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food source · 17
←Eggs
Egg is often used as the yardstick for protein quality, because its amino acid pattern is close to what the body needs. About 91% of cooked egg protein is digested and absorbed, against only about 51% of raw.
Mechanism · Heat lets enzymes cut
The amino acid pattern of egg protein is close to what the body needs, so egg is often used as the yardstick for judging protein quality. Heat unfolds the protein's structure so that digestive enzymes can cut it. That turns the idea that raw eggs are more nutritious on its head: you swallow the same grams, but nearly half as much is absorbed.
Numbers · The protein in one egg
One large egg has about 6.3 g of protein, about 3.6 g in the white and 2.7 g in the yolk, so eating only the white misses part of it. A human study using stable-isotope tracers (Evenepoel 1998) found that about 91% of cooked egg protein was digested and absorbed, against only about 51% of raw.
Chicken is complete protein and high in leucine. Breast and thigh carry about the same protein and differ mainly in fat; skinless breast gives that protein for the fewest calories.
Mechanism · What complete protein means
The body assembles protein chains in order, and if one essential amino acid is missing, the whole chain stalls. Complete protein means there is enough of every essential amino acid, with no obvious weak spot. Leucine also doubles as a start signal: when blood leucine is high, muscle knows there is material for building protein. In experiments that measure muscle building over a few hours, a meal with more leucine pushes building higher after that meal; but in training trials that measure how much muscle grew over several weeks, how protein is split across meals matters little, and getting the day's total first matters more.
In practice · Breast or thigh
Skinless breast is highest in protein and very low in fat; skinless thigh has close to the same protein, clearly more fat, and a little more iron and zinc; with the skin on, both step up in fat again, because chicken skin is almost pure fat. Choosing breast or thigh is choosing a calorie budget, not a protein quality. Chicken has essentially no carbohydrate.
←Tuna
Raw yellowfin tuna has about 24 g of protein and less than 1 g of fat per 100 g, which makes it almost pure lean protein, with all nine essential amino acids.
Mechanism · All nine essential amino acids
The body builds protein chains in order, and if one essential amino acid is missing, the whole chain stops. Tuna has all nine essential amino acids in useful proportions, so nothing has to be made up from other foods. Once eaten, stomach acid unfolds the protein, digestive enzymes cut it into short pieces, and the small intestine passes the amino acids into the blood; muscle, enzymes and antibodies are all built from this same supply.
Numbers · Raw weight and cooked weight
Raw yellowfin tuna has about 24 g of protein, under 1 g of fat and 0 g of carbohydrate per 100 g, at about 109 kcal. Cooked figures are higher almost entirely because water is lost: the denominator shrinks, and you are not getting more protein. Water-packed canned tuna stays close to the fresh figures; oil-packed tuna still has more fat and calories than water-packed even after draining.
Cooked shrimp has about 20–24 g of complete protein and only 1–1.5 g of fat per 100 g, so it delivers a lot of protein for its calories.
Mechanism · Too lean to carry much oil
Shrimp is complete protein with very little fat, so its protein density per calorie is excellent. For the same reason it carries little omega-3: long-chain omega-3 travels mainly with fat, and shrimp has very little fat. Seafood does not automatically mean omega-3; how much it holds depends mainly on how fatty it is.
Numbers · The protein in a serving of shrimp
Per 100 g, cooked shrimp has about 20–24 g of protein and 1–1.5 g of fat, almost no carbohydrate, and about 85–100 kcal. A palm-sized portion of cooked shrimp weighs about 85 g and gives 17–20 g of protein. Boiling or steaming keeps it light; battering and frying can multiply the fat and calories several times over, and the extra comes from the coating and the oil, not the shrimp.
White fish has almost no fat, so nearly all of its calories come from protein, which makes it one of the most protein-dense animal foods per calorie.
Mechanism · What is special is the denominator
White fish has almost no carbohydrate and almost no fat, so protein is left to fill the calorie column. Its high protein density does not come from an unusually large amount of protein but from how little of everything else it has. It is complete protein, with enough of all nine essential amino acids and plenty of leucine. Cooking mainly removes water, and the total protein barely changes.
