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The science behind a smoothie: The ingredients you choose makes a difference

Smoothies have become a popular choice for those seeking a quick and delicious way to consume the fruits and vegetables essential for a healthy diet. But could your go-to banana-blueberry blend actually be shortchanging you nutritionally? 

A new study from UC Davis has revealed that the mix of ingredients you throw into your blender is more crucial than you think in determining the nutritional output of your smoothie.

The power of flavanols

The study hinges on understanding flavanols, a class of bioactive compounds found in several fruits and vegetables like apples, blueberries, blackberries, grapes, pears, and even cocoa. 

Previous research has shown that flavanols benefit heart and cognitive health, positioning them as crucial dietary components. 

The UC Davis researchers aimed to investigate how these important compounds fare when included in smoothies, a widely popular dietary staple.

Study lead author Javier Ottaviani is the director of the Core Laboratory of Mars Edge and an adjunct researcher with the UC Davis Department of Nutrition.

“We sought to understand, on a very practical level, how a common food and food preparation like a banana-based smoothie could affect the availability of flavanols to be absorbed after intake,” said Ottaviani.

Focus of the study

When you slice an apple or peel a banana, you often see the exposed flesh of the fruit turning brown. This browning is due to the action of an enzyme known as polyphenol oxidase (PPO), which is naturally found in many fruits and vegetables. 

When these PPO-rich foods are cut, bruised, or exposed to air, the enzyme triggers the browning process. The UC Davis researchers were particularly interested in understanding whether this enzyme impacts the absorption of flavanols when consumed in smoothies.

How the research was conducted 

The researchers administered two types of smoothies to participants: one containing bananas, which are naturally high in PPO activity, and another made from mixed berries with low PPO activity. 

Blood and urine samples were taken and analyzed to measure the absorption of flavanols after the smoothies were ingested. Participants also consumed a flavanol capsule as a control.

What the researchers discovered 

The experts found that those who consumed the banana smoothie had a staggering 84% lower absorption of flavanols in comparison to the control group.

“We were really surprised to see how quickly adding a single banana decreased the level of flavanols in the smoothie and the levels of flavanol absorbed in the body,” said Ottaviani. “This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods.”

Study recommendations 

Last year, the Academy of Nutrition and Dietetics emphasized the importance of consuming between 400 to 600 milligrams of flavanols per day for cardiometabolic health. 

Based on the findings, Ottaviani suggests that people who aim to meet these flavanol intake recommendations should consider combining flavanol-rich fruits like berries with other low-PPO ingredients like oranges, pineapples, mangoes, or yogurt.

Ottaviani assures that bananas are still an excellent fruit to consume or include in smoothies. However, if the goal is to maximize flavanol absorption, it may be best not to combine bananas with flavanol-rich fruits like berries.

Future research 

The study opens up intriguing avenues for future research, exploring how the preparation of other foods might impact the availability of flavanols. 

Ottaviani noted that tea is a major dietary source of flavanols, and depending on how it is prepared, a different amount of flavanols would be available for absorption.

“This is certainly an area that deserves more attention in the field of polyphenols and bioactive compounds in general,” said Ottaviani.

The study is published in the Royal Society of Chemistry’s journal Food and Function.

Healthy smoothie ideas

  • Green smoothie: Spinach, banana, almond milk, and a dash of honey.
  • Berry blast: Mixed berries, Greek yogurt, and a splash of orange juice.
  • Tropical twist: Mango, pineapple, coconut water, and a bit of lime juice.
  • Protein power: Vanilla protein powder, almond milk, banana, and peanut butter.
  • Antioxidant boost: Blueberries, pomegranate juice, chia seeds, and a small banana.
  • Spiced up: Carrot, ginger, orange, and a sprinkle of cinnamon.
  • Chocolate avocado: Unsweetened cocoa powder, avocado, banana, and almond milk.
  • Morning coffee: Cold brew coffee, banana, oats, and almond milk.
  • Nutty banana: Almond milk, banana, and a scoop of almond or cashew butter.
  • Veggie delight: Kale, cucumber, apple, and lemon juice.


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