Definition of Protein

1. Atrial Fibrillation Slideshow Pictures
2. Bad Bugs and Their Bites Slideshow
3. Understanding Ulcerative Colitis Slideshow

Protein: One of the three nutrients used as energy sources (calories) by the body. Proteins are essential components of the muscle, skin, and bones. Proteins and carbohydrates each provide 4 calories of energy per gram, whereas fats provide 9 calories per gram.