In one pass Once a crab dies, bacteria start multiplying in the meat and can produce harmful small molecules that survive heat, so no amount of steaming removes them.
Educational content, not medical advice — consult a clinician.
Once a crab dies, bacteria start multiplying in the meat and can produce harmful small molecules that survive heat, so no amount of steaming removes them. That is why the hardest rule for eating crab is to eat only crabs that were alive, killed and cooked right away. Why cooking cannot undo this is walked through step by step in the chapter on purines, dead-crab safety and allergy.
Crab is a crustacean, a close relative of shrimp and lobster. In China the best known is the hairy crab (Chinese mitten crab), and its autumn roe and paste are a festive-table topic; sea crabs (swimming crab, flower crab, king crab) are available all year. The edible part of a crab comes in two kinds:
Meat: white muscle, high in protein and low in fatRoe and paste: in the female, the gonads plus the hepatopancreas (the roe); in the male, the gonads (the paste). Fat and cholesterol are concentrated here, and so is the flavor The arguments about crab — is the cholesterol high, can people with gout eat it, is it a "trigger food" — almost all come down to the roe and paste. If you are allergic to crustaceans and your lips or throat feel tight, or you have trouble breathing after eating crab, call emergency services right away.
Mechanism · crab meat and crab roe are not the same tissue
Take a crab apart and crab meat and crab roe are not two cuts of the same thing. They are two completely different tissues. Every nutrition gap later in this story grows from here.
Crab meat is muscle. It lives in the claws and walking legs. Its job is to let the crab walk sideways and let the claws grip. Muscle is built mainly from the proteins that contract, so crab meat is almost all protein and almost no fat — a tissue made to do work has no reason to store oil inside itself.
Roe and paste are viscera. Roe is the female's hepatopancreas plus gonads; paste is the male's gonads. The name hepatopancreas already writes the job on its face: it does both liver and pancreas work — it secretes digestive juices that take food apart, then receives, processes, and stores the lipids it pulled out, for the crab itself and for the eggs it will make.
So one crab carries a clean split: protein that does the work on one side, lipid that stores the goods on the other. Every nutrition argument you hear about crab — is the cholesterol high, is it "fa wu" (a so-called trigger food), can a patient eat it — loses half its force the moment you ask are you talking about the meat or the roe.
That also explains a piece of kitchen experience: crab meat barely changes year-round; what autumn prices is always that mouthful of paste and roe. Those are gonad stores piled up before the breeding season. Their amount follows the season. The meat does not.
Chapter 2
Lean meat, but the roe is different
A crab on the plate is really two foods in one shell.
Cooked crab meat (using USDA's cooked blue crab) has about 83 kcal per 100 g, about 17.9 g of protein and only about 0.7 g of fat. Crab meat is lean, high-protein seafood, lean protein in the same class as skinless chicken breast.
Count the roe and paste too, and a whole river crab carries four times the cholesterol of plain crab meat. All of that difference sits in the roe and paste. The hepatopancreas is the organ where a crab processes and stores lipids; cholesterol is itself a lipid, and fat-soluble nutrients such as vitamin A can only dissolve in fat, so they are locked in the roe together. That is also why the roe tastes so rich.
So eating only the meat and eating it with the roe are two different meals. No composition table has measured crab roe on its own; the fourfold figure comes from subtracting crab meat from the whole crab.
A CLOSER LOOK
Count meat and roe separately
Categories are compared, not proportional areas; plain meat figures do not describe the whole crab.
1The muscle portion
Crab meat is high in protein and low in fat, unlike the roe and paste inside the shell.
2The fat-rich portion
Fat and cholesterol are more concentrated in roe and paste; consider them separately from muscle.
Illustration for understanding; not to scale. Saved figures include explanations and sources.
Numbers · Nobody has measured crab roe alone
A whole river crab carries four times the cholesterol of crab meat. Here is how that figure was bracketed.
A data trap first: no authoritative composition table has measured crab roe on its own. USDA has no Chinese mitten crab; China's food composition tables carry only three crab entries — sea crab, river crab, crab meat — and none for roe. So those online figures for how many milligrams of cholesterol sit in 100 g of crab roe mostly cannot be traced to a checkable measurement.
But those three entries can bracket it — whole crab minus meat:
River crab, whole edible portion (meat + roe/paste): 267 mg cholesterol / 100 gCrab meat, listed alone: 65 mg cholesterol / 100 gSea crab, whole edible portion: 125 mg / 100 g Whole river crab is four times pure crab meat, and only one thing sits between those two entries: the roe and paste.
