# How Smoothie Ingredients Affect Nutrient Absorption
Flavan-3-ols are beneficial compounds found in fruits and vegetables that may improve health. Many people do not eat enough fruits and vegetables, so smoothies have become a popular way to increase intake of these important foods. However, this study found that certain fruits used in smoothies can actually reduce how much of these beneficial compounds the body absorbs.
The problem involves an enzyme called polyphenol oxidase, or PPO. Some fruits have high levels of PPO activity, which can break down flavan-3-ols before or after they enter the digestive system. This affects bioavailability, meaning how much of a nutrient actually gets absorbed into the bloodstream and becomes available for the body to use.
Researchers conducted a controlled experiment where eight healthy male participants consumed flavan-3-ols in three different ways. This was a crossover study, meaning each person tried all three options at different times. The study was single-blinded, so participants did not know which version they were receiving. One group took capsules containing flavan-3-ols as the control condition. Another consumed a banana-based smoothie with high PPO activity, and a third drank a mixed berry smoothie with low PPO activity.
The results showed a strong correlation between PPO levels and absorption. The capsule and low-PPO berry smoothie produced similar blood levels of flavan-3-ol metabolites, reaching about 680 nanomoles per liter. However, the high-PPO banana smoothie resulted in levels 84% lower, at only 96 nanomoles per liter.
In a follow-up study with 11 participants, flavan-3-ols were added to banana smoothies just before drinking to prevent mixing beforehand. Absorption was still reduced, suggesting PPO continues breaking down compounds even inside the stomach after consumption.
The researchers tested 18 different plant products and found substantial variation in PPO activity levels. These findings have important implications for dietary recommendations and food preparation methods at home and in commercial settings.