A placebo is an inert substance or treatment, such as a sugar pill identical in appearance to a drug, used as a control in clinical trials. Neither the participants nor, in double-blind designs, the researchers know who receives the active treatment, so any difference in outcome can be attributed to the treatment rather than expectation. The placebo effect itself, real physiological improvement driven by belief, conditioning, and the care context, is a genuine phenomenon that complicates nutrition research: people given placebo supplements often report better energy or digestion. In food and nutrition trials, designing credible placebos is challenging, since foods have obvious sensory properties; researchers use matched control products differing only in the active component. The randomised placebo-controlled trial remains the gold standard for proving that a nutrient, supplement, or functional food actually works.