Forever young.

It’s rare that a long, technical paper in a biology journal turns out to be a page-turner. But it happens.

A team of researchers published a thorough review of the science of why we age this week in the journal Cell.

It ties together that still-young field’s confusing, sometimes contradictory findings into a single coherent whole and offers the most complete explanation I’ve seen anywhere as to why human beings get old, as well as what we can do to slow the ageing process.

As a science writer – and reader – used to incomplete and occasionally absurd claims about staving off old age, I found this paper genuinely difficult to put down.

Here are some of its most important takeaways.

Ageing is all about your metabolism

All told, the authors identified nine key hallmarks of ageing on your metabolism.

Let’s be careful about our terms here: your metabolism isn’t some organ or group of organs in your body that determines how many sugary foods you can eat before noticing a bulge on your waistline.

Rather, it’s the billions of actions all of your cells take every second of every day to convert fuel into energy and put together the complex compounds necessary for your body to function.

As you get old, your metabolism becomes less efficient. Your DNA becomes more damaged, introducing errors and inefficiency to how your cells function. Your body’s process for destroying and eliminating old, exhausted cells ('autophagy') slows down, which has a number of negative effects on your well-being.

And all the stress your body has experienced over the course of your lifetime makes it less able to perform the daily quality-control tasks necessary for health.

We don’t know how to stop ageing, but we know of some things that can help

If ageing is a disease of the metabolism, it shouldn’t surprise anyone that the fuel you put into your body can have a serious impact on your longevity.

There’s a strong body of evidence to suggest that what’s known as a Mediterranean diet can extend your life.

That’s shorthand for a diet high in healthy fats like olive oil, vegetables, whole grains, nuts, and fish – and with little red meat or sugar. They make a point of noting that replacing proteins with healthy complex carbohydrates seems to offer serious benefits to longevity.

Also helpful: calorie restriction. In part, this practice simply refers to not overeating. But perhaps just as important is building periods of fasting into your routine – evidence suggests that doing this for just several hours a day might have a real benefit for some people.

Finally, and this should surprise no one, regularly exercise appears to help slow down all nine of the major hallmarks of ageing identified in the paper.

Our 'westernised' lifestyles are killing us

While improvements in healthcare and public safety have created drastic improvements in lifespans in the 'Western' world, there’s still a lot to worry about.

A high-calorie diet heavy in sugar, animal proteins from red meat, and unhealthy fats like margarine stresses our metabolisms and can increase the risks of obesity.

Many Americans fail to consume nutritious vegetables, fibres, and whole grains. And most of us simply do not work out enough and spend far too many hours not moving.

The problem is serious enough, the study authors write, that they end the paper with a call to action, ostensibly meant to encourage people to adopt healthier lifestyles.

There's a lot we still don’t know

The most significant part of this paper is that it brings together the dozens of disparate studies on ageing, identifying and highlighting both some of the common threads in the science and some of the major gaps in our knowledge.

One of the biggest problems with ageing research that the paper touches on, for example, is the fact that only a fraction of all of our 'ageing science' comes from studies of people. Instead, the vast majority of that research is done in lab animals like flies, worms, and mice.

There’s strong evidence for the positive impacts of interventions like caloric restriction on longevity in these animals, but the details are still fuzzy.

Hopefully, as more public health and biology research turns toward the question of ageing, we’ll get better at helping people across geographies and social classes live more healthily into their old age.

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