was associated with improvements in some markers. The participants’ ABO genotypes did not modify those associations.

Where did the blood type diet come from?

Naturopath Peter D’Adamo introduced it in his 1996 book Eat Right 4 Your Type. The plan did not originate from clinical trials. Claims about the book include 7 million copies sold in more than 60 languages, figures not independently confirmed here. The idea is that each ABO group emerged in a different era and is especially suited to that era’s foods. ABO alleles differ through changes in a gene encoding a glycosyltransferase, including individual base changes and the deletion described in an O variant. These genetic differences do not establish a dietary profile.

Which foods are included in the type O diet?

The O plan favors animal protein and vegetables, making it the most meat-centered of the four lists. It limits grains, dairy and legumes. The claim is that type O carries an inherited hunter’s ability to thrive on meat. A controlled intervention did not support the corresponding prediction about weight loss: on a plant-based diet, people with type O lost a similar amount of weight to the other participants.

Is the type A diet better for people with type A blood?

The controlled research discussed here has not demonstrated that advantage. The A plan is largely vegetarian, emphasizing vegetables, fruit, legumes and whole grains while limiting red meat. A secondary analysis of a 16-week randomized low-fat vegan diet trial determined blood group in 68 intervention participants. Type A participants did not respond better than everyone else. Average weight change was −5.7 kg versus −7.0 kg in the other participants.

Are lectins harmful depending on blood type?

The cited findings do not show selective harm based on blood type. Lectins occur in plant foods, with measurable activity particularly common in legumes. Soaking and cooking alter active lectin levels, but the effect depends on the food and preparation method. Soaking alone does not reliably make raw beans safe.

The documented harm discussed here was acute poisoning linked to inadequately cooked beans. An outbreak with 200 cases and a 12% attack rate was traced to chili con carne containing undercooked red kidney beans. The rate refers to 200 cases in a dining population of 1,700, not to a blood-type-specific response. This food-safety risk can exist independently of blood group; it does not mean everyone eating the meal becomes ill.

Why do people lose weight on the blood type diet?

All four plans remove major food categories. If that lowers calorie intake, weight can fall regardless of blood group. An inpatient study illustrates one general mechanism: all meals were provided and the offered diets were matched for macronutrients, but participants ate 508 kcal more per day with ultra-processed food. The study did not test blood type diets.

Other dietary programs can also produce weight loss. Across 48 randomized trials with 7,286 participants, low-carbohydrate and low-fat diets produced an estimated 8.73 kg and 7.99 kg more weight loss, respectively, than no diet at six months. Differences between individual named programs were small. These results help explain general routes to weight loss; they do not confirm a blood type effect.

What are the risks of eating by blood type?

A narrow choice of foods can leave nutrient gaps. Research on vegetarian diets reported vitamin B12 deficiency in 62% of the pregnant participants studied. In vegetarian adults, serum ferritin averaged 29.71 µg/L lower than in nonvegetarian adults, which does not by itself mean iron deficiency requiring treatment.

Another study found higher hip fracture risk in vegetarians, with a hazard ratio of 1.25, and vegans, with a hazard ratio of 2.31, compared with meat eaters after adjustment including BMI. It does not, by itself, establish that particular nutrient gaps caused the difference. These results come from different studies and are not direct risk estimates for blood type diets, nor do they apply uniformly to all vegetarians or vegans. Careful planning and appropriate follow-up can address possible shortfalls. The article on vitamin B12 deficiency provides further background.

What does blood type actually tell us about health?

Blood group is essential to transfusion compatibility: ABO incompatibility can cause hemolytic transfusion reactions. During pregnancy, RhD status also matters for maternal–fetal blood compatibility.

Population studies report an incidence rate ratio of 1.92 for deep vein thrombosis in non-O groups compared with O, and a pooled odds ratio of 1.11 for stomach cancer in type A. These population-level associations do not provide individual food rules. Their practical significance also depends on the underlying absolute risk.

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Additional background links; these are not independent scientific evidence for the blood type diet: