Not too long ago, Brian Wansink was one of the most respected food researchers in America.

He founded the Food and Brand Lab at Cornell University, where he won attention for studies that showed that small behavioral changes could influence eating patterns. He found that large plates lead people to eat more food because they make portions look smaller and that children eat more vegetables when they have colorful names like “power peas.” Dr. Wansink wrote best-selling books and published hundreds of studies. For over a year, he served in a top nutrition policy role at the Department of Agriculture under George W. Bush, where he helped shape the government’s influential Dietary Guidelines . His research even led the government to spend almost $20 million redesigning school cafeterias, an initiative known as the Smarter Lunchrooms Movement.

But this month, Dr. Wansink’s career at Cornell came to an unceremonious end. On Sept. 20, the university announced that a yearlong investigation had found that he committed “academic misconduct in his research and scholarship, including misreporting of research data,” and that he had tendered his resignation. The announcement came one day after the prestigious medical journal JAMA retracted six of Dr. Wansink’s studies because of questions about their “scientific validity.” Seven of his other papers had previously been retracted for similar reasons.

“I think the extent of misconduct that has occurred with this author is unique,” Dr. Howard Bauchner, JAMA’s editor in chief, said in an interview. “There are literally millions of authors, and there’s very few who have had numerous papers retracted.”

For more than a year, Dr. Wansink had been dogged by accusations that many of his studies were riddled with errors, data inconsistencies and evidence of fraud. In a statement, Dr. Wansink admitted to making “typos, transposition errors and some statistical mistakes” in his papers. But he defended his work and said that none of his mistakes “changed the substantive conclusions” of any of his papers. “I’m very proud of all of these papers,” he said, “and I’m confident they will be replicated by other groups.”