Soy foods and urinary isoprostanes: Results from a randomized study in premenopausal women

Abstract

In addition to their antiestrogenic effects, soy isoflavones may protect against cancer through alternate biologic actions including antioxidant properties. This randomized, crossover study explored the relation between dietary isoflavone intake through common soy foods and oxidative stress quantified by urinary isoprostane levels. Eighty-two women aged 39.2±6.1 years were randomized to a high soy diet of 2 soy food servings per day and a low soy diet of <3 servings per week for 6 months each, separated by a 1 month washout period. Urine samples were collected at baseline and at the end of each dietary period. Urinary isoprostane levels were measured using enzyme-linked immunosorbent assays (ELISA) and adjusted for creatinine levels. Mixed models using log-transformed values were applied to evaluate the effect of the high soy diet. Unadjusted isoprostane excretion levels were lower during the high than the low soy diet, but this effect was not statistically significant (p=0.81). After adjustment for urinary creatinine, isoprostane excretion was slightly higher during the high soy diet (p=0.02), an observation that was confirmed in a regression analysis between urinary isoflavones and isoprostanes during the high soy diet. The original association remained significant when restricted to adherent participants; however, this effect disappeared after exclusion of three extreme values. In agreement with several previous reports, these findings do not support the hypothesis that soy exerts antioxidant effects as measured by urinary isoprostane excretions, but additional markers of oxidative stress need to be investigated in future studies.

Soy provides modest benefits on endothelial function without affecting inflammatory biomarkers in adults at cardiometabolic risk

“…Consistent with the current study, other studies have not demonstrated a protective effect against oxidative stress . One of these studies found that neither a high or low soy diet revealed antioxidant effects, as assessed by urinary isoprostanes in women . This finding is particularly important, as isoprostanes are stable metabolic products of in vivo lipid oxidation and are considered the gold standard as a marker for oxidative stress .…”

“…Some studies have found beneficial effects of soy on biomarkers of oxidative stress when investigating other soy products and different oxidative stress biomarkers: reduced plasma malondialdehyde levels , increased total plasma antioxidant capacity , reduced LDL oxidative stress capacity lag time , and decreased advanced oxidation protein products . Consistent with the current study, other studies have not demonstrated a protective effect against oxidative stress . One of these studies found that neither a high or low soy diet revealed antioxidant effects, as assessed by urinary isoprostanes in women .…”

Acute health effects of desktop 3D printing (fused deposition modeling) using acrylonitrile butadiene styrene and polylactic acid materials: An experimental exposure study in human volunteers

“…Urine samples were analyzed for 8‐iso PGF 2α , an established marker of oxidative stress, via gas chromatography with tandem mass spectrometer (GC‐MS/MS). The detailed measurement procedure can be found in the supporting information S1.…”

“…In the analysis of urinary isoprostanes, it is common to adjust for creatinine levels, although the use of creatinine for this purpose has been questioned. 34 Indeed, the creatinine levels of the subjects varied widely between before and after exposure values. Twenty-five of the 182 urine samples showed a creatinine level out of the accepted range (30-250 mg/dL).…”

Effect of S-equol and Soy Isoflavones on Heart and Brain

“…We recently conducted a systematic review of RCTs of soy isoflavones where subgroup analyses were conducted by S-equol producing status [ 152 ]. Our systematic review identified 28 RCTs of soy isoflavones [ 9 , 45 , 153 - 178 ]. These RCTs were conducted mostly among women and varied as to the number of participants (32 to 175), duration of intervention (8 weeks to 1 year), dose of isoflavones (33 to 120 mg/day), outcomes (lipids, arterial stiffness, oxidative stress, endothelial function, inflammatory markers, etc .…”