Packing for Mars: The Curious Science of Life in the Void

by Mary Roach

IRONICALLY, IF YOU wanted to minimize an astronaut’s “residue,” you could have fed him exactly what he wanted: a steak. Animal protein and fat have the highest digestibility of any foods on Earth. The better the cut, the more thoroughly the meat is digested and absorbed—to the point where there’s almost nothing to egest (opposite of ingest). “For high-quality beef, pork, chicken, or fish, digestibility is about ninety percent,” says George Fahey, professor of animal and nutritional sciences at the University of Illinois at Urbana-Champaign. Fats are around 94 percent digestible. A 10-ounce sirloin steak generates but a single ounce of, as they say in George Fahey’s lab, egesta.* Best of all: the egg. “Few foods,” writes Franz J. Ingelfinger, a panelist at the 1964 Conference on Nutrition in Space and Related Waste Problems, “are digested and assimilated as completely as a hard-boiled egg.”