Tofu vs tempeh vs seitan

Tofu, tempeh, and seitan are the three most common protein anchors in vegan cooking — but they are not interchangeable. They differ in raw protein density, amino acid completeness, digestibility, mineral bioavailability, and who can safely eat them. Picking the right one for the right job is practical nutrition, not pedantry.

The tl;dr

	Tofu (firm)	Tempeh	Seitan
Protein per 100 g	~17 g	~20 g	~25 g
DIAAS score	79–97	~79–97 (soy proxy)	~28
Lysine-adequate	Yes	Yes	No
Gluten-free	Yes	Yes	No
Isoflavones	Yes	Yes (higher aglycone)	No
Sodium (plain)	Low	Low	400–770 mg/100 g

Sources: USDA FoodData Central; Herreman et al. (2020); FAO (2013).

Seitan has the most grams of protein. Tofu and tempeh have far better protein quality. That distinction matters.

Why protein quality matters as much as quantity

Protein quality is measured by DIAAS — the Digestible Indispensable Amino Acid Score — which replaced the older PDCAAS as the gold standard after a 2013 FAO expert consultation (FAO, 2013). DIAAS rewards proteins that provide all essential amino acids in adequate ratios relative to human requirements; it penalises proteins with a deficient limiting amino acid.

Tofu and tempeh are made from soy. Soy protein is one of the only plant proteins with DIAAS scores on par with animal sources: 79–97 depending on processing (Herreman et al., 2020). That range spans from roughly “good” to “excellent” by the FAO reference pattern.

Seitan is pure wheat gluten. Wheat gluten has a DIAAS of approximately 28 — extremely low — because it is severely deficient in lysine (Herreman et al., 2020). A DIAAS of 28 does not mean 28% of the protein is absorbed; it means the amino acid profile is so incomplete that the body cannot use most of it efficiently without complementary sources. Seitan is not a low-quality protein in a varied diet that includes legumes; it is a low-quality sole protein source.

One note on tempeh’s DIAAS specifically: controlled ileal digestibility studies on fermented tempeh are limited. The scores cited here are extrapolated from soy protein data — standard practice, but a proxy.

How fermentation changes tempeh

Tofu and tempeh share the same raw ingredient — soybeans — but fermentation by Rhizopus oligosporus transforms the nutritional profile in ways that matter.

Fermentation substantially reduces phytate content (phytic acid being the main antinutrient that binds iron and zinc and limits their absorption). Fermentation also reduces trypsin inhibitors, which otherwise interfere with protein digestion. The directional finding — fermentation meaningfully improves mineral bioavailability relative to unfermented soy — is well-supported in the fermentation literature (Paucar-Menacho et al., 2010, cited in multiple fermentation reviews). The exact percentage reduction varies by fermentation conditions and measurement method; treat published figures as indicative rather than universal.

The isoflavone picture also shifts. Tempeh fermentation converts isoflavone glucosides into aglycone forms, which are absorbed more readily by the gut. Neither form is harmful at typical food-level intakes — see the phytates and iron absorption article for the mineral side of this story.

Tempeh also provides about 20% more protein per 100 g than firm tofu (~20 g vs ~17 g) because the water content is lower and the protein matrix is denser after fermentation (USDA FoodData Central).

The seitan lysine gap in practice

Seitan’s lysine deficiency does not make it useless. It means seitan should not be the primary protein in a meal without a complementary lysine source. In practice, most seitan-forward meals — stir-fries with vegetables, sandwiches, grain bowls — do not automatically include legumes. That gap compounds if seitan is used as a daily protein anchor without thought (Mariotti and Gardner, 2019).

The practical fix is straightforward: pair seitan with tofu, tempeh, legumes, or edamame in the same meal or the same day. The amino acid profiles complement each other — seitan is relatively methionine-rich while soy and legumes are lysine-rich. Together they cover the full spectrum (Mariotti and Gardner, 2019).

