“I don’t eat much, but I can’t lose weight.” I’ve lost count of how many times I’ve heard this exact sentence, usually said with a mix of confusion and quiet exhaustion. And every time, my answer is the same: I believe you. Not because I’m being polite, but because the maths genuinely has changed, even if the plate hasn’t.

Last week I explained why weight gain after 45 isn’t a discipline problem. This week I want to zoom out a bit further, because “why is losing weight harder now” isn’t only a hormone story. It’s also a history story, a movement story, a sleep story, and — plot twist! — a food-industry story.

Let’s go through each one.

For years, the accepted wisdom was that repeated dieting (you know, the classic yo-yo pattern of losing weight, regaining it, losing it again) permanently damages your metabolism. It’s a scary story, and an understandably sticky one.

Here’s the more nuanced, more recent picture: a major review looking at decades of weight-cycling research found little convincing evidence that the cycling itself causes lasting metabolic harm. So if you’ve dieted on and off for twenty years, that alone probably hasn’t broken anything around your metabolism.
More about this: Is My Metabolism Broken?

What does seem to hold up, though, is something quieter: some research has observed that the rate of weight loss can slow with each subsequent attempt, even on an identical plan. 

And, speaking from working with real women rather than lab rats, I’d add a very unscientific but very real factor: after enough restrictive diets, your nervous system gets wise to the pattern. It stops trusting that food will reliably show up, and it responds accordingly. That’s not a broken metabolism. That’s a sensible body that’s learned from experience.

You’re probably moving less than you realise

This one’s sneaky, because it doesn’t feel like a change, it feels like life just staying the same, busy as ever.

But “busy” and “physically active” aren’t the same thing. A decade or two ago, movement was often built into the day without you clocking it: chasing and carrying toddlers, standing to cook proper meals, picking up toys and clothes off the floor, walking to more places, playing with the kids at weekend, less time parked in front of a screen after dinner.

As kids grow, jobs and chores get more sedentary, and evenings get swallowed by admin and screens (of all sorts), that incidental movement (what researchers call NEAT, Non-Exercise Activity Thermogenesis) quietly drops. You can be constantly busy and still be moving your body significantly less than you did ten years ago.
Worth an honest audit, not a guilt trip.

Muscle loss is doing more than you’d expect

I covered this properly last week, so I won’t repeat the whole explanation, but it belongs on this list, because it’s one of the biggest reasons the same eating habits stop “working.” From your thirties onwards, muscle mass declines gradually, and that decline speeds up through the menopause transition: postmenopausal muscle mass is estimated to fall by around 0.6% a year. So potentially, by the age of 50, you could have sneakily lost 15% of your muscle mass.

Doesn’t sound too scary like this, does it? But muscle is metabolically active tissue. Less of it means your body simply needs less fuel than it used to, for the exact same daily life. Numbers might help this one sink in better:
> 15% less muscle might translate into 100 fewer calories burned per day.
> That could turn into 0.5kg weight gain per month.
> Which would add up to 6kg per year.
Like that, without changing anything to your food or movement.

Stress is a metabolic event, not just a mood

We tend to file “stress” under mental health, and leave it there. But stress is deeply physical. Chronically elevated cortisol nudges the body to store fat centrally (read ‘belly fat’) and pushes insulin levels up, which over time raises the risk of insulin resistance.

If your stress load has genuinely increased over the last decade (more responsibility, more people depending on you, less time that’s actually yours), your body isn’t being dramatic. It’s responding accurately to a genuinely heavier load.

Sleep debt adds up quietly

Following on from stress: poor sleep and high stress feed each other, and both feed hunger. And fat storage. Short or disrupted sleep shifts the hormones that regulate appetite and satiety, making you hungrier and less satisfied by food the next day. This pattern shown clearly in controlled sleep studies.

Oh, and your insulin sensitivity drops by up to 30% than on a rested day, so you’ll be producing more of your storage hormone, just to add insult to injury.

If you’ve been averaging six broken hours a night for the last five years rather than seven or eight solid ones, that’s not a small detail. It’s a cumulative one.

Processed foods are engineered to be hard to stop eating

Here’s the one I find genuinely fascinating and absolutely infuriating. In a tightly controlled NIH study, researchers gave adults two weeks of meals made mostly from ultra-processed foods, and two weeks of meals made from minimally processed whole foods, with both diets matched for calories, sugar, fat, salt and fibre on paper.

Despite that matching, people spontaneously ate around 500 more calories a day on the ultra-processed diet, and gained weight, while they lost weight on the whole-food diet.

Same “nutrition label” maths. Very different result in the body. This is a big part of why “just eat less” advice so often collides with a food environment that’s engineered — genuinely, deliberately — to make eating less feel like a fight against your own appetite. It’s not that you lack willpower around these foods. It’s that these foods are specifically designed to override your fullness signals. That’s not a personal failing; that’s food science doing exactly what it was designed to do.

Sustainable habits, not another overhaul!

None of the six things above are solved by trying harder at the exact same strategy. They’re solved by adjusting the strategy itself:

Build movement back into ordinary life, not just workouts: walking meetings, walking faster in general, taking the stairs, standing more, fidgeting…

Protect muscle with protein at each meal and a couple of short strength sessions a week.

Treat stress and sleep as a non-negotiable part of the plan, not an afterthought to squeeze in once the “real” work is done.

Shift the ratio of whole foods to ultra-processed foods, gradually, without declaring all-out war on any one food (that tends to backfire too).

None of this is glamorous or insta-worthy. It’s also exactly why it works: sustainable habits, layered in gradually, hold up in real life in a way that another dramatic overhaul rarely does.

If your body feels like it’s playing by different rules than it used to, that’s because, in several genuine and measurable ways, it is. The good news is that once you understand the actual rules, you can finally stop fighting the wrong battle.

Ready to work with your body instead of against it?

Download our free guide, “5 Reasons Weight Loss Feels So Hard”, for the plain-English version of everything above.

References

Magkos F, Stefan N. Weight cycling and metabolic health — Personal View, The Lancet Diabetes & Endocrinology (2026), summarised via ScienceDaily — https://www.sciencedaily.com/releases/2026/05/260515233331.htm

“Does weight cycling promote obesity and metabolic risk factors?” — ScienceDirect — https://www.sciencedirect.com/science/article/abs/pii/S1871403X16303969

“Association between menopause-related symptoms and muscle mass index among perimenopausal and postmenopausal women,” NCBI — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12325020/

Stanford Lifestyle Medicine, “How Sleep Deprivation Affects Your Metabolic Health” — https://lifestylemedicine.stanford.edu/how-sleep-deprivation-affects-your-metabolic-health/

Hall KD, et al. “Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain,” Cell Metabolism (2019), NIH Clinical Center RCT — https://www.cc.nih.gov/news/2019/summer/story-01