Beef and tofu: what the protein swap trials actually compared

The strongest evidence on swapping animal protein for plant protein is a meta-analysis of 29 randomized trials in 2,363 adults aged 50 and over. It found no difference in lean mass or handgrip strength, and a marginal drop in total cholesterol favoring plant protein (Hedges g -0.31, 95% CI -0.62 to -0.00, with high heterogeneity between trials). That result is less about beef and tofu than it looks. In 25 of the 29 trials the plant protein was soy, in 23 it was an isolate, mostly tested against dairy, and the authors say their evidence cannot show that whole-food swaps are equivalent. The closest direct test fed 56 healthy young adults a single meal. Two ounces (56 g) of cooked beef sirloin raised whole-body net protein balance more than 4 ounces (112 g) of tofu (P < 0.05), although US dietary guidance counts both as the same protein serving. That was one 8.5-hour metabolic test with 8 people per food, and it tells you nothing about muscle over months.

How much is actually in it

• Raw beef tenderloin carries about 21 g protein and 2.5 mg iron per 3.5 oz (100 g), with iron varying 2.12 to 2.82 mg across 8 samples. — USDA Foundation Foods, Beef, tenderloin steak, raw, 8 analyzed samples (n = 8) Evidence E source
  Per 100 g: protein 21.09 g (range 20.61-21.84), iron 2.53 mg (range 2.12-2.82)
• Steamed tofu in the UK table has 8.1 g protein and 1.2 mg iron per 3.5 oz (100 g), well under raw beef by weight. — UK composition table entry Tofu, soya bean, steamed (13-570) Evidence E source
  Per 100 g: energy 73 calories, protein 8.1 g, fat 4.2 g, saturated fat 0.5 g, iron 1.20 mg, zinc 0.7 mg, water 85.0 g

What a real portion looks like

• The US ounce-equivalent rule treats 2 oz (56 g) of cooked beef sirloin and 4 oz (112 g) of tofu as the same protein serving, which is the pair this trial compared. — healthy young adults randomized to one of 7 protein foods (n = 56) Evidence B source
  Servings tested: 2 oz (56 g) cooked beef sirloin versus 4 oz (112 g) tofu, twice the ounce equivalent
• A cup of beef and tofu stir-fry with vegetables weighs 7.7 oz (217 g) in the US dietary survey, and an unspecified serving is 163 g. — FNDDS food Beef, tofu, and vegetables excluding carrots, broccoli, and dark-green leafy, no potatoes, soy-based sauce (27415220) Evidence E source
  1 cup = 217 g, quantity not specified = 163 g

What your body absorbs

• In a randomized trial of 56 young adults, a 2-ounce-equivalent serving of beef raised whole-body net protein balance more than the tofu serving that dietary guidelines count as equal. — healthy young adults, n = 8 per food group, single test meal after 3 days of controlled diet (n = 56) Evidence B source
  Net protein balance gain greater after beef, pork and eggs than after tofu and other plant foods (P < 0.01), response correlated with essential amino acid content (P < 0.001)
• Soy protein was the only legume protein that lowered heme iron absorption in 15 women, from 11.0% with heme alone to 7.3%. — adult women, 15 per study arm (n = 15) Evidence C source
  Heme iron absorption 11.0% alone versus 7.3% with soy, 8.1% pea, 9.1% lentil protein, only soy significant (p < 0.05)
• Replacing animal foods with 2 to 3 daily servings of soy foods for 10 weeks did not change iron or zinc status in 63 young women. — nonsmoking premenopausal women aged 18-28, soy food n = 31 versus animal food n = 32, 10 weeks (n = 63) Evidence B source
  No significant changes in hemoglobin, transferrin saturation, serum iron, ferritin or transferrin receptor, plasma zinc fell in both groups by 0.8 umol/L

What cooking and storage change

• Beef keeps nearly all its iron through cooking: 95% when broiled or fried and 100% when roasted. — USDA retention factors for the group Beef Products, BEEF,BROILED CUT (602), BEEF,FRIED (605), BEEF,ROASTED (601) Evidence E source
  Iron retention 95% broiled cut, 95% fried, 100% roasted

What it does to your health

• In groups of 8 young adults, beef stimulated protein synthesis more than kidney beans, peanut butter or mixed nuts (P < 0.05), while its edge over tofu came through net balance rather than synthesis alone. — healthy young adults, n = 8 per food group (n = 56) Evidence B source
  Net balance increased more in beef, pork and egg groups than in all plant groups (P < 0.05), protein synthesis higher in beef than kidney beans, peanut butter, mixed nuts (P < 0.05)
• Observational data link about 0.95 oz (27 g) of tofu a day with an 18% lower risk of cardiovascular disease. — prospective studies pooled, follow-up 2.5 to 24 years, 54,213 CVD events Evidence C source
  Tofu 26.7 g/day, total relative risk 0.82 (95% CI 0.74-0.92) for CVD

