Protein and muscle: your nutrient shield in a deficit

Understanding your stats · Protein

In Strathlon, the Protein section of your Trends shows how your daily protein intake is holding up over time, and the protein-per-kg tile in Review turns your raw gram total into a single number you can judge against an evidence-based target. This page explains what that number really means — the reliable science of protein and muscle, the honest limits, and the misconceptions that make people either under-eat protein or waste effort chasing more than they can use.

We'll start with what you see in the app, go deep on the physiology, and finish with practical, Strathlon-specific takeaways. Accuracy is the point of this page, so where a claim is commonly overstated online — "more protein equals more muscle," "protein wrecks your kidneys," "you can't build muscle on plants" — we flag it and correct it. Everything here is a population average or range; your right target depends on your size, training, age, sex and goal.

1. What protein-per-kg is: grams per kilogram of body weight

Protein-per-kg is simply your average daily protein intake in grams, divided by your body weight in kilograms. If a 75 kg person eats 150 g of protein in a day, that's 150 ÷ 75 = 2.0 g/kg. It's a small piece of arithmetic, but it's the piece that makes your intake comparable to the science.

Strathlon normalises by body weight for a good reason: protein needs scale with body size. "150 g of protein a day" means something very different for a 55 kg person than for a 100 kg person — plenty for one, possibly short for the other. Expressing it per kilogram lets the app compare you against evidence-based targets that are themselves stated per kilogram, rather than against a one-size-fits-all gram number.

So the tile does two jobs. It turns a raw total into a number you can judge against a target, and the Trends Protein section shows whether that number is holding steady over the days and weeks — which matters more than any single day, because muscle responds to what you do consistently.

A note on body weight versus lean mass

Strictly speaking, the cleaner scientific basis is grams per kilogram of lean (fat-free) mass, because fat tissue has very low protein turnover and doesn't drive protein needs the way muscle and organs do. For someone carrying a lot of excess fat, a target based on total body weight can overshoot true needs somewhat. We mention this for honesty, but don't over-engineer it: total body weight is the standard, practical basis that nearly all published ranges use, and it's the number everyone actually has. The per-kg framing is a proxy — a very useful one — not a lab measurement.

2. Why protein matters: the muscle protein synthesis mechanism

Muscle isn't a static block of tissue. It's in constant turnover — being built up and broken down every single day. Two processes run in parallel: muscle protein synthesis (building new muscle protein) and muscle protein breakdown (recycling old protein). Whether you gain, hold, or lose muscle over time comes down to the net balance of the two.

How protein tips the balance

When you eat protein, it's digested into amino acids. Among them, the essential amino acids — and especially the branched-chain amino acid leucine — are the main dietary trigger for muscle protein synthesis. Leucine is the most potent amino-acid activator of a cellular signalling hub called mTORC1, which acts as a master switch that turns up the machinery translating your genetic instructions into new muscle protein.

So a protein-containing meal briefly raises synthesis above breakdown, nudging the net balance in the muscle-preserving and muscle-building direction. Crucially, resistance training amplifies and prolongs that response: a muscle that has been trained is far more responsive to the protein you eat. Training and protein work together — neither does the whole job alone. That's why every recommendation on this page pairs "eat enough protein" with "keep training."

How this connects to training, fat loss and health

• Training: the muscle-building signal from protein is much stronger in a loaded, trained muscle, which is why your training volume matters alongside your protein number.
• Fat loss: in a calorie deficit, the body can draw on muscle for fuel and amino acids. Adequate protein plus continued resistance training biases the body toward burning fat while sparing muscle — the subject of section 4.
• Health: muscle is metabolically and functionally valuable. It supports strength, glucose handling, and — especially as you age — mobility and independence.

In short, protein is both the raw material and the signal for maintaining and building muscle. The app's protein stat is a practical proxy for "am I giving my body enough of that material and signal each day."

3. The evidence-based target: roughly 1.6–2.2 g/kg per day

For active people whose goal is building or maintaining muscle, the well-supported daily target sits at roughly 1.6 to 2.2 g/kg per day. This is the range the protein-per-kg tile should orient you toward for general training goals — and it's best read as a range, not a magic single number.

Where does that come from? Meta-analytic evidence suggests the muscle and strength benefits of higher protein tend to plateau around 1.6 g/kg for the average trained person — above that, extra protein adds little on average for building muscle. The International Society of Sports Nutrition position stand states that 1.4 to 2.0 g/kg per day is sufficient for most exercising individuals. Extending the practical target up to about 2.2 g/kg gives a sensible safety margin and room for individual variation, which is where many practitioners set the upper end. So 1.6–2.2 g/kg is a defensible, mainstream "active person" range.

