Blue Blood, Narrow Window

Sofi cooked pulpitos on Monday, after an afternoon at the pool with the kids. Baby octopus, a hot pan, about four minutes. Then I went and read the literature, which is a habit that has now cost me two evenings and turned up exactly one number I did not expect — and it is not the one printed on the label. Mushrooms were her first lesson. This is the second.

The number on the label and the number you keep

USDA FoodData Central lists cooked octopus at 36 µg of vitamin B12 per 100 g. The adult RDA is 2.4 µg. A 150 g portion therefore reads as 54 µg, or 2,250% of the requirement, and every nutrition site on the internet will print that figure in bold.

It is true and it is close to meaningless, because B12 does not cross the gut in proportion to how much of it is on the plate. There are two routes. The intrinsic-factor route is the efficient one and it has a hard ceiling: it saturates at roughly 1.5 to 2 µg per dose, and past that no amount of additional B12 in the same meal moves anything more through it. The second route is passive diffusion across the gut wall, which picks up on the order of 1% of what is left.

Run 54 µg through that pair and you land somewhere around 2 to 2.5 µg absorbed. Be careful with the comparison that suggests itself: the 2.4 µg RDA is an intake recommendation that already has normal absorption priced into it, so absorbed micrograms and RDA micrograms are not the same unit and should not be divided by each other. The honest version is simpler. Absorption does not scale with the number on the chart, and a 2,250% plate does not deliver 2,250% of anything.

This is not an octopus problem. The same ceiling sits under liver and under clams, which are among the richest sources anyone actually eats at roughly 99 µg per 100 g cooked. It is also the reason B12 tablets are dosed at 1,000 or 5,000 µg instead of 2.4 — at that size the 1% passive route alone hands over tens of micrograms, which is the entire design of a megadose. Octopus is simply where a food gets big enough to make the arithmetic visible. A portion covers your day comfortably and feeds stores that last months. What it does not do is deliver 2,250% of anything, and the percentage in the table is describing the food, not you.

Blue blood

Octopuses do not use haemoglobin. Their oxygen carrier is hemocyanin, a copper-based protein that floats free in the hemolymph rather than being packed into cells, and it is blue when oxygenated rather than red. It outperforms haemoglobin in cold, low-oxygen water and underperforms it in warm water, which is one reason cephalopod distributions move when sea temperature does.

The nutritional consequence is the copper column. Cooked octopus carries about 0.74 mg per 100 g — roughly 82% of the adult RDA in 100 g, and comfortably over it in the 150 g portion this article uses elsewhere — against something like 0.07 mg in beef. Not much in an ordinary diet reaches that density; liver, oysters, cocoa and some nuts and seeds are the company it keeps. Hemocyanin is the obvious suspect, though a composition table cannot tell you how much of the copper in edible tissue is residual hemolymph. It is still the rare case where the most interesting fact about an animal turns up on its nutrition label.

The same fact should make you careful about the line below it. Cooked octopus lists 9.5 mg of iron per 100 g, which reads like a red-meat number and gets quoted like one. Heme iron is the fraction humans absorb well — something like 15–35%, against 2–20% for non-heme iron depending on the rest of the meal. But FoodData Central reports total iron and says nothing about its chemical form; this is an animal that does not run an iron-based oxygen system; and I could not find a human absorption study on cephalopod iron at all. A real number of unknown speciation and unestablished bioavailability. Anyone treating octopus as an anaemia intervention is extrapolating past the data.

The protein ledger, and a claim that does not survive it

First, the trap that catches most write-ups. FoodData Central has two octopus entries — raw, and cooked with moist heat — and the cooked numbers are close to double the raw ones because the animal loses about half its weight in water. Protein does not appear from another dimension. One hundred grams raw and one hundred grams cooked are not the same amount of octopus.

Worth knowing how that cooked entry is built: it is not an independent assay. It is the raw values run through yield and nutrient-retention factors. Energy and protein take the full 2× concentration from water loss. The water-soluble nutrients take less — B12 comes out at about 1.8×, copper at about 1.7× — because part of them leaves the animal and ends up in the pot. Hold on to that. It decides what you should do with the cooking liquid, and we will come back to it. One caveat that covers every figure in this article while we are here: these are modelled FoodData Central values for common octopus, Octopus vulgaris, cooked with moist heat. Species, origin, size and processing move several of these columns.

