Disclaimer: This blog post is for informational purposes only and should not be considered medical advice. Please consult with a qualified healthcare professional regarding any health conditions or before making any changes to your diet or exercise routine.

“I’m blood Type A, so I stopped eating meat and am focusing on a plant-based diet. What do you think?” - my patient asked during our first appointment, eager to hear my thoughts. 

I’ll admit, it had been many years since I last looked into the evidence behind blood type diets. You’ll often hear me say, 'Medicine keeps us humble,' and this was yet another example. I listened to my patient, understood where she got her information, and told her honestly that I hadn’t reviewed this topic in the past five years. I promised to look into it for her and get back to her.

Science is ever-evolving, and medicine moves forward at an incredible pace. What we knew as a fact a few years ago might no longer hold today. So, once again, with an open mind, I went to PubMed, Google Scholar, and Consensus GPT to explore the science behind blood type diets. And here is what I found. But first, some basics:

What Is the Blood Type Diet?

First popularized in the 1990s, the blood type diet claims that your ABO blood group determines what you should eat to optimize health and prevent disease, and even lose weight. According to this theory:

• Type A individuals thrive on vegetarian diets.

• Type O should focus on high-protein, meat-based meals.

• Type B can tolerate dairy and a variety of foods.

• Type AB gets a mix of everything.

The premise hinges on the idea that antigens that determine blood type, aka proteins on the surface of red blood cells, react differently to specific foods. Some argue that eating the “wrong” foods can trigger inflammation, poor digestion, weight gain, and chronic disease.

It’s a compelling theory. After all, who wouldn’t want a diet tailored to their biology? So, here is what I found. 

What Does the Evidence Say?

Nothing. I was able to find zero credible evidence to support the claims of the blood type diet. A systematic review published in The American Journal of Clinical Nutrition in 2013 analyzed over 1,400 references and found zero studies that provide solid evidence to validate the health benefits tied to this diet. Two other publications I found worth mentioning are 

• “ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors” - this study with over 1,400 participants looked at ABO blood type and cardio-metabolic biomarkers. While the change in diet improved participants’ health, it was unrelated to blood type

• Another publication remotely related to this topic is “The Potential Impact of Bood System on Dietary Habits and Smoking” - it shows some mere correlations between blood type and food preferences but not health outcomes. 

And that’s the extent of what I found!

Now, while following a ‘blood type diet’ may not directly harm a patient’s health, and while eating more vegetables or reducing processed foods is undoubtedly healthy, attributing those benefits to blood type distracts from scientifically grounded advice.

You may ask, “what’s the harm?” The harm lies not in the healthier food choices themselves but in misleading connections. This can erode trust in evidence-based medicine and divert attention from proven strategies.

What About Future Possibilities? 

Medicine evolves rapidly, and fields like precision medicine and nutrigenomics are revolutionizing how we approach health. These disciplines explore how our unique genetic and molecular makeup, including nutrient metabolism, can influence disease risk and wellness.

One day, we may uncover evidence linking blood type to dietary needs. I would welcome such findings with open arms. But as of now, I cannot recommend a patient follow a specific eating plan based on zero scientific evidence.

Our Role as Physicians and Educators

Every physician wants to have answers to all patient questions. And conversations like these are not easy. It’s our job to stay curious, separate fact from fiction, and educate patients. The blood type diet is one of many health fads that sound promising but fail under scientific scrutiny. While it’s tempting to embrace quick fixes, our focus should remain on sustainable, evidence-backed strategies. 

So, what’s the “diet” I recommend for most of my patients? Plant forward, optimized protein, Omega 3 rich, minimal ultra-processed foods. These are basics that work for almost everyone. 

If you or someone you care about has considered the blood type diet, share this message. Together, we can help promote evidence-based health practices.

About the Author
Dr. Lipartia is a double board-certified physician specializing in obesity medicine and metabolic health. Passionate about translating complex research into practical advice, she empowers patients and readers to make informed decisions for long-term health.