Soy flour: a heart claim on the label, no LDL drop in the trial

In a 6 week randomized double-blind trial in 243 Canadian adults aged 30 to 70 with raised LDL cholesterol, muffins carrying 12.5 or 25 g of protein from defatted soy flour did not lower LDL compared with a whey protein control. The mean changes were +0.01 mmol/L on the higher dose and -0.04 mmol/L on the lower, against -0.04 mmol/L on control, and 213 of the 243 finished. That result sits awkwardly beside US labeling rules. They still allow a claim that 25 g of soy protein a day, in a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. The FDA proposed revoking that claim in 2017, and we found no final rule. The EU refused two similar claims for soy protein. Blood sugar is where soy flour did show something, in a small study. In a randomized crossover trial in 17 adults with overweight or obesity, replacing 30% of refined flour with soy flour lowered the post-meal glucose curve for bread (p = 0.03) and arepas (p = 0.04). Insulin, hunger and fullness did not differ. These were single test meals, and the abstract gives p values without the size of the drop.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• In 5 USDA samples, defatted soy flour held 7.34 mg iron, 338 mg calcium, 313 mg magnesium and 1.51 mg copper per 3.5 oz (100 g), with little spread between samples. — 5 samples, USDA Foundation Foods (n = 5) Evidence E source
  Iron 7.34 mg (6.89 to 7.98), calcium 338 mg (307 to 358), magnesium 313 mg (298 to 327), copper 1.51 mg (1.49 to 1.56) per 3.5 oz (100 g)

What your body absorbs

• In a randomized trial in 8 people with ileostomy, replacing 25% of meal protein with soy protein products lowered protein digestibility but did not clearly change mineral absorption. — 8 ileostomy subjects, 2-day diet periods (n = 8) Evidence B source
  Lower protein digestibility with soy diets; no obvious effect on apparent mineral absorption at 25% replacement
• In radiolabelled meal tests, replacing 25% of chicken protein with defatted soy flour did not change zinc absorption, while adding milk to a soybean meal lowered it. — Adults eating composite test meals labeled with 65Zn Evidence B source
  No significant change in zinc absorption for chicken meal with 25% soy flour
• In a randomized crossover trial in 12 volunteers, adding soy flour to an isoflavone capsule did not change absorption of daidzein and genistein, but equol producers excreted less daidzein. — 12 healthy volunteers, single doses (n = 12) Evidence B source
  Bioequivalent formulations; lower daidzein excretion in equol producers

What it does to your health

• In a randomized crossover trial in 17 adults with overweight, replacing 30% of refined flour with soy flour lowered the post-meal glucose curve for bread and arepas without changing insulin or liking. — 17 adults aged 21 to 45 with overweight or obesity, single test meals (n = 17) Evidence B source
  Glucose AUC reduced for breads (p = 0.03) and arepas (p = 0.04); insulin unchanged
• In a 6-week randomized double-blind trial in 243 adults with high LDL, 12.5 or 25 g of protein from defatted soy flour in muffins did not lower LDL cholesterol. — Adults aged 30 to 70 with LDL 116 to 193 mg/dL (3.0 to 5.0 mmol/L), Canada, 6 weeks (n = 243) Evidence B source
  LDL change: control -0.04, high-dose soy +0.01, low-dose soy -1.5 mg/dL (-0.04 mmol/L) (ns)

Safety, limits and interactions

• In a 6-month randomized trial in 270 postmenopausal Chinese women, 1.4 oz (40 g) of soy flour a day did not change thyroid function markers versus placebo. — 270 Chinese equol-producing postmenopausal women, 6 months (n = 270) Evidence B source
  No significant difference in 6-month thyroid marker changes; modest FT4 decrease in women with lowered thyroid function
• Among 131 atopic children with a positive soy skin test, 8 (6.1%) reacted to a blinded soy challenge, while none of 131 skin-test-negative children did. — 704 atopic children aged 1 month to 18 years, Milan allergy clinic (n = 131) Evidence C source
  6.1% (8/131) clinical soy allergy among skin-test-positive children

What people believe that the data does not support

• US rules still allow a label claim that 25 g of soy protein a day in a diet low in saturated fat and cholesterol may reduce heart disease risk, though FDA proposed revoking it in 2017. — US food labeling Evidence E source
  Authorized health claim, regulatory
• The EU refused to authorize a claim that soy protein lowers blood cholesterol and may reduce heart disease risk. — EU labeling Evidence E source
  Non-authorized
• The EU also refused a claim that 25 g of soy protein daily helps maintain healthy cholesterol levels. — EU labeling Evidence E source
  Non-authorized

Who this works differently for

• In a San Francisco case-control study, western foods with added soy flour or soy protein were not linked to thyroid cancer risk, unlike traditional soy foods. — 608 cases and 558 controls, San Francisco Bay Area (n = 1166) Evidence C source
  No effect on risk for foods with added soy flour

