A popular diet claims that you need to eat right for your blood type. What’s the evidence?
Should you match your diet to your blood type? A popular diet claims that you need to eat right for your blood type. What’s the evidence?
Nutrition Diva is hosted by Monica Reinagel. A transcript is available at Simplecast.
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Hello, I’m Monica Reinagel and you’re listening to the Nutrition Diva podcast. Welcome!
I got an email this week from a listener who wanted to know if I’d ever done an episode on the blood type diet.
“I recently ran across a quick mention of the blood type diet and wanted to hear your take on the legitimacy of it. If you’ve previously talked about it, I would greatly appreciate it if you could point me to that episode.”
In fact, I talked about the blood type diet way back in 2009, toward the end of my very first year doing the podcast. After I sent this listener a link to that episode, though, I started to wonder whether any new research had been published since then. And, sure enough, there was a study published in 2014 that shed some new light on this old idea. So, I thought an update was in order.
The blood type diet was proposed by naturopathic physician Peter D’Adamo way back in the 1990s. His book Eat Right For Your Blood Type was a best-seller. The basic idea is that your blood type may be the key to what type of diet is best for you, and that you won’t feel as well or be as healthy if your diet is inappropriate for your blood type.
The different blood types—O, A, B, and AB—are genetic variations that appeared at various points in human evolution. Type O blood is thought to be the oldest surviving blood type, corresponding with the hunter-gatherer period. Type A blood appeared roughly twenty thousand years ago, coinciding with the dawn of primitive agriculture and the introduction of things like legumes and cereal grains to the human diet.
The other blood types emerged even later, when humans were not only farming but also keeping livestock and consuming dairy products. They’d also begun to travel the globe, interbreed, and encounter a much wider variety of food species.
Dr. D’Adamo’s central hypothesis is that you will be best nourished by the diet that was predominant when your blood type emerged. In other words, Type O folks thrive on lots of meat and very few grains and dairy products. People with Type A blood will be healthier eating a more plant-based diet. Lucky Types B and AB get to eat a wider variety of foods. In his books, he’s laid out detailed lists of foods that are good and bad for each blood type.
It’s a very interesting hypothesis.
Your blood type is determined genetically, and things like your predisposition to various diseases and conditions are also, in part, genetic. And there is some evidence that certain conditions occur more frequently in those of certain blood types. For example, people with Type A blood are more likely to suffer from a lack of stomach acid. But people eating a plant-based diet, as people with Type A blood are advised to do, need less stomach acid than people whose diet is higher in protein.
Dr. D’Adamo had dug through a century’s worth of medical literature and culled out a handful of findings like this one that support various parts of his argument. But you’d never get a conviction based on evidence like this in a court of law. It’s circumstantial at best.
When I reviewed this diet back in 2009, there was really only anecdotal evidence to support the blood type diet. But there was plenty of it. Lots of people tried this system and found it life-changing. I was not one of them.
I have Type O blood, so according to D’Adamo, I should thrive on eating lots of meat and almost no grains or dairy products.
Actually, I choose to eat meat in fairly limited quantities, mostly for environmental and ecological reasons, but also because I don’t feel particularly well on a high-protein diet. My diet is higher in grains and legumes than the diet recommended for Type Os. I also eat a fair amount of eggs, dairy, and foods from the cabbage family—all foods that Type Os are supposed to avoid. Despite all this, I feel great and do not have any elevated risk factors for disease.
Now, of course, no single person’s individual response—positive or negative—can prove or disprove the validity of this theory. At the time, I put this diet in the “Might Help, Probably Won’t Hurt” category. The diet plans for the various blood types are all reasonably healthy. For example, none of them include Twinkies or french fries. (Apparently, the blood type that thrives on the typical modern diet has yet to emerge.)
And anyone who eliminates junk food, refined sugar, and processed foods and replaces them with whole fruits and vegetables and lean protein is probably going to be a lot healthier. And that’s what everyone following D’Adamo’s dietary advice will end up doing—regardless of their blood type.
But, as the listener who first asked me to weigh in on the Blood Type diet back in 2009 pointed out:
“It seems that a lot of the foods that I’m supposed to avoid are foods that you and other nutritionists say are great for me,” he wrote. “There are a lot of fruits and vegetables that don’t fit my blood type.“
Although I was trying to keep an open mind, it did seem to me at the time that people following this advice were likely to be giving up some healthy foods for no good reason. And there is now some new evidence to support that.
In 2014, a group of researchers from the Department of Nutritional Sciences at the University of Toronto looked at diet and health records for 1400 people who were participating in the Toronto Nutrigenomics and Health study to see whether they could find evidence to either confirm or disprove D’Adamo’s hypothesis.
First, they rated how well the participants’ diets adhered to each of the 4 blood-type diets, based on their diet records. Then, they cross-referenced their diets with their blood type. And they found that those whose diets were “correct” according to their blood type weren’t any healthier than those who were eating the “wrong” diet for their blood type. In other words, their findings did not support the blood type diet hypothesis.
But they did find something else that was interesting. Regardless of their actual blood type, the people whose diets were most aligned with the diet recommended for Type A blood had, on average, lower BMI, smaller waist circumference, lower blood pressure, cholesterol, triglycerides, and insulin. Folks following the AB diet did almost as well—it had positive effects on all of the blood markers but no effect on BMI or waist circumference. Again, this was completely independent of their actual blood type. The only benefit observed in the people following the Type O diet was lower triglycerides. And people following the Type B diet didn’t seem to have any benefits at all.
Sometimes intriguing studies like this one will trigger more research by other investigators—and the more research there is, the more confident we can feel about our conclusions. However, there do not appear to have been any further studies on the blood type diet published in the intervening 8 years.
If you do still have an old copy of the blood type diet lying around, perhaps your best bet is to flip to the section intended for those with Type A blood, regardless of what your own blood type is.
Nutrition Diva is a Quick and Dirty Tips podcast. It's audio-engineered by Nathan Semmes with script editing by Adam Cecil. The rest of the team includes Morgan Christianson, Holly Hutchings, and Davina Tomlin.
If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206.