Safety, limits and interactions

• Lab data pooled from 28 articles found more of the four indicator PAH compounds in heat-processed beef than in control beef, with smoking raising them more than grilling or barbecuing. — beef and beef products analyzed after thermal processing, 28 articles Evidence D source
  Thermally processed versus control beef g = 1.64 (P < 0.001), smoking above grilling and barbecuing (g > 0.8)

What people believe that the data does not support

• Four weeks of Kori-tofu improved cholesterol and blood pressure no more than a whey protein control in 45 adults with mildly high cholesterol. — adults aged 40-70 with mildly elevated cholesterol, 4-week crossover with 4-week washout (n = 45) Evidence B source
  Within-arm decreases in total, LDL and HDL cholesterol, HbA1c and systolic blood pressure also seen with whey, only adiponectin change differed between treatments
• US labels may still say that 25 grams of soy protein a day in a diet low in saturated fat may reduce heart disease risk. — — Evidence E source
  Authorized health claim, 25 g soy protein per day
• The EU did not authorize the claim that isolated soy protein lowers blood cholesterol and heart disease risk. — — Evidence E source
  Status Non-authorized

Who this works differently for

• In 23 people with a history of calcium kidney stones, two daily servings of beef and an equal protein amount from plants gave the same stone risk index. — normocalciuric patients with a history of calcium kidney stones, 8 women and 15 men, mean age 50.7 (n = 23) Evidence B source
  Urinary calcium, oxalate, magnesium, citrate, phosphorus, volume and Tiselius risk index did not differ between diets
• A meta-analysis of 29 trials in adults over 50 found plant and animal protein broadly equal, with only a marginal total cholesterol drop favoring plant protein. — adults aged 50 and older, 29 randomized trials, interventions longer than 1 month (n = 2363) Evidence A source
  Total cholesterol Hedges g = -0.31 (95% CI -0.62 to -0.00), I2 = 86.20%, no difference in lean mass or handgrip strength

What is still unknown

• In 23 of 29 trials comparing plant and animal protein the test food was an isolate, mostly soy against dairy, so the evidence cannot show that swapping beef for tofu as whole foods is equivalent. — adults aged 50 and older, 29 randomized trials (n = 2363) Evidence A source
  25 of 29 trials used soy, 23 of 29 used isolates rather than whole foods

The bottom line

Gram for gram, raw beef tenderloin carries 21.1 g of protein and 2.53 mg of iron per 3.5 oz (100 g), with iron running from 2.12 to 2.82 mg across 8 USDA samples. Steamed tofu in the UK table has 8.1 g of protein and 1.2 mg of iron per 3.5 oz (100 g), and that is a watery tofu, since firm tofu in the USDA data reaches about 17 g of protein. Cooking barely touches the iron in beef: USDA group factors keep 95% after broiling or frying and 100% after roasting. Soy has a reputation for blocking iron, and the data split. In a non-randomized study with isolated proteins, soy protein cut heme iron absorption from 11.0% to 7.3% in groups of 15 women, and the test used no whole tofu or beef. Over 10 weeks, about 19 g of soy protein a day from soy foods in place of animal foods had no significant effect on iron or zinc status in 63 young women without anemia. Ten weeks may be too short for ferritin to move. For the heart the picture is weaker than the label. Observational data link about 0.95 oz (27 g) of tofu a day with an 18% lower risk of cardiovascular disease (relative risk 0.82, 95% CI 0.74 to 0.92), an association that leaves room for confounding. When 45 adults with mildly high cholesterol ate frozen-dried Kori-tofu for four weeks, it did no better than a whey protein control. US labels may still say that 25 g of soy protein a day in a diet low in saturated fat may reduce heart disease risk. The EU did not authorize a similar claim for isolated soy protein. For people who have had calcium kidney stones, a small crossover of 23 patients found the same stone risk index on two daily servings of beef as on an equal amount of plant protein, although that plant protein came from beans, nuts and grains and the test phase lasted two days. The only safety card here concerns cooking beef. Lab measurements pooled from 28 articles found far more of four indicator PAH compounds in heat-processed beef than in controls (g = 1.64), with smoking adding more than grilling or barbecuing. That measures compounds in meat and says nothing yet about disease in people. We have no card on soy allergy, pregnancy, children or medicines for either food, so this page makes no claim about them. A cup of beef and tofu stir-fry weighs about 7.7 oz (217 g) in the US dietary survey.

