Nutrition6 min read

Why You're Losing Muscle After 40 — And How to Stop It

The mechanics of age-related muscle loss, and the two variables that actually reverse it.

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Somewhere in your 40s, you might notice clothes fit differently even though the number on the scale hasn't moved much. That's not just "getting older" in some vague sense — there's a specific, well-documented process behind it, and it's one you have real control over.

What's actually happening

From roughly your 30s onward, the body naturally loses muscle mass at a gradual rate each decade if nothing is done to counteract it — a process researchers call sarcopenia. It accelerates further from your 60s onward. The causes are a combination of hormonal changes, declining physical activity, and — critically — a drop in how efficiently your body uses protein to repair and build muscle tissue as you age.

The result isn't just cosmetic. Less muscle means a slower metabolism, weaker bones, and reduced functional strength for everyday tasks — carrying, lifting, getting up off the floor.

In short

Muscle loss after 40 is normal, but not inevitable
Resistance training and adequate protein intake are the two levers that matter most
The body needs a stronger stimulus and more protein per meal than it did at 25 to build the same muscle

The two things that actually move the needle

1. Resistance training, consistently

This is the single most effective countermeasure. Muscle responds to being challenged — lifting weights, using resistance bands, or bodyweight training all send the same signal: this tissue is needed, keep it. Skip resistance training and the body has no reason to hold onto muscle it's not using.

If you're not currently doing any strength training, our beginner routine is a sensible starting point — three sessions a week is enough to start reversing the trend.

2. Protein intake, spread through the day

As we age, the body becomes somewhat less efficient at using protein to build muscle — a phenomenon sometimes called "anabolic resistance." Practically, this means it's worth paying more deliberate attention to protein than you might have needed to in your 20s, and spreading it across three or four meals rather than loading it all into one.

General guidance from sports nutrition research suggests active adults over 40 often benefit from higher protein intakes than younger adults doing similar training — but the right target depends on your body weight, activity level, and goals, so it's worth discussing specifics with a doctor, dietitian, or nutrition-qualified trainer rather than following a generic number.

Muscle isn't lost because you got older. It's lost because it stopped being asked to do anything.

What doesn't help much

Cardio alone — running, cycling, swimming — is excellent for heart health but doesn't provide the specific stimulus muscle needs to grow or even maintain itself under age-related pressure. It's a complement to resistance training, not a replacement for it.

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A note before changing your diet or supplement routine: if you have any underlying health conditions, are on medication, or are unsure what's appropriate for you, speak to a doctor or registered dietitian before making significant changes.

The bottom line

Muscle loss after 40 is a real, measurable process — but it's also one of the most controllable aspects of ageing. Consistent resistance training and adequate, well-distributed protein intake are unglamorous, unfashionable, and they work.