Numbers · Protein and calories in cod
Raw cod has about 82 kcal, about 17.8 g of protein and about 0.7 g of fat per 100 g. A 150 g serving of cooked cod gives about 30 g of protein for 130–150 kcal; the same protein from lean pork costs more than 200 kcal. Shop and log food by raw weight, because mixing raw and cooked figures overcounts.
Soy is one of the few complete plant proteins, with all nine essential amino acids on its own, which sets it apart from starchy staples. Tofu takes its protein quality from the soybean; how much protein it has depends on how much water it holds.
Mechanism · Complete protein, rare in plants
Most grains fall short on lysine, and most beans fall short on the sulfur-containing amino acids. Soy has enough of all nine essential amino acids and needs no pairing the way lentils and rice do. Tofu is soy milk protein set into a gel: its quality is the soybean's, and its concentration depends on its water content.
Numbers · Firm tofu and silken tofu
According to USDA, firm tofu has about 12–17 g of protein per 100 g, silken tofu about 5–8 g and dry soybeans about 36 g. A palm-sized piece of firm tofu has about as much protein as a small piece of chicken. Choosing silken or firm changes the water content, not the protein quality; tempeh, pressed from whole beans, is denser in protein than watery tofu.
Salmon is complete protein. Its fat is woven through the muscle and cannot be removed, so the protein arrives together with fat rich in omega-3.
Mechanism · Protein and good fat come together
Salmon has all nine essential amino acids and is highly digestible, in the same class as lean beef and chicken breast. Its fat is woven into the muscle, so every bite carries protein together with EPA and DHA, and the two cannot be separated.
Numbers · The protein in a fillet
Cooked farmed Atlantic salmon has about 22–25 g of protein and 12–13 g of fat per 100 g. A typical fillet weighs about 150–180 g, which gives more than 35 g of protein in one meal.
←Pork
Lean pork is complete protein with all nine essential amino acids, and thiamin (vitamin B1), zinc and B12 sit in the same lean meat, so choosing a lean or a fatty cut changes more than the calories.
Mechanism · The nutrients follow the lean
Pork protein is complete, with all nine essential amino acids and plenty of leucine. Protein, B1, zinc and selenium sit in muscle tissue, because they are parts muscle needs for its work; fat tissue supplies little besides calories. So for the same hundred grams, tenderloin versus belly changes not only the calories but the concentration of that whole list of nutrients.
Numbers · Tenderloin versus belly
Raw pork tenderloin has roughly 20–22 g of protein, 3–5 g of fat and 0 g of carbohydrate per 100 g, at about 120–145 kcal. Pork belly often runs 30–50 g of fat per 100 g, pushing calories above 500 kcal. Keep raw and cooked weights apart: cooking drives off water, so the figures per 100 g go up.
←Crab
Cooked crab meat has about 17.9 g of protein and 0.7 g of fat per 100 g, lean protein like skinless chicken breast. The roe and paste are a different food, far higher in cholesterol.
Mechanism · Two foods in one shell
Crab meat is lean, complete protein, in the same class as shrimp. The roe and paste are the crab's hepatopancreas and gonads, where fat-soluble nutrients and cholesterol are concentrated. So eating only the meat and eating it with the roe and paste are two different meals.
Numbers · Meat, roe and sodium
USDA's cooked blue crab meat has about 83 kcal, about 17.9 g of protein and about 0.7 g of fat per 100 g. Whole river crab, roe and paste included, has about 267 mg of cholesterol per 100 g against about 65 mg in the meat alone, and the fourfold gap is all in the roe and paste. Cooked crab meat already carries about 395 mg of sodium per 100 g, and dipping sauce adds a second helping on top.
←Milk
Milk protein is complete, with enough of all nine essential amino acids. About 80% is casein, which curdles in the stomach and digests slowly; about 20% is whey, which digests fast and is rich in leucine. A 250 ml glass holds about 8 g.
