Americans may love to eat junk, but we’re nearly as passionate about doing penance, with more than half of us scarfing down dietary supplements on a regular basis. From herbal remedies to energy boosters, vitamins and weight-loss pills, supplements form a massive global industry — one that’s expected to reach $200 billion in value by 2025, according to the AMA Journal of Ethics. Trouble is, it’s a largely “Wild West” scene — and that’s by design, believe it or not. The Dietary Supplement Health and Education Act of 1994 limits the ability of the Food and Drug Administration to regulate...