BACKGROUND: Isoflavones are a subfamily of plant antioxidants known as
flavonoids. Research has shown that isoflavones may reduce the risk of
breast cancer in women, as well as menopausal hot flashes. In men, research
has found that isoflavones may reduce the risk of prostate cancer. Most
isoflavone supplements are derived from either soybeans or red clover. The
types of isoflavones differ slightly between the two, with soy containing
primarily genistein and daidzein and red clover containing primarily their
precursors (biochanin and formononetin).
RESEARCH: Researchers compared the absorption of approximately 30 mg of
isoflavones from soy and red clover by incorporating them into breakfast
foods. Fourteen men and women consumed a soy-enriched cereal for two weeks. Then, after a two-week "washout" period, they consumed a red clover- enriched cereal for two weeks. Inferences about the absorption of
isoflavones was based on the amount excreted, a common medical technique.
RESULTS: Individuals vary greatly in their absorption of isoflavones, due
largely to individual differences in the numbers of intestinal bacteria
that aid digestion. However, the individual subjects in this study
consistently excreted - and presumably absorbed -- approximately the same
amount of both soy and red clover isoflavones.
IMPLICATIONS: This study shows that excretion, and likely absorption, of
soy and red clover isoflavones is similar in any given individual. Although
the composition of individual isoflavones is somewhat different between soy
and red clover, individuals absorb roughly the same amounts of isoflavones,
regardless of the source.
Tsunoda N, Pomeroy S, Nestel P., "Absorption in humans of isoflavones from
soy and red clover is similar," Journal of Nutrition, 2002;132:2199-2201.
For the original abstract, visit: http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12163662&dopt=Abstract