A few months ago a 2023 study shocked banana lovers with the possibility that putting bananas in our smoothies would ruin their nutritional value. Is this true? In this article we will explain the study and whether its findings truly mean we have to skip the bananas in our next smoothie.
This is all about the Flavanols
Flavanols – often termed flavan-3-ols – are special compounds in fruits and veggies. They are really good for our health, as they render many health benefits. But it’s hard to get enough of them because most people don’t eat a lot of fruits and veggies every day.
Flavanol compounds include epicatechin and catechin among others.
Including flavanol-rich foods such as fruits, vegetables, tea, cocoa, and certain nuts in our diet contribute to better health and well-being. However, it’s essential to consume them as part of a varied and balanced diet rather than relying solely on one type of food or nutrient for health benefits.
Flavanols, which are a type of flavonoid, offer several potential health benefits:
1. Antioxidant Properties: Flavanols are powerful antioxidants, which means they help protect cells from damage caused by free radicals. This antioxidant activity may reduce the risk of chronic diseases such as cancer, heart disease, and neurodegenerative disorders.
2. Heart Health: Some research suggests that flavanols may help improve heart health by lowering blood pressure, improving blood flow, and reducing inflammation in the arteries. These effects can contribute to a lower risk of heart disease and stroke.
3. Improved Blood Sugar Regulation: Flavanols may play a role in improving insulin sensitivity and glucose metabolism, which can help regulate blood sugar levels. This benefit is particularly important for individuals with diabetes or those at risk of developing diabetes.
4. Brain Health: There is emerging evidence to suggest that flavanols may have neuroprotective effects and could help maintain cognitive function and reduce the risk of age-related cognitive decline, including conditions like Alzheimer’s disease.
5. Skin Health: Flavanols have been shown to protect the skin from UV damage, reduce inflammation, and improve skin elasticity. These effects can contribute to overall skin health and may help prevent premature aging and skin conditions like wrinkles and sunburn.
6. Anti-inflammatory Effects: Flavanols possess anti-inflammatory properties, which can help reduce inflammation throughout the body. Chronic inflammation is linked to various diseases, so reducing inflammation can have broad health benefits.
7. Weight Management: Some studies suggest that flavanols may aid in weight management by increasing fat oxidation and improving metabolism. Incorporating foods rich in flavanols into a balanced diet may support weight loss efforts.
The Academy of Nutrition and Dietetics issued a recommendation suggesting we eat 400–600 milligrams of flavanols each day to maintain our health.
What foods contain the highest levels of flavanols?
Foods that are high in flavanols include:
1. Fruits: Many fruits contain flavanols, with higher concentrations found in berries (such as strawberries, raspberries, blueberries, and blackberries), apples, grapes, cherries, and citrus fruits (such as oranges and grapefruits).
2. Vegetables: Certain vegetables also contain flavanols, including onions, kale, spinach, and broccoli.
3. Tea: Herbal tea, green tea and black tea, which contain high levels of flavanols called catechins.
4. Cocoa and Dark Chocolate: Cocoa beans and dark chocolate are rich sources of flavanols, specifically flavanols such as epicatechin and catechin.
5. Legumes: Beans, lentils, and peas are sources of flavanols, particularly catechins.
6. Nuts: Some nuts, such as almonds and walnuts, contain flavanols.
7. Seeds: Flaxseeds, sesame seeds, and sunflower seeds are sources of flavanols.
Incorporating a variety of these foods into our diet can help ensure we get a good intake of flavanols and other beneficial nutrients. Keep in mind that processing and cooking methods can affect the flavanol content of foods, with raw and minimally processed forms often retaining higher levels of these compounds.
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| Flavanols are good for you. |
So what is the issue with bananas and smoothies?
People often drink smoothies to try to get more fruits and veggies into their diet. However, some fruits used in smoothies contain an enzyme called polyphenol oxidase (PPO). This is a compound that causes some fruits to brown when the fruit pulp is left out.
PPO can apparently reduce levels of flavanols according to a recent study.
To test this, researchers from the University of California at Davis and the UK’s University of Reading did a study with healthy men in the fall of 2023. In this cross-over trial, the subjects drank a banana smoothie with high PPO (which means it has a lot of the enzyme). At another time they drank a mixed berry smoothie with low PPO levels. Then later they took the flavanols in a pill.
After each of these, their blood levels of flavanol byproducts were measured.
The researchers found that flavanol levels in their blood were highest after taking the pill or the low PPO smoothie. But after drinking the high PPO banana smoothie, the levels were much lower.
In another part of the study, they gave subjects the high PPO banana smoothie without letting it mix with their saliva first. Even then, the levels of flavanols in their blood were lower.
These investigations indicated that PPOs appear to reduce immediate flavanol bioavailability in the stomach and in the glass. When this happens, fewer flavanols are released into the blood.
The researchers also looked at the PPO levels in many different fruits and veggies. They found that PPO levels vary a lot.
So, in simple terms, if you eat or drink things with high PPO levels, there can be a reduced amount of immediate release of flavanols into the blood.
How the study has been misunderstood
This finding doesn’t mean that polyphenol oxidase necessarily reduce the overall availability of flavanols. Yes they did test the flavanol derivatives in the urine and blood for 24 hours. But they could not possibly test for all the different flavanol metabolites that are released gradually.
Indeed, the researchers appear to have missed is the effects of our intestinal bacteria (probiotics) on flavanols.
Let’s look a bit closer at the realities of flavanol assimilation.
