After 40: what changes in your body

01Mechanism

Resting metabolism drops, slowly

Your body spends energy constantly, even at rest: breathing, holding its temperature, repairing tissue. This is resting metabolism, and it accounts for the largest share of your daily expenditure — far more than exercise.

From the forties, that expenditure gradually declines. The drop is modest year on year, but it accumulates. Eating exactly as you did at thirty therefore creates, mechanically, a small daily surplus.

Why eating less is the wrong answer

It's almost everyone's reflex, and it backfires. Marked restriction pushes the body to economise: it lowers resting expenditure further to adapt. You eat less, you spend less, and the slightest return to normal ends in regain. That's the yo-yo mechanism, and it has nothing to do with willpower.

The lever isn't quantity. It's what the meals contain and how they're spread across the day.

02Mechanism

Muscle mass declines without showing

This is the most underestimated point, and by far the most important. From the forties the body naturally loses a little muscle each year unless it is used and fed to keep it.

It's discreet because the scale doesn't show it: lost muscle is often replaced by fat mass at near-constant weight. You're “the same weight as before” while feeling less firm, less toned, and more easily tired.

The direct link with energy

Muscle is the most expensive tissue you have: it consumes energy constantly. Less muscle means less resting expenditure — which compounds mechanism 01. The two reinforce each other, which is why food alone is never quite enough.

Protecting muscle takes two things, and only two: enough protein, well spread out, and regular use. Neither requires a gym.

03Mechanism

Hormones reshuffle the deck

Perimenopause often begins long before anyone expects it, sometimes in the early forties, and it spans several years. The hormonal variation of that period affects three things at once: appetite, how the body stores, and sleep quality.

In practice, many women describe hunger becoming harder to read, a storage pattern shifting toward the abdomen, and more fragmented nights. These three effects aren't independent: each amplifies the others.

What belongs to your doctor

The thyroid, hormone treatment, a gynaecological condition: all of that is diagnosed and followed medically, and it isn't mine to handle. If you have any doubt, that's the first door to knock on. My work begins after that, alongside: adapting food to the stage you're actually at.

You don't “correct” hormones with a plate. You can, however, substantially reduce what they put you through: blood-sugar swings, inflammation, and the fatigue-sugar loop.

04Mechanism

Sleep and stress stop being negotiable

At twenty-five a bad night is made up for. At forty-five it's paid for — and it's paid for on the plate. After a short night, hunger rises, the pull toward sugar and fat rises, and the capacity to decide falls. This isn't psychological, it's hormonal.

Chronic stress produces a neighbouring effect. Lived over months, it favours abdominal storage and sustains a hunger that isn't hunger — the one that pushes you toward the cupboard at 5pm without the body asking for anything.

Why this chapter sits in a nutrition document

Because food can no longer be treated separately. A perfect eating plan applied on five hours of sleep will never deliver what it should. That's why I always start with the whole day, not with the meals.

The timing and composition of dinner influence your night more than most of the sleep advice you've been given.

05Mechanism

Digestion becomes more talkative

Over the years digestion slows and individual tolerance becomes more defined. Foods that went unnoticed for twenty years start to weigh. This isn't deterioration: it's a sensitivity becoming audible.

The usual reflex is elimination. Out goes gluten, then dairy, then raw vegetables, and six months later you have an impoverished diet and the same symptoms. Blind elimination is the most common trap of the forties.

The order we look in

1. 1How fast you eat — by far the most frequent cause, and the easiest to correct.
2. 2Hydration, and when you drink relative to meals.
3. 3The amount and type of fibre, and how quickly it was increased.
4. 4Finally, and only finally, individual foods — one at a time, methodically.

If a digestive symptom settles in, worsens, or comes with unintended weight loss, it isn't a nutrition subject: speak to your doctor.

Six common situations, and what they point to

Here's how I connect, in a first session, a feeling to a mechanism. This table isn't a review — it shows how the reasoning works.

“I eat as I always did and I'm gaining weight”

Mechanisms 01 and 02 — meal composition and muscle mass

“I collapse at 4pm”

Lunch composition, long before the tiredness itself

“I crave sugar every evening”

An underfed day, or too short a night — mechanism 04

“I sleep eight hours and wake exhausted”

Dinner timing and content — mechanism 04

“My stomach bloats every evening”

Speed, hydration, fibre — in that order, mechanism 05

“I feel soft although my weight is stable”

Masked muscle loss — mechanism 02

The four levers that still work

They apply to almost everyone. That's exactly their limit: they're general.

To close

What a document cannot do

If you apply these four levers, you'll feel a difference. That's deliberate: they work for almost everyone, because they target no one in particular.

And that's exactly where what I can write stops. This document doesn't know which of the five mechanisms applies to you first. It doesn't know your ferritin has been low for two years, that your thyroid is monitored, that raw vegetables have become impossible, that you work shifts, or that your day starts at 5.30am. These aren't details: they decide the order we work in, and therefore whether any of it will work for you.

That's the work of the review. Forty-five minutes to lay it all out — your food, your days, your digestion, your energy, your test results if you have them — and leave with a plan written for you, in the right order.