Here's the useful part for reading your tile: most casual exercisers eating a normal mixed diet already land near the bottom of this range, or a little below it, without trying. So deliberately aiming for the range is where the app's nudge earns its keep. If your protein-per-kg is reading well below about 1.6, that's the clearest signal there's room to improve. Once you're comfortably inside 1.6–2.2, the marginal value of pushing higher is small for most goals.

4. Protein in a deficit: the "nutrient shield"

This is the headline idea of the page. When you eat fewer calories than you burn, your body has to cover the gap partly from stored energy. Ideally that's body fat — but without enough protein and a training stimulus, some of it can come from muscle.

A calorie deficit lowers the body's overall anabolic environment and, left unchecked, tends to tip net protein balance toward breakdown. Two levers push back. Higher protein intake raises the synthesis side and supplies amino acids, and resistance training provides the "keep this tissue" signal. Together they bias the body toward drawing on fat while preserving lean mass. Protein is the shield; training is what tells the body the muscle is worth keeping.

This is why deficit targets sit at the upper end of, or above, the maintenance range. The ISSN position stand notes that around 2.3 to 3.1 g/kg per day may help resistance-trained people maximise lean-mass retention during hypocaloric (deficit) periods. In other words, when energy is scarce, protein does more work — so you give the body a bit more of it.

The practical, one-sentence version, and the single most actionable line on this page: when you're in a deficit, aim toward the higher end of your protein range, and keep resistance training. This ties directly to the app — your energy balance showing the deficit and your Protein section together tell you whether you're cutting with your shield up. The goal of a good cut is to lose fat, not scale weight indiscriminately, and adequate protein plus training is the best-established lever (alongside a moderate deficit and adequate sleep) for making the weight you lose come disproportionately from fat.

5. Protein for muscle growth: sufficient, not excessive

For building muscle — which needs progressive training and, for meaningful growth, enough total energy — you need enough protein. But "more and more" stops helping, and this is where a lot of effort is wasted.

Once daily protein is adequate (roughly 1.6 g/kg or more for most people), the muscle-building response is largely saturated with respect to protein. The limiting factor then becomes your training stimulus and your total energy and recovery — not extra grams of protein. Above roughly 2.2 g/kg, additional protein tends to give diminishing returns for muscle growth in the average trainee. It isn't harmful for healthy people (see section 7); it just isn't buying much more muscle.

This reframes how to read the tile. "Good" isn't "as high as possible" — it's "comfortably inside the range." If your protein-per-kg reads 2.6, you don't need to chase 3.0. You'd get far more from improving your training and your sleep than from the extra protein.

6. What moves your target within the range

The range exists because of individual variation. Here's why your personal number might sit higher or lower within it:

• Age. Older adults tend to show anabolic resistance — a blunted muscle-building response to a given protein dose. Many experts suggest older active adults aim toward the higher end (around 2.0+ g/kg) and pay attention to getting enough protein per meal. The direction here is well established; the exact number is reasonable expert consensus, not a hard law.
• Sport type and training volume. Higher training volume, more muscle-damaging work, or endurance-heavy training tends to push needs up within the range. Someone lifting heavy five times a week, or training for an endurance event, sits higher than a light, casual trainer.
• Sex. Protein needs scale with body size and lean mass more than with sex as such, and the per-kg framing already handles most of that. There's no need for separate male and female targets.
• Body composition. Leaner people in a deficit have more reason to push toward the top of the range — less fat to draw on, more muscle to protect. People with more fat to lose generally don't need the extreme high end (see section 4).
• Genetics and individual response. Real, but not something you can measure or act on — worth knowing so you understand that variation exists, not something to chase.

The app gives you a personal per-kg number; where in the range you aim depends on your age, goal, and how hard you train.

7. Is high protein safe?

It's a fair question to ask, and the honest answer is reassuring for most people. In healthy individuals with healthy kidneys, higher protein intakes within these athletic ranges are not associated with kidney damage. The popular "protein wrecks your kidneys" claim is not supported for healthy people. Adequate hydration and a varied diet are the sensible companions to a higher-protein diet, and that's about it.

There is one important caveat that must be stated plainly: people with existing kidney disease, or certain other medical conditions, should follow professional advice — which may involve limiting protein. This is exactly where the "general education, not medical advice" line at the foot of this page earns its place. If you have a relevant condition, your target is a conversation with a doctor or registered dietitian, not a number from an app.

