September 2026

Muscle Loss After 40: Why Protein Needs Change for Men

Somewhere around your late 30s, your body starts losing muscle mass, quietly, gradually, and often without you noticing until strength or fitness starts to feel harder to maintain than it used to. This process is called sarcopenia, and while it sounds dramatic, it's a completely normal part of ageing that's also very manageable, provided you know what's actually driving it.

Why muscle loss happens with age

From around age 30, adults lose roughly 3–8% of muscle mass per decade if nothing is done to counter it, with the rate typically accelerating after 40. A few things drive this:

  • Reduced anabolic response. As men age, muscle becomes less responsive to the same amount of protein, meaning you often need more, not less, to trigger the same muscle-building signal.
  • Naturally declining activity levels. Busier lives, less incidental movement, and less structured training all compound over time.
  • Gradual testosterone decline. Testosterone does decrease slowly with age (this is normal and different to clinically low testosterone), which plays a role in muscle maintenance.
  • Under-eating protein relative to need. Many men eat roughly the same diet at 45 that worked fine at 25, but the body's requirements have shifted.

Why this actually matters

Muscle isn't just about how you look. It's directly tied to metabolic health, insulin sensitivity, bone strength, balance, injury resilience, and, perhaps most practically, how independently you're able to move as you get older. Preserving muscle mass in your 40s and 50s is one of the most protective things you can do for long-term health.

How protein needs actually change

General population guidelines (around 0.8g of protein per kg of bodyweight) are based on preventing deficiency in sedentary adults, not on preserving muscle as you age. For men over 40, particularly those doing any resistance training, the more relevant range is considerably higher:

  • General maintenance and muscle preservation: roughly 1.2–1.6g per kg of bodyweight
  • Actively strength training or in a calorie deficit: often 1.6–2.2g per kg

For an 85kg man, that's the difference between roughly 68g of protein a day (old general guideline) and 135–190g a day (age- and activity-adjusted). That gap is a big part of why muscle loss creeps in, many men simply aren't eating enough protein for what their body now needs to maintain what it already has.

It's not just about the number

Two other factors matter almost as much as total protein:

  1. Distribution across the day. Getting most of your protein in one big dinner is far less effective than spreading it across 3–4 meals, since the body can only use so much at once for muscle repair.
  2. Resistance training. Protein without a training stimulus won't build or preserve muscle on its own...the two work together. Two to three resistance sessions a week is a reasonable, sustainable target for most men.

Practical ways to close the gap

  • Add a protein source to breakfast, not just dinner (eggs, Greek yoghurt, a protein shake)
  • Keep a convenient protein option on hand for busy days, a shake or bar is genuinely useful here, not just marketing
  • Prioritise protein first at meals, then build the rest of the plate around it
  • Don't fear "too much" protein within these ranges, for active men, it's a common under-consumption problem, not an over-consumption one

The bottom line

Muscle loss after 40 isn't inevitable decline, it's largely a mismatch between what the body now needs and what most men are still eating and doing. Adjusting protein intake upward and staying consistent with resistance training are the two highest-impact changes available, and neither requires anything complicated to get started.

This article is general information, not medical or dietary advice. If you have specific health conditions, speak with your doctor or a dietitian before making significant dietary changes.