Soy protein concentrate: an ingredient, not a treatment

Soy protein concentrate is an industrial ingredient, and the two things it is sold for both failed in trials. In 159 adults with raised cholesterol, five weeks of water washed concentrate moved blood lipids no more than the milk protein control, with no difference between the groups at any point and no association between blood isoflavones and lipids. Everyone's cholesterol had already dropped during the three week run-in, by 19 mg/dL total and 11 mg/dL LDL. The authors put that down to regression to the mean and to the supplement displacing other food, and it is exactly the fall a trial without a run-in would have credited to soy. In 75 untrained young men doing 12 weeks of resistance training, fifteen of them on the concentrate, it added nothing. Every group including placebo gained about 4.9 lb (2.2 kg) of muscle, and fifteen men in the soy arm over twelve weeks is too few to rule out a small difference. Those men already ate more than 1.1 g of protein per kg, so the question answered was whether extra protein helps on top of enough, not whether soy protein works. The firm number here is composition. The acid wash concentrate holds 63.63 g of protein per 3.5 oz (100 g), 127 percent of the Daily Value, from one USDA reference record with no measured spread behind it and no British entry to check it against.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• Soy protein concentrate made by acid wash carries 63.63 g of protein per 3.5 oz (100 g), which is 127% of the Daily Value, alongside 108% of the Daily Value for copper and 85% for folate. — USDA reference record Soy protein concentrate, produced by acid wash, FDC 174301, Legumes and Legume Products (n = 2 records) Evidence E source
  Protein 63.63 g per 3.5 oz (100 g) (127% DV), copper 0.976 mg (108% DV), folate 340 ug (85% DV)

What your body absorbs

• In growing pigs the concentrate carried more usable energy than plain soybean meal, while the digestibility of most amino acids and of phosphorus was the same. — three experiments in growing barrows of 29 to 31 lb (13 to 14 kg), with ileal cannulation for amino acids, metabolism crates for energy and a phytase arm for phosphorus (n = 73 pigs) Evidence D source
  Digestible and metabolizable energy greater in the concentrate than in soybean meal and corn (P < 0.01), standardized ileal digestibility greater only for isoleucine, leucine, phenylalanine, proline and tyrosine, phosphorus digestibility no different and improved in both by microbial phytase
• Measured against other plant proteins in pigs, soy protein concentrate digested as well as potato protein concentrate and soy isolate and far better than linseed meal. — 20 cannulated barrows of about 55 lb (25 kg) fed potato protein concentrate, soy protein concentrate, soy protein isolate or linseed meal in a replicated crossover, with a nitrogen free diet for endogenous losses (n = 20 pigs) Evidence D source
  Apparent and standardized ileal digestibility of nitrogen similar for potato concentrate, soy concentrate and soy isolate and greater than linseed meal (P < 0.05), with all essential amino acids similar between soy isolate and soy concentrate

What cooking and storage change

• USDA has no retention factor for this ingredient itself, only for the legume group it belongs to, where boiling for 15 to 20 minutes keeps 55% of folate and 70% of copper. — USDA retention factors for the group Legumes and Legume Products, code 16, boiled and drained at two cooking durations Evidence E source
  15 to 20 minutes boiled and drained: folate 60%, thiamin 65%, copper 70%, magnesium 80%, iron 85%, zinc 85% · 2 to 2.5 hours: folate 30%, thiamin 40%, copper 55%, magnesium 70%, iron 75%, zinc 85%
• Processing that concentrates soy protein can also damage it: in weanling pigs the digestibility of total amino acids was lower in soy protein concentrate than in enzyme-treated soybean meal. — 27 weanling barrows of about 21 lb (9.3 kg) fitted with an ileal cannula, fed cornstarch diets in which each of seven protein sources was the only source of protein and amino acids (n = 27 pigs) Evidence D source
  Standardized ileal digestibility of crude protein and of total amino acids greater in enzyme-treated soybean meal than in soy protein concentrate, with arginine, histidine, isoleucine, leucine, methionine and phenylalanine also lower in the concentrate