Sources

1. btf-r7-14 · USDA FoodData Central Foundation Foods, dataset
   Beef, tenderloin steak, raw: Protein 21.09375 G (20.6125-21.8375); Iron, Fe 2.53 MG (2.12-2.82, 8 samples)
   USDA FoodData Central, Foundation Foods, release 2026-04-30, FDC 2727573 · checked 2026-09-29
2. btf-r7-15 · CoFID 2021, dataset
   Tofu, soya bean, steamed (13-570): energy 73 kcal, protein 8.1 g, fat 4.2 g, saturated fat 0.50 g, iron 1.20 mg, zinc 0.7 mg, water 85.0 g
   CoFID 2021, Public Health England / OGL v3.0, code 13-570 · checked 2026-09-29
3. btf-r7-02 · randomized controlled trial
   2 ounces (56 g) of cooked beef sirloin, 2 ounces (56 g) of cooked pork loin, 2 cooked eggs, ½ cup (140 g) of red kidney beans, 2 tablespoons (30 g) of peanut butter, 4 ounces (112 g) of tofu, and 1 ounce (28 g) of mixed nuts.
   J Nutr, 2021 · checked 2026-09-29
4. btf-r7-17 · FNDDS, dataset
   Beef, tofu, and vegetables excluding carrots, broccoli, and dark-green leafy; no potatoes, soy-based sauce (27415220): 1 cup 217 g; Quantity not specified 163 g
   USDA FNDDS (FoodData Central Survey Foods), food code 27415220, FDC 2706745 · checked 2026-09-29
5. btf-r7-01 · randomized controlled trial
   Consumption of ounce equivalents of animal-based protein food sources (beef sirloin, pork loin, eggs) resulted in a greater gain in whole-body net protein balance above baseline than the ounce equivalents of plant-based protein food sources (tofu, kidney beans, peanut butter, mixed nuts; P < 0.01).
   J Nutr, 2021 · checked 2026-09-29
6. btf-r7-04 · controlled clinical trial
   In study II, heme Fe absorption was 7.3%, 8.1% and 9.1% with the addition of soy, pea and lentil proteins, respectively. Only soy proteins decreased heme Fe absorption (p < 0.05).
   Nutrients, 2015 · checked 2026-09-29
7. btf-r7-05 · randomized controlled trial
   Incorporating ∼19 g soy protein from soy foods for 10 weeks had no significant effect on iron or zinc status, bone resorption or formation, or thyroid hormone status in premenopausal women.
   J Womens Health (Larchmt), 2011 · checked 2026-09-29
8. btf-r7-16 · USDA Table of Nutrient Retention Factors, dataset
   BEEF,BROILED CUT (USDA-RETN-R6:602): iron_mg 95%. BEEF,FRIED (USDA-RETN-R6:605): iron_mg 95%. BEEF,ROASTED (USDA-RETN-R6:601): iron_mg 100%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Codes 601, 602, 605 · checked 2026-09-29
9. btf-r7-03 · randomized controlled trial
   NB increased more in the beef, pork, and eggs groups than all of the groups consuming plant-based protein food sources (P < 0.05). NB increased less in the mixed-nuts group than in all of the other groups. Protein synthesis increased more (P < 0.05) in the beef group than in the groups consuming kidney beans, peanut butter, or mixed nuts.
   J Nutr, 2021 · checked 2026-09-29
10. btf-r7-10 · meta-analysis of cohorts
    A daily intake of 26.7 g of tofu reduced CVDs risk by 18% (TRR = 0.82, 95% CI: 0.74-0.92) and 11.1 g of natto lowered the risk of CVDs by 17% (TRR = 0.83, 95% CI: 0.78-0.89), especially stroke.
    Nutrients, 2023 · checked 2026-09-29
11. btf-r7-11 · meta-analysis of food chemistry studies
    A meta-analysis of 28 articles indicated that thermally processed beef had significantly higher PAH4 levels than did the control beef (g' = 1.64; P < 0.001). Smoking caused greater PAH4 buildup than did grilling and barbecuing (g' > 0.8; P < 0.001).
    Meat Sci, 2026 · checked 2026-09-29
12. btf-r7-09 · randomized controlled trial
    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 2026-09-29
13. btf-r7-12 · regulation
    (2) Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease. One serving of [name of food] provides ____ grams of soy protein.
    21 CFR 101.82, Health claims: Soy protein and risk of coronary heart disease · checked 2026-09-29
14. btf-r7-13 · regulatory decision
    POL-HC-6237 Isolated soy protein Protein-rich soybean component has been shown to lower/reduce blood cholesterol; blood cholesterol lowering may reduce the risk of (coronary) heart disease. -/- Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6237, snapshot 2026-09-21 · checked 2026-09-29
15. btf-r7-06 · randomized controlled trial
    Urinary calcium, oxalate, magnesium, citrate, phosphorus, volume, and TRI did not differ between diets.
    J Am Diet Assoc, 2001 · checked 2026-09-29
16. btf-r7-07 · meta-analysis
    A marginal reduction in total cholesterol (T-CHOL) favored plant protein with substantial between-study heterogeneity (Hedges' g = -0.31, 95% CI: -0.62 to -0.00; I2 = 86.20%).
    Clin Nutr ESPEN, 2026 · checked 2026-09-29
17. btf-r7-08 · meta-analysis
    The results should be interpreted as evidence from controlled protein-source interventions rather than as evidence of equivalence between whole-food plant and animal protein substitutions.
    Clin Nutr ESPEN, 2026 · checked 2026-09-29