Soybeans & Tofu

Food · Grains & Legumes · Legumes

Connected to · 2

food source · 2

Protein
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 · 2
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.
Calcium
The calcium in tofu mostly comes in with the coagulant: firm tofu set with calcium sulfate (gypsum) can have 150–350 mg of calcium per 100 g, while tofu set with nigari or glucono-delta-lactone carries almost none, so check the coagulant on the label.
Mechanism · 2
Mechanism · The coagulant brings the calcium
Soybeans are not especially rich in calcium, and neither is soy milk; it is the setting step that puts calcium into the curd. Set with calcium sulfate, the calcium goes straight into the tofu; set with nigari (magnesium chloride) or glucono-delta-lactone, it carries almost none. So checking which coagulant is on the label tells you more than the slogan that tofu is good for calcium.
Numbers · Calcium in gypsum-set tofu
Firm tofu set with calcium sulfate can have 150–350 mg of calcium per 100 g, more than the same weight of milk, and it is absorbed about as well as milk's; tofu set with nigari or glucono-delta-lactone has much less. If you are counting on tofu for calcium, check the coagulant first.

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The many foods made from one bean

EVIDENCEGUIDE 1

READ THE ORIGINAL

The isoflavones in soy can sit in the estrogen receptor, but they push it only very weakly and prefer a different receptor, so eating normal soy foods is not the same as taking estrogen. The chapter on what phytoestrogens are explains this starting from the receptor.

Soy is also not one food but a whole family made from one bean. Edamame is the whole bean; soy milk is the ground slurry; tofu is that slurry set into a gel with a coagulant, and which salt is used decides how much calcium ends up in the block. Industrial extraction goes further, to soy protein isolate, which is not the same thing as the whole bean. The estrogen myths online often lump these shapes together.

Educational content, not medical advice — consult a clinician.

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