Sept. 12, 2023 – A daily smoothie has transformed Lindsey Seegers’s life. After doctors said her disabling long COVID would be the new normal, she sought out an expert in alternative medicine, known as a naturopath. Among her recommendations: a smoothie for breakfast, chock-full of berries, banana, cashew milk, MCT coconut oil, and other ingredients.
“As a foodie, I resented the notion of drinking a meal. I’d rather be chewing, enjoying an avocado toast. But it’s really helped me feel so good,” said Seegers, a nonprofit director in San Diego. While there is no evidence that smoothies can cure long COVID (nothing does, as far as we know) after just a few weeks, she began to feel better.
But new research suggests that if you’re drinking a smoothie for certain perceived health benefits, combining some fruits may backfire.
Focus on Flavanols
The study, in the journal Food & Function, looked specifically at the flavanol content of certain fruits. It found that a banana-berry smoothie might not have as many health benefits as you think. When you blend together fruits high in the enzyme that turns fruit brown when exposed to oxygen, like bananas, with fruits high in the beneficial plant compounds known as flavanols, like berries, the flavanol content declines quickly. After 30 minutes, the amount of one flavanol dropped by 80%.
Flavanols, also known as flavan-3-ols, are a common type of flavonoid – plant compounds that have been shown to boost health. Last year, for the first time ever, the Academy of Nutrition and Dietetics issued guidelines for consumption of flavanols after assessing the available research. The group found that these compounds, found in tea, apples, berries, grapes, red wine, and cocoa, promote cardiometabolic health.
“If you’re aiming at increasing your intake of flavanols through smoothies, you shouldn’t combine flavanol-rich ingredients like berries with fruits that will easily turn brown when you cut them,” said the study’s lead author, Javier Ottaviani, PhD, director of the Core Laboratory of Mars Edge, part of Mars Inc., and an adjunct researcher with the University of California, Davis, Department of Nutrition. “That could destroy the flavanol.”
This effect doesn’t happen only in smoothies, he said. “Whenever you pulverize or destroy the structure of the fruit, allowing contact between the enzyme and flavanols, it will result in that loss.” For instance, avocados also contain the enzyme, so you can expect to find reduced flavanol content in guacamole.
The Bigger Picture
This may sound like a recipe for disaster, but don’t give up your regular smoothie (or guacamole) just yet.
“The last thing we want is for people to think, ‘Oh, if I make a smoothie, it’s not going to be healthy,’” said Mary Ann Lila, PhD, director of the Plants for Human Health Institute at North Carolina State University. A smoothie is an extremely healthy way to get all the bioactives in the fruit, she said – as long as you drink it right away. “If the integrity of the bioactive compounds is being destroyed, you’ll see it. If I left my smoothie there and it turned brown, I wouldn't drink it.”
Plus, Ottaviani’s advice applies only if you’re looking specifically to boost your flavanol intake through smoothies. Most people don’t need to do that. A varied diet – especially with a daily cup of green or black tea, which provides more than half the recommended flavanols – can make up for a banana’s flavanol-killing power. And bananas offer some impressive benefits of their own.
“When you add the banana into your smoothie, you get potassium, phosphorus. Maybe not so many flavanols,” said Wintana Kiros, a clinical dietitian in the Washington, DC, area. “But if you have other foods at lunch or dinner, you’re eating them throughout the day. The all-or-nothing mindset is the problem.”
The study’s lead author agrees. “Bananas remain a great fruit,” Ottaviani said. “You can still use them for smoothies. The important thing is to have a balanced diet.”
Just get your flavanols elsewhere.
Where Smoothies Go Wrong
While you probably don’t need to worry about the flavanol content of your smoothie, it is possible to drink a smoothie that backfires.
For instance, too much fruit can lead to trouble. “One huge issue with smoothies is the total amount of calories and sugar. We want you to eat fruit for sure, but not overconsume it,” said Joanne Slavin, PhD, a professor of food science and nutrition at the University of Minnesota. “For most people, when they start mixing it up, it becomes a lot of calories.”
A related mistake: leaving out key nutrients. “Especially for people on a lower-calorie diet, for a smoothie to be a meal replacement, it has to have protein,” Slavin said. She’s done research into the power of protein in smoothies. Together with the fiber in fruit, protein can help you feel satisfied for longer.
Store-bought smoothies may also pose a problem. For one thing, you have no control over how much sugar is added. Plus, “at home, nutrient and bioactive compounds are unimpaired by processing,” Lila said. “But they can be impaired by commercial processing, if they use heat or put additives in there.”
Secrets of a Nutritious – and Delicious – Smoothie
So, you’re ready to pull out the blender. What should go in? Aim for a mix of nutrients. “I recommend a cup of berries, a cup of spinach, and Greek yogurt or protein powder,” Kiros said. “You need a fiber source, a fat source, and a protein source.”
Don’t be afraid to get a little creative, either. Here are some ideas:
- Fruit, of course. Frozen fruit is especially good here. It helps thicken the smoothie, and it may contain more bioactive compounds than fresh fruit, since it’s frozen at peak freshness. Lila opts for blueberries in her own morning smoothie. Her research has found that daily consumption can reverse a decline in thinking skills in older people. But don’t restrict yourself to the usual banana and berries – go tropical by adding pineapple and mango, or try peach, melon, or kiwi.
- Surprise: Vegetables. You’ll get more bioactive compounds with less sugar if you add vegetables to your smoothie. Avocado, for instance, provides a creamy texture, mild flavor, and healthy fat. Lila recommends blending kale with yogurt or a splash of juice before adding the remaining ingredients – the vegetal flavor blends right in. Kiros has spinach. And Seegers, the foodie who was so reluctant to drink her breakfast, adds frozen carrots.
- Protein, for sure: If you tire of the usual yogurt and milk, try adding kefir, cottage or ricotta cheese, tofu, peanut powder, your favorite nut butter, edamame, canned white beans, or seeds like chia, flax, and pumpkin.
- Tasty extras: “In order to be healthy, it's got to be something you want to consume,” Lila said. “I believe in making things palatable.” That might mean a drizzle of honey or maple syrup, spices like cinnamon, nutmeg, and cardamom, cocoa powder, or vanilla extract. Seegers is a big fan of frozen cubes of crushed ginger.
In fact, Seegers has become a big fan of smoothies in general. “I can’t ditch the smoothies,” she said. “They’re my thing now, this is my life.”