Middle-aged spread is a myth!” screamed headlines last year, after a study by an international team of researchers revealed that the body’s metabolism doesn’t actually slow down until we reach our 60s.

But while science might say one thing, millions of people in their 40s and 50s contemplating their own widening waistlines would argue otherwise. For men, a thicker waist tends to present as a “beer belly”, thought to be because men are more predisposed to visceral fat — fat wrapped around the organs — which pushes the abdomen outwards and feels hard to the touch. Women tend towards all-round thickening, thanks to subcutaneous fat that sits directly under the skin and feels softer.

Either way, as a high waist measurement is correlated with an increased risk of type 2 diabetes and heart disease, it’s something we should all worry about. (Quick tip: if the circumference of your waist is more than half your height, that counts as high.)

But if our rate of metabolism — how fast the body burns calories — can’t be held responsible for a widening waist as we age, what can? And, crucially, is there anything we can do about it?

With the help of experts, we’ve identified five reasons your stomach might be less svelte now than in your youth — and what you can do to regain your waist.

Less diversity in gut bacteria

Solution “Focus on diversifying your microflora,” says Emma Bardwell, a registered nutritionist and women’s health specialist. “Forget expensive probiotic supplements: I’d advise starting to increase the amount of plant fibre in your diet. Research shows an association between increased gut diversity and eating at least 30 different types of plant foods a week — not just fruit and vegetables; it includes whole grains, nuts, seeds, herbs and spices. Don’t fret too much over numbers, though: aim for a plant-focussed diet (it doesn’t have to be vegan, by any stretch) and just try to add in some variety, so you’re not eating the same plant foods each day.”

You now have less muscle mass

Solution: Keep an eye on your portion sizes and avoid snacking. Yes, your general diet is more important than the fact that the amount of calories going in needs to be equal to, or fewer than, the amount of calories going out to avoid gaining weight. But, as Bardwell explains, “If you eat proper, filling, satiating meals, you’ll keep blood-glucose levels steady and avoid crashes and dips in energy that inevitably leave us reaching for ultra-processed quick energy fixes.” Just as importantly, try to integrate calorie-burning activity into your day that isn’t organised exercise: take the stairs instead of the lift, walk to the shops, do gardening and housework. And when you do work out, choose exercises that will help build muscle. Do at least two muscle-strengthening sessions every week. The more muscle mass you have, the more calories it will burn, but gaining it doesn’t have to mean pumping iron: sit-ups, push-ups, lunges and squats all strengthen muscles, as do yoga, pilates and tai-chi.

You’re stressed

Solution: It’s not a revolutionary approach, but it works: if you cannot avoid stress, instead find ways to mitigate its effects. That means making sure you are getting enough sleep, and trying anything else that helps to get your brain back in balance, such as mindfulness, meditation or yoga.

You’ve hit the menopause

Solution: For many women, HRT, which replaces the hormones that are naturally lost, is a great solution. And when it comes to weight and where fat is stored, it’s certainly effective. One study found BMI was significantly higher in peri and postmenopausal women than in those yet to reach menopause, but also discovered that women taking HRT had similar levels of fat and fat distribution to premenopausal women.

While the balance of oestrogen and progesterone is often the focus when dealing with menopause, the balance of another hormone, insulin, is often overlooked, points out Dr Estrelita van Rensburg, who is author of Eat Well or Die Slowly. “Carbohydrate-rich diets that are typical in the Western world can lead to high levels of insulin and subsequently insulin resistance. And there’s evidence that insulin resistance can exacerbate menopause symptoms, such as fatigue, headaches, brain fog and muscle weakness.”

Your diet is catching up

Solution: Overhaul your diet. It is possible to reverse insulin resistance through a combination of diet, exercise and weight loss — and there are no quick and easy fixes. It’s the same dietary advice you will have heard before: cut out processed foods and avoid simple sugars and starchy carbs. But don’t worry that you’re going to feel hungry. “Once you start eating good protein and fat, you’ll find it’s very satiating,” says Dr van Rensburg. “It doesn’t drive you to eat more in the way sugar and starch keeps you feeling hungry [because sugar and starch cause blood-sugar peaks and troughs].”

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