What is actually in tofu

Two things drive every number

Tofu is soybeans, water and a coagulant. How much water was pressed out and which coagulant was used explain almost all the variation you will see between packages, and both are why figures quoted online so often disagree.

Water content. Firmness is a measure of how much water was removed. Since the remaining protein and fat are concentrated into less weight, a firmer block carries more protein per hundred grams than a softer one. Nothing was added. There is simply less water diluting it.

The coagulant. Calcium sulfate contributes a substantial amount of calcium. Magnesium chloride, often labeled nigari, contributes very little. Two packages with near-identical ingredient lists can differ several-fold on the calcium line for this reason alone.

The practical consequence: the label on the block in your hand is more reliable than any table, including the one below.

Some reference figures

The United States Department of Agriculture's FoodData Central database holds separate entries for tofu set with different coagulants, and the gap between them illustrates the point better than any explanation.

Both entries are labeled firm. The difference between them is larger than the difference most people imagine exists between tofu and other proteins, and it comes down to water content and coagulant rather than to anything the manufacturer added.

Commercial blocks in a supermarket sit across this whole range and beyond it. Silken tofu is considerably lower in protein per hundred grams because it is mostly water. Super-firm vacuum-packed tofu is at the top end because it has been pressed hardest.

Protein quality

Soy is one of the few plant foods that contains all nine essential amino acids in useful quantities, which is what people mean by a complete protein. That is a genuine point in its favor and it is also frequently overstated, since a varied diet supplies the full range regardless of whether any single food does.

What matters more practically is protein per serving, and that is a firmness question. A block of super-firm tofu delivers considerably more than the same weight of silken.

Cooking does not destroy the protein. Pressing removes water rather than nutrients, so a pressed block is slightly smaller and slightly more concentrated, which is the same relationship as everything else on this page.

Calcium and iron

Calcium-set tofu is one of the more substantial plant sources of calcium available, and this is entirely down to the coagulant rather than to the soybean. If calcium is a reason you are eating tofu, read the ingredient list for calcium sulfate and check the nutrition panel, because a nigari-set block will not do the same job.

Tofu contains a useful amount of iron, in the non-haem form found in plant foods, which the body absorbs less efficiently than the iron in meat. Vitamin C in the same meal improves that absorption, which is a reasonable argument for the lime, lemon or vinegar that most recipes here already include for flavor reasons.

Tofu contains no vitamin B12 unless a manufacturer has fortified it.

Potassium and sodium

Two things are true here and they pull in different directions, so it is worth separating them.

The ratio is excellent. In the USDA entries, calcium-sulfate-set firm tofu works out to a potassium-to-sodium ratio of roughly 17 to 1, and the nigari-set version to about 12 to 1. Very few foods people eat regularly sit anywhere near that.

The absolute amount is modest. About 237 mg of potassium per 100 g, which is roughly 5 to 7 percent of a day's target. Half a block gets you to somewhere between 10 and 14 percent. Tofu is not a potassium food the way beans, potatoes, leafy greens and most fruit are, and nobody should be eating it for the potassium.

That matters because the two minerals work against each other on blood pressure. The 2025 American Heart Association and American College of Cardiology guideline recommends keeping sodium below 2,300 mg a day while getting 3,500 to 5,000 mg of potassium. Most Americans do the opposite: analysis of NHANES data puts average intake at about 3,569 mg of sodium against 2,745 mg of potassium, so more sodium than potassium.

The same analysis found each additional 1,000 mg of potassium a day associated with systolic blood pressure roughly 1.24 mmHg lower, and each additional 1,000 mg of sodium with it about 1.04 mmHg higher. Those are population associations rather than promises about any individual.

So the useful point is about what the ratio protects rather than what it provides. Tofu contributes protein and calcium without dragging sodium along with it, which is unusual for a protein and means the rest of the plate decides the outcome. A tablespoon of soy sauce adds roughly 900 mg of sodium to a block that started with about 20 mg, reversing the ratio in one spoon.

Nothing about that makes soy sauce wrong. It is simply worth knowing which ingredient on the plate is actually carrying the salt, and it is never the tofu.

Lemon, vinegar, garlic, smoked paprika, herbs and nutritional yeast all add flavor without sodium, and reduced-sodium soy sauce cuts it by roughly a third to a half depending on brand. The kids page has the same point with the lower limits that apply to children.

General information from public dietary guidance rather than advice for your situation. If you have a kidney condition or take medication that affects potassium, your doctor's guidance governs rather than anything on a cooking site.

How cooking changes the numbers

Pressing removes water, so the same block weighs less afterward and every figure per hundred grams rises slightly. Nothing has been gained. The weight has just gone down.

Oil is the real change. Two to three tablespoons in a pan for one block adds a substantial amount of fat and calories to the finished dish, although well-pressed tofu absorbs far less of it than people assume and most stays in the pan. Air frying uses a small fraction of that, which is the clearest nutritional argument for the air fryer method.

Starch coatings add a small amount of carbohydrate. Sauces are usually where the sugar and sodium enter, and a heavy barbecue or sweet glaze contributes more of both than the tofu contributes of anything.

Freezing changes texture and not composition. A frozen and thawed block has the same nutrients in a chewier arrangement, as the freezing guide explains.

Reading a package properly

Three lines are worth checking before anything else. The firmness word tells you roughly where on the range the block sits. The ingredient list tells you which coagulant was used, and therefore what the calcium figure will look like. The net weight tells you whether a recipe written for sixteen ounces will be under-seasoned with the twelve ounce block in your hand.

Ingredient lists on plain tofu are usually three items long. Anything with a longer list is a flavored or marinated product, which is a different food with different numbers, usually more sodium.

The types guide covers what the firmness labels mean in practice and which block suits which dish.

Where this fits

Nutrition is the second most common reason people ask about tofu. The first is whether soy affects hormones, which has its own page covering what the research supports and where it is genuinely mixed: soy, hormones and the questions people actually ask.

If the practical questions are what brought you here, the storage page covers shelf life and the techniques section covers the cooking.