Seitan and tofu: two protein blocks, very different evidence

A meta-analysis of 43 controlled trials in adults with raised LDL found that about 25 g of soy protein a day, for a median of 6 weeks, lowered LDL cholesterol by 4.76 mg/dL against other proteins (95% CI -6.71 to -2.80). Those trials mixed soy isolates with soy foods, so tofu itself was never isolated. The same body of soy research, mostly isolates and supplements rather than tofu, speaks to two popular worries. Across 41 clinical studies in men, soy protein and isoflavones did not change testosterone or estrogen at any dose or duration. Across 18 randomized trials, thyroid hormones stayed the same and TSH rose by 0.248 mIU/L, a rise the authors call of unclear clinical meaning. Seitan has no human outcome study of its own that we could find. Per 100 g, the dry wheat gluten flour it is made from carries about 75 g protein and 370 calories, while firm calcium-set tofu carries about 17 g and 144 calories. Cooked seitan is diluted with water, so the flour figure overstates it. In minipigs both proteins were digested at 95 to 97%, and seitan ranked last for protein quality because of its amino acid make-up.

How much is actually in it

• Per 100 g, the wheat gluten flour seitan is made from has about 75 g protein and 370 calories, against about 17 g protein and 144 calories in firm calcium-set tofu. — US reference food composition Evidence C source
  Wheat gluten flour: 75.16 g protein, 370 calories, 142 mg calcium, 5.2 mg iron; firm tofu (calcium sulfate): 17.27 g protein, 144 calories, 683 mg calcium, 2.66 mg iron; regular tofu: 8.08 g protein, 76 calories, 350 mg calcium

What a real portion looks like

• A half-cup serving of firm calcium-set tofu weighs 4.4 oz (126 g) and works out to about 22 g protein and 181 calories. — US reference portion Evidence C source
  126 g: about 21.8 g protein, 181 calories, 861 mg calcium (recalculated from 100 g)

What your body absorbs

• In minipigs, seitan and tofu proteins were both highly digestible (97% and 95%), but seitan scored lowest for protein quality because wheat protein is low in lysine. — minipigs fed seitan, tofu, soya milk or pea emulsion Evidence D source
  True ileal protein digestibility: seitan 97%, tofu 95%; DIAAS ranking soya foods > pea > seitan
• In a crossover RCT on 14 vegetarian women eating 6.1 oz (173 g) tofu a day for 30 days, adding 303 mg vitamin C raised hemoglobin more than tofu alone. — 14 premenopausal lacto-ovo vegetarian women, two 30-day periods (n = 14) Evidence B source
  Greater hemoglobin increase with tofu plus vitamin C (p = 0.036 and p = 0.009); no difference in serum ferritin

What cooking and storage change

• In UK composition data, frying steamed tofu raises it from 73 to 261 calories and from 4.2 to 17.7 g fat per 3.5 oz (100 g), as water is lost and oil is taken up. — UK food composition Evidence C source
  Steamed: 73 calories, 4.2 g fat, 8.1 g protein; steamed then fried: 261 calories, 17.7 g fat, 23.5 g protein per 3.5 oz (100 g)

What it does to your health

• A meta-analysis of 43 controlled trials found that about 25 g soy protein a day for about 6 weeks lowered LDL cholesterol by 4.76 mg/dL versus non-soy protein. — adults with LDL 110 to 201 mg/dL, 43 trials identified by the FDA (n = 43 trials) Evidence A source
  LDL -4.76 mg/dL (95% CI -6.71 to -2.80), about 3-4%; total cholesterol -6.41 mg/dL
• In a double-blind crossover RCT on 45 adults with mildly high cholesterol, 4 weeks of Kori-tofu did not improve cardiometabolic markers more than a whey protein control. — 45 adults aged 40-70 with mildly elevated cholesterol, two 4-week periods (n = 45) Evidence B source
  Within-group falls in LDL, HbA1c and systolic pressure, but no difference from whey control except adiponectin
• Observational data from 15 cohorts of 565,810 people link higher tofu intake to 8% lower type 2 diabetes risk. — 565,810 adults in 15 prospective cohorts (n = 565810) Evidence C source
  Tofu RR 0.92 (95% CI 0.84 to 0.99)

