Which nutrient is primarily found in animal products but can also be sourced from plants?

Protein is primarily found in animal products such as meat, dairy, and eggs, which are complete sources of protein containing all nine essential amino acids. However, various plant-based foods can also provide protein, albeit often in incomplete forms. Foods such as legumes (like beans and lentils), nuts, seeds, and whole grains offer protein, but they may not contain all essential amino acids in the quantities found in animal sources. This makes protein unique among the choices presented, as it is a nutrient that can be obtained from both animal and plant-based sources.

In contrast, while vitamins and minerals can also be found in both animal and plant products, many vitamins are more readily absorbed from animal sources, and some minerals (like iron and zinc) may be in forms that are less bioavailable in plants. Carbohydrates are primarily found in plant foods such as fruits, vegetables, grains, and legumes, making them less relevant for this question regarding animal products. Thus, protein stands out as the nutrient that has significant presence in animal products while still being accessible from various plant sources.