A note on commercial sodium: plain homemade seitan has modest sodium. Commercial seitan products commonly contain 400–770 mg sodium per 100 g (USDA FoodData Central). At high intake volumes — as might be typical for an athlete eating seitan as a primary protein — sodium can accumulate quickly. Tofu and tempeh do not carry this issue in plain form.

Who should avoid seitan

Seitan is 100% wheat gluten. Three distinct conditions require its avoidance:

1. Celiac disease — an autoimmune condition affecting roughly 1% of the global population; gluten causes intestinal damage regardless of symptom severity (Ludvigsson et al., 2015).
2. Non-celiac gluten sensitivity (NCGS) — a clinically recognised condition producing gastrointestinal and systemic symptoms in response to gluten, without the autoimmune mechanism of celiac disease; diagnosed by exclusion (Catassi et al., 2013). Prevalence estimates are contested — ranges from under 1% to 13% depending on diagnostic criteria used.
3. Wheat allergy — an IgE-mediated allergic response to wheat proteins, distinct from both celiac disease and NCGS (Ludvigsson et al., 2015).

Together, these three conditions likely affect somewhere between 5% and 10% of the population. Seitan is not a default safe food — it requires an explicit check, especially when cooking for others.

Tofu and tempeh are gluten-free. They are appropriate for people with celiac disease, NCGS, or wheat allergy, assuming no soy allergy.

Practical guidance

Use tofu when:

• You want complete, high-quality protein with a neutral base that absorbs sauces and marinades.
• You are cooking for anyone whose gluten status is unknown.
• Silken or soft textures suit the dish (smoothies, sauces, scrambles).

Use tempeh when:

• Protein density and mineral bioavailability are priorities (e.g., iron-limited diets).
• You want a firmer, more textured protein that holds up to grilling or roasting.
• The nuttier, more complex fermented flavour works for the dish.

Use seitan when:

• You need the highest protein density per gram and your diet reliably includes legumes or soy for lysine balance.
• Meat-like texture is important — braised, sliced, or pulled formats.
• No one in the meal has celiac disease, NCGS, or wheat allergy.

Combine them when:

• You are building a high-protein meal for athletes. A base of tofu or tempeh with seitan added for volume and texture covers quality and quantity simultaneously. The protein for vegan athletes article covers meal targets in detail.

Common misconceptions

• “Seitan is the best vegan protein because it has the most grams.” Protein density and protein quality are different things. Seitan’s DIAAS of approximately 28 means the amino acid profile is severely incomplete; the body cannot use those grams efficiently without a complementary lysine source. Tofu and tempeh score 79–97.

• “Tempeh and tofu are basically the same food.” They share a soy base but fermentation meaningfully changes tempeh: more protein per 100 g, reduced antinutrients, and a different isoflavone profile. They are more like cousins than twins.

• “Soy foods mess with your hormones.” The clinical and epidemiological evidence at food-level doses is clear: soy isoflavones do not meaningfully disrupt estrogen, testosterone, thyroid function, or reproductive health in healthy adults (Messina, 2016). The concern applies to pharmacological doses, not tofu in a stir-fry. Individuals with estrogen-sensitive cancers or thyroid conditions on medication should check with a clinician before large increases in intake.

• “Tempeh is a reliable B12 source.” It is not. B12 in tempeh is produced by contaminating bacteria during fermentation and varies widely — often near zero in controlled commercial conditions. Never count tempeh as a B12 source. Supplement separately.

• “I only need to avoid seitan if I have celiac disease.” Non-celiac gluten sensitivity and wheat allergy also require avoidance. Together, these three conditions may affect 5–10% of the population. Seitan requires an explicit safety check.

The punchline

The three proteins are not ranked — they serve different roles. Tofu and tempeh are complete proteins with strong quality scores; tempeh adds fermentation benefits that matter for mineral absorption. Seitan delivers the highest protein density but is amino-acid-incomplete and off-limits for a meaningful share of the population. Use them together and none of these limitations applies.

For the full picture on how plant proteins stack up across amino acid quality, DIAAS scoring, and daily targets, see the protein pillar.