Study finds blood type not associated with effects of plant-based diet

A new study published in the Journal of the Academy of Nutrition and Dietetics by researchers with the Physicians Committee for Responsible Medicine found that blood type was not associated with the effects of a plant-based diet on body weight, body fat, plasma lipid concentrations, or glycemic control.

The study, a randomized control trial, randomly assigned overweight participants with no history of diabetes to an intervention or control group on a 1:1 ratio for 16 weeks. Participants in the intervention group followed a low-fat, plant-based diet. The control group made no diet changes, according to the study.

The study found that a plant-based diet ramps up metabolism as measured by an increase in after-meal calorie burn of 18.7 percent, on average, for the intervention group over the control, the researchers said.

To consider a potential connection between blood type and diet, researchers took the additional step of conducting a secondary analysis among intervention-group participants of the 16-week randomized clinical trial. They considered whether the effects of a plant-based dietary intervention on body weight, blood lipids, and glycemic control are associated with ABO blood type. The "blood type diet" recommends a mainly plant-based diet for those with blood type A, while it recommends a diet heavy in meat for people with blood type O.

Main outcomes that were measured were body weight, fat mass, visceral fat volume, blood lipids, fasting plasma glucose, and HbA1c. T-tests compared participants with blood type A to all other participants (non-A), and individuals with blood type O to all other participants (non-O), according to the study.

There were no significant differences in any outcome between individuals of blood type A and non-A, or between individuals of blood type O and non-O, the researchers said. Mean body weight change was -5.7 kg for blood type A participants and -7.0 kg for non-A participants, and was -7.1 kg for type O participants and -6.2 kg for non-O participants. Mean total cholesterol decreased 17.2 mg/dl in the type A group and 18.3 mg/dl for non-A participants, and decreased 17.4 mg/dl among type O participants and 18.4 mg/dl for non-O participants.

"We found that blood type made no difference," said Neal Barnard, MD, study author and president of the Physicians Committee for Responsible Medicine, in a statement. "While the blood type diet says that a plant-based diet should be better for blood type A and less so for blood type O, it turned out to be beneficial for people of all blood types, and there was no evidence that meaty diets are good for anyone. Our research shows that all blood types benefit equally from a vegan diet based on the consumption of fruits and vegetables, legumes and whole grains, looking specifically at weight loss and cardiometabolic health in overweight adults.”