Bananas and berries are popular fruits to throw into smoothies, but are they really a good combination? According to a study in Food & Function, not so much. In fact, blending a banana with berries can decrease that smoothie’s nutritional value.
It’s easy to understand why bananas are often a main ingredient in hearty smoothies. They add both taste and texture, and they are dense enough to keep you satiated and stave off hunger until your next meal. Nutritionally, they’re a good source of fiber, potassium, vitamin B6, and provide some magnesium, vitamin C and protein.
But if you’re going to use a banana to make a smoothie, be choosy about what you’re pairing it with. It turns out bananas contain an increased level of an enzyme called polyphenol oxidase, or PPO, which is responsible for its browning when they’re cut or bruised. When a high-level PPO fruit is combined with one high in flavanols (natural healthy compounds), it can reduce the levels of the flavanols your body consumes.
Why are flavanols so important?
First, it's helpful to know that flavanols are found in mangos, pineapple, pears, blueberries, blackberries, strawberries and cocoa, which are all common smoothie ingredients. They’re also vital to our overall health.
“Research over the past 20 years has shown flavanols can help to maintain health as we age,” says lead study author Javier Ottaviani, Ph.D., director of the Food & Nutrition Core Laboratory of Mars Edge (part of Mars, Incorporated), and an adjunct researcher in the department of nutrition at the University of California, Davis. “For example, one large and rigorous clinical trial in The American Journal of Clinical Nutrition showed that a daily intake of 500 mg of flavanols reduced cardiovascular deaths, including heart attacks and stroke, by 27%.”
Additionally, the Academy of Nutrition and Dietetics (AND) recommends people should consume 400 to 600mg of flavanols daily to support cardiometabolic health. “Cardiometabolic health contributes to a healthy lifespan by reducing risk factors for cardiac and metabolic diseases, including obesity, hypertension, and diabetes,” Ottaviani says.
Other research has found flavanols exhibit antibacterial, antiviral, anti-inflammatory and neuroprotective properties. Studies also suggest that they have prebiotic potential, which is important for maintaining a healthy gut.
What happened in this study?
The study, led by Ottaviani and his fellow researchers at the University of California, Davis in collaboration with the University of Reading in the UK, came about because “we wanted to understand, on a very practical level, how common foods and food preparations, such as smoothies, could affect the availability of flavanols to be absorbed by the body after intake,” says Ottaviani.
The scientists knew from previous studies that flavanols can be broken down by polyphenol oxidase. However, “there were no previous studies investigating if bananas could affect the absorption of flavanols,” Ottaviani explains.
For this study, the researchers looked at a small group of eight healthy men aged 25 to 60. To control the levels of flavanols in their diet, the subjects were asked to follow a low-flavanol diet the day before and during the study days.
All of the study participants were given a smoothie with high PPO activity consisting of banana and almond milk, as well as another with low PPO activity, (a mix of strawberries, blueberries, blackberries, raspberries, water, almond milk and yogurt). The subjects also took a flavanol capsule (containing cocoa extract) as a control. A small amount of cocoa extract was also added to the different smoothies.
What did the researchers find?
After analyzing the participants’ blood and urine samples to measure the amount of flavanols in their bodies, researchers discovered that after drinking the mixed-berry smoothie, the subjects had similar flavanol levels to the control, but consuming the banana smoothie resulted in having 84% lower levels of flavanols in their body. Plain and simple, the high PPO content of the banana destroyed the flavanols, practically making the idea of consuming a banana-berry smoothie a moot point.
If you’re wondering if the effects would be the same for women as men, Ottaviani says the answer is most likely yes. “The results showed that the effects of PPO on flavanol availability occurred during smoothie preparation, before consumption,” he explains. “Because of this, sex differences are less relevant for this study, and we consider that the findings are generalizable to both men and women.”
Should you avoid bananas in all smoothies?
No, you can certainly have bananas in your smoothie, but based on the study’s findings, you may want to reconsider using berries in the same recipe. “Bananas remain a great fruit and a great option for smoothie preparation, but not if you’re aiming at maintaining the flavanols in your smoothie,” says Ottaviani.
Bananas go great in a smoothie with peanut, or another nut butter, or you can pair it with another high PPO fruit such as papaya, avocado or pear. If you want a fruity banana blend with less PPO, you can try combining it with pineapple, oranges or mangos.
But if you’re craving a berry smoothie, and you’re only adding the banana for sweetness or texture, there are some viable alternatives, according to Carolyn Williams, Ph.D., R.D., a professor of culinary arts and nutrition at Shelton State Community College in Tuscaloosa, Alabama, author of Meals that Heal and host of the Happy Eating podcast.
Thinking about why you’re using the banana in the first place can help you figure out what to swap it out for, says Williams. “If the banana is adding sweetness and/or creaminess, you may want to replace it with ingredients that add those same qualities. For instance, I like including a little honey for sweetness, and for texture, you can add some mango and Greek yogurt, which has a higher protein content compared to regular yogurt.”