Octopus is lean and its protein is dense, and it is nowhere near the top of the table. It ties chicken breast almost exactly and loses to three cheaper animals. A 150 g cooked portion is about 45 g of protein for 246 kcal and 3 g of fat, which is a complete protein hit on a plate you can still put potatoes on — but if protein per calorie is what you are shopping for, buy the cod.

Nobody should buy octopus for its macros. Buy it for the next table, or because it tastes like nothing else on the counter.

What is actually unusual

Selenium is the one worth counting rather than celebrating. A 150 g portion supplies about 134 µg, which is a third of the 400 µg per day tolerable upper limit. That is comfortable as a meal. The ceiling is a daily habitual-intake figure rather than a weekly allowance, so what matters is the total column — Brazil nuts, tuna, and a multivitamin that threw selenium in without asking — rather than the octopus on its own. Upper limits are ceilings, not targets.

Taurine, and the year the story broke

Cephalopods sit at the top of the dietary taurine table. Reported values for octopus run from roughly 300 to 1,600 mg per 100 g depending on species, tissue and assay method; one composition database that maps onto the USDA raw entry reports about 390 mg for common octopus. A fivefold spread tells you how soft the number is, and I would not build anything on a single figure inside it. Even the lower end sits above most terrestrial meat, though dark poultry closes the gap more than the usual framing admits.

The physiology is not in dispute. Taurine conjugates bile acids, supports retinal function, participates in cardiac and skeletal muscle calcium handling, and does osmoregulatory work in cells. It is genuinely important, which is a different claim from the one that made it famous.

In 2023 a Science paper reported that taurine declines with age in mice, monkeys and humans, and that supplementation extended median lifespan in mice by roughly 10–12% while improving several health measures in mice and middle-aged rhesus monkeys. Supplement sales moved within weeks — one US brand reported a roughly 300% jump inside a month.

In June 2025 a second Science paper — led out of the National Institute on Aging, and longitudinal rather than cross-sectional — went looking for that decline and did not find it. Across three geographically distinct human cohorts, plus monkeys and mice, circulating taurine rose or stayed flat with age. Variation within a single person over time was large, and variation between people of the same age was larger. The conclusion was that taurine is not a usable biomarker of aging and that its effects are context-dependent.

The mouse lifespan result still stands as a mouse lifespan result. What 2025 took down is the claim that circulating taurine is a universal clock of aging; it did not test supplementation and it certainly did not test dinner. Eat the octopus because it is a dense source of a nutrient that does real work. Not because you are buying years — neither paper went anywhere near that.

And taurine is water-soluble, which brings us back to the pot.

The omega-3 claim dies here

Octopus gets marketed as an omega-3 food on the general principle that it came out of the sea. The numbers do not support it.

Roughly a seventh of salmon, and the reason is not mysterious: octopus is about 2% fat. You cannot extract much of a fat-soluble compound from a food that is almost entirely water and protein. Leanness and omega-3 density are in direct tension and octopus went all in on leanness. If EPA and DHA are the objective, this is the wrong animal — buy the oily fish. Octopus has other work to do.

Cholesterol: neither poison nor imaginary

Cooked octopus carries 96 mg of cholesterol per 100 g, about 144 mg in a portion. Cephalopods generally sit high here — raw squid is 233 mg per 100 g, which is more than a large egg carries.

The 2015 Dietary Guidelines Advisory Committee recommended dropping the old 300 mg per day cap on the grounds that the evidence did not support that specific population-wide number, and the final 2015–2020 guidelines did not carry it forward. On the internet this became “dietary cholesterol does not affect blood cholesterol,” which is not what was said and is not true.

Controlled feeding studies do show that adding dietary cholesterol raises LDL on average. The effect is smaller than what you get from swapping unsaturated fat for saturated fat, and it varies a great deal between people. A 2019 pooled analysis in JAMA covering six US cohorts — 29,615 adults, median 17.5 years of follow-up — found higher dietary cholesterol associated with higher incident cardiovascular disease and higher all-cause mortality. That is observational, with every confounder that implies, and it does not convict a specific food.

Absorption efficiency and the ability to compensate by downregulating your own synthesis vary genetically — NPC1L1, ABCG5/8 and APOE are the usual suspects. If you are a hyper-responder, the population average is not your average. For most people the total diet matters more than this one line and 144 mg is not a large number. If you have familial hypercholesterolaemia, elevated ApoB, or a documented LDL response to dietary cholesterol, you already know that the answer comes from a blood draw and not from an argument.