One subtraction is still only arithmetic. What turns it into a conclusion is a second, fully independent clue pointing at the same place:
In the same table, vitamin A points the same way — whole river crab 389 µg , whole sea crab only 30 µg.
Vitamin A is fat-soluble. It does not pick a species on its own; it follows fat. When you eat river crab the roe and paste go into the edible portion whole; when you eat sea crab they make up a much smaller share — so the same organ lifts vitamin A and cholesterol together. Two unrelated components piled high in the same organ at once means what piled them is not coincidence. It is the organ itself.
That is also the most reliable kind of inference when you have no direct measurement: do not stop at one subtraction. Find a second independent clue and see whether it points the same way. Two independent clues in the same direction are more worth trusting than one clue calculated more precisely.
So the accurate statement is not how many milligrams of cholesterol crab roe contains (nobody measured it alone), but: the roe and paste pull a whole crab's cholesterol to four times that of its meat. Meat alone can pass as a meal for cutting weight; meat with the roe is in a different class.
Numbers · why the two cholesterol figures do not match
China's table puts crab meat at 65 mg of cholesterol; USDA's cooked blue crab is at 97 mg. The two numbers do not conflict: the Chinese entry has 84.4 g of water per 100 g, while the USDA one is cooked meat with 79.7 g of water — cooking drives off water and lifts the concentration, and the species differ too. Raw versus cooked, and where the crab came from, always have to be read separately.
This mismatch is worth a page of its own, because it is the trap you hit reading any composition table.
Every number in a composition table has a denominator of one hundred grams of food in that state. When you steam a crab, water leaves the meat. Protein, cholesterol, and minerals have not gone anywhere, but the hundred grams that held them has shrunk — so the same piece of meat, weighed cooked, reads a higher concentration than raw. The steamer did not make cholesterol. The denominator got smaller.
So when two numbers fight, ask three things first: raw or cooked? which species? how was the edible portion counted? If any one of those three answers differs, the two numbers are not comparable.
Most online screenshots of this food's cholesterol is shocking put numbers from different states next to each other, or pick the state with the highest concentration on purpose. Once that habit is in place, it is not only useful for crab: dried versus fresh, raw meat versus cooked, skin-on versus skin-off — all the same trap.
Numbers · How much sodium crab meat already has
One number often skipped: cooked crab meat already carries about 395 mg sodium per 100 g, and the dipping sauce is added on top of that base.
Steamed, no salt added does not mean low sodium — this figure is what the meat itself brings. The ginger-vinegar dish, that little dish of soy sauce, is a second serving of sodium on top of this floor. For people who need to watch salt, dipping less is less work than eating less: you still want the protein and zinc in the meat; you do not want the sodium in the sauce.
Protein quality: complete, all amino acids present (same tier as shrimp). For the protein mechanism, see Protein & Amino Acids.
Chapter 3
Should the roe's cholesterol worry you
The cholesterol argument about crab centers on the roe and paste. Subtracting the meat from the whole crab brackets the size: a whole river crab has 267 mg/100 g, plain crab meat 65 mg/100 g, and the fourfold gap comes from the roe and paste. The meat itself is not low either — 65 mg in China's table, 97 mg for USDA's cooked blue crab. That is moderate to high, in the same range as shrimp and eggs, and not "very low".
For most people, the cholesterol you eat moves blood lipids less than total saturated fat does, because the liver makes a little less to compensate. The US expert committee on dietary guidelines no longer sets a daily limit for dietary cholesterol (the full argument is in Shrimp and Eggs). Lines like "one crab equals so many eggs" scare you with a total and ignore absorption and compensation.
What matters more is how much roe you eat and how often: it is the part where fat and cholesterol are concentrated. For healthy people in crab season, watching the amount and the frequency is enough; if your blood lipids are sensitive, eat less roe and more meat.
The body compensates by down-regulating its own synthesis — left unopened, that sounds like comfort. Opened, it is a negative feedback you can walk yourself.
First, correct a default premise: most of the cholesterol in your blood was not eaten. The liver makes it. Liver cells run a full cholesterol-making line, because the body cannot do without it — every cell membrane needs it for stiffness, and bile acids, cortisol, and sex hormones all start from it. A thing you use every day, the body will not leave to luck.
If it makes its own, it needs a way to know whether it has enough. Liver cells watch their internal stock: the part you ate is absorbed in the gut and sent to the liver first; when stock in the liver rises, that line is slowed; when stock falls, the line speeds up again. That is negative feedback — a shop floor that schedules production from its own warehouse, cutting output when the warehouse is full, overtime only when it is empty.
