Blood Type Diets Lack Scientific Evidence
There is no scientific evidence supporting the claim that different blood types require specific nutrition, and following blood type-based diets does not improve health outcomes. 1
The Evidence Against Blood Type Diets
A systematic review specifically examining blood type diets found zero studies validating the purported health benefits of ABO blood type-based dietary recommendations 1. The review searched major medical databases and identified only one marginally relevant article that studied LDL-cholesterol responses in different MNS blood types (not ABO), which did not directly address whether blood type diets improve health 1.
Multiple high-quality studies have definitively shown that any health benefits from these diets occur regardless of blood type matching:
In a study of 1,455 adults, adherence to certain "blood-type" diets showed some favorable effects on cardiometabolic risk factors, but these associations were completely independent of the individual's actual ABO genotype 2. This means the diet effects had nothing to do with blood type matching.
A 2018 study of 973 overweight adults found that ABO genotype did not modify any association between blood-type diets and biomarkers of cardiometabolic disease 3. When individuals increased adherence to various blood-type diets, some showed improvements in BMI and waist circumference, but matching the diet to their actual blood type made no difference whatsoever 3.
A 2021 plant-based diet intervention study found no significant differences in weight loss, fat loss, cholesterol reduction, or glycemic control between blood type A individuals and others, or between blood type O individuals and others 4. Mean weight loss was similar regardless of blood type (type A: -5.7 kg vs others: -7.0 kg, P=0.09; type O: -7.1 kg vs others: -6.2 kg, P=0.33) 4.
What Actually Matters for Nutrition
Standard evidence-based nutrition principles apply to all individuals regardless of blood type:
No single ideal percentage of calories from carbohydrates, protein, or fat exists that is optimal for all people, including those with specific conditions like diabetes 5. Nutrition therapy should be based on individual eating patterns, preferences, and metabolic goals—not blood type 5.
The concept of "precision nutrition" based on population subgroups (which could theoretically include blood type) remains aspirational, as authoritative bodies have made no precision nutrition recommendations for chronic disease reduction beyond age and life stage 5.
Current dietary recommendations appropriately differ based on physiological state (age, pregnancy, lactation), sex, and certain lifestyle factors like smoking, but blood type is not among validated factors 5.
The Bottom Line
Any observed health benefits from following blood type diets are attributable to general healthy eating principles embedded within them (such as emphasizing whole foods, vegetables, and reducing processed foods), not to blood type matching 2. The theory behind blood type diets has been invalidated by research 3.
Patients should follow evidence-based dietary guidelines from authoritative sources like the American Diabetes Association, which emphasize nutrient-dense foods, appropriate macronutrient distribution based on individual metabolic goals, and lifestyle factors—completely independent of blood type 5, 6, 7, 8.