Do Smoothies Make You Sharper or Is It Just Juicy Gossip?
The outrageous science behind the pro-berry headlines.
Posted Apr 06, 2018
Earlier this week, The Times of London published an article entitled "Eat Yourself Smarter? Try dark chocolate, green salad — and gum."
Articles like this one always get my goat (maybe that's why I haven't seen my goat in such a long time). Create a hopeful headline, toss in a bunch of studies that support your headline (without references so I have to dig my way through PubMed to find them), interview an expert researcher or two for some quick enticing quotes, and then take a wildly irresponsible leap into making specific and appealing recommendations about what people should eat/drink to be smarter. Often, including in this case, these prescriptions for brain health are not only wrong, they are dangerously wrong.
As a psychiatrist who has worked in college mental health for more than 12 years—first at Harvard and now at Smith College in western Massachusetts, I know a thing or two about student exam pressures, student eating habits, and student beliefs about food and the brain. I spend most of my time trying to dislodge unscientific myths about nutrition and replace them with biological facts and common-sense approaches that actually have the potential to improve brain health.
That Times of London article makes some excellent points about college mental health and the pressures students face to perform well on exams, and then launches into a laundry list of foods, supplements, and beverages that are supposed to boost brain function. I'm going to focus on one of the claims made repeatedly in the piece that I think is most important — that berries and fruit juices will make you smarter.
These claims are based on studies of fruit juices that are supposed to be good for the brain because they contain special plant compounds called flavanols and other flavonoids,
Let's take a quick peek under the hood of each of the claims.
Claim: “Psychologists and nutrition scientists at the University of Reading have shown that berries have a particularly potent effect on cerebral function. One study showed a significant boost in the brain performance of children after they had consumed the equivalent of 220g of fresh blueberries, served in a drink form.”
After some internet sleuthing, I believe this is the study they are referring to: The effect of cognitive demand on performance of an executive function task following wild blueberry supplementation in 7 to 10 years old children. This study compared a drink made from water and freeze-dried wild blueberry powder (containing lots of anthocyanins, which are flavonoids) to a control beverage of water, sugar, and vitamin C (containing no anthocyanins). Children who drank the blueberry juice performed faster in a modified version of a test called the Attention Network Task than children who drank the sugar water.
How much faster? Whoosh: 41 milliseconds — a whopping 41 thousandths of a second! [There goes my goat...]
Even if you find the results impressive, all this study tells you is that blueberry juice is better than sugar water (or, put another way, that sugar water is worse than blueberry juice). It can’t tell you whether blueberry juice is better than water or better than drinking nothing at all. For all we know, this juice slows the brain down compared to water, milk, or kale smoothies.
Even if you find the results impressive, how do you know the faster speed was due to the anthocyanins and not some other component of the blueberry powder? If researchers wanted to convince us that anthocyanins are the magic ingredient, why didn't they simplify things and compare a glass of water with anthocyanins in it to a glass of water without anthocyanins in it?
Since glycemic index wasn’t measured, we don’t know whether the berry juice was a tad better than the sugar-water beverage because it may have caused a smaller spike in blood sugar and insulin. We’ll get to why blood sugar and insulin are so critically important to brain function in just a bit.
Claim: “A more recent, unpublished study suggests that the findings are consistent in young adults,” says the researcher Dr. Daniel Lamport. “When young adults drank a 500ml serving of a commercially available berry-based fruit juice, their brains responded positively within two hours and there were improvements in their cognitive performance, alertness and mood.”
Since this study is unpublished, I can’t comment on it, and I would argue that it shouldn't have been included in the article: Until it's published, it's no more credible than hearsay.
The Times wraps up by making specific recommendations to the public about how to improve brain function through diet, including the following berry-positive recommendations:
Recommendation: “Make a berry smoothie: Have a juice or smoothie made of 220g of fresh blueberries two hours before your exam for a proven increase in BDNF (brain derived neurotrophic factor).”
Well, maybe … if you’re a rat. My search for scientific studies to support this statement only found a few rodent studies; there appear to be no human studies so far looking at berries and BDNF, a protein that supports brain cell health and growth. Of the handful of animal studies, this was the most relevant study I could find, and, interestingly, it didn’t use juice or even berries: It used pure, unsweetened flavanol extracts. It is illogical to conclude from this study of pure extracts in rats that human students should be drinking berry smoothies before their exams. Trust me: You do not need to twist students’ arms to get them to drink more smoothies—they drink smoothies CONSTANTLY.
Claim: “A mixed-berry drink (75g each of strawberries, raspberries, blackberries and blueberries) improved cognitive performance six hours later.”
Turns out this study is also unpublished, so all we have are summaries of it in the lay press like this one that don’t provide enough detail for me (or any of us) to properly evaluate its findings.
