Background: Although 7 million copies of Eat Right 4 Your Type have been sold in >60 languages, there has been a lack of evidence supporting the "blood-type" diet hypothesis.
Objective: The present study aimed to examine the validity of this diet in overweight adults.
Methods: A total of 973 adults [mean ± SEM age: 44.6 ± 0.4 y; mean ± SEM body mass index (BMI; kg/m2): 32.5 ± 0.2; 758 women, 215 men] were participants of the Toronto Healthy Diet Study. A 1-mo, 196-item food-frequency questionnaire was used to determine dietary intakes before and after a 6-mo dietary intervention. Diet scores were calculated to determine relative adherence to each of the 4 blood-type diets as a secondary analysis. ABO blood group was determined by genotyping rs8176719 and rs8176746. ANCOVA was used to compare cardiometabolic risk factors across tertiles of diet scores.
Results: At baseline, individuals with a higher adherence score to the type A diet had lower diastolic blood pressure (tertile 3 compared with tertile 1: 70.9 ± 1.1 compared with 73.3 ± 1.1 mm Hg; P < 0.01). Lower waist circumference was observed in individuals with higher adherence to the type B (tertile 3 compared with tertile 1: 100.8 ± 1.8 compared with 105.4 ± 1.7 cm; P < 0.01) and type AB (tertile 3 compared with tertile 1: 101.2 ± 1.8 compared with 104.8 ± 1.7 cm; P < 0.01) diets. After a 6-mo dietary intervention, individuals with increased adherence to the type A and type B diets had greater reductions in BMI and waist circumference, respectively (P < 0.01). Individuals with an increase in type O diet adherence showed decreases in both BMI and waist circumference (P < 0.01). However, matching the diets with the corresponding ABO genotype of each individual did not change the effect size of any of these associations either at baseline or at 6 mo.
Conclusions: ABO genotype does not modify any association between blood-type diets and biomarkers of cardiometabolic disease in overweight adults, suggesting that the theory behind this diet is not valid This study was based on the data of a trial that was registered at www.clinicaltrials.gov as NCT00516620.