The primary ingredient in a traditional lentil soup is lentils. These small, lens-shaped legumes come in various colors, including brown, green, and red, and are known for their high nutritional value. Lentils are an excellent source of protein, dietary fiber, and essential vitamins and minerals, making them a staple in many vegetarian and vegan dishes. Traditional lentil soup often features a combination of lentils, vegetables like carrots and onions, herbs, and spices for added flavor. It's a comforting, hearty dish enjoyed worldwide, known for its warming qualities and health benefits.