If tasked to design a randomized controlled trial to test whether a high-phytochemical diet reduces systemic inflammation, which feature is most essential to strengthen causal inference?

• A. Recruiting participants and asking them to self-report their diet once at the end of the trial while using subjective wellness surveys as the only outcome measure to capture the broadest range of effects.
• B. Random assignment of participants to a well-defined whole-food dietary pattern high in diverse phytochemical-rich foods versus a control diet matched for macronutrients and energy, with objective inflammatory biomarkers measured longitudinally and adherence monitored by biomarkers.
• C. Using a single phytochemical supplement given at very high doses without matching macronutrient content, because isolating one compound is always superior to testing whole-diet patterns for making dietary recommendations.
• D. Selection of only participants who already have the lowest baseline inflammation and allowing them to choose whether to eat phytochemical-rich foods so that uptake is voluntary and more naturalistic.

Answer: (B)