January will mean back to normality and routine: commuting to the office and restarting the school run. But it also signifies a fresh slate. Time to hit the gym and give up red meat, drinking or smoking in order to keep healthy and ultimately, live longer.

But why should we deprive ourselves of some of life’s enjoyments—such as Big Macs and skipping the gym—will it actually prolong our life?

Susannah Mushatt Jones, the world’s oldest person until she died in 2016, said she ate bacon daily. While the former world’s oldest man, Juan Vicente Perez, who died in April 2024, put his longevity down to drinking a strong liquor every day.

So, if these centenarians can prolong their lives with booze and processed foods, can’t we too?

Well, probably not.

Mark Cortnage, Public Health and Nutrition course leader at Anglia Ruskin University, U.K., told Fortune: “The reason why there aren’t another 100 million centenarians is because [many] who have smoked or drunk so much every day, are sadly not with us anymore.” Sure, you could pick up some unhealthy habits and live to be 100—like Jones and Perez—but you’re more likely to live to 100 if you don’t.

We like to follow the health and lifestyle advice of centenarians because of what’s known as “survivorship bias”—essentially we think they know the key to longevity because they’ve lived a long time.

But Richard Faragher, professor of biogerontology at the University of Brighton, UK, told the Guardian that you should “never, ever take health and lifestyle tips from a centenarian.”

He said that two huge factors that affect whether a person lives to 100 are luck and genetics, neither of which we can control—so hearing about centenarians who have unhealthy lifestyle habits isn’t really beneficial to us.

Cortnage agreed that we should be careful about which advice to listen to. “If [a centenarian] has something negative to say, like, ‘If you drink 15 pints of beer a day, you’ll live to 100’, then you know they’re not worth listening to,” he said.

So changing luck and genetics are out of the window, is there anything a person can do to prolong their life? The answer is yes—as lifestyle factors are hugely important to longevity too.

Keeping active is key, Cortnage said

Another factor is “Ikigai”, which means having a sense of purpose. He explained: “retiring and then doing nothing from that point is not really good for health.”

Cortnage added that eating well can also be conducive to living longer, suggesting a Mediterranean diet which includes lots of vegetables, fish, wholegrains and olive oil and not too much red meat.

But while living longer may seem appealing, it’s not everything.

“You may live to 84 or 83 years of age, but you could spend 15 years of those in poor health,” Cortnage said. “For me, it’s not about longevity. It’s more about healthy life expectancy and living or being as functional as possible.”

That gym membership doesn’t sound so bad.