Banana reduces polyphenol absorption in fruit smoothies

8 min read – fact checked

Smoothies are often seen as an easy, delicious way to pack in nutrients and functional compounds known as polyphenols, especially those from fruits and vegetables. But a growing body of research shows that what you mix together in a smoothie may influence how many of those beneficial functional compounds your body actually absorbs, which can then influence the extent of their beneficial effects on human health. A recent study in humans [1] published in Food & Function Royal Society of Chemistry (fig.1), has brought attention to a surprising factor, an enzyme found naturally in some fruits that may break down polyphenols before you drink them.

What did the study look at?
Researchers investigated whether polyphenol oxidase (PPO), an enzyme responsible for browning in fruits like apples and bananas, could reduce the absorption of flavan-3-ols, a group of ‘polyphenols’ which when consumed regularly, is strongly linked to improved cardiovascular and metabolic health outcomes [1–3].

Methodology of the study
The study consisted of a cross-over, single-masked (researchers analysing data), controlled, and single acute intake trial, in the course of which participants were asked to consume the two different flavan-3-ol containing smoothies and a flavan-3-ol containing capsule on different days. The study was divided in to two parts, study 1, and study 2.

For study part 1, volunteers were asked to consume two different fruit smoothies with different PPO activities as detailed below.

1) A capsule
2) A berry smoothie (low PPO activity)
3) A banana smoothie (high PPO activity)

The banana smoothie was prepared with 177 g of ripe, frozen bananas and 240 g of almond milk. The mixed berry smoothie was prepared with 50 g each of strawberries, blueberries, blackberries and raspberries, 120 g of almond milk, 70 g of water, 105 g of crushed ice, and 95 g of yogurt.

For study part 2, test drinks resembled the composition of the banana-based smoothie used in study part 1 but prevented the exposure of the flavan-3-ol epicatechin with banana PPO prior to intake.The smoothies were prepared separately and consumed simultaneously by alternating sips from each drink.

Study outcomes
1) Capsules had the highest absorption, with participants showing high flavan-3-ol levels in the blood after taking capsules (fig.2).
2) Berry smoothies performed just as well. Berries contain very low PPO activity, so polyphenol availability stayed high as expected.
3) Banana smoothies significantly reduced absorption of polyphenols in the added fruits. The banana smoothie led to an 84% reduction in flavan-3-ol bioavailability compared with capsules and berry smoothies [1].

Why could this be?
This is because bananas naturally contain high PPO levels, which can oxidise flavan-3-ols during blending, making them harder for the body to absorb (fig.3).

Why Does This Matter?
Flavanols are natural compounds found in foods like cocoa, berries, apples and grapes. They’re part of a larger group of plant nutrients called polyphenols and are known for supporting heart and brain health. Research suggests that when consumed regularly, flavanols can help improve blood flow, support memory, reduce inflammation, improve blood vessel function [2,3], reduce cardiovascular risk [4], improve overall metabolic health and inflammation control [3]. However, If a smoothie preparation reduces their availability, some of those benefits may not be as efficacious, even if you’re using ‘healthy’ ingredients. This doesn’t mean bananas are unhealthy, it simply suggests that enzyme interactions between ingredients matter when your goal is maximising specific polyphenols.

Tips to get the most from your smoothies
Choose low-PPO fruits when maximising polyphenol availability, you can see a table of the PPO and polyphenol (epicatechin) content of various fruits and vegetables for your knowledge (fig.4). Great options: berries, mango, pineapple, citrus, kiwi, or beet greens. For context, . Drink smoothies soon after blending, the longer the smoothie sits (ie takeaway smoothies), the more time enzymes have to degrade polephenols.

Use bananas mindfully
Bananas are still a nutritious fruit, but the authors advised that if you enjoy banana smoothies, it may be best not to mix them with flavanol-heavy foods like berries, grapes, or cocoa, or just consume bananas separately some time before or after that smoothie. If your goal is flavan-3-ol absorption (e.g., adding cocoa, tea extract, or berries), consider using less banana or pairing banana with a Vitamin C-rich citrus, which lowers PPO activity, helps reduce oxidation and preserve polyphenols in food blends [5].

Limitations of the study
The study had several limitations that needs to be considered. Outcomes were observed as a result of a single day acute intake, thus it is possible that despite the reduced absorption of polyphenols with the addition of banana, that benefits of the remaining (absorbed) polyphenols, and that of the other functional compounds also present in the banana per se, may still be confer health benefits in the short and longer term.

It is worth noting that this study was conducted in male participants, thus representing another limitation of the study. While there is limited information regarding sex-based differences in flavan-3-ol absorption and metabolism, it is possible that the findings presented in this work are also relevant for women as the major effects mediated by PPO took place prior intake>

A further limitation of the study consisted in the addition of flavan-3-ols to fruit smoothies to standardized content of these bioactives. In this context, it is possible that the reactivity of PPO with added flavan-3-ols dissolved in the drink presents differences with flavan-3-ols intrinsically present in the fruit

Word of warning
Using banana, citrus or any of cocoa, tea extract, or berries may not suitable for person a wide variety of gastrointestinal conditions, so nuance and personalisation is required. This is where my knowledge in nutrition science and clinical training can help your personalise your food intake

Summary
Smoothies are still a nutritious, convenient way to increase fruit intake, but if you’re blending specifically to boost polyphenol levels, the choice of fruit matters. Berries may support polyphenol absorption, whilst bananas may reduce it because of high PPO activity. With a few simple ingredient swaps, you can enjoy your smoothie and maintain more of its health-boosting compounds.

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