So one more mouthful of paste does not mean one more mouthful of cholesterol in the blood. It means the liver makes a little less. Adding the milligrams on a food label straight onto blood lipids is, mechanistically, the wrong arithmetic.
Two honest boundaries, so you do not remember this backwards:
Compensation is not unlimited, and it is not equally sharp in everyone. A share of people are more sensitive to dietary cholesterol; after high-cholesterol food their blood rises more.Compensation only covers the cholesterol line. It does not mean anything goes — guidelines moved the focus from how many milligrams of cholesterol a day to total saturated fat precisely because the latter moves blood lipids more, and it does not walk this compensated path. In other words: what to watch was never how many milligrams sit in that crab. It is the shape of your diet over a stretch of time.
Mechanism · Why cholesterol piles up in the roe
What piles up in the roe and paste is not only oil but also phospholipid and cholesterol — there is a clean reason behind that sentence, clean enough that you can predict it the other way.
One use of the roe is to make eggs. One egg has to grow from a single cell into thousands of cells, and every extra cell needs a cell membrane built on the spot. The main materials of a membrane are exactly these two: phospholipids line up as the frame, cholesterol sits in the middle and decides whether the membrane is soft or stiff. The female has to pack the whole kit into the egg in advance, so besides oil meant to be burned, what piles up in the gonads and hepatopancreas includes building material.
Follow the same line and two more things fall out:
Why the fat-soluble nutrients are there too. Vitamin A and vitamin E do not dissolve in water; they only dissolve in fat. What the female stocks for the egg is not only building material, but these essentials — they share the same package as the roe's fat. Whole river crab has far more vitamin A than whole sea crab because this package is counted in its edible portion.Why the paste smells so rich. Most aroma molecules are fat-soluble too; wherever there is fat, flavor collects. The richness, the cholesterol, and the vitamin A are three faces of the same thing. So the right question about the paste is not whether you can eat it, but how much, and how often: it is one whole package, the wanted and the unwanted locked together. You cannot pick only the fragrant half — the only thing you can tune is the amount.
Chapter 4
Rich in what · zinc, selenium, B12 in the meat
The micronutrients in crab meat are the standard crustacean set:
Zinc: about 3-5 mg per 100 g, in a form the body absorbs easilySelenium: a core part of antioxidant enzymes, present in useful amounts in crabVitamin B12: needed for making blood and for the nerves; more in Vitamin B12Copper, phosphorus and niacin: moderate amounts The roe and paste add fat-soluble nutrients (vitamins A and E) and lecithin, but these come bound to fat — the vitamin A you get from the roe arrives together with the cholesterol.
So crab meat is good protein plus good micronutrients, and the roe is flavor, fat and cholesterol. Each has its place, but do not treat the roe as a tonic; it is first of all the high-fat part.
To compare shellfish, see Shrimp, or read the Oysters story.
Mechanism · what zinc and selenium actually do in the body
Just saying contains zinc, contains selenium leaves the reader with nothing to take. Put them back in the body for a look, and you can walk yourself through what happens when they are missing.
Zinc: a metal ion enzymes borrow as a nail
Zinc does not make energy. Its use is shape. A large share of enzymes and regulatory proteins in the body must first fold into a precise shape before they can work, and what holds that fold up is a zinc ion — like a nail, pinning several points on the protein chain together so the whole structure stands.
A large share of the work this nail holds is making new cells: wound healing, mucosal turnover, immune-cell proliferation, and letting taste buds replace themselves on schedule. So zinc deficiency shows up as a string of things that look unrelated — slow wounds, recurring problems in the mouth lining, easier infection, food that has no taste. What they share is not the word immunity. It is that they all belong to tissues that keep making new cells: the tissues that turn over fastest show the crack first.
Selenium: one atom on the enzyme's cutting edge
Selenium is not something you pile up either. The body makes it into a special amino acid and sets it in the active center of antioxidant enzymes. Those enzymes have a concrete job: as cells use oxygen they keep leaking peroxides (think of a batch of reactive molecules that bite whatever they meet); this enzyme takes them apart into water on the spot so they cannot bite. Without that one selenium atom, the enzyme is a pair of pliers with no blade.
So selenium's workplace is not a slogan like whole-body antioxidant. It is inside every cell that is using oxygen, and the more oxygen a tissue burns, the more it depends on it.
