The Family of Wellness Grifters

Peter D’Adamo is a naturopath with a thirst for trying his hand in different areas. To maintain the illusion of authority, D’Adamo casts himself as a polymath—ranging from horologist to software developer—positioning him as a 'guru' whose expertise transcends traditional medical boundaries.

“Peter D'Adamo is a naturopathic physician who is also an author, researcher-educator, Ivesian, amateur horologist, budding software developer and air-cooled enthusiast. He is considered a world expert in glycobiology, principally the ABO (ABH) blood groups and the secretor (FUT2) polymorphisms.”

According to his website, there is almost nothing he can’t do and isn’t an expert in. However, the vast majority of what he does hinges on one central idea: that your blood type affects your diet. James L. D’Adamo, Peter’s father, was the man with the original theory, though Peter has taken it and run with it.  

Blood Type Diet

The Blood Type Diet is exactly what it sounds like: a diet that claims that there is a right way and a wrong way to eat, depending upon your blood type. The problem with the Blood Type Diet is that it has been thoroughly debunked. ACSH’s own Mauro Proença debunked the blood type diet in early 2025. The Journal of the Academy of Nutrition and Dietetics published a study that thoroughly debunks the diet's premise. A 2013 systematic review found no evidence to support it. 

As Robert H. Shmerling of Harvard Health Publishing notes, “there is no proven connection between blood type and digestion. So, in addition to a lack of evidence that the diet works, serious questions remain about why it should work in the first place.”

I will only briefly touch on some significant flaws in the blood type diet's premise. Blood types are more complicated than just being type O, A, B, or AB. For example, the Blood Type Diet completely ignores the Rhesus factor, which determines whether a type is positive or negative, e.g., O- or AB+. If blood types were the "blueprint" for nutrition, ignoring the Rhesus factor is like a mechanic ignoring whether a car is automatic or manual—it's a massive oversight that proves the theory is arbitrary. If the antigens are essential for the diet, it would stand to reason that the Rhesus factor would be too. Alas, no mention of it.

Additionally, the Blood Type Diet posits that lectins interact with the blood types differently. However, there isn’t any good evidence that lectins interact with blood types in the way that D’Adamo asserts. Most break down with cooking, and it largely doesn’t matter what your blood type is. 

“Overall, however, it appears that the majority of agglutinating lectins react with all ABO blood types. This means that lectins in the diet may not be blood-type specific, except for a few varieties of raw legumes.”

--Healthline, The Blood Type Diet, An Evidence-Based Review

However, like any good wellness grifter, just because the theory and diet have been debunked, that won’t stand in D’Adamo’s way. Instead, he’s doubled down. While the scientific community sees a lack of evidence, Peter D’Adamo sees a market opportunity. The failure of the 'Blood Type' theory to withstand scrutiny has not hindered the commercial expansion of products. If anything, it has incentivized it.

The Website

At D’Adamo Personalized Nutrition homepage, you can find all of the usual grifter products: supplements, books, tests, apps, and long-form advertising in the form of a blog. Underlying all of it is the Blood Type Diet.

The entire website is designed for shopping. Supplements are, of course, the grift’s bread and butter, and in keeping with the theme, many are “designed” for Type O, A, B, or AB blood. If you don’t know your blood type, fear not! There are plenty of generic supplements that aren't targeted to blood type. If you want to do the daily essentials for Type A blood, it will only set you back $156. 

When you finally get to the blog, you find the same tropes as other Wellness Warriors peddle along with diets and products. For example, “How to Keep Your New Year’s Resolutions Within The Blood Type Diet” and “Meal Planning Tips for the New Year.” The storefront monetizes his theory through a library of 22 books, targeting vulnerable populations ranging from pregnant women to cancer patients. There is Eat Right for Your Type (the Blood Type Diet book), along with many spin-offs, such as:
 

• Personalized cookbooks for blood types O, B, A, and AB
• Food, beverage, and supplement lists for blood types O, B, A, and AB
• A book on recommendations for healthy living with your specific blood type
• Individual books dedicated to fighting specific processes and diseases with the blood type diet, including but not limited to menopause, aging, fatigue, and cancer.
   

A Family Affair

This story does not stop with Peter. Peter D’Adamo’s son, Chris D’Adamo, is no stranger to ACSH. He was the lead author on a study that used naturopaths and supplements to “treat” twins with autism. He co-authored another paper with infamous supplement huckster and member of the Disinformation Dozen, Dr. Joseph Mercola. While Chris D’Adamo is not a naturopath, he’s clearly sympathetic to their cause and has a track record attempting to legitimize both naturopathic medicine and supplements as treatments for conditions. 

Chris’s work in "Functional Medicine" is the modern, next-gen, evolution of his father’s work—it’s the "academic rebranding" of the same debunked ideas.

The apples really haven’t fallen far from the tree in the D’Adamo family. For three generations, this family has worked in the wellness world. You might see it as a family business of sorts. James D’Adamo brainstorms a pet theory. Peter advances pet theory through products for sale. Chris attempts to legitimize those types of products.

Brandolini’s Law

"The amount of energy needed to refute bullshit is an order of magnitude larger than to produce it."

It may be easy to think that, because they have been working in similar fields for generations, they have accumulated a lot of knowledge that they pass down from father to son. However, for that to be effective, the information being passed down needs to be accurate, and, as many have demonstrated, the primary underlying theory linking blood type and diet has been debunked. 

The D’Adamo dynasty illustrates the true cost of Brandolini’s Law. What has been passed down is a "perpetual motion machine" of misinformation: one generates the theory, one sells the cure, and one attempts to provide an academic veneer of similar products and procedures. For three generations, the family has spun a web of theories, products, and academic veneers that take minutes to market but decades for scientists to untangle.