How was daily protein amount historically determined?

• A. Nitrogen balance studies
• B. Hormone assays
• C. Calorie counting
• D. Growth charts

Answer: (A)

Nitrogen balance studies are used to determine daily protein needs. Since protein contains nitrogen, researchers compare how much nitrogen a person consumes (from protein in the diet) with how much nitrogen is excreted (primarily in urine, and also in feces and other losses). When intake equals losses, nitrogen balance is zero, indicating the current protein intake supports maintenance. By adjusting intake and observing balance across individuals or groups, scientists estimate the amount of protein required to meet daily needs. This approach directly targets protein requirements, unlike hormone assays (which measure endocrine signals), calorie counting (which tracks energy, not protein), or growth charts (which monitor growth outcomes rather than nutrient adequacy).