India, Nov. 25 -- A new study from UC Davis has raised a practical question for anyone who blends fruit each morning. The research suggests that adding a banana to a smoothie can sharply reduce how much of certain heart-healthy nutrients the body takes in. The issue isn't sugar or calories. It's an enzyme.

The study was published in the Royal Society of Chemistry's journal Food and Function, and focused on flavanols - plant compounds linked to heart and brain health.

Flavanols are commonly found in cocoa, apples, grapes, berries, and other smoothie staples. Researchers wanted to see whether mixing fruits with different enzyme levels would change how much of those flavanols end up being absorbed.

Polyphenol oxidase, or PPO, became the c...