Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ZZ2 > Phytoestrogens > Flashcards

Phytoestrogens Flashcards

1
Q

What are phytoestrogens?

A
  • Type of phytochemical
  • Non-steroidal plant compound that is able to exert estrogenic effects
  • Similar in structure to endogenous (eg. estradiol) and synthetic estrogens
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the major classes of phytoestrogens?

A
  1. Isoflavones
    - Received the most attention
    - Found in highest concentrations in SOYBEANS, legumes, and clover
    - Also a type of flavonoid (has the 3 ring structure)
  2. Lignans
  3. Coumestans
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the forms of isoflavones found in soy? Which form is absorbable?

A
  1. Glycoside forms: found in this form in the plant for polarity and storage, need to get rid of carb moiety to absorb it
    - Genistin
    - Daidzin
    - Glycitin
  2. Aglycone forms: fermented foods contain some
    - Genistein
    - Daidzein
    - Glycitein
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What isoflavones are found in clover?

A
  • Formonoetin (precursor to daidzein)

- Biochanin A (precursor to genistein)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Discuss isoflavone intakes around the world, and in regards to quantifying it.

A
  • Asian intakes are much higher (decreasing due to Westernization)
  • Need to standardize whether “isoflavone intake” refers to glycoside or aglycone
  • Glycosides weigh heavier due to carb moiety ⟶ overestimate isoflavone intake
  • Has own completed database (USDA and Iowa State University joint effort)
  • Increases accuracy of intake estimates from dietary assessments
  • Relates intake to disease risk by comparing intakes to biomarker of disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are isoflavones absorbed?

A
  • Precursors are converted to isoflavones in the intestine (before absorption)
  • Intestinal bacteria produce enzymes that convert glycosides to aglycones
  • Therefore, if doing a study, consider ANTIBIOTICS (introduce variability in soy bioavailability) and PROBIOTICS
  • Aglycones can be absorbed or further metabolized to metabolites (which are then absorbed)
  • Genistein ⟶ p-ethyl phenol (metabolites)
  • Daidzein ⟶ equol + ODMA (metabolites)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is equol and its effects? What are the implications?

A
  • Metabolite of daidzein
  • Only 30-40% of people produce/excrete equol

1) Most potent of isoflavones; binds to estrogen receptor with higher affinity
2) Longer half life; stays in circulation longer
3) Inversely associated with breast cancer risk

Distinguishing people from producers to non-producers can explain variance in reported data on health benefits of soy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does historical data say about isoflavones and hormonal effects?

A

Clover Disease ⟶ fertility problems in sheep in Australia due to high intake of clover (formononetin); all sheep produce equol

Captive cheetahs fed high amounts of genistin and daidzin; linked to liver disease

California quails had infertility (protective mechanism) in the dry months due to higher phytoestrogen content of their forage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do human studies say about isoflavones and hormonal effects?

A
  • No reports of ferility problems associated with isoflavones
  • Reports of [anti-]hormonal effects; magnitude not shown to interfere with fertility but related to risk of hormone-dependent diseases
  • One study concluded isoflavones do NOT have feminizing effects on men at high levels
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How does isoflavone exert its hormonal effects?

A
  • Isoflavones can bind to estrogen receptor due to structural similarities
  • Potency is 1/1000 the potency of endogenous estrogen (estradiol)
  • Quantity in blood is 1000x more (nano or low micro compared to pico) so still biologically relevant
  • Exerts estrogenic OR anti-estrogenic effects, depending on concentration of endogenous estrogen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the net estrogen effect in premenopausal women? Why?

A

High endogenous estrogens:

  • Isoflavones compete with endogenous estrogens for estrogen receptor
  • Because isoflavones are weaker than estrogen ⟶ net anti-estrogenic effect
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the net estrogen effect in postmenopausal women not on HRT? Why?

A

Low endogenous estrogens:

  • Isoflavones have no competition for estrogen receptor (no ovarian estrogen production)
  • Net estrogenic effect
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the 5 areas of health effects that isoflavones are being researched for?

A
  1. Cancer
    - Hormone-dependent (breast, prostate)
  2. CVD
    - Estrogen is protective for the heart
  3. Osteoporosis
  4. Menopausal symptoms
  5. Cognitive function
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Discuss the evidence and research surrounding isoflavones and breast cancer.

