During the transition into menopause, women experience an accelerated decline in muscle mass, linked with a marked reduction in estrogen. While hormone therapy (HT) can have beneficial effects on skeletal muscle, it is known to be associated with an increased risk of cancer in estrogen receptor (ER-α) rich tissues.
Isoflavones are the most common and potent type of phytoestrogen (polyphenolic non-steroidal compounds with estrogenic activity). They are found in legumes, such as soy and red clover (RC) and mimic the actions of estrogen through ER binding and activation of ER-dependent gene transcription.
However, compared to estrogen, which has relative high binding affinity for the ER-α and ER-β, isoflavones demonstrate up to ~1600 times lower affinity for ER-α meaning they should not increase the risk of cancer.
Soy isoflavone supplementation has been found to increase lean body mass in obese-sarcopenic postmenopausal women but little attention has been given to RC isoflavones. Compared to soy, RC contains high amounts of formononetin and biochanin A, plus RC derived products have shown to elicit higher estrogenic activity.
There are currently no reports of clinical trials investigating the effects of RC extract on skeletal muscle. Therefore, the aim of the present pilot study was to investigate the effect of 14 days of fermented RC extract supplementation on signaling proteins related to muscle protein synthesis and breakdown at rest and in response to a resistance exercise bout. A secondary aim was to elucidate whether RC extract supplementation would affect muscle strength.
The research team, from Aarhus University, Denmark, hypothesised that RC extract supplementation would positively influence skeletal muscle by increasing muscle strength and the anabolic response to a resistance exercise bout.In a double-blinded cross-over trial, subjects (n = 10) completed two different intervention periods in random order: (A) Intake of fermented RC extract twice daily for 14 days, and (B) intake of a placebo drink (PLA) twice daily for 14 days.
The intervention periods which involved a number of strength and muscle tests, were separated by a two-week washout period. The resulting data revealed that protein expression of FOXO1 and FOXO3a—two key transcription factors involved in protein degradation—to be significantly lowered following RC treatment compared to PLA.
The team concludes future clinical trials need to enrol and randomise a larger number of subjects and prolong the intervention period to investigate effects of RC extract both with and without training on skeletal muscle, preferably using a double-blinded controlled design.
The study
The RC extract used in the present study was a commercially available drink produced by Herrens Mark Aps, consisting of juice from pressed RC plants mixed with probiotic lactic acid bacteria to facilitate cold fermentation.
On day 1 and day 14 of each intervention period, subjects performed a maximal handgrip and maximal elbow flexor strength test. Additionally, on day 14 a muscle tissue sample was obtained before and three hours after a resistance exercise bout performed on one-leg. In the second intervention period, exercise and biopsies were performed in the contralateral leg.
Prior to the exercise bout, subjects received the RC or PLA drink and immediately after exercise they consumed 25 g of whey protein. All tests were performed at the same time of the day and by the same test personnel at all test days.
To standardise activity and diet prior to the experimental days, subjects were instructed to: abstain from any strenuous and/or unaccustomed activity 48 h before the experimental days, monitor their number of steps using a step counter before experimental day 14A and replicate the number of steps on the day before experimental day 14B, eat a similar meal the night before each experimental day, and meet in the lab after an overnight fast.