I’m susceptible to this kind of thinking myself — I fast for more than 12 hours a day, in homage to the findings of Satchidananda Panda at the Salk Institute for Biological Studies. Sometimes it seems as though everyone I know is adding a new supplement to their diet or subtracting a food group or component like gluten. We all want the same thing: to believe we have the power to stave off the ravages of old age.

But how much do our individual choices really matter?

The question sent me on a safari through the obituary pages, hunting for dead longevity experts so that I could find out how their experiments had ended. I conducted my search in the same spirit in which Dr. Brouchkov swallowed his permafrost extract — driven by curiosity, aware that my “findings” would be only anecdotal. Nonetheless, what I learned was enough to make you choke on your keto coconut-oil coffee.

Let’s start in the 1930s, when an American nutritionist named Clive McCay designed a low-calorie diet for his lab rats at Cornell that gave them all the nutrients they needed but kept them as thin as supermodels and (presumably) ravenous. The diet seemed to act like a time machine, and Dr. McCay’s hungry rats maintained their dapper, glossy coats of fur and frisked about their cages; their well-fed counterparts doddered about in shabby coats and then died. “In the laboratory today are two male white rats that are the equivalent in age to men more than 130 years old,” Dr. McCay announced, promoting the benefits of calorie restriction.

A gentleman farmer, Dr. McCay applied his theories to himself, nibbling on morsels from his own fields. But he didn’t make it close to 130. Though trim and athletic, he had two strokes and died at 69.

Over the decades that followed, research teams would repeat his experiments and confirm that calorie restriction almost always prolonged the lives of lab animals. One of the most prominent of those scientists, Roy Walford, showed that a strict diet could double the life span of mice. Dr. Walford himself stuck to a 1,600-calorie-a-day diet. In the 1980s, he wrote “The 120 Year Diet” and then followed it up with even more misery and abnegation in “Beyond the 120 Year Diet.” He became a cult figure to thousands of CRONies (“calorie restriction with optimal nutrition” enthusiasts) who hoped to live past 100. But he himself died of A.L.S., or Lou Gehrig’s disease, at age 79.