Why Eating Less Is Slowing Your Metabolism After 35
If eating less actually worked, you wouldn't still be here.
You wouldn't be tracking calories, skipping meals, choosing the "good" option, or wondering why weight feels harder to shift now than it ever did before.
Yet for many women in their late 30s, 40s and 50s, the pattern looks like this: you're eating less than you used to, often less than your partner, you're trying to be disciplined — and your body responds by holding on tighter.
I know how isolating this feels. You're doing everything the internet tells you to do, everything that worked in your 20s, and your body seems to be working against you. You might even feel like you're failing at something that should be simple.
This isn't a willpower problem. It's a physiology + context problem.
And once you understand what's really happening inside your body, the struggle starts to make sense.
Why "Eat Less, Move More" Stops Working So Well in Midlife
The basic principle of energy balance still applies at any age: fat loss ultimately requires a sustained negative energy balance.
What changes after 35 is how the body responds to dieting.
Much of the traditional advice around weight loss:
didn't account for perimenopausal hormonal shifts
didn't consider chronic stress and sleep disruption
and often ignored age-related loss of lean muscle
In midlife, these factors interact in ways that make aggressive restriction harder to tolerate and less effective over time.
And here's what makes this so frustrating: the advice you're following isn't wrong for everyone — it's just incomplete for where you are now. Your body has different needs than it did a decade ago, and no one warned you about that shift.
What Happens When You Undereat for Too Long
Low Energy Availability Is a Physiological Stressor
Consistently eating too little for your body's needs is recognised as a form of low energy availability.
The body responds by shifting into an energy-conserving state:
slowing processes that aren't essential for immediate survival
prioritising blood sugar stability over fat loss
This isn't dysfunction — it's adaptation.
Thyroid Hormone Conversion Can Downshift
Prolonged calorie restriction — particularly when combined with low carbohydrate intake — is associated with:
lower circulating T3
reduced conversion of T4 to active T3
lower resting energy expenditure
This pattern has been described in studies of low energy availability and chronic dieting.
Importantly, this can occur even when basic thyroid screening appears "normal", especially if only TSH and T4 are measured and T3 is not assessed, or if values sit within wide reference ranges.
If you've been told your thyroid is "fine" but you still feel exhausted and cold all the time, this might be why. It's incredibly invalidating to feel terrible while being told everything looks normal on paper. This is where I would normally suggest we get a blood test with a full Thyroid panel done so we can learn exactly what’s going on regarding TSH, T4, T3, thyroid antibodies and Reverse T3. Only then can we have a true understanding of your current thyroid health.
Common experiences associated with this possible underactive thyroid state include:
feeling colder than usual
low energy
reduced exercise tolerance
Cortisol Helps Maintain Function — at a Cost
In energy deficit, counter-regulatory hormones such as cortisol help maintain blood glucose.
When restriction, stress and poor sleep persist together, cortisol exposure over time is associated with:
increased central (abdominal) fat storage
muscle breakdown
disrupted sleep
increased cravings
Not every woman will experience all of these — but this pattern is well-described in chronically stressed, under-fuelled states.
Why Very Restrictive Dieting Can Backfire Around the Middle
To be clear: in controlled conditions, sustained calorie deficits reduce total and abdominal fat.
The problem arises when very low or prolonged dieting is layered onto:
perimenopausal hormonal change
chronic stress
sleep disruption
and age-related muscle loss
In this context, aggressive restriction:
increases metabolic adaptation
reduces resting energy expenditure
and raises the likelihood of weight regain — often preferentially around the abdomen — when normal eating resumes
This is the cruel irony that so many of my clients describe: the harder they try, the worse it seems to get. You're not imagining it, and you're not doing it wrong. The approach itself needs adjusting.
This is why many women report "doing everything right" yet cycling between loss and regain, particularly around the middle.
The Metabolic Adaptation No One Prepared Women For
Metabolic adaptation (also called adaptive thermogenesis) is well-documented.
After sustained dieting, the body may:
burn fewer calories at rest than predicted
reduce spontaneous movement
become more energy-efficient
This occurs at all ages, but its impact is greater in midlife when:
lean mass is already declining
recovery capacity is lower
stress load is higher
Repeated dieting without adequate recovery often leads to diminishing returns.
Possible Signs You May Be Under-Fuelled
These signs are not diagnostic and can overlap with other conditions (such as anaemia, thyroid disease or depression), but they can be compatible with low energy availability:
stalled or reversing weight loss
fatigue that doesn't improve with rest
hair thinning or brittle nails
low motivation or flat mood
exercise feeling harder over time
If you're reading this list and nodding along to most of them, I see you. These symptoms are real, they're disruptive to your life, and they deserve proper attention — not another round of "just try harder."
Clinically, these patterns warrant proper assessment rather than further restriction.
What Helps Restore Metabolic Responsiveness
Adequate Energy Comes First
For women with a long history of dieting and high stress, restoring sufficient energy intake, sleep and recovery often needs to happen before another fat-loss attempt.
This allows some of the body's conservation responses to ease.
I know this can feel counterintuitive — even scary. After years of restricting, the idea of eating more can trigger real anxiety. But this isn't about giving up on your goals; it's about creating the foundation that actually allows them to happen.
I'm currently working with several women where undereating was actually contributing to their weight gain. Once I had them eating more regularly and more of the right foods, they began burning fat. For example, one client on my 3-month program is at the 7-week mark and has lost 6.6kg and 6cm off her waist — not by eating less, but by eating appropriately for her body's needs.
Protein Supports Lean Mass and Satiety
Adequate protein:
helps preserve muscle during weight loss
supports appetite regulation
increases post-meal energy expenditure via the thermic effect of food
While this thermic effect is modest, it contributes to overall metabolic health.
Carbohydrates Have a Role — When Used Appropriately
Very low-carbohydrate intake, particularly alongside low energy intake, has been associated with:
lower T3
higher cortisol responses
For some women, reintroducing appropriate carbohydrate (especially around training or in the evening) can:
improve sleep
reduce perceived stress
support thyroid hormone patterns
This doesn't mean "more is better" — it means context matters.
Why Repair Often Comes Before Sustainable Fat Loss
From a physics standpoint, fat loss still requires a calorie deficit.
The clinical reality is that in chronically under-fuelled, high-stress midlife women, repairing metabolic stress first often makes later, moderate restriction:
more effective
more sustainable
and far less miserable
In other words: addressing low energy availability, sleep and stress doesn't replace fat loss — it enables it.
The Bottom Line
If eating less was the answer, you wouldn't still be struggling.
Your body isn't lazy. Your metabolism isn't broken. And pushing harder isn't the solution.
You've been working so hard for so long. The exhaustion, the frustration, the feeling like you're fighting your own body — it all makes sense now. Understanding why your body is responding the way it is changes everything.
Want to Understand Your Own Metabolic Pattern?
If you're eating well, trying hard, and still not seeing results, your metabolism is giving you information — it just needs to be interpreted correctly.
I've created a free Metabolism Detective Quiz to help identify which metabolic patterns may be at play for you, and what your body likely needs next.
👉 You can download the Metabolism Detective Quiz from its own tab on the homepage of my website.
Clarity is the first step toward working with your body instead of against it.