Why the same milligrams go in more readily from crab meat
Take zinc. Zinc from beans and whole grains gets wrapped by phytate — phytate is the molecule plants use to store phosphorus, and the negative charge it carries grabs zinc ions; once grabbed they get excreted together. Animal foods have no phytate, and the amino acids released when you digest protein also hold zinc in solution.
That is what high bioavailability actually means: not that seafood is more elite, but that this bite has nothing competing with you. You can run it the other way too — for someone who mainly covers zinc from beans and grains, soaking, fermenting, and sprouting (the moves that lower phytate) do more than eating another handful of beans.
Chapter 5
What it lacks · how to pair
What crab lacks is fiber, carbohydrate and vitamin C: it is almost all protein and lipid, so a meal of crab alone is all meat.
A few practical pairings:
Ginger and vinegar: the idea that crab is "cold" by nature is folklore, but ginger's heat and vinegar's sourness really do lift the flavor and cut the richness. Ginger's antimicrobial effect is weak (see garlic), so it cannot act as a disinfectant; the pairing works through taste and texture, not by "warming" youWhole grains or congee: add carbohydrate and fiber so the meal is completeLeafy greens: add vitamin C and fiber On gout: like shrimp and oysters, crab is one of the higher-purine foods. Purines are broken down into uric acid in the body, so people with high uric acid should hold back. That is a separate issue from cholesterol, covered in the chapter on purines, dead-crab safety and allergy.
Myth · ginger-vinegar is seasoning, not a disinfectant
Ginger-vinegar with crab is the right pairing, but many people treat it as a layer of insurance: dip it in ginger-vinegar and the crab is safe. That step is wrong, and the wrongness has a cost.
Keep two things apart:
On flavor: ginger's heat and vinegar's acid do lift taste and cut richness, so a mouthful of thick paste does not sit heavy. That part is real, and it is the real reason this pairing has not changed for centuries.On safety: ginger's antimicrobial meaning is modest — and modest is the key word here. It means that little dish on the table, in concentration and contact time, is nowhere near enough to handle a crab that has already gone off. The sauce stays in your mouth a few seconds; spoilage has already been running inside the crab for hours. The two steps that actually decide safety both happen before the plate: was the crab alive, and was it steamed through. Those two done, ginger-vinegar is only there to taste good; those two not done, ginger-vinegar cannot save it.
Folk practice often hides a correct move under a wrong explanation. The move — ginger-vinegar with crab — is worth keeping. The explanation — dip it and you are fine — has to be swapped out. Keep that explanation and you will not throw the crab when you should.
There are three things to remember about eating crab, in order of importance:
1. Never eat a dead crab — this is the hardest rule. After a crab dies, its own digestive enzymes start breaking down the meat, then bacteria (including Vibrio) multiply and can produce heat-stable harmful small molecules. Cooking kills the bacteria but cannot remove what they have already made. Kill live crabs and cook them right away; throw out any that have died, especially ones that have been dead a long time.
2. Purines and gout — hold back, but do not overreact. Like shrimp, oysters and sardines, crab is one of the higher-purine foods, and purines are broken down into uric acid in the body. People with high uric acid or an acute gout attack should eat less of both the roe and the meat; healthy people with normal uric acid do not need to worry about purines.
3. Allergy — a crustacean allergen. Like shrimp, crab contains the allergen tropomyosin, so people allergic to shrimp are likely allergic to crab too and should avoid it. If your lips or throat feel tight or you have trouble breathing after eating crab, call emergency services right away.
The first rule is talked about least but is the hardest; the other two get more attention, but each applies to a clear group of people. For healthy people in crab season: live crabs, cooked fresh, in moderation, with vegetables on the side.
Mechanism · why cooking cannot save a dead crab
Cooking will not take it away is the most counter-intuitive sentence: cannot high heat kill bacteria? It can. The problem is that by then what you have to deal with is no longer the bacteria.
Split the hours after a crab dies into three steps:
Step one, it starts digesting itself. A live crab's digestive enzymes are held in the hepatopancreas, meant to take apart what it ate. The moment the heart stops, they cannot be held; the enzymes leak into nearby tissue and start taking apart the crab's own protein — what they leave is a pile of free amino acids. This step happens on the crab itself. It needs no outside bacteria, and it is why dead-crab meat goes mealy and soft.
Step two, bacteria take over. The crab's gut and surface already carry bacteria (Vibrio is among the most common in aquatic settings). While it is alive, its own immunity and hemolymph hold them down. The host dies, the hold lifts, and step one has just set out a ready table of amino acids. The warmer it is, the faster they grow — that is why a dead crab left on a room-temperature stall for half a day is far more dangerous than one on ice.