Mechanism · One slow protein and one fast
Casein curdles when it meets stomach acid and is released slowly and steadily; whey does not curdle, is digested and absorbed quickly, and is rich in leucine, and it is the raw material of the whey powder people drink after a workout. A glass of milk carries both, so one share arrives quickly and the other is released slowly.
Numbers · Whole milk versus skim
Milk has about 3.2–3.4 g of protein per 100 g, or about 8 g in a 250 ml glass. Whole milk has about 60–65 kcal per 100 g and skim milk about 34–36 kcal; a glass comes to roughly 150 kcal for whole and 85 kcal for skim. The gap is real but not large, and both carry about the same protein. Carbohydrate is about 4.8 g per 100 g, mostly lactose.
Greek yogurt is yogurt with the whey drained off, so it has roughly twice the protein by weight: about 8–10 g per 100 g, against about 3.5–4 g in regular plain yogurt.
Mechanism · Strained, not a different culture
Greek yogurt does not use a different culture; the whey is drained off. With the water gone, the protein becomes denser, and part of the lactose leaves with the whey. Its protein is still casein plus whey, one digested slowly and the other quickly.
Numbers · Protein in three kinds of yogurt
Per 100 g, regular whole-milk plain yogurt has about 3.5–4 g of protein and whole-milk Greek yogurt about 8–10 g. Non-fat Greek yogurt still has about 8–10 g of protein with almost no fat, an efficient choice when you want more protein and less fat. The carbohydrate in plain yogurt is lactose; the extra carbohydrate in a flavored cup is mostly added sugar.
Hard aged cheese is almost all protein and fat: Cheddar has about 25 g of protein and 33 g of fat per 100 g. It is usually eaten a small piece at a time, as a small, dense source of protein and calcium.
Mechanism · Water content sets the density
Cheese protein is complete, with enough of all nine essential amino acids. Cheeses differ mainly in how much water they hold: hard aged cheese has little, so it is almost all protein and fat; cottage cheese is watery, so the same weight holds much less protein. A small piece of hard cheese gives a fair amount of protein, but its calories come along with the fat.
Numbers · Protein across cheeses
Cheddar has about 25 g of protein, 33 g of fat and about 403 kcal per 100 g; a small 30 g piece gives about 7.5 g of protein and about 120 kcal. Parmesan is drier, with up to 35 g of protein per 100 g. Cottage cheese has about 11 g of protein per 100 g. Cream cheese is nearly pure fat, with only about 6 g of protein.
Quinoa is one of the very few plant foods with enough of all nine essential amino acids, lysine especially, which is exactly what grains lack most. But it does not have much protein: cooked quinoa has about 4.4 g per 100 g.
Mechanism · It has what grains lack
Grains such as rice and wheat mostly fall short on lysine. Quinoa has enough of all nine essential amino acids, lysine especially, so it is complete on its own and does not need pairing the way rice and beans do. It is not a grass grain but the seed of a plant in the amaranth family, a close relative of spinach and beets, which is why its amino acid pattern is unlike that of wheat or rice.
Numbers · Strong on balance, not on amount
Complete protein means no weak spot, not more protein than meat: cooked quinoa has about 4.4 g of protein per 100 g against about 2.7 g in white rice, far less than the same weight of tofu or egg. For vegetarians, making quinoa a staple eases the amino acid balance, but the total still has to come from beans and soy foods. The bitter saponins coating the seed should be rinsed off before cooking; what washes away is the bitterness, not the protein.
Lentils are a high-protein bean that can serve as a staple: cooked lentils have about 9 g of protein and 8 g of fiber per 100 g, and protein supplies about 30% of their calories, which is rare for a staple food.
Mechanism · Its gap is not the grain's gap
Lentil protein is incomplete: it is rich in lysine and low in methionine. Grains are the other way round, which is why lentils with rice turn up in many cuisines: the two gaps offset each other. There is no need to pair them precisely in one meal; eating both over the day is enough.
