By JOSEPH STRONGOLI, Featured Columnist
The Atkin’s Diet, the South Beach Diet, the Mediterranean Diet, the Paleo Diet. Dieting fads have come and gone, promising miraculous quick fixes to lose weight, get fit, and cure ills.
One such panacea-promising diet is the Blood Type Diet, first introduced to the mainstream public in 1996 in Dr. Peter D’Adamo’s book, Eat Right 4 Your Type. The naturopath’s book took the dieting and self-help industry by storm, with over 7 million print copies translated to more than 50 languages.
The book’s latest revised editions are replete with exuberant testimonials and ecstatic personal anecdotes detailing how the Blood Type Diet has changed lives. Can it be true? Has the miracle cure-all diet, promised and failed by so many diets before, finally arrived? Before we take a look at the legitimacy of the Blood Type Diet, let’s begin with a little exposition on what exactly this diet is all about.
It’s All In Your Blood
The underlying premise of the Blood Type Diet is this: your blood type – A, B, AB, or O – affects various key factors in your health, such as the way your immune system responds to viruses, bacteria, and infections (i.e., disease susceptibility), the different antigens and antibodies that each type creates, and most importantly, the way your blood reacts chemically to the food you eat.
The last point is crucial, according to the theory, because of a diverse and abundant class of proteins called "lectins".
These lectins are found in many foods, and they react in radically different ways to the different blood types, potentially causing a wide range of health problems, including irritable bowel syndrome, cirrhosis of the liver, inflammation, slow metabolism, autoimmune disorders, allergies, asthma, cancer, heart disease, and chronic fatigue.
Essentially, your whole system can get out of whack if you don’t obey your blood type. Thus goes the logic, then, that your blood type should determine your diet, your exercise regimen, and your medical choices.
But how can something so fundamental in human physiology as your blood type cause such dramatic differences in other fundamental bodily processes such as metabolism, digestion, immune response, etc.?
The answer, according to D’Adamo’s theory, is that the blood types evolved differently, or in other words, split off from one another some time throughout the course of human evolution and therefore each represents a different evolutionary heritage.
So, because each blood-type bears a distinct profile, Dr. D’Adamo proposes detailed, extensive and elaborate dietary and exercise regimens for each, with hundreds of food and exercise do’s and don’ts.
Essentially, he provides four comprehensive and independent diets, one for each blood type.
I will provide only a rough outline of each here. According to D’Adamo, blood-type O is the most ancient blood type, flourishing in the time when humans were hunter-gatherers. Therefore, people with this blood type (around 45% of the population) should stick to a diet high in animal proteins and get vigorous exercise, just like our more robust ancestors did.
The A blood type (40% of population), on the other hand, emerged around the time when humans settled down into agrarian societies. Therefore, a more plant-based diet and a gentler exercise regimen such as yoga is better suited for the A’s.
The B blood type (11% of pop.) is believed to have originated in nomadic tribes; therefore a varied diet including dairy products is best, in addition to moderate exercise such as swimming and walking.
The AB blood type, (4% of pop.) being the most recently evolved, is said to be the most flexible of the blood types, and a diet mixture of the A and B types will work best, supplemented by calming exercises and relaxation techniques.
Super Science or Pseudoscience?
The Blood Type diet, like many diets that passed before it, has its appealing qualities. But theory is one thing; does the science back it up in practice? Because of all the hype surrounding this new diet, its only natural and right that the scientific community put the theory to the test.
The first pass was a systematic review conducted by Dr. Leila Cusack et al., published in 2013 in the American Journal of Clinical Nutrition.
In it, Dr. Cusack and her colleagues assessed the supporting evidence for the effectiveness of blood-type diets in the scientific literature, by conducting a systematic search to answer the question: in humans grouped according to blood type, does adherence to a specific diet improve health and/or decrease risk of disease compared with nonadherence to the diet?
The researchers combed through the Cochrane Library, MEDLINE, and Embase, all massive databases that collectively, are near exhaustive.
Result? The authors found that no existing studies which showed any evidence to indicate the positive health effects of blood type diets. The authors suggested that in order to validate these claims, specific studies would have to be conducted.
Not a good start for the blood type diet theory; nothing in the existing literature provided any evidence whatsoever validating its claims.
But Dr. Cusack’s review just showed that nothing in the current literature provided any evidence linking blood-types and diet practices to improved health.
The next step would be to carry out experiments explicitly designed to test Dr. D’Adamo’s hypothesis.
In 2014, Dr. Ahmed El-Sohemy and his colleagues at the University of Toronto did just that.
The researchers studied 1,455 participants, mostly young and healthy adults, who provided detailed information over a one-month period about their usual diets and provided fasting blood that was used to isolate DNA to determine their blood type and the level of cardiometabolic risk factors, such as insulin, cholesterol, and triglycerides.
Diet scores were then calculated based on the food items listed in Eat Right 4 Your Type to determine relative adherence to each of the four blood type diets.
Again, the researchers found that there were no associations between an individual’s blood type, their diet, and their health.
The suspicions raised in Dr. Cusack’s literature review were confirmed in Dr. El-Sohemy’s experiments: the blood type diet has no scientific basis.
That whooshing "poof" you hear is the fading of another mirage in the desert of failed diets.