A

1) Beyond blood and urine, isoflavones are bioavailable and can reach the breast tissue
- Bioavailability must be established before studies can be done

2) Reduction of breast cancer risk due to anti-estrogenic effect
- Epidemiological studies show inverse relationship between risk and dietary intake, urinary excretion, and blood concentrations of isoflavones
- Asian populations have lower rates of hormone-dependent cancers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the age/timing of exposure hypothesis? Discuss the relevant study and its implication.

A
  • AGE/TIMING OF EXPOSURE is hypothesis that may explain inconsistencies among isoflavone and cancer studies done in adults:
  • Many early life events that contribute toward breast cancer risk
  • Rat study evaluated effect of genistein consumption on the number of tumours following DMBA (chemical) induced breast cancer
  • Found that rats who were exposed to genistein pre-puberty AND adulthood had lowest numbers of tumours
  • Second best was rats who were exposed during prepuberty only
  • Being exposed in adulthood or prenatally was the same as no exposure
  • Implies that interventions done in adulthood may have no effect
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the mechanism in which isoflavones reduce prostate cancer?

A

1) Reduced concentrations of reproductive hormones through estrogen receptor and inhibiting enzymes involved in hormone synthesis

2) Antioxidant effects
- Remember that isoflavones are flavonoids as well

3) Induce apoptosis, inhibit DNA topoisomerases (stabilize DNA)

17
Q

What do animal studies show for prostate cancer and isoflavones?

A

Animal studies show that feeding isoflavones is effective in the reduction of tumour growth

18
Q

What do studies show about isoflavones and CVD? What is something you need to note?

A
  • Soy protein has been shown to reduce blood lipids (cholesterol, triglycerides, LDL)
  • Also increases LDL resistance to oxidation
  • Health claim is for soy protein, NOT isoflavones specifically
  • Extracted isoflavones do NOT lower blood lipids; needs to be part of soy matrix
19
Q

Discuss isoflavones and its relevance to osteoporosis.

A
  • Most relevant to postmenopausal women
  • Decline in estrogen production is major contributing factor
  • Soy may be an alternative to HRT
20
Q

What do studies show about osteoporosis and isoflavone intake?

A
  • Osteoporosis is measured with hip fractures or bone mineral density
  • Asian women shown to have lower number of hip fractures
  • Positive association found between soy isoflavone intake and BMD
  • Intervention studies showed increased bone formation and decreased resorption
21
Q

What do studies show about isoflavones and menopause? What are the issues?

A

Studies show that soy isoflavones decrease hot flash frequency and severity

  1. Placebo effect
    - Hot flashes are subjective
    - People may experience an improvement simply because they expect one
  2. Time
    - Symptoms are not static and can wax and wane
22
Q

Discuss isoflavones with respect to cognition.

A
  • Recent interest

- Relates to soy isoflavones as an alternative to HRT

23
Q

What are the 2 considerations to keep in mind about isoflavones and health effects?

A
  1. Consider form (soy or extract)
    - Efficacy (if you extract phytochemical, will it still have biological effect?)
    - Safety (lack of data regarding extracted isoflavones in supplemental form)
  2. Curvilinear relationship between intake and plasma concentrations (bioavailability)
    - Blood levels increased with consumption but then plateaus
    - Hypothesized that absorption is saturable process (enzymes required to cleave glycosidic linkage may be maxed out)
    - Possibly more difficult to obtain pharmocological levels with food (less concerned about safety!)
24
Q

Do infants fed soy formula have adverse effects? Discuss.

A
  • Infants fed soy formula have circulating isoflavones up to 22,000x higher than estradiol
  • Studies showed no relationship between soy infant formula (compared to cow milk formula) and adverse outcomes
  • NOTE that babies don’t have gut bacteria to produce equol ⟶ may explain why they don’t have negative outcomes
25
Q

Discuss coumestans.

A
  • Lesser known
  • Found in sprouts and clover
  • Main type is coumestrol
26
Q

Where are lignans found? In what form?

A
  • More widespread in plants than isoflavones
  • Found in flaxseed and whole grains
  • Plant lignans are found in food sources
  1. SECO (secoisolariciresinol)
  2. Matairesinol
27
Q

What are mammalian lignans?

A

Plant lignans are precursors to mammalian lignans (bioavailable and have biological effects); converted by intestinal bacterial enzymes

  1. SECO ⟶ enterodiol
  2. Matairesinol ⟶ enterolactone
28
Q

Discuss health effects of lignans.

A
  • Less human data available on health effects
  • Observational studies report inverse relationship between breast cancer risk and dietary intake + urinary excretion of lignans
  • Consumption of flaxseed reduced serum lipids

ZZ2 (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions