In the years following World War II, physicians in the U.S. and Europe noticed a surprising phenomenon: rates of heart attack and stroke fell dramatically in many places. Autopsies from this period also revealed reduced rates of atherosclerosis, which is a buildup of fatty arterial plaques that causes cardiovascular disease.

At first, experts were perplexed. But as time passed, many concluded that wartime food deprivations and the forced shifts in people’s diets—namely, big reductions in the consumption of red meat and other animal products—contributed to the heart-health improvements. Later work, particularly the famous Framingham Heart Study, helped establish that blood cholesterol levels, driven in large part by a person’s diet, tended to overlap closely…