Which research question would most directly address the uncertainty that high protein intake may displace other important nutrients at the population level?

• A. Do all proteins from animal sources provide identical amino acid profiles and health effects without considering total caloric context, as determined by theoretical nutrient composition tables only?
• B. Does a long-term diet that provides protein at 40% of calories, compared with one at 20% while holding total energy constant, lead to measurable reductions in dietary fiber, calcium, and certain micronutrients and corresponding negative health outcomes over 3 years in healthy adults?
• C. Are people who prefer meat-based diets more likely to exercise, based solely on a one-time questionnaire about food likes and gym membership?
• D. Does acute ingestion of a high-protein meal increase immediate satiety compared with a high-sugar beverage, as measured by subjective appetite ratings over 2 hours?

Answer: (B)