Try it Tuesday: Blood (Sweat and Tears) Type Diet Trial

Blood type diet.jpg

If you’ve enjoyed any of our recent posts from IFIC Foundation staff trialing various diets and eating styles, then you may be interested in this one as well. I came across this diet many years ago—never followed it (until know, that is), but never forgot about it either. After all, who could forget hearing that the key to optimal eating is as simple as knowing your blood type? For what it’s worth, I never heard this diet discussed (seriously, anyway) one time in all my years of schooling or training.


I’m embarrassed to say that I didn’t know my blood type. My ignorance made the first action item for this diet trial very simple: find out my blood type. A quick trip to donate blood took care of that. Turns out, I’m O negative.


Next step, do some research. I knew nothing about this diet, besides its name. Is there any science behind it? More importantly, what would I be allowed to eat? What wouldn’t I be allowed to eat? I broke into a cold sweat, frightened that all of my faves might be blackballed. In the name of science, I forged ahead.

As luck wouldn’t have it, many of my fears came to fruition. Type O’s are encouraged to eat lean, organic meats and select fruits and vegetables, while avoiding wheat (because … gluten), dairy and added sugars. Every blood type is also instructed to avoid GMOs. I’ve documented a more detailed list of type O do’s and don’ts below.

This diet was already approaching cruel and unusual, and then I read this: Type O’s should also avoid caffeine and alcohol. Surely this was a typo about type O. It wasn’t.


After I finished crying, I made my shopping list and moped my way through the grocery store maze. While some sections and aisles were off limits, I was able to visit many that I normally do. This wasn’t so bad after all! I would focus more on what I could eat rather than what I couldn’t eat—advice I’ve given others many times.

My enthusiasm, however, was short lived. While I enjoy all the foods I ate as part of this diet, putting them together in tasty, compelling meals all day, every day was a huge challenge. Related to that, the even bigger challenge was navigating how to modify my old habits in immediately adopting this new eating style. Full disclosure, while I adhered to the no dairy, no wheat, no added sugars (mostly), no caffeine, no alcohol rules, I didn’t follow the exclusive organic and non-GMO instructions.


To report the results of my five-day diet trial, I’ve created the table below so you can quickly scan how my blood type O diet differed from my typical diet, my commentary about the changes, and a few pre and post measurements.


Typical Week

Type O Week

My Verdict


Coffee (a lot of it) w/ creamer or half ‘n’ half, flavored Greek yogurt w/ cereal

Decaf coffee, steel cut oats, walnuts, grapes

Big change without dairy, wheat or added sugars. Less protein, flavor, and caffeine make me way less amiable in the AM.


Sandwich (e.g., peanut butter and jelly, turkey and cheese), fruit

Canned tuna w/ rice crackers or veggie salad, select fruit

Slight change with fruit limitations and lack of dairy and wheat. I missed PB&J’s.


Protein bar, nuts, office sweet treats or fruit

Walnuts or almonds and select fruit

Slight change with fruit limitations and no office scavenger hunts.


Veggies w/ chicken, pork or seafood (usually as part of a Mexican-themed meal with tortillas, cheese, sour cream, salsa, avocado)

Select veggies, salad w/ chicken or salmon

Big change without dairy, wheat or pork. Veggie limitations didn’t bother me as much as fruit. I can’t (and won’t) live without my Mexican-themed cuisine.


Almost never


No change. Hands down, easiest part about this diet for me.


Coffee, water and occasional tomato juice, sparkling flavored water or diet soda

decaf coffee, water, tomato juice

Big change without caffeine, dairy, some added sugars or low-calorie sweeteners. I enjoy (and badly missed) more flavorful hydration staples.


Water, wine (white or sparkling) or cocktail, occasional juice


Big change. Unwinding simply doesn’t work as well with water.


*for my family of 2



No change. I did not, however, adhere to the blood type diet’s organic or non-GMO guidance.

The following measurements were taken pre- and post-diet trial





Full octane coffee. I’d be lying if I didn’t say I immediately missed my morning pick-me-up.

Caffeinated coffee, cheese and (wheat) crackers, a good happy hour

Big change. I held off my urges for the sake of science.

PERCEIVED MENTAL ACUITY (1 = dense as fog, 5 = sharp as a nail)

3—that’s pretty much my max for a Monday

2—I fluctuated between 1 and 2 all week long

Big change. Could have been the lack of caffeine, but found it harder than normal to focus this week.


Normal peppy self

Low, and consistently low all week long

Big change. Likely a combo of zero caffeine and my first week back from traveling.


177.2 lbs.

174.6 lbs.

Slight change. As most of us do, I typically fluctuate a few pounds every week. This week I lost 2.6 lbs.



You want the good, bad or ugly first? Ok, let’s start with the good. Overall the type O diet plan is full of beneficial foods and beverages. I ate lean meats, fish multiple times, an array of fruits and vegetables (including their 100 percent juices), less than the recommended amount of added sugars, and plenty of nuts. Many of these same food categories and targets of the blood type diet are recommended by the 2015-2020 Dietary Guidelines. And, if you use weight as a sole metric for health (which I don’t), I lost 2.6 pounds this week.

Now for the bad. My experience on this diet (for just five days, granted) was that it’s unnecessarily challenging to put in practice. The anxiety associated with knowing which foods are approved, which are forbidden, and then ultimately how to blend the approved foods together into flavorful (a touch of low-calorie sweetener or added sugar would have done wonders for my oatmeal) and coherent meals was more than this registered dietitian bargained for. And, I didn’t eat out once this week, which is normal for me, but can only imagine the difficulties for people that dine out more frequently.

I love food, but I don’t love spending my days avoiding perfectly safe and healthy foods and ingredients that I enjoy and am not allergic to. The amount of worry and work I put in this week made me even more sympathetic to those with diagnosed food allergies, intolerances and disorders.

Finally, the ugly. As a registered dietitian, I hold nutrition science in high regard: evidence over anecdote every time. Benefits from following the blood type diet are not supported in the reputable published scientific literature. That doesn’t mean that one’s health can’t improve from following the blood type diet, it just means that an improved diet (not matching diet to blood type) would be the cause.

Science doesn’t conclude that eliminating entire food groups, safe and approved ingredients, and plant breeding/farming techniques will improve health, yet the blood type diet makes this promise. A quick PubMed and Google scholar search yielded links to several books, reviews, commentaries and grad student theses, but only one published peer-reviewed scientific study—an unfavorable article published in PLOS one in 2014. Most telling perhaps, is that the blood type diet isn’t mentioned once in the latest Dietary Guidelines for Americans, and there’s a reason for that.

If you enjoy firing “magic bullets” at the bullseye of health, give the blood type diet a shot. Just don’t be surprised if it’s a blank.


More specifics of the blood type O diet advice:


  • Lean protein: Beef, lamb and venison are encouraged and are best.
  • Fruits: Cherries, plums, figs and prunes are best.
  • Vegetables: Plenty of beets, broccoli, onions, sweet potatoes, turnips, dandelion greens, escarole, romaine lettuce, Swiss chard and okra are best.
  • Nuts and seeds: Walnuts and roasted pumpkin seeds are best.


  • Pork
  • Cow’s milk and dairy products
  • Wheat, not even whole wheat (because … gluten), and couscous
  • Lentils, corn, kidney beans, cabbage, eggplant, mushrooms, red or white potatoes, cauliflower, and corn
  • Peanuts and pistachios
  • Cantaloupe, strawberries, blackberries and tangerines
  • Any product that contains refined sugar
  • Alcohol
  • Caffeine
  • Low-calorie sweeteners
  • Most types of caloric sweeteners
  • All GMO foods