What it does to your health

• Five weeks of water-washed soy protein concentrate did not move blood lipids at all in 159 adults with raised cholesterol, while the milk protein control did just as little. — 159 hyperlipidemic men and women, randomized after a 3 week run-in on milk protein to soy protein concentrate or continued milk protein for 5 weeks, double blind (n = 159) Evidence B source
  No significant difference between groups at any point and no association between blood isoflavones and lipids, while during the run-in alone total cholesterol fell 19 mg/dL and LDL 11 mg/dL in everyone
• Soy protein concentrate added nothing to 12 weeks of resistance training in 75 untrained young men: every group including placebo gained about 4.9 lb (2.2 kg) of muscle. — 75 untrained college-aged men, average 21 years and 175 lb (79.2 kg), randomized to placebo, leucine, whey concentrate, whey hydrolysate or soy protein concentrate standardized to about 3.0 g of leucine per serving, training three days a week for 12 weeks (n = 75) Evidence B source
  Muscle mass up about 4.9 lb (2.2 kg) with no difference between supplements, type I fiber area up 394 um2 and type II up 927 um2 in all groups, satellite cell number up only in the two whey groups
• Swapping 60% of dietary protein for soy concentrate for 28 days changed serum cholesterol by +1 mg/dL in 20 middle-aged volunteers, while the more refined isolate lowered it by 8 mg/dL. — 57 healthy volunteers of mean age 46 years fed controlled diets for 45 days, 17 staying on casein, 20 switching to soy protein isolate and 20 to soy protein concentrate for the 28 day test period (n = 57) Evidence C source
  Mean change in serum cholesterol +1 ± 10 mg/dL on soy concentrate, -8 ± 12 on soy isolate and -2 ± 10 on casein, with no difference in lipoprotein composition between casein and concentrate

Safety, limits and interactions

• Seventeen healthy men lived 11 weeks on soy protein concentrate as their only source of dietary nitrogen at 0.8 g per kg a day, with immunological testing finding no allergic responses in those men and nitrogen balance holding steady. — 17 healthy young adult men in an 11 week metabolic study, 9 on Danpro-S and 8 on Danprotex-H 40, each concentrate the sole source of dietary nitrogen at 0.8 g per kg per day (n = 17) Evidence C source
  Body weight, lean body mass, creatinine excretion and basal metabolic rate unchanged, nitrogen balance fluctuating around equilibrium, no allergic responses on immunological testing
• Calves fed milk replacer in which soy protein concentrate covered 60% of the protein grew 0.62 lb (0.281 kg) a day against 0.76 lb (0.344 kg) on all-milk protein, and added glutamine did not repair it. — 30 Holstein calves, 10 per group, fed all-milk-protein replacer, replacer with 60% of protein from soy protein concentrate, or the same soy replacer plus 1% L-glutamine, from day 3 to 4 weeks of age (n = 30 calves) Evidence D source
  Average daily gain 0.344, 0.281 and 0.282 kg per day, jejunal villus height 713, 506 and 464 um, with protein intake adequate in all groups

What people believe that the data does not support

• The United States still allows a label saying 25 g of soy protein a day may reduce the risk of heart disease, and the European register holds no authorized claim for soy protein concentrate at all. — 21 CFR 101.82, the authorized US health claim for soy protein and coronary heart disease, beside the EU Register on nutrition and health claims, snapshot 2026-09-21 Evidence E source
  US threshold 25 g of soy protein a day as part of a diet low in saturated fat and cholesterol, against zero authorized claims and one rejected claim naming soy protein concentrate in the EU register of 2330 claims
• The only entry naming soy protein concentrate in the European register is a rejected claim for an energy and muscle supplement, so Europe refused the right to say it. — EU Register on nutrition and health claims, snapshot 2026-09-21, claim POL-HC-7138 on a mixture in which soy protein concentrate is the fifth of ten named substances (n = 2330 EU claims) Evidence E source
  One entry naming the substance, status non-authorized, and zero authorized claims

What is still unknown

• Whether soy protein concentrate does anything for people whose cholesterol is normal was called unclear in 2000, and the trial that said so tested soymilk instead, where total cholesterol fell 10.9 mg/dL. — 60 premenopausal normolipidemic Japanese women, 27 of them drinking 14 fl oz (400 mL) of commercial soymilk daily over two menstrual cycles against 25 controls (n = 52) Evidence B source
  Total cholesterol down 10.9 mg/dL or 5.3% in the soymilk group, still significant after subtracting the estimated effect of the polyunsaturated fat in soymilk

