Soy

SOY ISOFLAVONES

Isoflavones are polyphenols belonging to the class of flavonoids. They are not steroids but are structurally similar to oestrogens, particularly oestradiol.
This gives them pseudormonal properties, including the ability to bind to oestrogen receptors, and they are therefore considered phytoestrogens or plant oestrogens. 1

Genistein, daidzein, glycitein are contained in high amounts in soya; lower concentrations also in beans, lentils and peas. Formononetin, biocyanin A zono present in red clover are completely dimethylated in the body to genistein and daidzein.
Isoflavones occur naturally in complexed form with sugar molecules and are called 'glycones'. Glycone must be free of the glucose ingredient in order to act. Glycones, after ingestion, are converted to aglycones by the action of hydrochloric acid in the stomach, which separates the sugar). Approximately 1/3 of the aglycones are absorbed, while the remaining portion is degraded by intestinal bacteria into isoflavonoids (such as equol) which, in turn, can be absorbed by the intestinal wall.
The characteristics and microbial properties of the gut may therefore influence the metabolism of isoflavones by influencing their effects. Most isoflavones are eliminated from the body within 24 hours of ingestion through the urine.

Isoflavones and neurovegetative symptoms Soy isoflavones are called phytoestrogens. They can have both agonist and antagonist action: they have the same affinity as oestradiol for type II oestrogen receptors, although they are a thousand times less potent; in this case they are therefore agonists. However, they can also inhibit the binding of oestradiol to its receptor, thus acting as antagonists. Many of the effects derive precisely from the fact that isoflavones can either act as a supplement to oestrogens or combat them when their level in the body is too high. A 1996 2 double-blind study shows that soy isoflavones significantly decrease menopausal symptoms, particularly hot flashes. This study was done on postmenopausal women supplementing their diets with either soy flour or wheat flour; a 40 per cent decrease in hot flushes was observed in the first group, compared to 10 per cent in the second group. Several studies have been conducted, and all of them lead to the same conclusion: the phytoestrogens contained in soya can be an excellent alternative to hormone replacement therapy, which is sometimes responsible for unpleasant side effects, and not always usable due to important contraindications.

Isoflavones and the cardiovascular system Genistein, along with the other phytoestrogens, also appears to be able to lower the risk of cardiovascular disease, thanks to its anti-platelet action and ability to reduce blood cholesterol levels. In particular, isoflavones are capable of reducing LDL cholesterol level and increasing the HDL one. The mechanism of action is poorly understood; however, an antioxidant activity on LDL-cholesterol appears to be involved.3
Many other possible mechanisms of action have also been indicated, including their ability to block the growth of blood vessels of cancer cells (angio-modulation) and stimulation of the sex hormone controlling globulin SHBG, thereby influencing testosterone and oestradiol levels. The discovery of the existence of oestrogen receptors at the level of the vessel wall, especially beta-type receptors, made a functional role of female oestrogen on the cardiovascular system plausible

The isoflavones contained in soy are apparently able to bind to beta oestrogen receptors with an affinity up to 6 times higher than to alpha oestrogen receptors.4
There are numerous publications on the beneficial effects of soy isoflavones in menopausal women. Below are some of the most significant highlights.

The effect of isoflavones extracted from soya in inducing a significant increase in arterial elasticity has been demonstrated.5

The administration of soy containing isoflavones appears to slow down the progression of atherosclerotic lesions more significantly than the use of soy deprived of isoflavones, and this would support the role of isoflavones in the biology of atherosclerosis. 6

Research conducted on vascular cells in culture has shown that isoflavones are capable of modifying the cellular changes associated with the development of atherosclerotic lesions. Finally, isoflavones appear to have a protective effect against oxidative processes of LDL-cholesterol particles. Although there are still widely differing views on the real role of isoflavones in protecting against cardiovascular risk in postmenopausal women, the use of these modulators of oestrogenic action is widely used in the population and research is increasingly focusing on the reasons for such variable data. Among the reasons for such variable results, a key role is played by the gut microbiota, the main bio-transformer of isoflavones equally absorbable, and the low standardisation of soy products used in the trials.11

Isoflavones and bone metabolism Pharmacological studies in animals have shown that a soy-based diet decreases bone loss caused by oestrogen deficiency 7; the same result was observed with the administration of genistein in ovariectomised rats.8 The first clinical evidence linking soy isoflavone supplementation to bone metabolism dates back to 2001.5

According to the most recent research, a 2012 meta-analysis has shown that soy isoflavones significantly (54%) increase bone mineral density and reduce deoxypyridoline (a urinary marker of bone resorption) by approximately 23%. From this meta-analysis, the authors conclude that soy isoflavone supplements significantly increase bone mineral density. There were no significant changes in serum levels of bone alkaline phosphatase. The reason why soy isoflavones may be useful in bone protection is essentially related to their ability to bind with good affinity the Beta oestrogen receptor (ER-Beta) of the osteoblastic cell line by inducing production of Osteoprotegerin (OPG); this mechanism leads to an inhibition of signalling for RANKL which, together with the M-CSF factor, is an activator of osteoclastic differentiation. 9

Another mechanism of action associated with soy isoflavones relates to the elevation of Vitamin D receptors (VDRs) in osteoblastic-like cells and Vitamin D metabolites (1,25-dihydroxy vitamin D), preventing the lowering of serum calcium levels, parathormone release and subsequent osteoclastic activation. The combination of soy isoflavones and vitamin D is therefore synergistic for effective bone protection. 10

 

Bibliography

1 were identified. Tham DM, Gardner CD, Haskell WL. Potential health benefits of dietary phytoestrogens: a review of the clinical, epidemiological, and mechanistic evidence. J Clin Endocrinol Metab 1998;83:2223-2235

2 were identified. Eden J, et al, "Hormonal effect of Isoflavones," Program & Abstract Book, Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Sept 15-18, 1996

3 were identified. Kanazawa, 1996; Schoene, 1996; Ruiz- Larrea, 1997 et Wang, 1996

4 were identified. Kuiper GG, Carlsson B, Grandien K. et al. Comparison of the ligand and binding specificity and transcript tissue distribution of estrogen receptors alpha and beta. Endocrinology 1997;138:863-870

5 were identified. Nestel PJ, Yamashita T, Sasahara T, et al. Soy isoflavones improve systemic arterial compliance but not plasma lipids in menopausal and perimenopausal women. Arterioscler Thromb Vasc Biol 1997;17:3392- 3398.

6 were identified. Anthony MS, Clarkson TB. Comparison of soy phytoestrogens and conjugated equine estrogens on atherosclerosis progression in postmenopausal monkeys (abstract). Circulation 1998;97:829

7 were identified. Gail A et al. Dietary Soy Isoflavones and Bone Mineral Density: Results from the Study of Women’s Health Across the Nation. American Journal of Epidemiology. 2014

8 were identified. Bahram H Arjmand et al. Bone-sparing effect of soy protein in ovarian hormone-deficient rats is related to its isoflavone content. Am J Clin Nutr 1998

9 were identified. Wei P eta l. Systematic review of soy isoflavone supplements on osteoporosis in women. Asian Pac J Trop Med. 2012

10 were identified. Clara Y et al. Vitamin D Interactions with Soy Isoflavones on Bone after Menopause: A Review: Nutrients 2012

11 were identified. Dubey RK, Gillespie DG, Imthurn B, Rosselli M, Jackson EK, Keller PJ. Phytoestrogens inhibit growth and MAP kinase activity in human aortic smooth muscle cells. Hypertension 1999;33:177-182.