There is a lot of information out there about the best foods to help us lose weight, prevent cancer, fight inflammation – the list goes on. In fact, for everything about our health we try and improve, there’s someone out there with a new theory on how to do it. But what does the science say?
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to give you the evidence-based approach to take the mystery out of the best way to live a healthier, longer life.
Today we continue with our series highlighting one special food that contains demonstrable health benefits. And the star of today’s episode? The mighty Blueberry.
In our first story, blueberries are put to the test against insulin resistance, oxidation, and DNA damage.
A famous pair of Harvard studies, which involve so many people over so long a time they’ve by now chalked up millions of “person-years” of data, found that the consumption of “anthocyanin-rich foods,” foods containing those bright-colored plant pigments was associated with a lower risk of developing type 2 diabetes over time, “particularly blueberries.” Just two or three servings a week associated with a 23 percent lower risk. In my Daily Dozen, I recommend berries every day.
Why, though? What do berries have to do with diabetes? Well, type 2 diabetes is caused by insulin resistance, and interventional studies evidently “clearly show” that dietary berries can “ameliorate insulin resistance.” Yeah, but that was in “diabetic mice.” What about in men and women? Those consuming lots of anthocyanin-rich foods, like berries, didn’t just have less inflammation, but significantly lower insulin resistance. Okay, but by how much? By as much as you would get walking like an hour a day, seven days a week. Wow, how many berries were they eating?
That was for 35mg of anthocyanins a day. So, like a cup of strawberries or cherries, a half a cup of raspberries, just a quarter cup of blackberries, or even just a few spoonfuls of blueberries. But that was just a snapshot-in-time cross-sectional study. 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.
Okay, here you go. So they could fake people out with a placebo, they used powdered blueberries, the equivalent of about two cups of fresh blueberries’ worth in a smoothie and got a significant improvement in insulin sensitivity.
Two cups is a lot, though. Any benefits for just a typical half-cup serving? This study demonstrated a significant reduction in postprandial oxidation, meaning all the free radicals created when you eat some sugary breakfast, like corn flakes. Here’s the antioxidant capacity of your bloodstream taking a nosedive two hours afterwards, as your body tries to cope. But eat it with a half cup of blueberries, and you start out higher and stay higher after the meal. Note they also tried just adding a quarter cup of blueberries, and that was clearly not enough; so, we should strive for a full serving.
The reason we care about free radicals, though, is that they can damage our DNA. Can a single portion of blueberries really improve protection against DNA damage?: “A single portion of blueberries can improve protection against DNA damage”! They drew blood from people before and after they ate some frozen blueberries, and exposed their white blood cells to free radicals in the form of hydrogen peroxide. And, “blueberries significantly reduced the DNA damage done within a single hour after berry consumption.” “However, the protective effect was transient, and our DNA vulnerability returned within two hours.” So, we want to be eating super-healthy foods like berries at every meal. In conclusion, “one portion of blueberries can improve our cellular resistance to DNA damage, “thus supporting the importance of consuming healthy plant foods regularly.”
Next we discover how blueberries can significantly improve cognitive performance within hours of consumption.
When you search the medical literature for studies on berries, papers pop up: A “‘Blueberry Muffin’ Rash”, ahh. Or, pictures of “strawberry tongues,” or as a way to describe “stool appearance,” though “stools truly resembling currant jelly” are not very common. What is it with pathologists’ love affair with food terminology? The grossest of which may be the way amoeba chest infections are described, where you spit up pus that looks like “anchovy sauce,” which sounds gross even without the pus.
There are actual studies on berry supplementation, like on how they can mitigate the negative effects of a “high saturated fat diet on the brain and behavior,” but that was in mice. Maybe a better way to mitigate would be to not feed your pet mouse a stick of butter in the first place.
Then, there are studies of proprietary berry-based nutraceutical supplements, purported to improve cognitive performance. There are studies of actual berries on actual humans, but when they’re funded by berry industry trade groups, you get studies like this: “An afternoon snack of berries reduces subsequent energy intake.” Great! But that’s compared to candy. Strawberries, raspberries, blackberries, blueberries, fantastic, compared, to a handful of “Jelly Babies,” which are just like coated gummy bears. Do berries offer so little that you have to compare them to candy to make them look good?