Okay, so many of these PPO producing foods are pretty healthy in their own right. Bananas contain a number of important nutrients. For example, one medium banana can contain about 20% of our vitamin B6 daily needs, 17% of our vitamin C, and 8% of our magnesium requirements.
Bananas and other PPO-containing foods are some of the healthiest foods available. Avocados, apples, bananas, mushrooms, all have tremendous nutritional properties. What are we missing?
The reality is that bananas and these other PPO-producing foods are also tremendous prebiotics. They feed our gut bacteria.
What do prebiotics have to do with flavanols?
Well, other research has found that most flavanol absorption doesn’t take place immediately as assumed in this study of banana smoothies. A 2013 study from the UK’s University of Surrey found that over two-thirds of flavanols consumed will not pass directly into the bloodstream. They will be carried into the colon where intestinal bacteria will convert them into other health-promoting compounds such as phenylvalerolactones.
Some of these flavanol metabolites are released into the bloodstream gradually, and sometimes as needed. Furthermore, some of them will not be measurable in the urine and blood.
Yes, our probiotics help process the flavanols and prepare them for absorption into the bloodstream. Therefore, most of the flavanols are not even affected by the PPOs that exist in bananas and apples and so forth.
Curiously, our intestinal bacteria also utilize polyphenol oxidase. It helps facilitate adhesion within intestinal bacteria.
Indeed, a 2022 study found that polyphenol oxidase helps maintain something called “flavone synthase-like activity.” Basically, some of the bonds are changed and this produces another type of enzyme process.
This is likely part of the process that intestinal bacteria are involved in. Notably, bacteria thrive from the processes of browning. This is how they increase their fermentation activity. (Fermentation relates directly to bacteria growth.)
The bottom line is that the investigation is not over. It is quite easy to assume that the body just assimilates nutrients and releases them into the bloodstream. But this is not a complete picture of the digestive system and its complex array of intestinal bacteria.
As such, this UC-Davis study on bananas and berry smoothies cannot be accepted as enough information for us to stop mixing bananas with our smoothies.
Perhaps, if we are looking for an immediate rush of flavanols, we eat our bananas later. But because bananas and other PPO-rich foods are potent prebiotics, they are worth keeping in our smoothies.
These intestinal probiotics not only help convert flavanols into health-sustaining benefits. They also produce a number of other antioxidant compounds and immune-boosting compounds. And if they are helping produce healthy flavanols later on, we should not have a problem including bananas in our smoothies.
In order to test this banana-smoothie hypothesis accurately, the researcher needs to address and measure the effects of our intestinal probiotics. These intestinal probiotics are stimulated by special fibers in plant-based foods, one of them being bananas.
In the meantime we can enjoy our bananas in our smoothies. We can know those bananas will feed our intestinal bacteria. And we can get achieve substantial flavanols of different types within the coming days.
Now what about polyphenol oxidase?
Before we part, let’s discuss a little more about polyphenol oxidase containing foods.
Foods that are known to contain polyphenol oxidase (PPO) include:
1. Bananas: Bananas have high PPO content, particularly when they are ripe. This enzyme is responsible for the browning of bananas when they are exposed to air. Ripe bananas contain about 3250 KU of PPO per 100 grams.
2. Apples: Like bananas, apples also contain significant levels of PPO. When apples are cut or bruised, the enzyme is activated, leading to browning. But apples only contain about 570 KU of PPO per 100 grams.
3. Pears: Pears contain PPO, although typically in lower levels compared to bananas and apples. Like 147 KU per 100 grams.
4. Potatoes: Potatoes contain some PPO, which is why they tend to turn brown when they are cut and exposed to air.
5. Stone Fruits: Fruits like peaches, plums, and cherries also contain PPO, contributing to the browning reaction when these fruits are damaged or cut. But their PPO content is a fraction of bananas. For example, peaches contain about 41 KU per 100 grams of PPO.
6. Avocado: Avocado contains PPO, and the enzyme activity increases as the fruit ripens, leading to browning of the flesh when exposed to air. But avocado only contains about 24 KU of PPO per 100 grams. A fraction of bananas.
7. Mushrooms: Certain varieties of mushrooms contain PPO, which can contribute to browning when they are cut or bruised. But again, their levels are only a tiny fraction compared to bananas.
These foods may undergo enzymatic browning reactions when they are damaged, cut, or exposed to air due to the activity of polyphenol oxidase. While PPO is a natural enzyme found in many plant-based foods, its activity can be minimized through various methods such as blanching, acidification, or refrigeration.
Can we add something to our smoothie to block PPO?
This brings us to another point. That we can dramatically inhibit the action of PPOs in bananas and other foods, simply by adding a few other compounds to our smoothies:
Citric acid significantly reduces PPO enzyme action. Citric acid is derived from citrus fruits like oranges, lemons and pineapples. So we can add some of these to our smoothies to inhibit PPO activity.
Cysteine (amino acid) also reduces PPO activity.
Acetic acid also reduces PPOs according to the research.
So we can simply add some vitamin C, citrus and perhaps some apple cider vinegar to our smoothies to reduce PPO activity. We can also use less-ripe bananas, which will contain less PPOs.
The bottom line is that we can add banana to our smoothies without any guilt. Bananas that are a little green are probably better. And adding an orange or lemon, or even a little apple cider vinegar to our smoothie for good measure can help too.
Watch the video: https://youtu.be/T93OLHq3-ks?si=P-U2gYKuTd_ZAbYk
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