The bottom line

Per 100 g, defatted soy flour held 7.34 mg iron, 338 mg calcium, 313 mg magnesium and 1.51 mg copper across 5 USDA samples, with little spread between them. Full-fat soy flour is a separate record in the table. We have no card on how baking changes these numbers, and no standard portion. Absorption was tested in meal studies, most of them small and old. In a randomized trial in 8 people with an ileostomy, replacing 25% of meal protein with soy protein products lowered protein digestibility and had no obvious effect on apparent mineral absorption. In meals labeled with radioactive zinc, replacing 25% of the chicken protein with defatted soy flour did not significantly change zinc absorption. The same swap in a beef meal lowered both the zinc content and the zinc absorbed, and the abstract does not say how many people took part. In 12 healthy volunteers, adding soy flour to a capsule of soy isoflavone extract did not change isoflavone absorption. That was a capsule study, so it tells us little about bread or muffins. Volunteers classed as equol producers excreted less daidzein. Who should be careful. Among 131 children with allergies and a positive soy skin test at a Milan clinic in 1991 and 1992, 8 (6.1%) reacted to a blinded soy challenge, and none of 131 children with a negative skin test did. Those children were already seen for allergy, so the figure does not describe children in general. On the thyroid, 270 postmenopausal Chinese women who all produced equol ate 1.4 oz (40 g) of soy flour a day for 6 months in a randomized trial, and their thyroid markers changed no differently from placebo. In the subgroup whose thyroid function was already lowered, FT4 fell modestly, a signal to raise with whoever treats a thyroid condition. A San Francisco case-control study of 608 cases and 558 controls found that western foods with added soy flour or soy protein did not affect thyroid cancer risk. It relied on food questionnaires and gave no separate estimate for flour.

Sources

1. sofl-daily-r1-01 · dataset
   Flour, soy, defatted (Foundation Foods 2026-04-30): Iron, Fe 7.34 MG, range 6.89-7.98, samples 5; Calcium, Ca 338.0 MG, range 307.0-358.0, samples 5; Magnesium, Mg 313.0 MG, range 298.0-327.0, samples 5; Copper, Cu 1.51 MG, range 1.49-1.56, samples 5
   USDA FoodData Central, Foundation Foods, release 2026-04-30, FDC 1104705 (Flour, soy, defatted) · checked 2026-09-28
2. sofl-daily-r1-05 · RCT
   A significantly lower protein digestibility was observed when the diets containing soy protein were fed. No difference in protein digestibility was found between the different soy protein products. A 25% replacement by soy protein had no obvious effect on apparent mineral absorption.
   J Nutr, 1986 · checked 2026-09-28
3. sofl-daily-r1-06 · RCT
   When 25% of the animal protein in the chicken meal was replaced by defatted soy flour neither the zinc content nor zinc absorption were significantly influenced. The same substitution in a beef meal resulted in a decrease in zinc content and also a lower zinc absorption.
   Am J Clin Nutr, 1980 · checked 2026-09-28
4. sofl-daily-r1-07 · RCT
   Twelve healthy volunteers were recruited for a randomized, double-blind, two-way crossover trial and received a single dose of the two soy-based formulations, one containing a pure soy standardized extract of IF, and the other containing soy flour in addition to the standardized extract of IF. ... We demonstrated that daidzein excretion was significantly lower in equol producers compared with equol non producers over the entire elimination period of the soy IF.
   J Pharm Biomed Anal, 2007 · checked 2026-09-28
5. sofl-daily-r1-02 · RCT
   Results: Compared with the control condition, substituting 30% of refined flour with soy flour significantly reduced the area under the concentration-time curve for postprandial glucose for breads (p = 0.03) and arepas (p = 0.04), and reduced plasma glucose concentrations at 90-120 min for tortillas (p = 0.0009). In contrast, postprandial insulin concentrations and subjective hunger and satiety ratings did not differ across substitution levels or food matrices (all p > 0.05).
   Nutrients, 2026 · checked 2026-09-28
6. sofl-daily-r1-03 · RCT
   Despite a dose-dependent increase in plasma isoflavones (P < 0.001), neither HDS nor LDS had a significant effect on LDL cholesterol compared with control (mean ± SEM changes: control, -0.04 ± 0.05 mmol/L; HDS, 0.01 ± 0.05 mmol/L; and LDS, -0.04 ± 0.06 mmol/L).
   J Nutr, 2015 · checked 2026-09-28
7. sofl-daily-r1-04 · RCT
   Total 270 eligible women were randomized to either one of the three isocaloric supplements: 40 g soy flour (whole soy group), 40 g low-fat milk powder +63 mg daidzein (daidzein group) or 40 g low-fat milk powder (placebo) daily for 6 months. ... There was no significant difference in the 6-month changes of thyroid markers among the three groups. Subgroup analysis among women with lowered thyroid function suggested a modest decrease of FT4.
   Phytother Res, 2021 · checked 2026-09-28
8. sofl-daily-r1-08 · prevalence
   CONCLUSION: The prevalence of clinical soy allergy in our children with positive skin prick tests to soy is 6.1% (8/131), while none of 131 children with negative skin prick test to soy reacted to the challenge.
   Ann Allergy Asthma Immunol, 1996 · checked 2026-09-28
9. sofl-daily-r1-10 · 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.
   21 CFR 101.82, Health claims: Soy protein and risk of coronary heart disease (CHD) · checked 2026-09-28
10. sofl-daily-r1-11 · regulatory register
    POL-HC-6260 Soy protein Soy protein 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-6260, snapshot 2026-09-21 · checked 2026-09-28
11. sofl-daily-r1-12 · regulatory register
    POL-HC-7961 Soy protein Soy helps to control cholesterol. l. 25 g soy protein daily as part of a diet with few saturated fatty acids helps to maintain healthy cholesterol levels. Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-7961, snapshot 2026-09-21 · checked 2026-09-28
12. sofl-daily-r1-09 · case-control
    The consumption of traditional and nontraditional soy-based foods and alfalfa sprouts were associated with reduced risk of thyroid cancer. Consumption of "western" foods with added soy flour or soy protein did not affect risk.
    Cancer Epidemiol Biomarkers Prev, 2002 · checked 2026-09-28