Written by Joe Cannon, MS. Smoothies are a staple for many looking to lead a healthy lifestyle. Combined with other fruits, vegetables, and protein powders, they offer a quick and convenient way to boost your nutrition. Bananas, in particular, are a popular ingredient in smoothies because of their natural sweetness and creamy texture. However, research suggests that banana smoothies might not be as beneficial as you think, especially if you want to maximize the health benefits of phytonutrients such as those found in green tea, cocoa, and blueberries.
The Appeal of Bananas in Smoothies
Bananas add a rich, creamy texture that can turn a basic recipe into a satisfying meal replacement. Their natural sweetness means you can often skip adding extra sugar or sweeteners, making your smoothie healthier. Bananas are also packed with essential nutrients like potassium and dietary fiber, which are important for staying healthy.
Understanding Polyphenol Oxidase (PPO) in Bananas
An enzyme called polyphenol oxidase is the heart of why bananas might not always be the best choice for your smoothie. This enzyme is responsible for bananas' browning when exposed to air and when you slice them. Yes, brown bananas may taste better because they contain more sugar, but there is a potentially more important reason to avoid them.
What is Polyphenol Oxidase (PPO)?
When banana cells are damaged—such as when blended—the PPO enzyme breaks down polyphenols and appears to impact the nutritional
content of the other ingredients in your smoothie.
How Polyphenol Oxidase Interacts with Other Ingredients
The activity of PPO can reduce the bioavailability of certain nutrients, particularly antioxidants like flavonoids, found in other smoothie ingredients. This means that even if your smoothie is teeming with nutrient-rich foods, the presence of bananas could diminish the effectiveness of those nutrients.
The Impact of PPO on Flavonols
One of the most significant findings from the research is how bananas affect epicatechin flavonols in cocoa. Epicatechin is an antioxidant compound in cocoa, green tea, and apples, to name a few. Epicatechin is related to epigallocatechin gallate (EGCG), a potent antioxidant in green tea believed to play a vital role in many of the tea's health benefits, including reducing the risk of heart disease and cancer and managing cholesterol levels.
The Research Findings
A study involving healthy men revealed that when a ripe, frozen banana was added to a berry smoothie containing cocoa, the bioavailability of cocoa epicatechin flavonols was reduced by about 84%. In other words, only 16% of the flavonols were absorbed! This surprising side effect did not occur when a blended mixed berry smoothie consisting of blueberries, strawberries, blackberries, raspberries, and cocoa was consumed.
Additionally, this detrimental effect occurred rapidly, within just 1 hour after consuming the banana smoothie.
Furthermore, when the men were given the berry smoothie and banana smoothie in separate drinks, there was a 37% reduction in epicatechin metabolites compared to when they consumed just the berry smoothie.
This means that nearly all of the health benefits of epicatechin are lost when bananas are used in smoothies. This significant reduction is attributed to bananas' polyphenol oxidase activity, which breaks down polyphenols, rendering them less effective.
Why This Matters To You
This interaction is critical for those who drink smoothies to improve their health. If your goal is to consume smoothies because of the antioxidant and phytonutrient benefits, adding bananas could be counterproductive.
Other Nutritional Concerns
The effect of bananas on flavonols is one example of how bananas may interfere with absorbing other nutrients in your smoothie. The activity of PPO may also impact the availability of other antioxidants, vitamins, and minerals.
Possible Interference with Nutrient Absorption
Bananas could potentially affect the absorption of:
- Vitamin C. Vitamin C could be partially oxidized by PPO, reducing its effectiveness.
- Other Flavonoids. Similar to epicatechin, other flavonols present in fruits like berries could also be affected by the presence of bananas.
- Iron. PPO can also interact with non-heme iron, making it less absorbable by the body.
These interactions suggest that while bananas are nutrient-rich, depending on the combination, they could diminish the health benefits of other ingredients in your smoothie.
This interaction with the PPO enzyme may also reflect a heretofore unrecognized problem for processed, ready-to-drink smoothie beverages purchased from local health food stores and supermarkets.
Problems With The Banana Polyphenol Study
- It was a small clinical trial that consisted of less than 20 individuals.
- All the participants were men.
- The study was not double-blinded.
- The frozen banana used in the smoothies weighed 6.2 oz (177 g), which is more than the typical 150-170 grams. What happens if a smaller banana is used instead?
- Does polyphenol oxidase reduce the bioavailability of other polyphenols such as quercetin, resveratrol, or ellagic acid?
Additionally, some researchers were employees or associated with the Mars Inc. food and nutrition company.
What Foods Besides Bananas Contain the PPO Enzyme?
As you can see from this table, some very healthy foods also contain polyphenol oxidase.
| PPO Activity (KU/100g (3.5 oz) | |
| Bananas | 3,258 |
| Beetroot greens | 1594 |
| Red delicious apples | 570 |
| Pears | 147 |
| Beets | 94 |
| Peaches | 41 |
| Avocado | 24 |
| Strawberries | 18 |
| Wheatgrass | 15 |
| Blueberries | 12 |
Source: Impact of polyphenol oxidize on by availability of flavan-3-ols in fruit smoothies: a controlled single blinded crossover study.
The amounts are approximate and expressed in kilo units (KU), which refers to the amount of the PPO enzyme in each food's 3.5 oz (100 g). Surprisingly -and ironically-even blueberries contain some PPO, although the amount is far less than found in bananas.
Alternatives to Bananas in Smoothies
Given the potential downsides of using bananas in smoothies, what alternatives exist that can provide similar benefits without the negative impact on nutrient absorption? Here are some options that can keep your smoothies creamy, sweet, and nutrient-packed
Creamy Substitutes
Avocados. While avocados also contain the PPO enzyme, it is far less than found in bananas. Avocados also have healthy monounsaturated fats.
Greek Yogurt. Greek yogurt adds creaminess and protein to your smoothie, helping you stay full longer.
Tofu. Tofu provides creaminess and a protein boost without affecting other nutrients.
When It’s Okay to Use Bananas
Despite the concerns, there are still scenarios where using bananas in your smoothie might be perfectly fine. For example, bananas can still be a healthy choice if you focus on energy and flavor rather than maximizing antioxidant intake.
Post-Workout Smoothies
After a workout, your body needs quick carbohydrates to replenish glycogen stores and support muscle recovery. Bananas can be ideal for post-exercise smoothies.
Smoothies for Weight Gain
Bananas are an efficient way to boost calorie intake for those looking to gain weight or add calories to their diet.
Take Home Message
The presence of PPO in bananas seems to reduce the bioavailability of cocoa flavonols significantly. While this raises intriguing questions about the fate of other phytonutrients, the research does not suggest that banana smoothies increase disease risk. For those looking to maximize the benefits of plant bioactive compounds, consuming bananas and smoothies several hours apart may be beneficial.
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