Ancel Keys was born on January 26, 1904 in Colorado Springs. He had many jobs to support himself before becoming a renowned physiologist. As a boy he worked in a lumber camp for a while, and then shovelled bat guano in an Arizona cave. He served as a powder monkey in a Colorado gold mine and later as a clerk in a Woolworth store. In 1939 he married Margaret, a biochemist and they would go on to work together studying physiology (functions of living organisms) and nutrition.

Keys' initial work led him to study how the human body reacts to starvation. He had also been performing blood tests on himself in the Andes Mountains to see how the body reacts to high altitudes. The War Department heard about his work and asked him to develop pocket-size food rations for World War II paratroopers. This led to the legendary K rations (K for Keys) that were given to hundreds of thousands of American troops. There were many complaints from the soldiers about the small nutrition-packed meals. But some others were quite thankful, like the 25 soldiers who survived for 10 days in a half-submerged transport plane with nothing but 25 K rations and a gallon of water.

After the War, Ancel Keys began his landmark research study, the Seven Countries study. This work followed 12,000 healthy middle-aged men living in Italy, the Greek Islands, Yugoslavia, the Netherlands, Finland, Japan and the United States and led Keys to discover that saturated fats were a major cause of heart attacks. He determined that a Mediterranean diet, rich in fruits and vegetables, pasta, bread and olive oil was highly protective against heart disease. In Finland and the United States, which eat a lot of animal fats (in Finland it is common to spread butter on cheese!), the rate of heart attack was about 10 times higher. Following this discovery, Keys made it his mission to encourage people to eat less saturated fat, lower their cholesterol and prevent heart attacks. He became so well known that he once said, "There's a little hotel in Brussels that my wife and I stop at now and then, and every time I go in there the maitre d', a lady in her sixties, says, 'Ah, Monsieur Cholesterol!'"

Ancel Keys died November 20, 2004. He was 100 at the time of his death and had remained intellectually active through his 97th year. He and his wife spent much of their later years in Naples.