D’Adamo explains that blood types affect how we digest food. Different blood types vary in how they’re able to break down food proteins, called lectins. Taking in lectins that don’t mesh well with our systems will leave us with a slower metabolism, bloating, and digestive irritation. Okay, we’ve all been there. But is it really explainable by blood type?

Breaking Down the Types
The diet plan splits foods into three categories: highly beneficial, neutral, and avoid. Foods in the beneficial category act like medicine, nourishing our bodies and flushing out toxins. Neutral foods can be paired with beneficial foods, while foods in the avoid category “act like poison.” Yikes. Have I been poisoning myself unknowingly all these years? The book and Web site break down very detailed and specific suggestions for everything from food to exercise and more that each type should strive to embrace—and avoid at all costs.

• Type O: The O stands for old, as in humanity’s oldest bloodline. This means that these digestive systems fare best on an ancient human diet. These old-school humans benefit from eating animal proteins, like fish, poultry, and other lean meats, and from restricting grains, legumes, and dairy. O types should also aim for vigorous exercise on a regular basis, such as running, kickboxing, or intense hiking—think cavewoman hunting prey.
• Type A: A is for agrarian. These gentler souls thrive on vegetarian-based diets since, according to D’Adamo, they’re descendents of less warlike, farmer ancestors. This means eating soy protein, organic fruits and veggies, and grains will leave type A’s feeling invigorated, as will gentle exercise, like yoga or walking.
• Type B: This group needs to strive for balance. The nomadically inclined have more tolerant digestive systems, meaning they should enjoy meat and produce, as well as low-fat dairy. Foods to avoid include wheat, corn, and lentils. Exercise requirements include—you guessed it—physical and mental balance, like tennis, swimming, or cycling.
• Type AB: People with this most modern (and rarest) of the blood types have sensitive digestive tracts, meaning they should avoid land animals (pork, beef, and chicken) and opt instead for protein from seafood, dairy, tofu, and produce. This type is a combination of A and B, so incorporating some of the A and B exercises will be effective.

The Verdict
Critics point to a lack of published scientific evidence backing the blood type–based diet. To that I say: fair point. Official literature on this diet cites survey information researchers have compiled on people sticking to the diet plan. An impressive 75 percent of respondents reported a success rate in improving their health conditions over time. But in terms of actual scientific evidence and backing, the theory has been investigated without resulting in any scientific conclusions, according to WebMD.

That said, the diet plan is grounded in solid health advice. Regardless of whether I decide to follow my actual blood type, or just the suggestions regarding the type that most appeals to my lifestyle, I’ll be eating a well-rounded diet and incorporating exercise on a regular basis—the chief ingredients for health and vitality. Lean meats, fresh produce, and regular exercise certainly don’t hurt—and that’s advice that’s been proven time and time again.