There was that famous Harvard study I did a video about, where berry-eating appeared to delay brain aging by up to two-and-a-half years. But, you don’t know if it’s cause and effect until you put it to the test. And, “blueberry supplementation was able to improve memory in older adults” in just 12 weeks’ time. But, that was feeding them up to six cups of wild blueberries a day. Now, this was a proof-of-concept pilot study just to see if they could get any effect. We just didn’t have any studies using more realistic doses, until now.
How about just a cup a day of blueberries? They found that “the addition of easily achievable quantities of blueberries to the diets of older adults can improve some aspects of cognition,” like long-term memory. In terms of the number of errors, the placebo group got worse; the blueberry group got better.
You can even correlate the cognitive improvements with enhanced brain activation using fancy brain scan technology to actually visualize the improved blood flow to those same regions of the brain caused by the blueberry consumption.
Does it work in kids, too? “Blueberry treatments have shown positive effects on cognition in both” rats and adult humans. But, do those these “benefits transfer to children,” human children? How about a randomized, double-blind placebo-controlled study comparing about one cup of blueberries, to two cups, to zero cups. What did they find? “Cognitive performance improvements across all measures,” and the more berries, the better. And, this wasn’t after twelve weeks of eating berries, but within hours of just a single blueberry meal. Sounds like a good breakfast any day our kids are having their exams.
Finally today, what is the optimum dose of wild blueberries to eat at a meal?
“A single serving of blueberries can help mediate the arterial dysfunction induced by smoking a cigarette.” They “investigated the effect of a single serving of frozen blueberries on young smokers.” Smoke a single cigarette, and the ability of your arteries to relax naturally drops 25% within two hours. But, eat two cups of blueberries a hundred minutes before, and that same cigarette causes less than half the damage, demonstrating that “a single big serving of frozen blueberry could counteract the artery dysfunction induced by smoking.” However, of course, it should be noted that “blueberry consumption cannot be considered a means of preventing health consequences due to smoking; this can only be realized by” stopping smoking, or even better, not smoking in the first place.
Two cups of blueberries is a lot, though. Yeah, you could easily chug those down in a smoothie, but what’s like the minimum dose? We didn’t know, until a group of British researchers decided to put it to the test. To enable them to do a double-blind study, they had to create a placebo control fake blueberry drink. So, they used a freeze-dried wild blueberry powder to give people the equivalent of three-quarters of a cup of fresh blueberries, one and a half cups, one and three-quarters, about three cups, or four cups. They concluded “blueberry intake acutely improves artery function in an intake-dependent manner.”
Okay, so what’s the optimal intake? After the placebo, nothing happens. But, after eating one and three-quarter cup’s worth of blueberries, a big spike in artery function improvement within just one hour of consumption. And, that seems to be where the effect maxes out. Less than a cup is good, but between one and two cups seems better, with no benefit going beyond that in a single meal.
Can you cook them? What if you put them in a blueberry pie or something? The same remarkable improvement in artery function baked into a bun just spiking an hour later, since solid food passes more slowly through your stomach.
And, then, if you eat blueberries week after week, you get chronic benefits too, in terms of reduced artery stiffness, and a boost in your natural killer cells, which are one of your body’s natural first lines of defense against viral infections and cancer. But wait a second; how can blueberries have all these amazing effects, if the anthocyanins, the blue pigments in blueberries purported to be the active ingredients, hardly even make it into our system? Women were given more than a cup of blueberries to eat, and they couldn’t find hardly any in their bloodstream or flowing through their urine.
So, “Either anthocyanins are extremely potent, and, therefore, active at low parts-per-billion blood concentrations or somehow their bioavailability has been underestimated.” So, researchers decided to radioactively tag them and trace them throughout the body.
What happens is that blueberry pigments are metabolized by our liver and our microbiome, the good bacteria in our gut into these active metabolites that are then what’s absorbed into our system. So, it’s kind of a team effort to benefit from berries.
So, like a day later, we may still be experiencing berry benefits as our gut bacteria continue to churn out goodies that get absorbed back into our system, feeding us as we feed them. Eating blueberries can so feed our good bacteria that it’s like taking a natural probiotic: a win-win all around.
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For recipes, check out my “How Not to Die Cookbook.” It’s beautifully designed, with more than 100 recipes for delicious and nutritious meals. And all proceeds I receive from the sales of all my books goes to charity.
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