Mercury is usually low. Cadmium is the one to know about.

Octopus is not actually named on the FDA/EPA advice chart — squid is, in the Best Choices band, with an FDA monitoring mean around 0.023 ppm. Reported octopus muscle mercury generally sits in that same low range, roughly forty times under swordfish at about 1.0 ppm and fifteen times under albacore at 0.35 — with squid standing in as the proxy, which is itself the caveat. There is real geographic variation: some Mediterranean survey datasets have found a meaningful fraction of octopus flesh samples over the EU limit, so origin is not nothing. As a class, though, cephalopods are the low-mercury end of the seafood counter, and that is a genuine advantage over the big predatory fish.

Cadmium is the one that deserves the attention mercury gets. Octopus concentrates it in the digestive gland. A 2019 survey of Octopus vulgaris from two sites in the southern Tyrrhenian found mean digestive-gland cadmium of 2.6 and 3.0 mg/kg wet weight, against levels described as very low in the muscle; other cephalopod surveys have found digestive glands approaching 10 mg/kg. EFSA's tolerable weekly intake is 2.5 µg per kilogram of body weight — about 212 µg a week for an 85 kg adult. The EU maximum for cephalopod flesh without viscera is 1.0 mg/kg, which would put 150 µg into a single portion sitting exactly at the legal ceiling. That is an argument for variety, not for alarm.

Three smaller things. Octopus carries a moderate purine load — one cited composition analysis puts it near 140 mg per 100 g, which is nowhere near the sardine tier but enough that anyone managing gout should treat it as an occasional food rather than a staple. Sodium starts at 460 mg per 100 g cooked before you add any, so a portion arrives at about 690 mg on its own and brined or pre-cooked supermarket product goes higher; read the label. And octopus is a mollusc, which is a different allergy from crustacean shellfish — the two can cross-react, often through tropomyosin, but the reaction is not reliable in either direction. Tolerating shrimp does not clear you for octopus, and reacting to shrimp does not convict it.

The farm that did not happen

Common octopus is short-lived — one to two years — fast-growing, and it breeds once and dies; other species in the order differ, some of them considerably. That makes stocks unusually responsive to fishing pressure in both directions, which cuts both ways for management. Gear matters more than branding: pots and traps leave a very different seabed footprint from bottom trawls. Origin and method tell you more than any word printed on the packaging.

The fight over farming ran about five years and its largest single front closed last month. Nueva Pescanova proposed the world's first commercial octopus farm at the Port of Las Palmas in Gran Canaria — around a million animals a year, roughly 3,000 tonnes. The objections were density-housing a solitary and territorial animal, the feed arithmetic of farming a carnivore at all, and slaughter by ice slurry, which the scientific reviewers did not accept as humane. On 23 July 2026 the company formally withdrew the application. That ends the proposal. It does not end the question — the economics that produced it have not changed.

The sentience question underneath it is not a vibe. The UK's environment department commissioned an LSE review led by Jonathan Birch, which read more than 300 studies and concluded in November 2021 that cephalopods and decapod crustaceans should be regarded as sentient; cephalopod molluscs and decapod crustaceans sit inside the scope of the Animal Welfare (Sentience) Act 2022. Washington became the first US state to ban octopus farming, in March 2024, and California followed that September, banning both the farming and the sale of farmed octopus.

Deciding not to eat an animal that opens jars is a coherent position, and it does not require pretending the nutrition is bad. It is a values call and it is yours. I am reporting where it stands, not making it for you.

Two failure modes and the window between them

An octopus arm is a muscular hydrostat — no skeleton, crossed helical fibre architecture, held together by an unusually high proportion of collagen. That collagen is the entire problem. Short of the conversion point you get rubber. Well past it the tissue collapses and the skin comes off in sheets. The tender window sits at the end of a long cook rather than in the middle of it, which is the opposite of how most cooking intuition is wired.

Freeze it

Ice crystals rupture the muscle and connective structure from the inside. Beating a fresh octopus against a rock, the way it is still done on some Greek beaches, goes after the same thing by a cruder route — physical damage, concentrated where the rock landed rather than spread through the tissue. Most commercially sold octopus has already been frozen — here, “previously frozen” on the label is a feature, not an apology, and fresh is not automatically better. If yours genuinely is fresh, freeze it for 24 to 48 hours and thaw it slowly in the fridge.

