Q: Summer is a distant memory, the evenings are dark and I feel about a stone heavier than before those balmy holidays. I went for a run lately and I know I am carrying extra weight. I don't use a scales but my elasticated jogging bottoms are tight – really tight – and I can feel a much bigger wobble around my middle.

My run felt a lot harder than usual and I think at least half of that was because I was lugging around this weight. I'm so cross about it. I worked so hard all year to stay in shape and now it's all gone to pot and I am right back where I started. I feel like giving up and just accepting the middle age spread.

- Caro

A You and me both Caro. At the end of the summer I spent two weeks in France, which included only two runs and at least a year's worth of pastries. It might have been all right if I'd gone straight back to my running and healthy eating routine, but the subsequent lazy weeks encouraged all that pastry to really bed in and find a permanent home on my thighs, belly and upper arms.

What I thought during those first punishing 10 minutes of my run as I lugged this stiff old body round the woods – other than that everything wobbled with a lot more welly than I remembered – was, what’s the point? Why am I still doing this? Is it worth it?

But I found my answer almost immediately once those 10 minutes were up and I got into a groove and realised that, yes, it was worth it. I felt so much better afterwards, more relaxed and centred and happy – happier than I had been all summer, even on holiday.

Plus, I had much more energy to think and strategise logically about everything else going on in my life, including my spare tyre. It is not, I told myself, a train smash to have – temporarily – added more bingo to my wings.

Thank God the Grit Doctor has softened somewhat since motherhood. She didn't force me to look at myself naked in the mirror and call myself a "fat bitch" as she might have done in the past, but she did warn me that unless I wanted those wings to become a permanent fixture, a week of really strict eating and daily running was required to get me back on track.

If you are wondering what a really strict week of eating looks like for me – when the Grit Doctor is in my face – it mainly involves halving my portions of all protein, dairy and carbs other than fruit and veg at meals. There is absolutely no eating between meals. This means one measly slice of wholemeal toast for breakfast, half my usual (gigantic) sarnie for lunch. No second helpings of pasta. Loads more salad and veg. Way less dressing on it. Gallons of water.

No day wine (rosé drinking habit acquired in France) or night wine for that matter . . . except on weekends. Fewer lattes, more extremely skinny cappuccinos and macchiatos. You get my drift.

And, yes it’s agony for the first few days, because my tummy, my brain and my whole being have got used to a daily croissant the size of a small chair – and learned to expect it. But after a few days of this gritty routine and regular four-mile (6.5km) runs, I’m back on track.

So much of it is about being on the right track, because I won’t be back in shape or back to my previous level of fitness in a week. Five weeks of damage will take at least five weeks to undo. But if we continue along the summer holiday direction of “eat what we want, do no exercise and drink at will”, that middle age spread becomes inevitable, in my case it’s probably only a few months away.

But if we do an about-turn now and head back the other way, we will be running towards an altogether different future: one of better health, with a leaner body and stronger heart, greater mental strength, and a more balanced and positive outlook.

Think of yourself as a set of scales, not the weighing kind but the scales of justice. For the scales to be in balance requires that there be push on both sides – the definition of balance is a perfect tension of opposing forces. So, if over the weekend I feast and the scales tip one way, I need to act in an opposite manner on Monday and Tuesday to restore equilibrium.

The same applies to a two-week, ahem . . . or longer lapse. It will take the same amount of time at least to restore our equilibrium through behaving in the opposite manner. You are not right back where you were a year ago.

If you took an eight-week break, you are eight weeks away from where you once were. Isn’t that a more attractive option than a life time of middle-aged spread and regret?

With each year it may get harder to keep choosing the direction of “fit and healthy” as our energy levels flag and our motivation wanes, yet we need those runs and that healthy lifestyle more than we ever did in our youth. And it doesn’t have to be running every day or eating kale. But there does have to be exercise. Taken regularly. Think of it as a spoonful of medicine.

And imagine the Grit Doctor administering it. That ought to get us both running out the front door faster than I can say, "Deux croissants s'il vous plait".