The food group highest in protein content includes animal-based sources such as meat, fish, eggs, and dairy products. These foods provide complete proteins, meaning they contain all essential amino acids necessary for muscle repair and growth. Additionally, certain plant-based sources like legumes, nuts, and seeds also offer significant protein levels, although they may lack one or more essential amino acids and can be categorized as incomplete proteins. Incorporating both animal and plant sources can help ensure an adequate protein intake for various dietary preferences.