By Dr Michael Greger MD, FACLM

A famous pair of Harvard studies involved so many people over such long a time that they’ve accumulated millions of person-years of data. The studies found the consumption of anthocyanin-rich foods, those containing brightly colored plant pigments and “particularly blueberries,” was associated with a lower risk of developing type 2 diabetes. Just two or three servings of blueberries a week has been associated with a 23 percent lower risk. I recommend at least one serving of berries every day—a half-cup of fresh or frozen berries or a quarter-cup of dried.

What do berries have to do with diabetes? Well, type 2 diabetes is caused by insulin resistance, and interventional studies “clearly showed that dietary BBE [berries] ameliorates insulin resistance.”

 Sounds good, but that was in diabetic mice. What happens in people? Those consuming a lot of anthocyanin-rich foods like berries didn’t just have less inflammation, but significantly lower insulin resistance as well. By how much? By as much as you would get walking an hour or so a day, seven days a week.

How many berries were they eating? They were getting 35 milligrams of anthocyanins a day, which, would be equivalent to a cup of strawberries or cherries, a half–cup of raspberries, a quarter–cup of blackberries, or just a few spoonsful of blueberries. That was just a snapshot-in-time cross-sectional study, though. What we need are interventional trials, where you give people blueberries in a double-blind, randomized, and placebo-controlled clinical trial to truly put them to the test, and we got just that.

In order to fake out people with a placebo, the researchers used powdered blueberries equivalent to about two cups of fresh blueberries in a smoothie., the results demonstrated a significant improvement in insulin sensitivity.

There are a lot of blueberries in two cups! What benefits could be expected from a typical half-cup serving? Another study demonstrated a significant reduction in postprandial oxidation—that is, all of the free radicals created when you eat some sugary breakfast like cornflakes. The antioxidant capacity of your bloodstream takes a nosedive two hours afterwards, as your body tries to cope.

 But, eat it with a half-cup of blueberries, and your antioxidant levels start out higher and stay higher after the meal. The researchers also tried adding just a quarter–cup of blueberries, but that was not enough. So, we should strive for a full serving.