Soya

Question 1

What is the difference between soya consumption in americans and japanese?

Answer 1

americans eat about 3 pounds soy food/year whereas japanese ear about 24 pounds per year

Question 2

What link is there between breast and prostate cancer and soya ?

Answer 2

japanese women who eat a lot more soya food compared to americans have had the rate of breast cancer in comparison
death rates from prostate cancer is lower in asian countries in comparison to americans
when asians migrate to us breast cancer and prostate cancer risks increases

Question 3

What was the assumption with soya?

Answer 3

thought it may protect against hormone dependent cancer

- countries that ate lots of soya seemed to have a lot less hormone dependent cancers

Question 4

What compound in soya is related to estradiol and what does estradiol do which has been related to the effects of soya?

Answer 4

equol is the related compound in soya
- both estradiol and equol have phenolic components and hydroxyl components that are almost exact same distance apart
estradiol is involved in cell division and has carcinogenic effects so therefore this is thought to be associated to the mechanism of hormone related cancers

Question 5

What is equol ?

Answer 5

a metabolite (from the gut microflora) of daidzein, an isoflavone in soya
- you dont find equol in soya

Question 6

What is a major source of phytoestrogens ?

Answer 6

major source is soya - isoflavones: geinstein and daidzrin- levels vary from 1-100mg/100g

Question 7

What are the levels of phytoestrogens in soya milk and different soya protein fractions?

Answer 7

they are reduced compared to natural soya because some of the isoflavones are washed away

Question 8

What happens to fermented soya?

Answer 8

levels of phytoestrogens are reduced (and proportions of glycosides to aglycones change)

Question 9

Where are lignans founds ?

Answer 9

present in tea, cereals, berries, linseed oil, oat meal, lentils and asparagus- levels vary in these sources
most commonly found in western diets
they are in vivo metabolites

Question 10

Where are sources of isoflavones found?

Answer 10

soya flakes, tofu, soya flour and soya sauce, levels vary from 566-23 mg/g

Question 11

What compounds are all found in soya and all have a close structural relationship ?

Answer 11

daldzein, geinstein, coumestrol and equol and biochanin A

Question 12

Why are synthetic oestrogen’s bad?

Answer 12

they are known to be carcinogenic eg. hexestrol

zearalenonne causes reproductive disorders in animals

Question 13

How is equol produced and what is interesting about it ?

Answer 13

produced by gut microflora
you get poor and good equol producers- the good ones are able to produce at least 100x more equol - therefore if equol has substantial biological activity then you would expect to see very varying effects between individuals - nothing has yet been found

Question 14

What do hormones do ?

Answer 14

regulate almost every biological process:

• growth and development
• mental development, mood and memory
• sexual maturation
• immune function

Question 15

What is the oestrogen receptor and what is it involved in ?

Answer 15

it belongs to the nuclear receptor super family of ligand regulated transcription factors
controls cell growth and differentiation in a diverse array of tissues:
- reproductive system
- bone
- cardiovascular system
- central nervous system

Question 16

What happens when oestrogen binds to its receptor?

Answer 16

estrogen binds to inactive complex in the nucleus and activates it - causes ligand binding dimerisation DNA binding
dimer goes off to bind to DNA- binds to specific transcription factors and alters specific genes to produce enzymes and proteins
BUT
if the molecule binds to the inactive complex and it remains inactive then its said to be behaving as an antagonist preventing natural compounds binding

Question 17

What do the levels of estrogenicity of phytoestrogens vary between in comparison to estradiol?

Answer 17

vary from 0.20 to

Question 18

What links have been made between phytoestrogens and cancer prevention ?

Answer 18

hormone-related cancers are higher in western populations compared to certain asian populations
epidemiology links the consumption of soya and soya-derived foods as protective
mechanistic evidence suggests that certain phytoestrogens could play a role in prevention of hormone-related cancers

Question 19

What are the differences in the levels of genistein and daidzein in blood between Finnish and Japanese men (ng/ml) ?

Answer 19

Finnish men- genistein (1.7) and daidzein (1.6) whereas in japanase men- genistein (74.6) and daidzein (27.2)
these levels could be very significant biologically

Question 20

What discovery was observed about conjugated isoflavones and why was it relevant ?

Answer 20

45mg per day for 1 month led to an increase in follicular phase length and delayed menstruation
- fed the levels you expect in soya and in conjugated form
- if the menstrual cycle was a day longer and you multiplied this by a year, 10 years, 50 years, you’d be getting quite a substantially reduced amount of oestrogen stimulation
- therefore could this reduce cell division and was this the protective effect of soya
- the phytoestrogens would be acting to block the endogenous actions of estradiol
BUT
if this was happening across a population then you’d expect to see a reduction in fertility
NO actual evidence for reduced fertility due to increased soya consumption

Question 21

There was a suggestion that the phytoestrogens were acting as agonists in post-menopausal women and antagonists in pre-menopausal women but how ?

Answer 21

there are 2 oestrogen receptors so maybe this explains the different effects
alpha and beta receptors
they are similar in many ways - DNA binding domain has 90% homology but ligand binding domain only have 10% homology
also have differences in tissue distribution and promoter specificity
although this demonstrates that phytoestrogens could act different in pre and post-menopausal women why does adding oestrogen activity after the menopause induce a beneficial effect

Question 22

Overall what are the results for isoflavones and lignans?

Answer 22

epidemiology is less good for isoflavones and not good for lignans
the understanding of these compounds is very much lacking

Question 23

What was observed when whole soy extract and soy isoflavones were compared ?

Answer 23

they looked at the activity of these compounds on apoptosis in prostate cancer cells
- the extract worked the best therefore it is not the structure of estradiol thats involved in the mechanism

Question 24

What is soya high in and what is fermented soya high in and what are the differences in the compounds ?

Answer 24

soya has high levels of isoflavones glycosides - mostly genistin and daidzin
fermented soya has high levels of isoflavones aglycones- mostly daidzein and genistein

daidzin and genistin have sugars attached and whereas in fermented soya bacteria break off the sugar therefore the isoflavones aglycones should be absorbed better because they have lost their sugar molecule so they are less hydrophilic therefore they can cross cell membrane more easily
therefore reasonable to hypothesise that fermented soya would have more bioactivity