Tofu or tempeh: protein, calcium and fermentation, how to choose?

Tofu starts as soy milk. The liquid is curdled with a coagulant, such as calcium sulfate or magnesium chloride (nigari), then the curd is drained and pressed. The result is silken, soft, firm, or extra-firm tofu. The more water it contains, the less concentrated it is in nutrients.

Tempeh is made from whole soybeans, cooked and then inoculated with a fermentation fungus. Its white mycelium binds the beans into a compact cake. Some tempehs add rice, barley, millet, or seeds. The result has a stronger, slightly nutty flavor and a texture that slices or crumbles.

Values from the USDA FoodData Central database for raw products. Tofu curdled without a calcium salt contains far less: check the label.

Protein. Tempeh is often the most concentrated, but firm tofu comes close. Silken or regular tofu, with more water, contains about half as much. Soy provides all nine essential amino acids, which doesn't exempt you from varying your diet across the day.

Calcium. This is the most surprising point: it all depends on the coagulant. Tofu curdled with calcium sulfate can provide several hundred milligrams per 100 g, whereas tofu made with nigari provides much less. Tempeh contains a modest amount. Look for "calcium sulfate" in the ingredient list and the calcium line on the nutrition label.

Fiber and energy. Since it keeps the whole beans, tempeh retains more fiber than tofu, which is made from filtered soy milk. It's also more energy-dense. A rapid increase in fiber can cause bloating or discomfort: increase gradually.

A 2021 review, which surveyed more than 300 publications on tempeh, judges fermentation valuable from a nutritional, technological, and economic standpoint, but notes that more human studies are needed to clarify health effects. A 2025 review on fermented soy products describes compounds, such as certain peptides and isoflavones, whose potential effects remain to be confirmed.

Above all, tempeh isn't a probiotic in the strict sense. It's generally heated, pasteurized, or cooked before being eaten, which destroys most live microorganisms. "Fermented" describes a manufacturing process, not a health outcome. For the difference between a fermented food and a probiotic, see the article fermented foods: live microbes and pasteurization.

Soy contains isoflavones, plant compounds whose structure partially resembles human estrogens. This resemblance has fueled two widespread fears: that soy increases the risk of breast cancer, and that it lowers testosterone in men. Current human data support neither.

On breast cancer, initial concerns came from rodent studies, where high doses of isoflavones stimulated the growth of estrogen-sensitive tumor cells. Rodents, however, metabolize isoflavones differently from humans, and this effect hasn't been reproduced in human studies: major cancer research organizations now consider that usual soy consumption doesn't increase the risk of breast cancer, with some data even suggesting a protective effect in certain populations.

On male testosterone, a meta-analysis pooling available clinical studies found no effect of soy or isoflavones on reproductive hormones in men (testosterone or estrogen), contradicting the widespread idea of a "feminizing" effect from tofu or tempeh.

• Silken tofu: sauces, soups, creamy preparations, smooth dishes.
• Firm tofu: pressed, marinated, cubed, browned in a pan or oven. Its neutral flavor absorbs seasonings; watch the soy sauce and salt.
• Tempeh: sliced, crumbled, or cubed. A short steaming softens it before marinating; pan-frying, baking, or simmering develop its flavor. Tempeh is eaten cooked.

Pre-marinated or smoked versions are convenient, but often saltier, sweeter, or fattier than plain versions. For organizing plant proteins across the day, see the article plant proteins: do you need to combine foods at every meal?.

1. 01Compare the same amount, such as 100 g.
2. 02Note protein, fiber, calcium, sodium, and added sugars.
3. 03Read the ingredient list: coagulant, added grains, marinade.
4. 04Don't judge a low-calcium tofu as a bad food: it may be chosen for its texture, alongside other calcium sources during the day.