Step three, bacteria remake the amino acids into small molecules. Bacteria carry a class of enzymes that clip one end off an amino acid and turn it into a biogenic amine; histamine is the most famous of them. By this step the dangerous carrier has switched from live bacteria to a pile of compounds.
So the steamer can only solve step two: high heat denatures bacterial protein and the bacteria do die. But a biogenic amine is not a protein. It is a simple, heat-stable small molecule, and it is still there no matter how long you steam. You killed the workers who made it, not the thing itself.
One boundary so you do not remember the wrong object: histamine poisoning is more classic in high-histidine scombroid fish; on the crab side, what to remember is the post-death spoilage plus Vibrio route. What the two paths share is the same point — spoilage is irreversible; heat can stop it from continuing, it cannot roll it back.
That point applies far beyond crab. Next time the thought cook it and you are fine comes up, ask first: am I dealing with something still alive, or with what it has already left behind.
Mechanism · how a purine becomes the pain in a joint
Purines metabolize to uric acid in the body — both ends of that sentence are there; a few steps in the middle are missing, and the missing ones are exactly the ones that decide whether you should worry.
What a purine is. It is not a toxin. It is one of the parts of DNA and RNA; anything with cells contains it. The denser the cells, the more nuclei a tissue has, the more purine you get when you take it apart — this is the usual explanation for why viscera, roe, and crustaceans run high: they are either extremely metabolically active, or they hold a mass of cells waiting to develop. By the same logic, if crab roe is higher in purine, the reason would be that it holds eggs, not that it is oily (purine in crab roe has not been measured on its own).
Uric acid's trouble is that it will not stay dissolved. Plasma has an upper limit on how much uric acid it can hold. Below that line, uric acid stays dissolved in the blood and rides along, and nothing happens; once it exceeds, the extra may drop out of the blood as needle-like crystals. Crystals like to settle where flow is slow and temperature is lower — a toe joint happens to be one of the coldest corners in the body, which is why gout's classic first site is the big toe.
The real pain comes from the immune system, not the crystal itself. Immune cells treat these needle crystals as invaders and try to swallow them, but they can neither swallow them nor dissolve them, so they keep releasing inflammatory signals. The red, the swelling, the heat, the sharp pain are all products of that siege, not the crystal scratching the joint. Once you see that, you know why acute treatment is aimed at inflammation, not at dissolving the crystals on the spot.
With the chain connected, two sentences that look like they contradict each other both hold:
Why gout is mainly a metabolism and excretion problem, not one bite of crab triggering an attack. Most of the uric acid in blood comes from the body taking apart its own old cells; food is only one piece. And whether the water level is high depends more on the kidney's ability to send uric acid out. One crab meal can push the level up a little, but what sets the level is the tap and the drain, not this spoonful.Why you still hold back. For someone already sitting on that solubility line, one concentrated purine load may push the level over and set off an attack — a study that followed people with gout found more recurrent attacks after days when they ate more purines (an observed association). Over the long run, in a US cohort that followed tens of thousands of men (Choi and colleagues), the group that ate the most seafood had a higher risk of gout than the group that ate the least, while eating more of the higher-purine vegetables (spinach, asparagus and the like) was not linked to higher risk. These are observed associations, and they were seen only in men. In a gout diet, sugary drinks and alcohol come before seafood as the things to cut first; the gout story explains why.
So it is two different sentences for two different people: a healthy person with normal uric acid need not be anxious about purines when eating crab in autumn; someone already high in uric acid or recently flared should manage more than this one crab meal — they should manage the long-term water level. What to do in your own case, confirm with a doctor.
Mechanism · why a shrimp allergy usually includes crab
People allergic to shrimp are likely allergic to crab too — that is not coincidence, and it is not the loose category seafood doing the work. The reason sits on one specific protein.
The immune system recognizes an allergen by shape. An antibody is like a lock that only fits a particular set of bumps; it does not care which animal the protein came from. As long as the shape matches, it fires.
The main protein in crustacean allergy is tropomyosin, a structural piece in muscle that regulates contraction. The key: this protein does a job every animal that moves has to do, so evolution has barely changed it — the shrimp piece and the crab piece look extremely alike. So antibodies in a person that recognize shrimp tropomyosin still match the crab piece. That is cross-reactivity.
