A new study looking at data from a clinical trial investigating the beneficial effects of a plant-based diet has found a person’s blood type has no effect on weight loss or cardiometabolic health in response to the dietary intervention.

Popularized in the mid-1990s by naturopath Peter D’Adamo, blood type dieting proposes different dietary interventions depending on a person’s blood grouping. Type O, for example, is considered the most ancient ancestral blood grouping and conducive to Paleo-style diets high in animal proteins. Type A on the other hand is considered an agrarian blood grouping most suited to a vegetarian diet free of red meat.

D’Adamo’s book Eat Right for Your Type has sold millions of copies and the dietary intervention remains exceedingly popular to this day. However, no scientific evidence has ever been presented to validate the blood type diet claims.

The latest evidence to debunk this ongoing pseudoscientific dietary fad comes from a recently completed randomized clinical trial investigating the metabolic effects of a low-fat vegan diet. The trial recruited over 200 overweight subjects and randomly assigned them to either an intervention group tasked with eating a low-fat vegan diet for 16 weeks, or a control group making no diet changes.

The primary finding of the trial, published in the journal JAMA Network Open, was that the plant-based dietary intervention increased post-meal metabolic activity by around 20 percent. This, of course, led to increased insulin sensitivity and weight loss compared to the control.

A newly published secondary analysis of the trial data looked at the effect of the intervention based on participants’ blood type. If blood type diet recommendations were true then the dietary intervention studied in the trial should be much more beneficial for blood type A subjects and less effective for blood type O subjects.

“We found that blood type made no difference,” explains Neal Barnard, an author on the new study. “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.”

Alongside weight loss, the trial looked at measures such as blood lipid levels and glycemic control. No significant differences were detected between any of the different blood type groupings and the dietary intervention was found to be equally beneficial regardless of blood type.

“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,” adds Barnard.

While this trial investigated just one specific dietary intervention (eating low-fat and vegan), it is certainly not the first research to suggest blood type diets do not work. A systematic review from 2013 found no evidence in any scientific literature to suggest certain blood types benefit from particular dietary strategies.

The new research was published in the Journal of the Academy of Nutrition and Dietetics.

Source: Physicians Committee for Responsible Medicine