Yoshinori Ohsumi, a Japanese cell biologist, was awarded the Nobel Prize in Physiology or Medicine on Monday for his discoveries on how cells recycle their content, a process known as autophagy, a Greek term for “self-eating,” reports The New York Times.

It’s a crucial process. During starvation, cells break down proteins and nonessential components and reuse them for energy. Cells also use autophagy to destroy invading viruses and bacteria, sending them off for recycling. And cells use autophagy to get rid of damaged structures. The process is thought to go awry in cancer, infectious diseases, immunological diseases and neurodegenerative disorders. Disruptions in autophagy are also thought to play a role in aging.

But little was known about how autophagy happens, what genes were involved, or its role in disease and normal development until the early 1990s, when Dr. Ohsumi began studying the process in baker’s yeast.

Why did he win?

The process he studies is critical for cells to survive and to stay healthy. The autophagy genes and the metabolic pathways he discovered in yeast are used by higher organisms, including humans. And mutations in those genes can cause disease. His work led to a new field and inspired hundreds of researchers around the world to study the process and opened a new area of inquiry.

Who is he?

Dr. Ohsumi, who was born in 1945 in Fukuoka, Japan, and received a Ph.D. from the University of Tokyo in 1974, floundered at first, trying to find his way. He started out in chemistry but decided it was too established a field with few opportunities.

So he switched to molecular biology. But his Ph.D. thesis was unimpressive, and he could not find a job. His adviser suggested a postdoctoral position at Rockefeller University in New York, where he was to study in vitro fertilization in mice.

“I grew very frustrated,” he told the Journal of Cell Biology in 2012. He switched to studying the duplication of DNA in yeast. That work led him to a junior professor position at the University of Tokyo where he picked up a microscope and started peering at sacks in yeast where cell components are degraded — work that eventually brought him, at age 43, to the discoveries that the Nobel Assembly recognized on Monday. Dr. Ohsumi later moved to the National Institute for Basic Biology, in Okazaki, and since 2009, he has been a professor at the Tokyo Institute of Technology.

“All I can say is, it’s such an honor,” Dr. Ohsumi told reporters at the Tokyo Institute of Technology after learning he had been awarded the Nobel, according to the Japanese broadcaster NHK. “I’d like to tell young people that not all can be successful in science, but it’s important to rise to the challenge.”

What’s he like?

“He is a quiet man,” said Dr. Beth Levine, director of autophagy research at the University of Texas Southwestern Medical Center in Dallas. But he also is quietly daring.

“Unfortunately, these days, at least in Japan, young scientists want to get a stable job, so they are afraid to take risks,” he told the Journal of Cell Biology. “Most people decide to work on the most popular field because they think that is the easiest way to get a paper published.”

As for himself, he said: “I am not very competitive, so I always look for a new subject to study, even if it is not so popular. If you start from some sort of basic, new observation, you will have plenty to work on.”

Dr. Ohsumi’s Nobel Prize “was inevitable,” Dr. Levine said. Dr. Ohsumi, she said, “is venerated in the autophagy field.”

The Japanese prime minister, Shinzo Abe, called Dr. Ohsumi to congratulate him, saying “your research gave light to the people who suffer from serious diseases.”

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With announcements of this year’s Nobel Prizes set to kick off on Monday, here is how eight past winners got the word.

Speculation had it that the Nobel would go to researchers whose work was instrumental in developing new treatments that unleash the immune system to attack cancer cells. The list is long. Front-runners had included James P. Allison at the University of Texas M.D. Anderson Cancer Center; Craig B. Thompson of Memorial Sloan Kettering Cancer Center in New York; Gordon J. Freeman of Dana-Farber Cancer Institute; and Tasuku Honjo of Kyoto University. Another scientist often mentioned as a Nobel contender is Jeffrey Bluestone of the University of California, San Francisco, who works on the immune system in disorders in which it attacks normal cells.