Protein Say: PRO-teen Protein builds, maintains, and replaces the tissues in your body. (Not the tissues you blow your nose in! We mean the stuff your body's made up of.) Your muscles, your organs, and your immune system are made up mostly of protein. You'll find protein in lots of yummy foods like eggs, nuts, beans, fish, meat, and milk. Back to Articles Related Articles Vitamins How vital are vitamins? Find out in this article for kids. Read More Your Digestive System The digestive system breaks down the food you eat. Learn how in this article for kids. Read More Your Immune System The immune system keeps you healthy. How does it work? Find out in this article for kids. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.