The last juicy recommendation in the Times article is this:
Recommendation: “Drink orange juice: If berries aren’t your thing, another study at the University of Reading showed improvements in cognition and mood in young adults immediately after and two hours after drinking a 240ml orange juice drink.”
This study, conducted by Lamport and others, compared one cup of “flavonoid-rich” orange juice to one cup of control beverage containing no flavonoids. The “flavonoid rich” drink was Tropicana Pure Premium Orange Juice (made by PepsiCo) with “orange pomace fiber” added to it. Two of the study authors work for PepsiCo and the study was funded by PepsiCo. [Stop, thief: Come back with my goat!]
The control drink was sugar water made from glucose, fructose, sucrose and some citric acid (for flavor). Sugar (23 grams) and calories (93 cal) were identical but note that the orange juice contained fiber, vitamin C, and folate, which the sugar water did not. Again, why include so many variables? It makes it impossible to know what is going on.
But I digress. What did this study find?
Middle-aged men were given eight cognitive tests and two mood tests. Those who drank the Tropicana orange juice plus fiber performed better on only TWO of these tests:
- “Simple Finger Tapping Test.” This test is just as it sounds: It measures how many times you can tap your finger in 10 seconds. Six hours after drinking the orange juice, men were able to tap their finger two more times in 10 seconds—62 times, up from 60 times—compared to before drinking the orange juice. Men who drank the sugar water tapped their finger one less time compared to before drinking the sugar water (61 times, down from 62).
- “Continuous Performance Task” (CPT). This test flashes letters on a screen for 6 minutes and measures how quickly and accurately you can press a space bar or click a mouse whenever you see any letter that is not an X. On average, six hours after drinking the orange juice, men made 1.6 fewer errors on this test (7.6 errors, down from 9.2), whereas men who drank the sugar water made 0.6 more errors.
The magnitude of these differences gives new meaning to the word miniscule. [I may never see my goat again...]
Students, don’t drink the Kool-Aid!
Please understand that drinking more fruit juice will NOT protect or improve your brain because:
- The results of these studies are incredibly subtle and disappointing to put it mildly— outrageously misleading and irresponsibly misrepresented to put it boldly.
- Some of these studies are funded by PepsiCo, whose mission in life is not to improve your health but to sell you more beverages. The Times should have made this glaring conflict of interest clear.
- None of these experiments compared berry juice to proper controls, so we have no way of knowing whether the results are due to the flavanols, vitamin C, folate, fiber, or lower glycemic index of the “flavanol-rich” products.
- Most important: The last thing in the world you want to do if you care about your brain health is to drink sugar!
How Fruit Juice Actually Affects the Brain
These studies didn’t test whole fruits and vegetables—big corporations don’t make money convincing you to eat more whole foods, and they don't make money telling you to STOP consuming something. These studies tested commercially-available juices which are very high in sugar. Yes, they are naturally-occurring sugars—but the body can’t tell the difference. Frequent, dramatic blood glucose and insulin spikes are just as potentially damaging when they come from juice as when they come from soda. Juices are, by definition, “refined carbohydrates.” It is very difficult to consume high quantities of natural sugars when you eat whole fruits and vegetables because a) it takes a lot longer to chew and swallow fruit than it does to guzzle juice, so you can consume a LOT more sugar a LOT more quickly, and b) fiber and water in whole foods fill you up, providing a natural stop sign so you don’t overdo it. See this eye-opening infographic about how much sugar is in popular juices, sodas and energy drinks.
Giving yourself big insulin spikes by drinking juice on a regular basis puts you at higher risk for insulin resistance, which now afflicts more than 50% of Americans. Insulin resistance can gradually destroy your brain’s ability to turn sugar into energy, which not only has the potential to make symptoms of some mental health problems worse, but also puts you at very high risk for Alzheimer’s disease down the road. Who wants that? Nobody.
We all want to believe that simply adding something delicious or magical like a superfood or supplement is all it will take to improve brain function. None of us wants to believe that simply removing something delicious and addictive like sugar is the real magic bullet. That's the problem I call "the psychology of subtraction." Taking things away feels bad, negative and depriving. Adding things feels good, positive and proactive.
We Can Do Better
Articles like these are journalistically and scientifically irresponsible. Scientists and media outlets have big platforms from which to make influential proclamations—proclamations that shape people's beliefs and behaviors. As investigative journalist Jeanne Lenzer writes so convincingly in her article "Full Disclosure," we need to hold science journalism to a higher standard when it comes to sources and conflicts of interest.
When it comes to wise advice about how to help your brain function at the top of its game, I agree wholeheartedly with the very last recommendation in the article:
Recommendation: Drink water during the exam: don’t be tempted by too many sugary drinks.
Hallelujah! Is that my goat I see on the horizon?