You are designing a 12-week randomized controlled trial to test whether a psyllium supplement reduces LDL-cholesterol compared with placebo. Which study design element combination best synthesizes physiological understanding and methodological rigor?

• A. Double-blind, placebo-controlled randomization; daily psyllium dose known to form viscous gel; standardized background diet low in other viscous soluble fibers; primary outcome LDL measured fasting at baseline and 12 weeks; control for weight and statin use in analysis.
• B. Single-arm observational study giving psyllium to all participants for 12 months with LDL measured at the end and historical controls used for comparison, with no randomization or blinding.
• C. Crossover study with one day of psyllium and one day of placebo separated by one week, measuring immediate postprandial LDL and HDL to capture rapid cholesterol-lowering effects of viscous fibers.
• D. Open-label trial where participants choose psyllium or placebo; no dietary standardization; primary outcome change in self-reported satiety; no baseline lipid measurement required.

Answer: (A)