Safety, limits and interactions

• Data pooled from clinical programs suggest people with celiac disease on a gluten-free diet still take in about 150 to 400 mg gluten a day. — people with celiac disease following a gluten-free diet Evidence C source
  Mean inadvertent gluten about 150-400 mg/d (stool test), about 300-400 mg/d (urine test)
• In 142 oral challenges with 100 g silken tofu in Japanese children, 38.7% reacted. — 125 patients, mean age 2.8 years, tested 2004-2010 (n = 142) Evidence C source
  38.7% positive challenges; 7 anaphylaxis cases given epinephrine

What people believe that the data does not support

• A meta-analysis of 41 clinical studies in men found no effect of soy protein or isoflavones on testosterone or estrogen levels, whatever the dose or duration. — adult men; total testosterone measured in 1753 men (n = 1753) Evidence A source
  No significant effect on total or free testosterone, estradiol, estrone or SHBG
• A meta-analysis of 18 randomized trials found soy did not change thyroid hormones and raised TSH by only 0.248 mIU/L. — participants of 18 RCTs with soy as intervention (n = 18 trials) Evidence A source
  FT3 and fT4 unchanged; TSH +0.248 mIU/L (95% CI 0.001 to 0.494)
• Observational data from 14 studies link the highest tofu intake to lower, not higher, breast cancer risk (OR 0.78). — women in 2 cohort and 12 case-control studies (n = 14 studies) Evidence C source
  OR 0.78 (95% CI 0.69 to 0.88) highest vs lowest tofu intake

The bottom line

A half-cup of firm calcium-set tofu weighs 4.4 oz (126 g) and gives about 22 g protein, 181 calories and 861 mg calcium, recalculated from the 100 g values. There is no reference portion for seitan. Frying changes tofu more than people expect. UK tables list steamed tofu at 73 calories and 4.2 g fat per 3.5 oz (100 g) and steamed then fried tofu at 261 calories and 17.7 g fat, though these are two separate samples. In a small crossover trial, 14 vegetarian women ate 6.1 oz (173 g) of tofu a day for 30 days, and adding 303 mg of vitamin C raised hemoglobin more than tofu alone, with no difference in ferritin. A frozen Kori-tofu product given for 4 weeks to 45 adults with mildly high cholesterol did no better than a whey protein control. Observational data from 15 cohorts link higher tofu intake to 8% lower type 2 diabetes risk (RR 0.92, 95% CI 0.84 to 0.99), evidence the authors themselves rated low. Fourteen mostly case-control studies link the highest tofu intake to lower odds of breast cancer (OR 0.78, 95% CI 0.69 to 0.88). Both are associations, and neither shows that tofu caused the difference. Seitan is made almost entirely of gluten, the protein people with celiac disease have to avoid, so for them it is no substitute for tofu. Pooled clinical data suggest people with celiac disease already take in about 150 to 400 mg of gluten a day by accident while on a gluten-free diet. Soy allergy is real in young children. At one Japanese center, 142 challenges with 3.5 oz (100 g) of silken tofu in children referred for suspected allergy, mean age 2.8 years, gave a reaction 38.7% of the time, and 7 children needed epinephrine. We have no card on medicines or pregnancy for either food.

