Did you know things are perceived as being more truthful if they rhyme? Oh dear.

In his book “Eat Right For Your Type” some doctor claims that you need to eat different foods based on your blood type. 

It has sold over 7 million copies worldwide AND the title contains an internal rhyme so the allure is real. 

BUT is the science behind his claims real? Do we have a rich body of scientific literature supporting this proposition? Are books like this subject to peer review before being published? (no)

This is quite possibly the shortest episode I will ever record, leaving you plenty of time to, I don’t know, share a screenshot of the podcast on social media and/or leave a review or something…



Hello. Welcome back to the Bite Me podcast. Today, we're going to be talking about blood type diets. Well, we're not going to be talking about it. I'm going to be talking about it. Basically, it is the idea that you should be eating right for your type, which is the name of the incredibly famous book. And in that book they propose or rather the doctor proposes that certain blood types, A, B, AB, O should have different diets because your blood type will impact the way that you digest and absorb and assimilate all of these foods and nutrients. And he goes on to set out dietary recommendations that differ based on your blood type.

It's usually this point in the podcast that I would start to talk through the mechanisms, maybe explain why they're relevant and why they work, or potentially instead, how they have been misrepresented or misunderstood, and maybe where the person or the group of people making those claims has gone wrong. That's really difficult to do with the blood type diet though, because I'm pretty sure he just made it up. There's no science behind it. There's no studies behind it. I know in the book they kept talking about the fact that the studies are coming. I believe the book's been out for 20 years, still no studies.

And so in a sense, this stuff can be difficult to refute because I don't like refuting something by saying, "It's silly. Trust me." Right. I like to unpack it and explain, "They're making these claims. Here's why these claims don't hold up when we place them against the body of evidence as a whole." But it's again, disputing fiction is tough. All I can really give you is this diet is just a load of garbage. It is a work of fiction.

There's been a systematic review, which for those who are unaware is when someone does a big review through all of the databases of scientific literature, with certain criteria to find relevant studies, to answer their research topic. The research question in this was, "Is there enough evidence to support the use of blood type diets?" I believe they found one study and that wasn't even really on blood type diets. And that found no difference if you adjusted the diet based on your blood type. Now that review came out in 2013 and since then, there's been to all that I have found, is literally one clinical trial that is relevant and that came out in 2020.

The title was, "Blood type is not associated with changes in cardiometabolic outcomes in response to a plant-based dietary intervention." I don't love common studies. I feel study titles should hold some mystery, but they've just given the game up. As it said, no change has been associated with the blood type. So based on people's blood type in this, they put people of a certain blood type on a plant-based diet to see, the diet that was claimed to improve their health outcomes. They found nothing. All of this is to say, if you are following a diet based on your blood type, please stop.

There's no scientific benefit to it, to which the comeback is generally, "Well, this person or myself, I went on this blood type diet and I felt heaps better. I saw all of these improvements. How can you tell me that it doesn't work?" And this is a common theme with these sorts of diets as well. I see it often with something like the alkaline diet, which again has no scientific basis. But often the dietary patterns these diets encourage are still healthier than the dietary pattern someone was previously following. So for example, if you've followed a blood type diet and this blood type diet, according to whatever your blood type is, has encouraged you to eat more fruits and vegetables, or maybe it's encouraged you to eat more protein, it's included or it's increased the overall healthfulness of your current diet. Absolutely. You're going to see some benefits.

The only problem is you've also probably unnecessarily restricted certain foods or food groups based on this. I'm going to say it again, work of fiction. It's still not without risk because unnecessarily restricting foods can lead to nutrient deficiencies as well as definitely increasing your risk of disordered eating and just kind of a warped relationship with food. So, even though following this diet may improve the healthfulness of your diet, you can do that lots of other ways.

The other thing as well is typically if someone makes a change in their diet, they don't do that in isolation. They'll change their diet, and they will also get a bit more sleep, or they'll get more active, or they'll reduce their alcohol consumption. Usually health behaviors, they all team up, they all happen at once. So it's also difficult to know whether that improvement in their health was down to their diet or down to their kind of change in healthy behaviors as a whole.

So very quick one this week, because again, I can't debunk something that has no basis in science. So safe to say, leave this one on the shelf, ignore it.

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