Quick detour from vitamin K to report on a new study about the blood type diet.
I have posted a number of times about the blood type diet, as described in the book Eat Right For Your (Blood) Type (1996), by Peter D’Adamo (see posts).
I lived in Atlanta during the late 1990s and it was quite popular there. And why not? Who wouldn’t want to eat right for their blood type?
In my humble opinion, while the diet and book are a stroke of marketing genius, it is a pretty far-fetched piece of science. I’m talking way out there. La la land.
I should probably mention that this humble opinion is shared by every medical doctor, nutrition research scientist, and dietitian I’ve ever heard on the subject.
Most unfortunately, the blood type diet has never been tested with an actual clinical trial. Rather RDs, MDs, PhDs, and even WMDs, dismiss it by saying that there is simply no evidence to support it. And while I’m terribly sympathetic to the idea that there is no evidence to support it, I don’t think this is satisfying to a layperson who reads the book. When the subject comes up, I can almost see them thinking to themselves, “You silly dietitians are just brainwashed by the grain and dairy lobbies,” or whatever they think might be biasing that particular dietitian (such as the desire to promote veganism among people with all blood types).
We now have at least a cross-sectional study that provides more evidence about the (lack of) effectiveness of eating right for your blood type (1).
The participants were 993 women and 462 men, aged 20 to 29 years old, taking part in the Toronto Nutrigenomics and Health study.
Based on the food items listed in Eat Right for Your Type, subjects received a positive point for consuming a serving of a recommended food item for one’s blood type and a negative point for eating a food to avoid. The foods that were not listed either to consume or avoid were ignored.
Here is an idea of what the diets are like:
A – almost vegan (no meat, little dairy)
B – semi-vegetarian (low grains, more dairy)
AB – very similar to B with a little less fruits and vegetables and a little more meat
O – paleo (high-meat, high-vegetables, no grains and little dairy)
The data was analyzed in two different ways.
In the first, the entire population was separated into thirds according to their scores for each diet and regardless of their blood type. To make a long story short, the type A and type AB diets fared the best (see the abstract linked below for the details).
The second set of analyses had four separate sub-analyses in which everyone was divided according to how close they ate the particular blood type diet being examined. Then the people with that blood type were compared to the rest of the population. According to the authors, “no significant interaction effects were observed between diet adherence and blood group for most of the risk factors, suggesting that effects of following ‘Blood-Type’ diets is independent of an individual’s blood group.”
Note that they said no significant interaction was found for most of the risk factors. Given the number of data points they compared (hundreds), it is not surprising that they found some statistically significant, but still rather weak associations, and, in my opinion, the associations they found were inconsistent enough to be meaningless.
With this study, I think we finally have something that moves beyond “no evidence to support” to “evidence to disprove.” However, it still isn’t going to be very persuasive to a believer, especially given how hard it is to explain.
Clinical trials are expensive and since no researcher actually believes there’s anything behind the blood type diet, it’s no wonder that more money hasn’t been forked out to test it.
The diet seems to have gone out of fashion, but if it experiences a resurgence, it might be time to bite the bullet and spend the money on a clinical trial that, with little doubt, would finally allow us to show people that there is no need to eat according to your blood type.
1. Wang J, García-Bailo B, Nielsen DE, El-Sohemy A. ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors. PLoS One. January 15, 2014.
DOI: 10.1371/journal.pone.0084749 | link