Sam Beattie, PhD Responds:

Plant seeds are made up of a variety of compounds, including some that may be good for you, such as polyphenols, a type of antioxidant. However, many plants, especially those related to the rose (apples, apricots, peaches, plums), contain compounds that can be toxic or that may react with enzymes during digestion and become chemically activated to form toxic compounds, including cyanide.

Apple seeds contain cyanide, but you can eat several seeds without getting ill. The amount of cyanide is small, especially if you don’t chew the seeds. They simply pass through the gut and are excreted. However, ground apple seeds contain enough cyanide to be deadly.

The seeds in dark red and purple grapes, on the other hand, contain resveratrol, an antioxidant compound that has been studied for its potential to slow cancer growth in animals. Human studies of resveratrol and cancer are under way.