From there you can push three things outward yourself:
The closer the kinship, the higher the chance of cross-reaction. Shrimp, crab, lobster, and crayfish are all crustaceans; cross-reaction among them is the most common.Mollusks are another layer. Oysters, clams, and scallops are mollusks, further away, but they have their own tropomyosin, so a share of people still react to both — the probability is lower than among crustaceans, but it is not zero.Fish allergy is a different matter. The lead protein in fish allergy is another class, not in the tropomyosin family. So the word seafood allergy actually packs two completely different problems into one basket: being allergic to shrimp does not mean you cannot eat fish. One more point shares a root with the dead-crab rule: heat does not solve it. Tropomyosin is heat-stable; after steaming or boiling through, that shape is still there, and the antibody still recognizes it. Same point as the biogenic amines — high heat can change a living organism; it cannot change a molecule that was already stable.
For someone already diagnosed with a crustacean allergy, the only reliable move is to avoid it, and to have an emergency plan ready as the doctor directs. If your lips, tongue or throat swell or feel tight, or you have trouble breathing after eating crab or shrimp, that is a sign of a severe allergic reaction: call emergency services or go to the emergency department right away.
Buying: buy them alive — a live crab has alert eyes, blows bubbles and flips itself upright quickly. Do not buy dead crabs, especially ones with soft shells, a bad smell or missing legs. For hairy crabs, go by origin and season (autumn); for sea crabs, go by freshness.
Cooking: steam thoroughly (15-20 minutes after the water boils, depending on size), and never eat them half-raw; plain steaming keeps the most flavor. Throw out any crab that has died, even if it looks fine — this is the never eat a dead crab rule put into practice in the kitchen.
How much: for a healthy adult, 1-2 hairy crabs (or the same amount of sea crab) at a sitting is reasonable. Eat the roe and paste in moderation, not as the meal; the meat is lean protein, so you can eat more of it.
Who should be careful: people with high uric acid or gout (less roe, fewer crab meals), people with a crustacean allergy (avoid it), pregnant women (only fully cooked crab, nothing half-raw), and people whose blood lipids are sensitive (less roe). For specific medical questions, ask your doctor.
Mechanism · why steamed through is not just cooked
In steam thoroughly, the word that actually matters is through, not cooked.
Heat walks from the outside in. A crab's shell is thick and conducts slowly, and one crab's body is very uneven in thickness — shell, body, and claws are each their own thickness. The outer shell has already changed color while that small center mass may not yet be at a temperature that inactivates bacteria. That is why time has to follow size: a large crab does not need more heat. It needs more time, so the heat can finish the walk from shell to center.
Two practicals follow:
Stacked steaming does not count. A pot packed full, layer on layer, and steam never reaches the ones in the middle; the nominal time is up and they are still short. Better two pots.Count from when the water boils. If you start from cold water, the early stretch is not yet at steam temperature, and that stretch should not be counted. As for the color changed, so it is done: the shell turning red is pigment in the shell showing color after heat. It reflects how much heat the surface took, not how much the center took. It can be a hint. It cannot be a verdict.
One easy mix-up to clear: steam through and do not eat a dead crab are not two wordings of the same rule. They each cover a stretch — steaming through deals with something still alive; buying live crab deals with something already formed. High heat can solve the first; it cannot solve the second. So you need both. One short is not enough.
Chapter 8
Does one crab equal dozens of eggs
Two claims about crab get passed around the most.
Claim one: one crab has as much cholesterol as dozens of eggs. You do not need an argument for this one; do the arithmetic and it falls apart.
A 150 g hairy crab is about 42% edible, so about 63 g. At 267 mg per 100 g for a whole river crab, one crab carries about 170 mg of cholesterol. A 50 g egg carries about 186 mg, all of it in the yolk. One medium hairy crab has about the cholesterol of one egg — not dozens; the claim is off by about thirtyfold.
Claim two: crab is "fa wu" (a trigger food), so sick people cannot eat it. "Fa wu" is a folk idea with no agreed medical definition. Underneath it sit three unrelated real things — allergy, purines and fat — and each has a clear group of people and a clear mechanism, so each can be handled on its own. Instead of asking is it fa wu, ask: do I have a crustacean allergy, is my uric acid high, can my digestive system handle a fatty meal right now?
Myth · How this conversion inflates both ends
Where this conversion goes wrong: it multiplies the concentration of one mouthful of paste by the weight of the whole crab, and inflates both ends.
