Forget the gym, stuff running. All you need to do is walk, writes Polly Vernon.

There are times in life when you deserve to feel pleased with yourself and this was was one of them. Science, you see, recently confirmed something that I had worked out a decade and a half ago, namely: regular walking is the best thing you can do to achieve and maintain a healthy weight.

According to the study from the London School of Economics, brisk walking is a better deterrent against obesity than any other form of exercise. Forget the gym or five-aside, stuff running, spinning, Zumba and squash ... walking officially beats them all, hands (or trainer-ed feet) down.

People who walk briskly for more than 30 minutes a day were found to have lower BMIs and smaller waists than everyone else involved in the study. "Given the obesity epidemic, and the fact that a large proportion of people are inactive, recommending that people walk briskly more often is a cheap and easy policy option," said Dr Grace Lordon, who led the research.

This leaves me feeling validated. I've been boring on about how brilliant walking is for ages, how wildly underestimated its benefits are, how everyone should do it. And I should know: for the last 15 years, I've walked between 20 and 25km a day (25-30,000 steps). Every single day.

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Has it made me thin? It's certainly kept me thin. I was thin when I started (in my late 20s, single-digit dress size, one of the lower ones) but now into my 40s my weight hasn't fluctuated by so much as a couple of kilos, even during my cake-iest periods.

Inevitably, this made me a little smug. Equally inevitably, it made me tell anyone who'd listen that they, too, should do this amazing thing I was doing. Walking is the only thing I ever evangelise about, because, unlike everything else that makes me feel good (meditation, Jaffa cakes, the fantasy-fiction genre, the television show River and a good flat white) walking is the one thing I truly believe will work for everyone. Anyone who can walk, should walk.

It's free, it has purpose, you already know how to do it. It'll do for you, what it does for me.

And, in my considerable experience, walking doesn't just keep you thin. It keeps you sane too.

Mental health got me walking in the first instance. I was in my late 20s and beginning to understand that the love of my life (London) was also my chief tormentor. The stress of the city and the stress of my job as a journalist got the better of me and I became claustrophobic, which meant I could no longer stand to travel around London by Underground. So I ditched it for the bus.

Only one day - as is not entirely unusual - my bus simply did not come. I waited and I waited, and I waited some more, my blood pressure rising, spitting and swearing and huffing and puffing over the unimaginable injustice of a BUS THAT WOULD NOT COME, alongside gathering hordes of similarly frustrated non-passengers.

After 20 minutes, spurred onwards by a desire to demonstrate I simply would not stand for such abysmal service, I walked along my bus route, assuming that sooner or later, my arrival at another bus stop would coincide with the arrival of my bus. It didn't. So I walked some more, eventually making it to work, a mere 20 minutes later than I normally would have, calmer than I might have anticipated, and feeling like I'd accomplished something vaguely mammoth before 10am. I also felt liberated. Suddenly, I had another option.

The next day, I walked again. And the day after; and the day after that. After a month of walking to work, I couldn't help but notice my thighs were changing shape. They were leaner and firmer and more defined. After two months, I realised my bottom was altering, too, becoming neater and more contained. It was at that point that I decided to start walking home, too. The more I walked, the more thoroughly immersed I became in how miraculous it was. It calmed me down. I could start my daily tramp in a foul mood: riled by my partner, anxious about a meeting or wrong-footed by a nightmare; sad or scared or emotionally a little lost. By the time I arrived wherever I was supposed to be, I was fine. Something about walking gives you perspective.

It makes the world feel more fundamentally right. I think it's because our species is supposed to walk. We are built to walk. We are not built to sit, or crouch over computers or phones. We are not built to slump on sofas, binge-watching box sets. We are built to stand, swing our legs, plant our feet, and just go.

Walking also fixes hangovers, heartbreak, low-grade colds; boredom, loneliness, that nagging sensation that you haven't really achieved anything much today. It has a smattering of downsides. You will get rained on (but not as often as you think, and that's nothing a sturdy brolly can't help with). You'll need to carry posh shoes in a separate bag, and cyclists can be a nightmare, far more troublesome, in my experience, than cars.

But otherwise, walking really is as simple, blissful, effective and (in every sense) as good as I've always said it was. If you don't believe me, just ask science.