In the last couple of decades, scientists have discovered more reasons (beyond vitamins and fiber) to pack your diet with fruits and vegetables: phytochemicals. All plants contain these compounds, which protect them from a variety of dangers—from harmful UV rays to predatory pests. We take in phytochemicals when we eat fruits and vegetables and, as it turns out, they protect us too. Some act as antioxidants, mopping up unstable “free radical” molecules that can damage cells and lead to the development of heart disease, cancer, Alzheimer’s and other health issues. Others work by boosting the immune system.