Researchers suggest that blending certain ingredients in smoothies can influence whether your body is getting a nutritional boost. The study used smoothies to test how various levels of polyphenol oxidase, an enzyme in many fruits and vegetables, affects the levels of flavanols in food to be absorbed by the body. Flavanols are a group of bioactive compounds that are good for your heart and cognitive health and are naturally found in apples, pears, blueberries, blackberries, grapes and cocoa—common smoothie ingredients. Slice an apple or peel a banana and the fruit will quickly turn brown. That happens because of polyphenol oxidase,...