Plant-based meat substitutes taste and chew remarkably similar to real beef, and the 13 items listed on their nutrition labels—vitamins, fats and protein—make them seem essentially equivalent. But a Duke University research team's deeper examination of the nutritional content of plant-based meat alternatives, using a sophisticated tool of the science known as "metabolomics," shows they're as different as plants and animals. Meat-substitute manufacturers have gone to great lengths to make the plant-based product as meaty as possible, including adding leghemoglobin, an iron-carrying molecule from soy, and red beet, berries and carrot extracts to simulate bloodiness. The texture of near-meat is...