Wheat Bran and Soy Protein Feeding Do Not Alter Urinary Excretion of the Isoflavan Equol in Premenopausal Women

Abstract

The capacity to convert the soy isoflavone daidzein to equol in vivo is presumably determined by an individual's intestinal microfloral populations; however, diet may also influence this conversion. The objectives of the present study were to determine whether a 1-mo supplementation of dietary fiber as wheat bran increases urinary equol excretion in equol excreters and stimulates equol production in nonexcreters and whether longer-term soy isoflavone intake increases equol production or alters overall urinary isoflavone excretion. First, we screened 74 women, ages 20-40 y, and determined their equol-excreter status. In these women, health and lifestyle patterns and habitual dietary intake did not differ according to equol-excreter status. Next, 26 of the women (13 equol excreters and 13 nonexcreters) were assigned (blocked on equol-excreter status) to either longer-term (1 mo) or short-term (4 d) soy protein supplementation. Within each soy treatment group, women participated in two 1-mo intervention periods (the exact length was determined by each woman's menstrual cycle) during which they consumed their usual diets supplemented daily with either 0 or 16 g dietary fiber in a randomized crossover design. A 1-mo washout period separated the two diet periods. Among the 19 women who completed both periods, fiber supplementation did not increase equol production in equol excreters or nonexcreters. In addition, isoflavonoid excretion did not differ by fiber dose or length of soy intervention. These results suggest that a daily 16 g-fiber dose as wheat bran and the addition of soy protein do not alter significantly the capacity of colonic microflora to produce equol.

Consumption of Lactobacillus acidophilus and Bifidobacterium longum do not alter urinary equol excretion and plasma reproductive hormones in premenopausal women

“…Although equol excretion has been positively correlated with total fat and meat intake and fat-to-fiber ratio (Adlercreutz et al, 1991), processed and high-fat meat (Lampe et al, 1999) and carbohydrate, fiber, plant protein, and percent of energy as carbohydrate (Lampe et al, 1998;Rowland et al, 2000), our findings agree with other research showing no unique dietary patterns in equol excretors (Hutchins et al, 1995;Duncan et al, 2000;Lampe et al, 2001). Our results showing no differences in age, body weight, BMI, and cycle length between excretors and nonexcretors also agree with previously published results (Duncan et al, 2000;Lampe et al, 2001). However, these results must be interpreted with caution, as they are limited by small sample sizes, homogenous populations, and insensitive dietary assessment tools.…”

“…A more recent study using a soy or wheat-bran intervention was unable to alter excretion from baseline (Lampe et al, 2001). Probiotic consumption did not significantly reduce plasma reproductive hormones, although the bacteria provided were similar in dose and bacterial species to those previously shown to significantly lower fecal b-glucuronidase activity in humans (Goldin and Gorbach, 1984;Benno and Mitsuoka, 1992).…”

“…Two reported attempts have been made to increase equol excretion through dietary means. Lu et al (1996) reportedly increased equol excretion in six premenopausal women given soy milk for 1 month, while Lampe et al (2001) were not able to change equol-excretor status in premenopausal women after giving soy protein or wheat bran for 1 month.…”

Increased probiotic yogurt or resistant starch intake does not affect isoflavone bioavailability in subjects consuming a high soy diet

“…In the current study, 12 subjects (39%) consistently metabolized daidzein to equol, a similar proportion to that reported in other soy studies (52)(53)(54). All four soy dietary periods increased plasma equol levels in the initial (0 h) measurement, implying that 5 weeks of daily soy intake (with or without a probiotic or prebiotic) was sufficient to increase plasma equol in those who are predisposed to this conversion.…”

Urinary isoflavonoid excretion is inversely associated with the ratio of protein to dietary fibre intake in young women

“…Conversely, isoflavone excretion after a soy-rich meal was reduced by 13% when accompanied by a wheat fibre supplement (Tew et al, 1996). However, two other studies found no changes in isoflavonoid excretion after treatment for 1 month with soy combined with a wheat fibre supplement (Lampe et al, 2001) or an increased intake of fat and protein . Discrepancies could arise from differences in design: two studies Rowland et al, 2000) focused on equol and did not evaluate total isoflavonoids, while in two other trials (Tew et al, 1996;Xu et al, 2000), the experimental period of 1day may have been inadequate and data on the isoflavonoid metabolites were not reported.…”