Research Communication: Absorption in Humans of Isoflavones from Soy and Red Clover Is Similar

Abstract

The absorption of isoflavones varies substantially among individuals. It is unknown whether isoflavone absorption differs between those originating from soy and those from red clover, which contain different mixtures of isoflavones. Because both soy and red clover are increasingly used in foods and supplements, these issues were studied in 14 subjects in a single-blind, randomized, placebo-controlled, crossover trial. Soybean isoflavone glycosides and red clover isoflavone aglycones were incorporated into a breakfast cereal and eaten daily for 2 wk each, separated by a 2-wk control or washout period. The 24-h excretions of isoflavones in urine were measured; approximately 25% of each isoflavone was recovered in urine, suggesting that similar amounts were absorbed irrespective of their glycoside/aglycone nature or the differing compositions of their sources (daidzein and genistein in soy and formononetin and biochanin in red clover). Although interindividual variability was high, there was less intraindividual variability; the amounts excreted when subjects consumed the two sources of isoflavone were correlated (r = 0.69; P = 0.007).

A biochanin-enriched isoflavone from red clover lowers LDL cholesterol in men

“…The recovery during the intervention with F of 18.9 mg/day or just under 25% of the ingested amount is similar to amounts that we have reported (Nestel et al, 1997;Tsunoda et al, 2002). Nonurinary routes of excretion and failure to measure minor metabolites (only equol and O-desmethylangloensin were measured) contribute to underestimation.…”

“…Isoflavones recovered in urine showed as expected that most, but by no means all, the primary isoflavones, formononetin and biochanin were converted into daidzein and genistein, respectively (Tsunoda et al, 2002). Further, the total excreted by individuals consuming B was less than that excreted with the consumption of F, as noted by others (Busby et al, 2002).…”

“…Urinary isoflavones were measured as described by Tsunoda et al (2002). Briefly, aliquots of urine were incubated for 24 h at 371C with glucuronidase and the free isoflavones were eluted with 3 ml ethanol from a C-18 solid-phase extraction column (Waters, Sydney, Australia), and separated by HPLC.…”

“…Studies with intact soy protein have been conducted in both men and women with no apparent gender difference (Crouse et al, 1999). Adding to these variables is the large interindividual variation in isoflavone absorption (Tsunoda et al, 2002). A puzzling result is the apparent absence of a response to purified isoflavones when taken in amounts that show a benefit within soy protein.…”

Recovery of isoflavones from red clover flowers by a membrane-based process

“…The variations in isoflavone composition may be due to varietal diversity as well as differences in growth and storage conditions of the plant. Despite the compositional difference, the bioavailability of isoflavones from these two plant sources is similar (Tsunoda, Pomeroy, & Nestel, 2002). Nutritional studies also indicate that red clover-derived isoflavones do not show any estrogenic activity, thus making them superior to the soybased isoflavones for use in hormone replacement therapy (HRT) (Atkinson et al, 2004).…”