Phytonutrients - Lignans

Question 1

Lignans

Answer 1

Lignans can be metabolised by intestinal bacteria to form the phytoestrogen compounds enterodiol and enterolactone:
* They are said to be the ‘Western equivalent’ of phytoestrogens and are a soy alternative.
* It is thought that variations in the intestinal bacteria mean that in Western populations tend to tolerate lignans more than soy.
Lignan = derived from the Latin for ‘wood’
Phytoestrogen = plant compounds that produce oestrogen-like effects
Entero= intestine
-diol = alcohol with two hydroxyl groups
Lactone= compound containing an ester group

Question 2

Food sources:

Answer 2

• Flaxseeds (most abundant source).
• Sesame seeds, beans and pulses, cruciferous vegetables.

Question 3

Food sources table:

Answer 3

Food: Flaxseed
Serving: 1 oz
Total lignans (mg): 85.5

Food: Sesame seeds:
Serving: 1 oz
Total lignans (mg): 11.2

Food: Curly kale:
Serving: ½ cup, chopped
Total lignans (mg): 0.8

Food: Broccoli:
Serving: ½ cup, chopped
Total lignans (mg): 0.8

Food: Apricots:
Serving: ½ cup, sliced
Total lignans (mg): 0.4

Food: Cabbage:
Serving: ½ cup, chopped
Total lignans (mg): 0.3

Food: Brussels sprouts:
Serving: ½ cup, chopped
Total lignans (mg): 0.3

Food: Strawberries:
Serving: ½ cup
Total lignans (mg): 0.2

Food: Tofu:
Serving: ¼ block (4 oz)
Total lignans (mg): 0.2

Food: Dark rye bread:
Serving: 1 slice
Total lignans (mg): 0.1

Question 4

Functions:

Answer 4

• Oestrogen modulation
• Anti-cancer

Question 5

Oestrogen modulation:

Answer 5

Functions:
* Bind to oestrogen receptors exerting an oestrogenic effect that is milder than endogenous oestrogens.
* Where oestrogen levels are low the net effect is to ↑ oestrogenic activity.
* Where oestrogen levels are high, lignans antagonise endogenous oestrogens.
Therapeutic uses:
* Menstrual irregularities
o Dosage: 2 tbsp whole flaxseed per day (i.e. seed cycling).
* Menopause support —↓ frequency and intensity of hot flushes; improves vaginal atrophy and cognitive function; supporting bone density, ↓ osteoporosis risk.
o Dosage:2 tbsp flax per day.
endogenous = produced within the body

Question 6

Anti-cancer:

Answer 6

Therapeutic uses:
* Lignans anti-cancer properties —especially in hormonally-driven breast and prostate cancer. There is also evidence for a role in endometrial and ovarian cancer.
* The following anti-cancer mechanisms have been found:
o Modulation of oestrogen metabolism and receptor signalling pathways leading to decreased cell proliferation and angiogenesis.
o Strong anti-oxidant properties.
o Reduces 5α-reductase activity, thereby reducing the more biologically potent DHT (prostate).
* Dosage: 25 g / day (providing 50 mg lignans).
DHT = dihydrotestosterone
5α-reductase = enzyme that converts testosterone to DHT

Question 7

Intake and dosage:

Answer 7

• Consume 25 g flaxseed (approximately 50 mg lignans) daily.
• Lignans are not associated with the oil fraction of foods so intake of whole flaxseeds (ground) are needed to obtain benefits.
• Flaxseeds contain polyunsaturated fatty acids that are unstable and oxidise readily if exposed to oxygen, light and heat (avoid cooking —use to garnish).
• Best consumed from flaxseeds that are freshly ground. Ground flaxseeds also oxidise easily so do not purchase them ground.
  25 g flaxseed is approx. 2 tbsp

Question 8

Safety:

Answer 8

• Lignan precursors in foods are not known to have any adverse effects.
• Flaxseed may lower blood glucose levels and might have additive effects when used with anti-diabetic drugs.
• The safety of lignan supplements in pregnant or lactating women has not been established.