The Blood Type Diet

Ever considered that your blood type should influence decisions about your diet and exercise? 

Peter D’Adamo, a naturopathic physician, has made his fame by telling people just that. In 1996, D’Adamo published “Eat Right 4 Your Type,” a book outlining the physician’s health guidelines for the four ABO blood groups (O, A, B, and AB). The outlines included everything from claiming that people with blood type O should eat a diet high in animal proteins to suggesting that people with blood type A should engage in meditative exercises like yoga and tai chi. The book enjoyed a great deal of success and even spurred a sequel (“Live Right 4 Your Type”) that was published in 2000. 

So, what is the foundation for the blood type diet? And is it factual or just a fad?

D’Adamo boasts that within two weeks of adopting the diet, you could see increases in energy level, have fewer digestive complaints, lose weight, and even improve chronic conditions such as asthma and heartburn. The reason behind these transformative theories: lectins.

Lectins are a type of protein found universally in nature. These proteins can be specifically matched to a particular carbohydrate and cause the agglutination—or clumping together—of certain cells. While they are present throughout nature, it is hypothesized that lectins may have evolved in plants for the purpose of protecting seeds from human digestion. (Seed coats, which have a high lectin concentration, must pass through the digestive system intact if they are to be successfully dispersed.) This could explain why some lectins are extremely resistant to stomach acid and the other processes of digestion.

After consuming lectins in food, a certain percentage of these proteins (1 to 5 percent) may be absorbed directly into the bloodstream. This is where carbohydrate specificity comes into play. Your blood type is determined by the presence (or absence) of certain carbohydrates on the surface of your red blood cells. Specific lectins may recognize these carbohydrates (imagine a lectin key that only fits with its corresponding carbohydrate lock) and if your red blood cells have the appropriate carbohydrate “lock,” lectins may attach and cause these cells to clump together. 

Many lectins don’t discriminate and actually clump cells together no matter the blood type, but there are several lectins that are blood type specific. D’Adamo claims that to “eat right for your blood type,” you need to avoid foods that have lectins specific to the carbohydrates on your red blood cells. Furthermore, D’Adamo advises that you should eat a diet consistent with what would have been available during the period that each blood type evolved. For instance, people with blood type O (the oldest, according to D’Adamo) should eat as hunter-gatherers would have—feasting on lean meats and vegetables. 

But his guidelines don’t stop there. 

D’Adamo also provides suggestions for how people with each blood type should exercise and manage stress. He even proposes a connection between blood type and personality, claiming that type B individuals tend to be “insightful, mystical, idealistic…and good at imagining.” 

So, why haven’t you heard of this diet before? Why aren’t lectin-rich foods (beans, nuts, cereal grains, seeds, etc.) universally shunned? 

It turns out that with the appropriate preparation of these foods, you can drastically reduce the amount of available lectins they contain. Soaking and boiling beans and other grains can be enough to effectively denature, or neutralize, these proteins and even help to free up available nutrients. Fermentation also reduces lectin content as bacteria can breakdown lectins and convert them to other innocuous substances. Finally, the lectins in seed coats are metabolized during the process of germination—which means, sprouting is another healthy and harm-free way to prepare lectin-rich foods.

Most nutrition experts say that dietary lectins are not a significant health risk, as they are commonly consumed and widely distributed. Furthermore, lectins don’t have any long-reaching detrimental health effects and can easily be avoided by eating a varied diet.

In 2013, the American Journal of Clinical Nutrition published a systematic review asserting that blood type diets lack supporting evidence and that “truly appropriate” experimental studies have yet to be conducted. Of course, this hasn’t stopped D’Adamo from selling a line of supplements and “lectin-blockers” on his website, 4yourtype.com, where he also markets specialty foods, a skin care line, and promotes a “Sip Right 4 Your Type” line of teas. 

While the blood type diet argument can seem convincing on the surface, look a little deeper and you’ll uncover the truth. It’s just another hypothesis in the eat-this, not-that world that is diet hype.