Study: Blood type is not associated with effects of plant-based diet on body weight

A study published in the Journal of the Academy of Nutrition and Dietetics by researchers with the Physicians Committee for Responsible Medicine--a nonprofit of 12,000 doctors--debunks the "blood type diet" by finding 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.

This new study is based on a randomized control trial whose main findings were published in JAMA Network Open on Nov. 30. That 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. The key finding is that a plant-based diet ramps up metabolism as measured by an increase in after-meal calorie burn of 18.7%, on average, for the intervention group over the control.

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.

We found that blood type made no difference. 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."

Neal Barnard, MD, Study Author and President, Physicians Committee for Responsible Medicine

"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," he says.

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).

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. 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.