Apparent bioavailability of isoflavones after intake of liquid and solid soya foods.

Isoflavone (IFL) intake may provide numerous health benefits, but IFL bioavailability differences among soya foods remains uncertain. Urinary IFL excretion (UIE) was shown to provide a reliable surrogate for systemic IFL exposure and therefore can be used as a measure of 'apparent bioavailability' (AB). We investigated the AB of IFL in fourteen healthy adults, consuming two liquid and two solid soya foods in a crossover designed study. Volunteers consumed the foods with a self-selected breakfast, which was kept identical for all four soya items (soya nuts, soya milk, soya protein bar and soya protein powder drink in water; average 23.7 mg IFL, 88-96 % glycosides, by HPLC analysis) and collected all urine up to 26 h. Liquid foods showed initially higher UIE values than solid foods, but this difference was considerably reduced or disappeared entirely after 24-26 h. Conclusive AB results were obtained only after 24-26 h; earlier collections were not reliable. At 26 h, adjusted UIE values for daidzein (DE) were 20 micromol in the milk and bar and 17 micromol for the nut and powder; urinary genistein excretion was the highest in the milk group (10 micromol) followed by the nut, bar (both 6 micromol) and powder groups (5 micromol); the UIE for glycitein was the highest for bars (4 micromol), followed by powder and nuts (3 micromol), and milk (2 micromol). DE makes the largest contribution to urinary total IFL. The AB of IFL was found to be variable depending on the analyte and soya food consumed.

Urinary isoflavones are increased in adults, but decreased in children, consuming soy when on oral antibiotic therapy.

The goal of this study was to evaluate how oral antibiotics (OABX) change the appearance of isoflavones (IFLs) in adults and children after soy consumption. The urinary IFL excretion rate (UIER) known to reflect circulating IFLs was hypothesized to change due to intestinal microflora changes by OABX. Subjects provided urine collections in pairs of a baseline urine and an overnight urine before and after consuming soy nuts first during OABX treatment and then again when healthy. During OABX versus when healthy, UIER (nmol/h/kg) in adults (n = 12) was increased (P < 0.05) for daidzein (35.2 +/- 7.2 vs. 18.9 +/- 2.4), daidzein + genistein + glycitein [nonmetabolites (NM); 42.6 +/- 8.0 vs. 23.6 +/- 2.9), and total isoflavonoids (Total IFLs; daidzein + genistein + glycitein + dihydrodaidzein + dihydrogenistein + equol + O-desmethylangolensin) (51.5 +/- 10.3 versus 29.6 +/- 4.7). In contrast, children (n = 7) showed reduced UIER (P < 0.05) when on OABX versus when healthy for daidzein (36.3 +/- 6.4 vs. 46.8 +/- 4.7), dihydrodaidzein (1.2 +/- 0.6 vs. 3.0 +/-1.1), NM (46.3 +/- 8.2 vs. 59.5 +/- 6.0), dihydrodaidzein + dihydrogenistein + equol + O-desmethylangolensin (1.0 +/- 0.8 vs. 4.3 +/- 1.3), and Total IFLs (48.2 +/- 8.5 vs. 63.8 +/- 6.4).

Oral antibiotics decrease urinary isoflavonoid excretion in children after soy consumption.

How oral antibiotics (OABX) alter isoflavones (IFLs) in soy-consuming children is unknown. We evaluated OABX effects on urinary IFL excretion rates (UIERs) in 17 children, ages 4 to 17 yr, who provided 2 urine collections in pairs of a baseline urine and an overnight urine collection after consuming a body-weight-adjusted dose of soy nuts. The first collection was during OABX treatment for a bacterial infection and the second when healthy and off antibiotics. IFL food levels and UIERs were measured for nonmetabolites (NM), namely, daidzein, genistein (GE), and glycitein, and the metabolites (M) dihydrodaidzein, dihydrogenistein, equol, and O-desmethylangolensin (DMA), by liquid chromatography mass spectrometry. Urinary IFLs were hypothesized to change after OABX due to intestinal microflora alterations. A total of 11 children completed the study correctly. During OABX use, UIER (nmol/h/kg) for GE (6.4 +/- 1.0 vs. 10.1 +/- 1.6), all NM (27.5 +/- 4.8 vs. 36.2 +/- 4.7), and total IFLs (all NM + all M; 29.4 +/- 5.0 vs. 38.8 +/- 4.8) was reduced (P < 0.05) vs. when healthy. In contrast, a trend toward more DMA production during OABX was observed (1.2 +/- 0.6 vs. 0.4 +/- 0.3, P = 0.13). The reduction in urinary IFL appearance could be due to the changes of intestinal bacteria by OABX and/or due to processes related to the infection.

Isoflavones in children and adults consuming soy.

Soy and their isoflavones (IFLs) are believed to protect against breast cancer, particularly when exposure occurs during childhood. Little is known about the bioavailability of IFLs in children and how this is affected by oral antibiotics (OABX). We measured IFLs by LC/MS and found that the urinary IFL excretion rate (UIER) reflects circulating IFLs accurately when area-under-curve (AUC) and identical time intervals are used (r=0.93; p<0.001). UIER in children and adults was determined when healthy and when on OABX by collecting urine in pairs of baseline and overnight specimen before and after consuming soy nuts, respectively. Compared to when healthy, children on OABX showed significantly decreased UIER but adults on OABX showed increased UIER (p<0.05). All 37 healthy children showed significantly higher UIERs compared to all 34 healthy adults. UIER is an adequate surrogate for determining IFL bioavailability and for measuring soy or IFL exposure in epidemiologic and other studies.

Isoflavones from soya foods are more bioavailable in children than adults.

The purpose of the present study was to determine whether children experience a higher systemic exposure to isoflavonoids when consuming a body weight-adjusted dose of soya compared with adults. Forty study participants were recruited from a local Waldorf school, including twenty-one children and nineteen adults. Participants collected a baseline urine sample and ate immediately thereafter a body weight-adjusted dose of soya nuts (15 g/54.4 kg equivalent to 0.615 (SD 0.036) mg total isoflavones/kg) followed by a 12 h urine collection. Nineteen children and eighteen adults completed the protocol correctly (fourteen child-parent pairs). Children, compared with adults, showed a statistically significant (P < 0.05 by unpaired t test) higher urinary isoflavone excretion rate for daidzein (+39%), genistein (+44%), all non-metabolites (daidzein + genistein + glycitein; +41%) and total isoflavonoids (+32%). Isoflavones are more bioavailable in children v. adults. Urine is an excellent medium to determine systemic isoflavone exposure in children due to its non-invasiveness and high compliance, in particular when collected overnight; it also allows evaluation of completeness of specimen collection.