Split the two ends and look at each. Each is its own small move:
Left end inflated: let the densest part stand for the whole. The paste is a concentrate, but it is only a small piece of one crab; the rest is lean meat that holds almost no cholesterol. Multiplying paste concentration by whole-crab weight is assuming you swapped the entire crab for paste.Right end shrunk: treat live weight as edible portion. A crab feels heavy in the hand, but you do not eat the shell, gills, or viscera. A 150 g hairy crab is only about 42% edible, and converting to the edible portion is exactly the step scare-conversions love to skip. Move both ends at once and you can flip the result by tens of times. The shared structure of this genre: no single step is a lie on its own, but every step leans the same way.
Two further layers: ① dietary cholesterol moves most people's lipids less than total saturated fat, and the body compensates by down-regulating its own synthesis (the full argument is in Shrimp and Eggs); ② what sets blood lipids is long-term dietary pattern, not those few crabs in autumn.
In other words, even if that milligram figure were true, it would not become blood cholesterol one-for-one — each layer after the arithmetic shaves it.
When a conversion is meant to scare you, finish the multiplication first — most of this genre does not survive one pass on a calculator. You do not need to know nutrition. You only need to be willing to press the keys once.
Myth · what question should replace the 'fa wu' label
Fa wu is a folk concept with no unified medical definition — different people, different places, pack completely different things into this word. But it has lasted this long because a few real things sit under it. Taken apart, they are three mechanisms that each hold and have nothing to do with one another:
Allergy: people allergic to crustaceans do rash on crab, sometimes worse. This is the immune system misreading a protein, mechanism clear, population clear, and it only holds for this small share of people.Purines: people with gout and high uric acid do need to restrain. This is a uric-acid water-level problem, unrelated to immunity, and it corresponds to another group.High fat: pancreatitis recovery should moderate the paste. This is the digestive system's ability to handle fat, and it is another matter again from the first two. Three mechanisms, three groups, three ways to handle them. What the word fa wu does is mash them into one lump and drop it on everyone's head — so a person who is not allergic to crab, whose uric acid is normal, and whose digestion is fine, also gets told not to eat.
A fuzzy blanket term is dangerous not because it is all wrong, but because it makes two errors at once: the people who should avoid think they are only avoiding a food, and do not know where the real red line is; the people who should not avoid give up a good protein for nothing.
So the method is to swap the question. Do not ask is it fa wu. Ask for me specifically, what is the mechanism: do I have a crustacean allergy? where is my uric acid? is my digestive system in the middle of recovering from something? Answer those three and you do not need the label — and this way of asking still holds when you swap in any other fa wu.
In the end, crab's controversies (cholesterol, "fa wu") are mostly complex mechanisms compressed into scare slogans, while its genuinely hard safety rules (live, cooked, moderate) go unmentioned. Same reversal structure as Instant Noodles.
References · 13
U.S. Department of Agriculture, Agricultural Research Service. (2019). FoodData Central: Crustaceans, crab, blue, cooked, moist heat (SR Legacy, FDC ID 174205). Per 100 g cooked meat: 83 kcal, 17.9 g protein, 0.74 g fat, 97 mg cholesterol, 3.81 mg zinc, 42.9 µg selenium, 3.33 µg vitamin B12, 395 mg sodium. FDC has no record for Chinese mitten crab, and no record separates roe or hepatopancreas from meat. fdc.nal.usda.gov
Chinese Center for Disease Control and Prevention, National Institute for Nutrition and Health. China Food Composition Tables (6th ed.), official query platform, crab entries 1102 / 1103 / 1104. Per 100 g edible portion — river crab (Chinese mitten crab, whole edible portion including roe and paste; edible fraction 42% of live weight): 17.5 g protein, 2.6 g fat, 267 mg cholesterol, 389 µg RAE vitamin A, 3.68 mg zinc. Sea crab (whole edible portion, edible fraction 55%): 13.8 g protein, 2.3 g fat, 125 mg cholesterol, 30 µg RAE vitamin A. Crab meat alone (edible fraction 100%, water 84.4 g): 11.6 g protein, 1.2 g fat, 65 mg cholesterol. No Chinese or US composition table lists crab roe or hepatopancreas as a separate entry; the whole-crab minus meat-only difference is what bounds it. nlc.chinanutri.cn/fq/foodinfo/1103.html