The bottom line

Older feeding work points the same way. When 20 volunteers of about 46 years replaced 60 percent of their dietary protein with the concentrate for 28 days under controlled feeding, serum cholesterol changed by +1 plus or minus 10 mg/dL. The more refined soy isolate shifted it by -8 plus or minus 12 and casein by -2 plus or minus 10. That study is from 1982, it did not randomize its groups, the groups lost different amounts of weight, and concentrates made today are a different product. The longest human safety record is small and old. Seventeen healthy young men ate one of two commercial concentrates as their only source of dietary nitrogen at 0.8 g per kg a day for 11 weeks. Body weight, lean mass, creatinine excretion and basal metabolic rate stayed unchanged, nitrogen balance sat around equilibrium, and immunological testing found no allergic responses. Seventeen healthy men say nothing about people allergic to soy, and we have no card at all on children, pregnancy or kidney disease. Digestibility has been measured in animals only. In growing pigs the concentrate carried more digestible and metabolizable energy than plain soybean meal, while ileal digestibility of most amino acids and of phosphorus was no different. In a second pig study it digested as well as potato protein concentrate and soy isolate and better than linseed meal. In weanling pigs the digestibility of total amino acids was lower in the concentrate than in enzyme treated soybean meal, which those authors attribute to heat damage during processing. Pigs are the usual stand-in for human digestion and they remain pigs, and in each of these experiments the test protein was the only protein in the diet, which never happens at a table. Calves fed a milk replacer where the concentrate supplied 60 percent of the protein gained 0.62 lb (0.281 kg) a day against 0.76 lb (0.344 kg) on all-milk protein, with jejunal villus height 506 um against 713 um, and added glutamine did not repair it. A young ruminant is not a human infant, so that is a signal about immature digestion rather than evidence about babies. The two label regimes disagree. The United States still permits the statement that 25 g of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. The FDA proposed revoking that claim in 2017 over inconsistent evidence and has not settled the matter since, and the 25 g threshold covers soy protein in general rather than this ingredient. The EU register of 2330 claims holds no authorized claim for it. The single entry naming it is a rejected application for a ten-substance energy and muscle supplement in which the concentrate sits fifth, so the refusal is about the mixture. USDA has no retention factor for the ingredient itself, only for the legume group it belongs to, where boiling for 15 to 20 minutes leaves 60 percent of the folate and 70 percent of the copper. Nobody boils a dry industrial powder, so those figures describe a relative of this product. Whether the concentrate does anything for people whose cholesterol is normal was called unclear in 2000 and has not been answered since. The trial that said so tested soymilk instead, finding total cholesterol down 10.9 mg/dL, or 5.3 percent, in 27 premenopausal Japanese women drinking 14 fl oz (400 mL) a day across two menstrual cycles.

