What protein can and can't do.

Muscle is a balance, not a building site

Your muscle tissue is continuously broken down and rebuilt. Two rates run in parallel — muscle protein synthesis and muscle protein breakdown — and what happens to your muscle mass is simply which one is larger over time.

• Synthesis higher than breakdown → you gain muscle.
• Breakdown higher than synthesis → you lose it.
• Roughly equal → you stay where you are.

Eating protein raises synthesis for a few hours. Resistance training raises it for considerably longer — up to a day or more — and, importantly, makes muscle more sensitive to the protein you eat. The two combine; neither substitutes for the other.

Protein without training does very little

This is the part supplement advertising works hardest to obscure. Eating more protein without a training stimulus does not meaningfully build muscle in healthy adults. Your body has no reason to construct tissue it isn't being asked to use.

There is a real exception: during illness, injury, immobilisation or significant weight loss, higher protein helps preserve muscle even without training. Preserving is not the same as building, and it's a genuinely valuable thing on its own.

How big is the effect, honestly?

The 2018 meta-analysis by Morton and colleagues in the British Journal of Sports Medicine pooled 49 studies covering around 1,900 participants, comparing resistance training with and without extra protein.

Extra protein produced a statistically clear improvement in lean mass gain — on the order of an extra 0.3 kg over roughly 12 weeks — and a meaningful improvement in strength.

That number deserves to sit with you for a second. It is real, it is repeatable, and it is small. Over a year of consistent training it compounds into something worth having. It is not the difference between looking untrained and looking athletic, which is what supplement marketing implies.

The same analysis found the benefit plateauing around 1.6 g/kg/day. Beyond that, additional protein didn't reliably add anything.

What actually determines your results

Roughly in order of impact:

1. Training consistently for years. Nothing else comes close. Adaptation is slow and cumulative.
2. Progressive overload. Gradually demanding more — more weight, more reps, better control. Doing the same workout indefinitely produces the same body indefinitely.
3. Total calories. Building tissue in a deficit is possible but slow; a small surplus makes it considerably easier.
4. Total daily protein. Important — and it's the fourth item, not the first.
5. Sleep. Consistently under-slept people build less muscle and lose more of it while dieting.
6. Protein distribution and timing. Real, small, worth doing once the above are handled.

People tend to invert this list, because items 4 and 6 can be bought and items 1 and 2 can't.

How fast can muscle actually be gained?

Rates vary with genetics, age, sex, training history and how well the rest of life is going, but the broad picture is consistent:

Men typically gain faster in absolute terms than women, largely because of hormonal differences and higher starting muscle mass; the proportional rates are much closer. Everyone slows down as they approach their genetic ceiling.

Two implications follow. First, scale weight moves faster than muscle — a 3 kg jump in a fortnight is water, food and glycogen, not tissue. Second, no amount of protein overrides these rates. Someone eating 250 g a day does not build muscle three times faster than someone eating 130 g.

Can you build muscle while losing fat?

Yes, in specific circumstances — commonly called recomposition. It's most achievable for:

• People new to resistance training,
• People returning after a long break, regaining previously held muscle,
• People carrying a substantial amount of body fat, who have ample stored energy to draw on.

For a lean, experienced trainee, doing both at once is slow and frustrating, and most make better progress alternating phases.

This is the situation where protein intake matters most. In a deficit, protein is what keeps the weight you lose from including your muscle — which is why the recommendations rise to 1.6–2.4 g/kg when dieting rather than the 1.6 that suffices otherwise.

Where these numbers come from

Principally Morton et al. (2018), British Journal of Sports Medicine, for the meta-analysis, effect size and 1.6 g/kg plateau; the International Society of Sports Nutrition position stand on protein and exercise; and the broader resistance-training literature on rates of hypertrophy. The gain-rate table reflects widely reported ranges rather than a single study, and individual variation around it is substantial.