Carson, J. A. S., Lichtenstein, A. H., Anderson, C. A. M., Appel, L. J., Kris-Etherton, P. M., Meyer, K. A., et al. (2020). Dietary cholesterol and cardiovascular risk: A science advisory from the American Heart Association. Circulation, 141(3), e39-e53. Saturated and trans fats raise LDL more than dietary cholesterol itself. 10.1161/CIR.0000000000000743
National Institutes of Health, Office of Dietary Supplements. (2021). Selenium — Fact Sheet for Health Professionals. Table 2: Brazil nuts, 1 ounce (6-8 nuts), 544 mcg selenium (989% DV); the text says Brazil nuts contain 68-91 mcg per nut and could cause selenium toxicity if consumed regularly, and that values from other analyses vary widely. The version read carries 'Updated: April 15, 2024' (Wayback Machine snapshot of 31 December 2024), newer than the 2021 date above (fact sheet, read 2026-09-24). The September 4, 2025 update (Wayback snapshot 19 September 2026) adds: the body absorbs up to about 90% of selenium from selenomethionine, selenium-enriched yeast, selenite and selenate; selenium-only supplements typically contain 100 to 400 mcg; Keshan disease, an endemic cardiomyopathy first identified in 1935 in low-selenium parts of China, fell dramatically after selenium intervention trials in the 1970s-1990s; in 2017 the American Thyroid Association issued a weak recommendation against selenium supplements for TPOAb-positive pregnant women (fact sheet). ods.od.nih.gov/factsheets/Selenium-HealthProfessional
National Institutes of Health, Office of Dietary Supplements. (2024). Vitamin B12 — Fact Sheet for Health Professionals. Fact sheet (updated July 2, 2025; Wayback snapshot 20 September 2026): multivitamin/mineral supplements typically contain 5 to 25 mcg B12, B-complex products 50 to 500 mcg, B12-only supplements typically 500 to 1,000 mcg; absorption is only about 2% at 500 mcg and 1.3% at 1,000 mcg; a 2018 Cochrane review of 3 RCTs (153 participants) compared very high oral doses (1,000-2,000 mcg) with intramuscular B12; high oral doses (e.g. 1,000 mcg/day) might be equally effective in Crohn's disease and appear as effective as hydroxocobalamin injections after Roux-en-Y bypass. These are product contents and trial doses; the sheet gives no recommended daily supplement range (fact sheet). ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional
Jiang, D., Han, H., Guo, Y., Zhang, R., Zhan, L., Zhou, Y., et al. (2024). Epidemiological characteristics of sporadic foodborne diseases caused by Vibrio parahaemolyticus - China, 2013-2022. China CDC Weekly, 6(51), 1354-1359. 23,818 cases identified. 10.46234/ccdcw2024.269
Chen, L., Wang, J., Chen, J., Zhang, R., Zhang, H., Qi, X., & He, Y. (2023). Epidemiological characteristics of Vibrio parahaemolyticus outbreaks, Zhejiang, China, 2010-2022. Frontiers in Microbiology, 14, 1171350. 383 outbreaks, 4,382 illnesses; July-September accounted for 77.54%. 10.3389/fmicb.2023.1171350
Ladero, V., Calles-Enríquez, M., Fernández, M., & Alvarez, M. A. (2010). Toxicological effects of dietary biogenic amines. Current Nutrition & Food Science, 6(2), 145-156. Fermented foods contain histamine and tyramine; sensitive individuals and those on MAO inhibitors should limit high-tyramine fermented/cured foods (established drug-food interaction). 10.2174/157340110791233256
Zhang, Y., Chen, C., Choi, H., Chaisson, C., Hunter, D., Niu, J., & Neogi, T. (2012). Purine-rich foods intake and recurrent gout attacks. Annals of the Rheumatic Diseases, 71(9), 1448-1453. Acute purine-rich intake (including oily fish) was associated with a higher risk of recurrent gout flares. 10.1136/annrheumdis-2011-201215
Choi, H. K., Atkinson, K., Karlson, E. W., Willett, W., & Curhan, G. (2004). Purine-rich foods, dairy and protein intake, and the risk of gout in men. New England Journal of Medicine, 350(11), 1093-1103. Health Professionals Follow-up Study: 47,150 men with no gout at baseline, 12 years, 730 confirmed incident cases. Highest vs lowest fifth: meat RR 1.41 (1.07-1.86), seafood RR 1.51 (1.17-1.95), dairy RR 0.56 (0.42-0.74). Purine-rich vegetables and total protein intake were NOT associated with a higher risk (abstract, PMID 15014182). 10.1056/NEJMoa035700
U.S. Department of Agriculture, Agricultural Research Service. (2019). FoodData Central: Egg, whole / yolk / white, raw, fresh. One large egg ~72 kcal, 6.3 g protein, 5 g fat; yolk ~186 mg cholesterol and ~147 mg choline. fdc.nal.usda.gov