Numbers · Cooked and dry lentils
Cooked lentils have about 9 g of protein, 20 g of carbohydrate (about 8 g of it fiber) and about 0.4 g of fat per 100 g, at about 116 kcal; dry lentils are about 2.5 times as concentrated, with about 25 g of protein per 100 g. Protein supplies about 30% of their calories, against about 7–8% for rice. Lentils have a glycemic index (GI) of about 25–30, which makes them a low-GI food.
Peanuts are the seeds of a legume and have about 25 g of protein per 100 g, high among plant foods; but on their own they are not complete protein, being low in both lysine and methionine.
Mechanism · Count it as a bean
Peanuts are legumes: bacteria in nodules on their roots fix nitrogen from the air, and nitrogen is an essential building block of protein, which is why beans in general are high in protein. On their own peanuts are not complete protein, since they are low in both lysine and methionine; grains, milk, eggs or soy foods over the day fill the gaps. The kitchen treats them as nuts, but the nutrition works like a bean's.
In practice · Calories and allergy
Peanuts have about 25 g of protein per 100 g, and most of their calories come from fat; with peanut butter, also check for added sugar and salt. Peanut allergy is real and separate from their nutritional value: if the lips or throat swell or breathing becomes difficult after eating them, go to the emergency department or call emergency services right away.
Chickpeas are high in protein, about 17–22% on a dry-seed basis, but eaten alone they are not complete protein: they are rich in lysine and low in the sulfur-containing amino acids, and eating them with rice or wheat fills the gap.
Mechanism · High content is not completeness
Chickpeas are rich in lysine but low in the sulfur-containing amino acids, methionine and cysteine. Grains such as rice and wheat are the other way round, so chickpeas with rice or whole wheat bring the meal's protein close to complete; eating beans and grains over the same day is enough.
In practice · The catch in hummus
Chickpeas are about 17–22% protein on a dry-seed basis, low in fat, mostly unsaturated, and high in fiber. With hummus, what needs watching is the oil, tahini and sodium in it, not the protein quality of the beans.
Tempeh is whole soybeans bound into a cake by a mold, so it inherits soy's complete protein; because it is made from whole beans, it is denser in protein than watery tofu.
Mechanism · The protein quality comes from soy
To make tempeh, the threads of the mold Rhizopus oligosporus weave whole cooked soybeans into a cake, and its full set of nine essential amino acids is inherited from soy. During fermentation the mold releases phytase that breaks down part of the phytate, so minerals may be absorbed better, and its protein-cutting enzymes pre-cut some of the protein into short peptides. But fermentation does not create the protein quality.
In practice · Tempeh is not natto
A cake of whole beans holds less water than silken tofu, so it has more protein at the same weight. It is not natto either: natto's signature is MK-7, and tempeh's is this cake of complete protein. Nor is tempeh a reliable source of vitamin B12 for vegans.
synergy · 3
The mechanical signal from a muscle being pulled and the nutrient signal from the rise in blood leucine after eating protein meet at a switch inside the cell called mTORC1, and together they start muscle protein synthesis. So eating protein without training barely grows muscle, and training without enough protein grows it slowly.
After exercise, carbohydrate refills the muscle glycogen that was used (more GLUT4 glucose transporters sit on the muscle cell membrane at this point), and protein supplies the amino acids for building muscle protein, so one meal can do both. For muscle gain, though, the timing of protein matters little (Morton 2018): getting enough across the day matters more than racing the clock.
→Zinc
Animal protein loosens phytate's hold on zinc in the gut, so the plant-source zinc in the same meal is absorbed better too. Put the other way, this is one reason vegans need somewhat more zinc.
cofactor · 13
Older muscle responds less to protein (anabolic resistance): the same meal of protein produces less muscle building. Morton 2018 cites per-meal amounts at which muscle protein synthesis nears its plateau of about 0.24 g per kilogram of body weight in younger adults and about 0.40 g in older adults. The PROT-AGE 2013 consensus for adults over 65: 1.0–1.2 g/kg a day if healthy, at least 1.2 g/kg if exercising regularly, and 1.2–1.5 g/kg with acute or chronic illness, together with strength training. These figures do not apply to people with severe kidney disease who are not on dialysis; their protein intake is for the doctor to set.