Sources

1. spco-r4-01 · USDA FoodData Central SR Legacy, dataset
   Soy protein concentrate, produced by acid wash (FDC 174301, sr_legacy, Legumes and Legume Products): protein 63.63 g per 100 g = 127% DV; copper 0.976 mg = 108% DV; folate 340 ug = 85% DV; USDA records 2, Foundation samples 0, CoFID match none
   USDA FoodData Central, SR Legacy, FDC 174301 · checked 2026-09-25
2. spco-r4-08 · animal study in pigs
   In conclusion, the concentrations of DE and ME are greater in SPC than in SBM, but the SID of most AA and the STTD of P are not different between SPC and SBM.
   J Anim Sci, 2016 · checked 2026-09-25
3. spco-r4-09 · animal study in pigs
   The apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of N for potato concentrate, soy concentrate, and soy isolate were similar and greater than that for linseed meal ( < 0.05). ... The AID and SID of all essential AA were similar between soy isolate and soy concentrate.
   J Anim Sci, 2016 · checked 2026-09-25
4. spco-r4-02 · USDA nutrient retention factors, dataset
   USDA-RETN-R6:501 LEGUMES,CKD 15/20MIN,BOILED,DRAINED (group 16 Legumes and Legume Products): folate_total_ug 60%, vitamin_c_mg 65%, thiamin_mg 65%, copper_mg 70%, niacin_mg 70%, vitamin_b6_mg 70%, potassium_mg 75%, riboflavin_mg 75%, magnesium_mg 80%, calcium_mg 85%, iron_mg 85%, zinc_mg 85% || USDA-RETN-R6:541 LEGUMES,CKD 2/2.5HRS,BOILED,DRAINED: folate_total_ug 30%, thiamin_mg 40%, vitamin_b6_mg 50%, copper_mg 55%, niacin_mg 55%, potassium_mg 65%, vitamin_c_mg 65%, magnesium_mg 70%, iron_mg 75%, riboflavin_mg 75%, calcium_mg 85%, zinc_mg 85%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, codes 501 and 541 · checked 2026-09-25
5. spco-r4-07 · animal study in pigs
   Results of this research indicate that although processing of SBM results in increased concentration of CP, processing may also reduce the digestibility of AA, which is likely due to heat damage during processing.
   J Anim Sci, 2017 · checked 2026-09-25
6. spco-r4-03 · randomized controlled trial in humans
   Blood lipid levels were not significantly different between groups at any point in time; and there were no significant associations between blood isoflavones and lipid levels. ... These results do not support the hypothesis that water-washed soy protein has an effect on blood lipids.
   J Am Coll Nutr, 2005 · checked 2026-09-25
7. spco-r4-04 · randomized controlled trial in humans
   On average, all supplement groups including PLA exhibited similar training volumes and experienced statistically similar increases in total body skeletal muscle mass determined by dual X-ray absorptiometry (+2.2 kg; time p = 0.024) and type I and II fiber CSA increases (+394 μm² and +927 μm²; time p < 0.001 and 0.024, respectively).
   Nutrients, 2017 · checked 2026-09-25
8. spco-r4-05 · controlled clinical trial in humans
   Mean changes over the test period were -2 +/- 10, -8 +/- 12, and +1 +/- 10 mg/dl, respectively. ... The lack of effect of the less refined soy protein concentrate suggests that the dietary fiber and other nonprotein components of soy concentrate do not have, at least in the short-term, a favorable effect on serum cholesterol and lipoproteins in healthy adults.
   Am J Clin Nutr, 1982 · checked 2026-09-25
9. spco-r4-06 · controlled metabolic study in humans
   Subjects remained healthy, no problems of clinical or metabolic significance appeared, body weight remained constant, and body composition indices (lean body mass by H2(18)O dilution and creatinine excretion) and basal metabolic rate did not change. N balances fluctuated around body N equilibrium. Immunological studies confirmed the absence of any allergic responses in these subjects.
   Am J Clin Nutr, 1989 · checked 2026-09-25
10. spco-r4-10 · animal study in calves
    The ADG was greater for calves fed the all-milk control than for those fed SPC; glutamine did not improve ADG (0.344, 0.281, and 0.282 kg/d for diets 1 to 3, respectively).
    J Dairy Sci, 2006 · checked 2026-09-25
11. spco-r4-11 · US federal regulation
    (1) 25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of [name of food] supplies ____ grams of soy protein.
    21 CFR 101.82, Health claims: Soy protein and risk of coronary heart disease (CHD) · checked 2026-09-25
12. spco-r4-12 · regulatory register
    POL-HC-7138 Fructose, Glucose, Maltodextrine, Milk protein concentrate, 5.Soy protein concentrate, Creatine, Vitamin C, Magnezium Oxide, Zinc Oxide,Alimentary flavors energizer and proteic food supplement / recomended for fast increase of energy, strenght and muscular development / recovery musular energy after physical and mental effort Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-7138, snapshot 2026-09-21 · checked 2026-09-25
13. spco-r4-13 · randomized controlled trial in humans
    The hypocholesterolemic effect of soy protein concentrates on normolipidemic subjects still remains unclear. ... After the trial, we observed a significant decrease of 10.9 mg/dL, or 5.3%, in serum concentration of total cholesterol in the soymilk-supplemented group.
    Prev Med, 2000 · checked 2026-09-25