Does blood type (ABO or Rh) affect how the body metabolizes nutrients such as carbohydrates, proteins, and fats?

Blood Type Does Not Affect Food Metabolism

No, your blood type (ABO or Rh) does not affect how your body metabolizes carbohydrates, proteins, or fats. The popular "blood type diet" theory lacks any scientific validation, and multiple high-quality studies have definitively shown that ABO blood group does not modify metabolic responses to different dietary patterns 1, 2, 3, 4.

The Evidence Against Blood Type Diets

Systematic Review Findings

• A comprehensive systematic review using the GRADE approach searched the Cochrane Library, MEDLINE, and Embase and found zero studies demonstrating health benefits of ABO blood type diets 1
• Out of 1,415 screened references, only one article was identified, which studied MNS blood types (not ABO) and did not answer whether blood type affects dietary responses 1

Direct Testing of the Blood Type Diet Hypothesis

Plant-Based Diet Study:

• In a 16-week randomized trial of 68 participants following a low-fat vegan diet, blood type A versus all other types showed no significant differences in body weight change (-5.7 kg vs -7.0 kg, P=0.09) 2
• Blood type O versus all other types also showed no differences in weight loss (-7.1 kg vs -6.2 kg, P=0.33) 2
• Total cholesterol decreased equally regardless of blood type (17.2 mg/dL for type A vs 18.3 mg/dL for others, P=0.90) 2
• Blood type was not associated with changes in body fat, plasma lipids, or glycemic control 2

Large Population Study:

• In 1,455 participants of the Toronto Nutrigenomics and Health study, adherence to certain blood-type diets showed associations with improved cardiometabolic markers, but these associations were completely independent of the individual's actual ABO genotype 3
• Type A diet adherence correlated with lower BMI, waist circumference, blood pressure, cholesterol, triglycerides, and insulin—but this occurred regardless of whether the person actually had type A blood 3
• Matching the blood-type diet with the corresponding blood group did not change the effect size of any associations 3

Intervention Study Confirmation:

• A 6-month dietary intervention in 973 overweight adults confirmed that ABO genotype does not modify associations between blood-type diets and cardiometabolic biomarkers 4
• Individuals with increased adherence to type A and type B diets showed improvements in BMI and waist circumference, but matching the diet to their actual blood type made no difference 4

Why Some Blood Type Diets Appear to "Work"

The apparent benefits of certain blood type diets are explained by their inherent nutritional quality, not blood type matching:

• The Type A diet emphasizes plant-based foods, which naturally improves cardiometabolic markers in anyone who follows it 3
• The Type O diet restricts processed foods and emphasizes whole foods, which reduces triglycerides in all individuals 3
• These dietary patterns align with established nutritional principles that benefit everyone regardless of blood type 5

Universal Metabolic Principles

Carbohydrate Metabolism:

• Glucose metabolism operates through universal pathways (glycolysis, glycogen synthesis, pentose phosphate pathway) that are not influenced by ABO blood group 5
• The minimal carbohydrate requirement is approximately 2 g/kg/day for all adults, regardless of blood type 5
• Glycemic response is determined by food composition, processing method, fiber content, and individual factors like age and body composition—not blood type 5

Protein Metabolism:

• Protein requirements (typically 1-1.5 g/kg body weight/day or 15-20% of total calories) are individualized based on activity level, health status, and current eating patterns—not blood type 5
• Protein metabolism and amino acid requirements are universal across blood types 5

Fat Metabolism:

• Fatty acid metabolism and requirements are not modified by ABO blood group 5
• Recommendations to limit saturated fat to <7% of energy intake apply universally 5

Clinical Bottom Line

Focus on evidence-based dietary patterns that benefit all individuals:

• Mediterranean eating pattern with vegetables, fruits, whole grains, plant-based proteins, fatty fish, and limited processed foods 5
• Adequate fiber intake (minimum 14 g/1,000 kcal) 5
• Limitation of sugar-sweetened beverages and highly processed foods 5
• Appropriate caloric intake for weight management goals 6

Disregard blood type when making dietary recommendations. The theory has been thoroughly tested and definitively disproven 1, 2, 3, 4.