The recommended amount for ordinary adults, 0.8 g per kilogram of body weight a day, is a floor to prevent deficiency, not an amount set for training adaptation. The Morton 2018 meta-analysis found that for people doing strength training, muscle gains largely level off at about 1.6 g per kilogram a day; those who want to maximize gains can go up to about 2.2 g.
Muscle cells sense leucine, which flips mTORC1, the switch for making protein. On how much one meal needs, Morton 2018 cites a plateau in the synthesis response at about 0.24 g per kilogram of body weight in younger adults and about 0.40 g in older adults; larger amounts still add something and last longer, just with diminishing returns (Trommelen 2023). What decides how much muscle you build is the daily total: for people doing strength training, the benefit keeps rising up to about 1.6 g per kilogram a day (Morton 2018).
What the body runs short of is never the amino group but the carbon skeletons of the 9 essential amino acids: transaminase enzymes constantly move amino groups from one molecule to another, and the coenzyme that does this work is pyridoxal phosphate (PLP), the active form of vitamin B6.
Antibodies, complement proteins and immune cells are all built from protein, and older adults need more protein than younger ones: PROT-AGE advises 1.0–1.2 g per kilogram of body weight a day for healthy people over 65, together with exercise so the body can use it. Falling short costs twice: muscle is lost and the immune system runs short of raw material.
The Recommended Dietary Allowance of 0.8 g/kg a day is a floor against deficiency and may be low for women in midlife and beyond: the PROT-AGE consensus advises 1.0–1.2 g/kg a day for healthy people over 65, and at least 1.2 g/kg for those who exercise regularly. After menopause it matters even more to get enough protein, together with strength training.
Bone is not just mineral: its framework is collagen, and collagen is made from protein. The PROT-AGE consensus advises 1.2–1.5 g of protein per kilogram of body weight a day for people over 65 with an acute or chronic illness, spread so that every meal has enough; how it is spread across meals is easier to overlook than the total.
Biotin is the coenzyme for several carboxylases: one of them (3-methylcrotonyl-CoA carboxylase) breaks down leucine, and another helps break down amino acids such as isoleucine and valine. So biotin handles more than sugar metabolism; it also handles the breakdown of several branched-chain amino acids.
→HMB
HMB is a breakdown product of leucine; only about 5% of leucine ends up as HMB, and its effect leans toward reducing muscle breakdown. The signal that switches on muscle building (mTOR) comes mainly from leucine itself. They are different switches, so adding HMB when protein intake is already adequate adds little.
Making collagen needs a good supply of amino acids, especially glycine and proline, and that comes first from eating enough protein each day. In a small trial of 8 people, a gelatin supplement only raised a blood marker of collagen synthesis; whether injuries healed faster was not measured.
Strength training plus enough protein is the pair that actually preserves muscle here: the brief rise in testosterone after a session is not the point; what matters is the training signal plus leucine driving muscle protein synthesis through mTOR. No special testosterone-boosting program is needed; standard strength training is enough.
The body is doing different work at different points in the cycle: in one small trial, the group that concentrated leg strength training in the follicular phase improved more, though this needs more research to confirm. The uterine lining is rebuilt every month, and eating enough protein day to day supplies the raw material for that repair.
Not eating enough protein is an easily skipped item in a fatigue work-up, and those at risk are older adults and long-term dieters: when protein runs short, muscle is broken down for raw material first, and strength and stamina fall together.
depletes · 1
People who drink heavily over the long term often eat too little and absorb poorly, so they tend to run short of protein and energy, and their absorption of vitamin B1, B12 and folate falls; alcohol also damages muscle directly (alcoholic myopathy), speeding up muscle loss.
contrast · 1
The idea that protein harms the kidneys is a common misconception: in a meta-analysis of randomized trials, healthy adults on high-protein diets did not see their kidney function decline compared with those on normal protein. The main drivers of kidney damage are poorly controlled diabetes and high blood pressure, overuse of painkillers, and herbal products containing aristolochic acid. People who already have chronic kidney disease should follow their doctor on protein.