Ancel Keys, the University of Minnesota scientist who invented the K ration diet used by soldiers in World War II and who linked high cholesterol and fatty diets to heart disease, has died at the age of 100.

He died Saturday of natural causes at a Minneapolis assisted-living apartment he shared with his wife, Margaret.

Keys was a professor of physiology at the university from 1936 to 1972.

He demonstrated, through a landmark study on the eating habits of Minnesota businessmen in the 1950s, how fatty diets were linked to heart attacks. And he popularized the so-called Mediterranean diet, heavy on fruits and vegetables, light on fat and meat, with a touch of wine on the side.

His findings appeared in the 1959 best seller "Eat Well and Stay Well," which he wrote with his wife, and which led to his appearance on the cover of Time magazine in 1961.

Daughter Carrie D'Andrea of Bloomington said her father's attention to his diet was key to his longevity.

"Oh, that is why he lived so long," she said.

Colleagues recalled Keys as a demanding scientist who fought to win acceptance for work now viewed as groundbreaking. His belief that a person's diet and smoking habits could predict future health was "somewhat heretical" for his time, said Dr. Russell Luepker, Mayo professor of public health at the university.

He was an "incredible, detail-oriented, compulsive guy, and good scientists need to be that way," Luepker said. "You always knew where the guy stood. Some would say he was gruff and intolerant. He was intolerant of poorly done research."

Keys was born in Colorado Springs, Colo., and was an adventurous child. He worked in a lumber camp, shoveled bat droppings in an Arizona cave and mined for gold in Colorado, all before finishing high school. He enrolled at the University of California, Berkeley, in 1922, but took time off to sail to China as a crewman aboard the liner President Wilson.

He returned to college, earning a bachelor's degree in economics and political science and a master's degree in zoology at the University of California. By 1930 he had a Ph.D. in oceanography and biology from the Scripps Institute of Oceanography in La Jolla, Calif.

But his career didn't take shape until he went to Copenhagen to work with Nobel Prize winner August Krogh, a physiologist — someone who studies bodily processes and function. Inspired, Keys earned a second Ph.D. in physiology from Cambridge University in England and became an instructor at Harvard University.

In 1935 he launched his first exotic study, on the effects of high altitude on the human body. The next year he was lured to the University of Minnesota, where he began studying the physical differences between athletes and nonathletes.

Eventually he built his lab beneath the university's Memorial Stadium.

In 1941, Keys was asked to help develop an Army ration that soldiers could carry in combat. He purchased supplies, such as hard biscuits, dry sausage and chocolate bars, at a Minneapolis market. When the Army mass-produced the packages, he was surprised to see them marked with the letter K, for Keys. The K ration was born.

During World War II he also served as a special assistant to the secretary of war.

Afterward, Keys conducted one of his most famous studies, the Minnesota Starvation Experiment. He fed 36 volunteers a "semistarvation" diet, mirroring the conditions found in occupied Europe. The men lost an average of 25 percent of their weight, and Keys found that their hearts shrank, endurance fell and personalities changed. The study, he concluded, held a powerful lesson for those in charge of rebuilding postwar Europe: "Starved people cannot be taught democracy."

  Keys also noted that deaths from heart disease dropped dramatically in countries where food supplies had run short during the war. And he started looking for the connection.

He found his answer through a study of 286 middle-aged businessmen from Minneapolis and St. Paul that began in 1946. He concluded that those who suffered heart attacks had high levels of cholesterol in their bloodstreams. And he pinned that on their high-fat diets.

In addition to his wife and daughter, he is survived by his son Henry, eight grandchildren and six great-grandchildren. Another daughter, Martha Keys, was shot and killed by robbers in Jamaica in 1991.

A memorial service is scheduled for 11 a.m. Dec. 4 at Washburn-McReavy Funeral Home in Edina.