Blood type diet not based in science, new study says

Photo taken at the Bruce Randolph School In Denver, shows fresh fruits and vegetables
The blood type diet is based an abundance of fruit and vegetables, heart-healthy proteins, and moderate fat, but a new study did not find a link between the four blood types (type A, B, AB, and O) and health markers.Barry Gutierrez / Today

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By Madelyn Fernstrom, Diet and nutrition editor

A popular diet plan claims our bodies process food differently, depending on our blood type. According to to new research from University of Toronto scientists, that idea is, well, mis-bleeding.

The theory is, if you’ve got type A (blood, not personality), your nutritional needs aren’t the same as someone with type O blood and you need to adapt your diet to help with weight loss and protect your heart. While earlier research has suggested that the blood-type plan — made famous by the book “Eat Right for Your Type” — does not contribute to weight loss because of a different meal plan for a specific type, no study has directly addressed the plan's specific claims. 

Earlier work has pointed out that the calories for all blood type plans are reduced, and that these plans are all based an abundance of fruit and vegetables, heart-healthy proteins, and moderate fat. The new data did not find any association between the four blood types (type A, B, AB, and O) and health markers.

A total of 1,455 healthy research participants were studied. They received their blood type assignment, and baseline measure of health markers. Volunteers followed the specific diet assigned for that specific blood type, based on the book’s eating plan. They kept detailed Food Frequency Questionnaires for one month, and weight and health markers were repeated.

While the dieters did lose weight, and improved their blood pressure, cholesterol, and triglycerides, there was no association found linking these changes to a specific blood type.

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The bottom line? These data support that choosing any of these eating plans, independent of blood type, will promote good health. While the blood type theory might sound reasonable, the science does not support it.

As with any diet plan, choose one that you feel you can stick with for the long run. Make sure it is nutritionally sound and contains the foundation of healthy eating (with smaller portions for weight loss): 

  • Rich in fruit and vegetables as the main source of carbohydrates
  • Moderate amounts of heart health fats
  • Lean proteins from both animal and plant sources
  • Limited amounts of fiber-rich starchy carbohydrates (bread, rice, pasta, cereals)

The good news is that there are many ways to eat less and move more for both good health and weight loss.