Sources

1. stfd-daily-r3-01 · dataset
   Vital wheat gluten (FDC 168147): protein 75.16 g, energy 370 kcal, calcium 142 mg, iron 5.2 mg per 100 g; Tofu, raw, firm, prepared with calcium sulfate (FDC 172475): protein 17.27 g, energy 144 kcal, calcium 683 mg, iron 2.66 mg per 100 g; Tofu, raw, regular, prepared with calcium sulfate (FDC 172476): protein 8.08 g, energy 76 kcal, calcium 350 mg per 100 g
   USDA FoodData Central, SR Legacy, published 2019-04-01, FDC 168147, 172475 and 172476 · checked 2026-09-30
2. stfd-daily-r3-02 · dataset
   Tofu, raw, firm, prepared with calcium sulfate: portion 0.5 cup 126 g; protein 17.27 g, energy 144 kcal, calcium 683 mg per 100 g
   USDA FoodData Central, SR Legacy, published 2019-04-01, FDC 172475 · checked 2026-09-30
3. stfd-daily-r3-04 · animal study
   The TID of the proteins was high and not significantly different between the foods tested: 97% for seitan, 95% for tofu, 92% for soya milk and 94% for pea emulsion. There were only minor differences in individual amino acid TIDs. DIAAS ranking was thus essentially driven by the amino acid composition of the food: soya-based food > pea emulsion > seitan.
   Reynaud Y et al. Food Chemistry, 2021 · checked 2026-09-30
4. stfd-daily-r3-05 · RCT
   For the first 30 days, one half of the subjects (n = 7) received 6 oz (173 grams) of tofu/day (T) while the other half of the subjects (n = 7) received 6 oz of tofu/day along with 303 mg of vitamin C/d (TO). ... In conclusion, bioavailability of iron from tofu is enhanced by supplementation with ascorbic acid.
   Plant Foods Hum Nutr, 2002 · checked 2026-09-30
5. stfd-daily-r3-03 · dataset
   CoFID 2021 13-570 Tofu, soya bean, steamed: Energy 73 kcal, Fat 4.2 g, Protein 8.1 g per 100 g; 13-571 Tofu, soya bean, steamed, fried: Energy 261 kcal, Fat 17.7 g, Protein 23.5 g per 100 g
   CoFID 2021 (Public Health England), codes 13-570 and 13-571 · checked 2026-09-30
6. stfd-daily-r3-06 · meta-analysis
   Soy protein at a median dose of 25 g/d during a median follow-up of 6 wk decreased LDL cholesterol by 4.76 mg/dL (95% CI: -6.71, -2.80 mg/dL, P < 0.0001; I2 = 55%, P < 0.0001) and decreased TC by 6.41 mg/dL (95% CI: -9.30, -3.52 mg/dL, P < 0.0001; I2 = 74%, P < 0.0001) compared with non-soy protein controls.
   J Nutr, 2019 · checked 2026-09-30
7. stfd-daily-r3-07 · RCT
   Due to the lack of significant effects as compared to control, there is, however, currently no substantiating evidence to claim that Kori-tofu has beneficial effects on cardiometabolic health.
   Nutrients, 2022 · checked 2026-09-30
8. stfd-daily-r3-10 · cohort meta-analysis
   The summary RRs (95% CIs) of incident type 2 diabetes were 0.95 (0.79, 1.14; NS) for total legumes, 0.83 (0.68, 1.01; NS) for total soy, 0.89 (0.71, 1.11; NS) for soy milk, 0.92 (0.84, 0.99) for tofu
   Am J Clin Nutr, 2020 · checked 2026-09-30
9. stfd-daily-r3-12 · meta-analysis
   The average inadvertent exposure to gluten by CD individuals on a GFD was estimated to be ∼150-400 (mean) and ∼100-150 (median) mg/d using the stool test and ∼300-400 (mean) and ∼150 (median) mg/d using the urine test.
   Am J Clin Nutr, 2018 · checked 2026-09-30
10. stfd-daily-r3-13 · retrospective cohort
    Between July 2004 and May 2010, 142 cases (125 patients) underwent food challenge tests (100 g of silken tofu) for the diagnosis of soybean allergy or confirmation of their tolerance. ... The positive rate for the challenge test was 38.7%.
    Allergol Int, 2016 · checked 2026-09-30
11. stfd-daily-r3-08 · meta-analysis
    This updated and expanded meta-analysis indicates that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects TT, FT, E2 or E1 levels in men.
    Reprod Toxicol, 2021 · checked 2026-09-30
12. stfd-daily-r3-09 · meta-analysis
    Soy supplementation has no effect on the thyroid hormones and only very modestly raises TSH levels, the clinical significance, if any, of the rise in TSH is unclear.
    Sci Rep, 2019 · checked 2026-09-30
13. stfd-daily-r3-11 · meta-analysis of observational studies
    The overall OR of breast cancer for highest vs lowest intake of tofu was 0.78 (95% CI 0.69-0.88), with moderate heterogeneity (P = 0.011, I2 = 49.7%).
    PLoS One, 2020 · checked 2026-09-30