Is banana bad in a smoothie?
No. A medium banana adds about 105 calories, 14 g of sugar, 3 g of fiber and the thick, creamy texture most smoothies are built on, and none of its sugar counts as added. In one small study it cut how much of the flavanols from berries and cocoa reached the blood, so skip it when those are the point of the glass.
Bananas have been accused twice. The first charge was sugar. Then a 2023 study on flavanols, the plant compounds in berries, cocoa, apples and tea, turned into the idea that a banana ruins every nutrient in the glass. The sugar worry doesn’t hold up, and the flavanol finding is real but much narrower than that.
What we’d do
Keep the banana, frozen, in most glasses, and count it as one of your two fruit portions. When you’re drinking a berry or cocoa smoothie for its flavanols, get the creaminess from Greek yogurt or mango instead. In our chocolate peanut butter shake the cocoa is there for flavor and fiber, so the half banana stays.
Slice a banana, leave it on the counter, and it turns brown. That browning comes from the same enzyme the 2023 study was about.
With the banana
6.2 g fiber, 396 calories
Without it
3.2 g fiber, 291 calories
What does a banana add?
| Medium banana | 1 Medjool date | 1 cup mango | |
|---|---|---|---|
| Calories | 105 | 66 | 99 |
| Sugar | 14 g, none added | 16 g, none added | 23 g, none added |
| Fiber | 3 g | 1.6 g | 2.6 g |
A banana also has 422 mg of potassium, about 9% of the FDA’s Daily Value. One date has more sugar than the whole banana, and a cup of mango has a lot more, so if sugar is the worry, the banana isn’t the fruit to blame. The 2025 to 2030 US guidelines don’t count the sugar in whole fruit as added sugar at all.
What did the banana study find?
In 2023, researchers gave 8 healthy men three drinks on different days: a banana smoothie, a mixed berry smoothie and a capsule, each with the same dose of flavanols added. After the capsule, flavanols in the blood peaked at 680 nanomoles per liter, and the berry smoothie matched it. After the banana smoothie the peak was 96, about 84% lower.
Bananas carry a lot of an enzyme called polyphenol oxidase, the one that browns a cut banana, and it breaks flavanols down. In a second test with 11 people, the researchers kept the flavanols away from the banana drink until the moment it was swallowed, and blood levels still fell, which points to the enzyme working in the stomach.
How much should that worry you?
Very little, for most glasses. The study had 8 men, one family of plant compounds, and flavanols added to the drink in a measured dose, so it says nothing about the vitamins, minerals or fiber in your glass. Mars, the chocolate company, funded the work, and three of the nine authors worked there. It’s an interesting result and a good reason to leave the banana out of a glass you’re drinking for cocoa or berry flavanols, and no reason to give up bananas.
The banana myth goes deeper on the study, and what to use instead of banana has the swaps.
6 sources
- USDA SR Legacy, bananas, raw (FDC 173944), via nutritionvalue.orgnutritionvalue.org
- Ottaviani JI et al., Impact of polyphenol oxidase on the bioavailability of flavan-3-ols in fruit smoothies: a controlled, single blinded, cross-over study, Food and Function, 2023europepmc.org
- US Department of Agriculture and US Department of Health and Human Services, Dietary Guidelines for Americans, 2025 to 2030, January 2026cdn.realfood.gov
- USDA SR Legacy, dates, medjool (FDC 168191), via nutritionvalue.orgnutritionvalue.org
- USDA SR Legacy, mangos, raw (FDC 169910), via nutritionvalue.orgnutritionvalue.org
- US Food and Drug Administration, Daily Value on the Nutrition and Supplement Facts labelsfda.gov
