A quick skim of the other faces on the Zoom call shows that I’m clearly the oldest person on the personal training course. They’re probably wondering whether I’m having a midlife crisis triggered by the pandemic. Maybe I am. Aren’t we all?

I’ve always enjoyed fitness, physical activity, sport – really any kind of movement. This intensified while working under intense pressure and scrutiny during the Covid-19 pandemic: I coped by using exercise as time for daily meditation and reflection. When you’re being shouted at from all directions, and asked to predict the future, creating silence is vital to think.

But taking the step to becoming a personal trainer myself was about something more as well. Often people in public health combine their work with a clinical career. This means they see things at a wide, population-based level, and they also see individual patients coming in for treatment. But to me, preventing people becoming sick in the first place is at the core of public health.

Exercise is the most effective intervention to stay healthy and avoid disease and chronic pain. If you add physical activity to a balanced diet, sleep and friends, that is a recipe for good physical and mental health. In public health we collect data and publish studies on what makes people healthier at a population level. Yet this often can feel abstract when we’re dealing with huge datasets and talking about people in their hundreds of thousands and millions.

I wanted to support people in their health journeys. And I wanted to meet them in a gym or park and ask why they wanted to be fit and stay healthy. Here are just a few things that I learned.

First, you’re never too old to start over and get a new qualification. We live in a strange system where teenagers are asked to decide what they want to do for the next 50 years of their life. But whether it’s at 25, 38 like me, or 65, there’s always the chance to go in a new direction, or re-evaluate where you are in life. It’s never “too late”.

Exercise is too often seen as a luxury for young people and those who are already fit. Instagram hasn’t helped this image: of women in spandex with Kardashian-like curves and men with shiny six-packs. But you don’t need designer outfits or an expensive gym membership to get going. Outdoor fitness classes, low-cost basic gyms and even community yoga classes are increasingly available.

And the people you find in these come in all shapes, sizes and ages. It’s more about how you feel (and exercise does release dopamine and feelgood hormones) and less about how you look. And besides, no one looks like they do on Instagram: images are largely filtered and Photoshopped. So get off social media, and get into places with real people trying to feel better.

Harmful stereotypes can become self-fulfilling, especially for brown women. In Britain (and globally), south Asian women are the group that exercises the least, and this starts at an early age. If you’re raised in a cultural context where you’re told exercise isn’t a priority or that exercise is for boys, then of course you avoid it because you feel like you don’t belong. There are few role models and little general encouragement. And I’ve lost track of the number of times in a gym that I’ve been asked which tanning studio I used because my darker colour was “so natural”. It seemed easier to believe that I’d sprayed myself with paint than accept that a brown woman would be dead-lifting.

I also learned that we obsess too much about weight and body mass index (the relationship between weight and height), rather than basic assessments that are better at catching health conditions before they become disease. A basic measure of your blood pressure, body fat, and cardio and strength fitness over time will give you a holistic benchmark to work from.

I learned that, as the saying goes, “you can’t outrun a bad diet”. What you eat matters just as much as how much you move. Fad diets have overcomplicated what is a relatively simple rule: just avoid ultraprocessed foods as much as you can. These foods are produced in factories with chemical processes that trick our body to overconsume. Eat real food, with ingredients you can pronounce and that goes bad within days, not years.

Also, eat until you’re full, then stop. Food is often used to cope with emotional challenges: I stopped eating for months out of grief after my father died, while other times I coped with exam stress by binge-eating late at night. It took me a while to realise that food is often relied upon as an antidepressant, especially for those without access to support or therapy.

Of course, healthy choices are easier for those with time and money. Public policy is crucial to enable anyone who wants to lead a healthier lifestyle to be able to, and there should be no blame put on individuals who cannot.

I’ll continue to do high-level public health analysis and publish on what more governments can be doing. But numbers hide the stories and faces of real people. People who want to takes steps to be healthier. This new year, we should all resolve simply to move and exercise more. And I’m planning to start a weekend park training session that people can attend for free. Who knows who might be there? Nicola Sturgeon and Lorraine Kelly have both said they’d like to join. That’s inspiration enough to get going and get moving.

• Devi Sridhar is chair of global public health at the University of Edinburgh

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