Clean it

Cut out the eyes, push the hard beak out of the centre of the arms, and remove everything inside the mantle. That last step is also the cadmium step. Buying it already cleaned skips the whole conversation.

Scare it

Asustar el pulpo, the Galician move: hold the animal by the head, lower it into boiling water for about three seconds, lift it out, and repeat twice more before it goes in to cook. The curling is observable, and it is why the arms look the way they do on a Galician plate. The skin-protection half is what every cook there will tell you and I have not found it tested. Either way it is a technique for shape and appearance, not a tenderiser — the collagen deep in the arm is unaware that anything happened.

Do not put a wine cork in the pot

There is no evidence for it and no plausible mechanism behind it. Cork is suberin and lignin and it does not leach anything into water at 95 °C that dismantles collagen. The myth survives because octopus cooked with a cork in the pot does eventually become tender — exactly like octopus cooked without one, in the same amount of time.

How to know it is done

A thin knife or a skewer into the thickest part of an arm, where it meets the head. It should go in with roughly the resistance of a cooked potato. Springy pushback means the collagen has not converted yet and time is the only fix. Note that this does not scale linearly with weight — arm diameter is what you are actually cooking, so the knife is the instrument and the clock is only a hint. If the skin tears away with the blade and the flesh collapses around it, the window has closed.

The sear, and when to skip it

Let it rest in its liquid for ten minutes, then drain it and dry it aggressively — surface water is the enemy of browning. Oil the arms and put them on a screaming grill or a cast-iron pan for 60 to 90 seconds a side, until the edges of the suckers char and the skin crisps. Here the advice has to split, because a Galician would object to the blanket version. Pulpo a la gallega is served straight from the pot — sliced over boiled potato, dressed with olive oil, coarse salt and pimentón, no sear at all — and it is correct exactly as it stands. The sear belongs to the grilled preparations. For pulpo a la parrilla, keep the arms whole and char the edges hard. If you are making the Galician dish, skip this step entirely.

Salt and acid, both at the end

Galician practice leaves the cooking water unsalted and seasons after slicing. The reasoning holds up: the animal already brings 460 mg of sodium per 100 g of its own, and salting the pot gives you less control over where you land. Acid is more preference than law — octopus is braised in wine and tomato all over the Mediterranean and comes out fine, so concentration and time matter more than any rule about it. For the simmer-then-sear route, keep the lemon or vinegar for the end: applied raw and early it denatures the surface and leaves you a chalky exterior without doing anything useful to the centre.

Cook it in its own liquor

This is the payoff of that retention-factor detail from earlier. Octopus releases a startling amount of water — enough that in a heavy covered pot over low heat it braises itself with nothing added. A share of everything water-soluble ends up in that liquid — taurine, part of the B12, part of the copper, and most of the flavour. Nobody has quantified it for your particular pot. But draining a large volume of salted water pours whatever it was down the sink. Reducing the animal's own liquor into a sauce does not. If you take one technique out of this article, take that one.

Pulpitos cook on a different clock

They are literally small octopus — pulpito is a size description, not a species, and baby octopus on a label can mean juveniles or any of several genuinely small species. What matters is that they are a different cooking problem wearing the same shape. Thin arms, very little connective mass, a few minutes from raw to perfect and a few more from perfect to ruined. Clean them, dry them, and put them straight into a very hot pan or onto a grill for three to five minutes with oil, garlic and nothing else; blanch for a minute first if they are on the larger side. Applying an adult braise to pulpitos produces grey porridge, and it is the most common way this dish gets destroyed.

Where it actually fits

Buy it frozen and cleaned — the freezing did work you would otherwise have to do yourself, and the cleaning removed the organ that holds the cadmium. Cook it slowly in its own liquid until a knife slides in, dry it, then burn the outside. Baby octopus skips everything except the burning.

It ties chicken breast on protein and beats it comfortably on B12, selenium, copper and taurine. It loses to salmon on the one thing salmon is for. It is a low-mercury animal with one organ you discard. It slots into a high-protein plan without argument. I am not going to hand you a frequency, though — that depends on body weight, on the rest of your seafood, and on a cadmium concentration neither of us can measure. Rotate your protein sources and it never becomes a question. Eat it daily and it quietly becomes one.

Sofi's pulpitos took four minutes and needed none of this. Two evenings of reading arrived at the pan she was already using.