Which of the following statements correctly contrasts experimental clinical trials with observational studies in nutrition?

• A. Clinical trials manipulate exposure through random assignment and can support causal inference, while observational studies only observe naturally occurring exposures and generally show associations, not causation
• B. Observational studies always provide stronger causal evidence than randomized trials because they reflect real-world behavior without researcher interference
• C. Clinical trials and observational studies are identical; both randomly assign exposures and therefore both equally demonstrate causation
• D. Clinical trials are used only in laboratory animals and cannot be applied to human nutritional questions, whereas observational studies are the only human-friendly approach

Answer: (A)