Nigeria, April 20 -- Everywhere you turn in the modern health marketplace, there is always some miracle herb, packaged as tablets, capsules, or powders, carrying the familiar promise to boost metabolism. The phrase also appears in fitness advertisements, diet plans, and wellness blogs, even by nutrition science writers, and it is repeated so often that it begins to feel like a basic truth rather than a marketing idea. Somewhere in the background is always the same suggestion that metabolism is a kind of internal engine sitting quietly, waiting for someone to press the accelerator and bring it to life.

It is an appealing idea, especially in a world where many people feel tired, stuck, or frustrated with their health. The promise that som...