What percentage of a diet should be protein?

• A. 30
• B. 15
• C. 10
• D. 5

Answer: (B)

Protein should contribute about 15% of daily energy. This target balances providing enough essential amino acids for growth, maintenance, and repair with leaving sufficient energy for carbohydrates and fats. In practical terms, a 2000 kcal/day diet aiming for 15% from protein would allocate about 300 kcal to protein, which is roughly 75 g (since protein provides about 4 kcal per gram). This aligns with the common guideline of roughly 0.75–0.8 g of protein per kilogram of body weight for adults, translating to around 11–15% of energy depending on body size. The other options would either exceed typical energy distribution or fall short of meeting protein needs for maintenance in most adults, so 15% is the best target.