One more note on honesty: protein is genuinely valuable for muscle and appetite, but we won't dress it up with claims it can't support. It's true, directionally, that protein has the highest thermic effect of the macronutrients — your body spends a bit more energy digesting it than it spends on carbs or fat — but that's a modest effect, not a fat-loss hack, and we won't attach a precise percentage to it. Beyond "safe for healthy people and valuable for muscle," we're not going to promise protein "boosts your metabolism" or fixes anything else.

8. How to raise a low intake

If your tile is reading low, the fix usually isn't a dramatic diet overhaul. The single most effective, least intimidating tactic is this: anchor each meal with one clear protein source. If most of your meals and snacks contain a deliberate high-protein food, your daily total rises naturally without you having to weigh and count every gram.

Good everyday sources to build meals around:

• Animal and dairy: eggs, Greek yogurt, cottage cheese, chicken, fish, lean beef, milk, whey.
• Plant: legumes (lentils, chickpeas, beans), soy foods (tofu, tempeh, edamame), seitan, higher-protein grains and pseudograins, and soy or pea protein powders.

A few other gentle levers help: choose the higher-protein version when it's easy (Greek versus regular yogurt), add a protein source to carb-heavy meals, and spread your protein across the day rather than loading it all into one giant dinner. Spreading it out is soft advice, not a strict rule — it may modestly favour muscle and satiety — but the big win is simply hitting your daily total.

The app tie-in: if the tile is low, add one protein anchor per meal and watch the Trends Protein section climb over a week or two. That's a change you can actually sustain, which matters far more than a heroic overhaul you abandon.

9. Vegan and vegetarian considerations

Plant proteins are perfectly capable of building and preserving muscle. But they differ from animal proteins in two well-established ways that are worth understanding, so plant-based eaters can read their tile with the right expectations.

• Lower average digestibility. On average, a somewhat smaller fraction of the amino acids in plant foods is absorbed and used, compared with animal sources.
• Amino-acid profile. Many single plant sources are lower in leucine and/or one or more essential amino acids — grains tend to be low in lysine, some legumes lower in methionine — so any one source, on its own, gives a slightly weaker per-gram muscle-building signal than, say, whey or eggs.

The practical consequence is modest and easy to handle: to get the same usable amino-acid delivery, plant-based eaters may benefit from a slightly higher total protein intake and from combining complementary sources across the day (for example legumes with grains) so the overall amino-acid profile is complete. Note "across the day" — the old idea that you must combine proteins within a single meal is outdated and unnecessary.

Just as important is what not to over-state. At adequate total intake with varied sources, plant-based diets support muscle just fine, and well-dosed plant proteins such as rice and pea have produced results comparable to whey in research. So the accurate framing is: plant-based eaters may need to be a little more deliberate — slightly more total protein, varied and combined sources — not that plant protein is inferior or can't build muscle.

10. Practical takeaways in Strathlon

• Aim for the range, then stop optimising the number. Roughly 1.6–2.2 g/kg per day covers most training goals. If your tile is well below 1.6, that's your clearest win; once inside the range, put your effort elsewhere.
• In a deficit, aim high in your range. When your energy balance is negative, edge toward the top of the range — protein does more work when energy is scarce. That's cutting with your shield up.
• Pair protein with training. Protein is the shield; your resistance training is what tells the body the muscle is worth keeping. Maintaining your lifts in a deficit is a sign the weight you're losing is fat, not muscle.
• Don't confuse "more protein" with "more muscle." Above sufficiency, extra grams add little. Growth comes from progressive training and enough total calories, with protein as a requirement, not an accelerator.
• Fix a low intake with one anchor per meal. A deliberate protein source at each meal raises your total naturally — no gram-by-gram counting required. Watch the Trends line climb.
• Individualise where it matters. Older, leaner, higher-volume, or plant-based? Aim a little higher in the range. Have a medical condition? Make it a conversation with a professional.

This is general educational information, not medical or dietetic advice. Individual variation is large, and figures such as the 1.6–2.2 g/kg range and per-meal guidance are approximate, evidence-based estimates rather than exact prescriptions. Anyone with kidney disease, diabetes, a history of disordered eating, or who is pregnant, as well as any athlete concerned about under-fuelling, should consult a qualified physician or registered dietitian before making significant changes to how they eat or train. See our Terms for more.

Understanding your stats · Energy balance · Training volume · User guide · Home