Soy

Soy/Nutrient Depletion:

  • CalciumCalcium: Theoretically, soy protein may inhibit calcium absorption. In humans, urinary calcium excretion was significantly less with consumption of a soy diet vs. a control diet, and fractional calcium absorption was unaffected (317). In a study in women, urinary calcium did not differ with the type of protein (animal vs. soy) (318). However, in a subset of subjects, intestinal calcium absorption was slightly lower when they consumed the soy diet. In clinical research, a combination of soy isoflavones, lactobacilli, calcium, vitamin D3, magnolia bark extract, and magnesium decreased menopausal symptoms and increased well-being (319).
  • GlucoseGlucose: Data from a meta-analysis suggest that a whole soy diet, but not supplementation with isolated soy protein, reduces fasting glucose (64). In clinical research, consumption of soy nuts reduced fasting plasma glucose in women with metabolic syndrome on the DASH diet (149). In other clinical research, compared with other sources of protein in a meal, soy protein decreased postprandial area under the curve for glucose, as well as the insulin:glucose and insulin:C peptide ratios (62). In clinical research, use of isoflavone supplements in women decreased fasting glucose (63). Also, use of a soy-based meal replacement compared with an individualized diet plan as recommended by the American Diabetes Association resulted in a greater number of patients reducing use of sulfonylureas and metformin (261).
  • IronIron: Soy protein has been shown to modify iron status in various studies in humans. Changes include a reduction in the percentage of nonheme iron absorption (69; 70). Other research suggests enhanced iron absorption with increased soy food intake in humans (67) or no effect (300). Phytic acid and a protein-related moiety in the conglycinin fraction of soybean-protein isolates may be responsible for the potential inhibition of iron absorption (301). A study of 242 Indian women found iron absorption to be enhanced by silken tofu, natto, tempeh, rice miso, barley miso, and soybean miso (67). Another study found the iron status of 69 perimenopausal women to be unaffected by a soy protein isolate diet (300). A clinical study of 10 infants found that the removal of phytic acid or increasing ascorbic acid in soy-based infant formulas improved the bioavailability of iron in the formulas (168).
  • LipidsLipids: In human research, total and LDL cholesterol and triglyceride levels were reduced, and HDL levels increased, with soy products (7; 381; 149; 383; 132; 76; 133; 77; 78; 227; 264). In one study, cholesterol absorption from the human small bowel was reduced from 56% to 38% when patients ingested soy sterol ester for a period of three weeks (384). In postmenopausal women, soy isoflavones increased HDL levels in a particular subgroup of estrogen receptor-beta(cx) Tsp509I (genotype AA) (385).
  • PhosphorusPhosphorus: Theoretically, soy protein may inhibit phosphate absorption.
  • SeleniumSelenium: In clinical research, infants fed soy formula were found to have lower plasma, red blood cell, and urine selenium concentrations than infants fed soy formula with added selenium (339).
  • ZincZinc: In human research, infants four months of age fed a soy-based formula had lower plasma zinc levels than breastfed infants (244).