Soy lecithin

1.1. Sources

Lecithin is a term used to refer to a glycerol molecule with two fatty acids attached to it with the last open binding position being bound to a phosphatidic acid molecule, which can then be further bound to other molecules such as amino acids. The term 'soy lecithin' is used to described the lecithin from soy, and it is sometimes a vessel for phosphatidylserine (PS) due to it not requiring solvent extraction (Internal report^[1]) and has a phosphatidylcholine,^[2] phosphatidulethanolamine,^[2] and phosphatidylinositol^[3] content as well.^[3]

Soy lecithin is lecithin (a category of molecules based on a certain structure) that is derived from soy, conferring a few phosphatidic acid related structures (the most common being phosphatidylserine and phosphatidylcholine, PS and PC respectively)

1.2. Composition

Soy lecithin contains:

• Phosphatidylserine (PS; phosphatidic acid bound to serine) at around 3% total phospholipids^[4]

• Phosphatidylcholine (PC; phosphatidic acid bound to choline) at up to 29-31.7% of phospholipids^[5][4]

• Phosphatidylethanolamine (PE; phosphatidic acid bound to ethanolamine) at up to 20.8-23% of phospholipids^[5][4]

• Phosphatidylinositol (PI; phosphatidic acid bound to inositol) up to 15-17.5% of phospholipids^[5][4] 

• Phosphatidic acid (PA; 7-17.5% of total phospholipids^[5][4])

• Phytosterols (most as glycosides) including β-sitosterol, sitostanol, and sitosteryl β-d-glucoside^[6]

• Phytoglycolipids (14.8% total phospholipids^[4])

With the lipid composition of the above phospholipids accounting for:

• Linoleic acid at 64%^[4]

• Palmitic acid at 14%^[4]

• Oleic acid at 10%^[4]

• Linolenic acid at 7%^[4]

• Stearic acid at 4%^[4]

Relative to other sources of lecithin, soy appears to be comparatively high in PI with 15% of the phospholipids as PI^[5] and 287mg/100g food product (soy overall, not just oil) being PI;^[7] another popular lecithin, derived from egg yolk, is much lower in PI.^[8]

2.1. Serum

Phosphatidylserine from soy lecithin appears to be absorbed by the body rapidly, reaching a T_max at 90 minute after ingestion and reaching near baseline levels in serum at 180 minutes (Internal report, not peer reviewed^[1])

Relative to 2.3g choline from choline chloride (3g), lecithin with an equal amount of choline has a lower value when measured at 30 minutes post ingestion (33% relative to 86%) but continues to rise over the course of 12 hours (265% of baseline).^[9]

3.1. Aging

One study using a rat model of premature aging (SAMP8) noted that, relative to a group fed 5% lard for their lifetime, the active groups of soy lecithin (at 2% of the diet with 3% coming from soy oil) was associated with more survival than lard when measured at 12 months (although less than a diet with 2% fish oil instead of lecithin) although the lecithin outperformed all other groups in a cognitive test of aging (passive avoidance).^[10]

4.1. Stress

A study using 400-800mg of phosphatidylserine and 450-900mg phosphatidic acid via soy lecithin (total oral dose of soy lecithin being 1,980-3,960mg) in 80 otherwise healthy adults subject to a stress test (Trier Social Stress Test) noted an anti-stress effect that peaked at the lowest dose as assessed by salivary ACTH and cortisol (both salivary and serum) as well as the STAI rating scale (particularly the subscale of distress); this study was funded by a producer of soy lecithin.^[11]

2g soy lecithin appears to confer an anti-stress effect, with doubling the dose reducing the efficacy in otherwise healthy persons

5.1. Lipids

In animals with hypercholesterolemia (high blood cholesterol), supplementation of the diet or isolated phosphatidylcholine appears to reduce circulating cholesterol secondary to stimulating bile acid secretion (a similar mechanism to most dietary fiber products that form gels).^[12][13] This has been noted once with dietary soy lecithin in rats with normal cholesterol^[14] although another study using 7 days supplementation of 2g/kg soy lecithin (31.7% PC, 20.8% PS, 17.5% PA; 14.8% phytoglycolipids) failed to find such an effect in rats with normal cholesterol.^[4]

Administration of 500mg soy lecithin (68% phosphatidylcholine and 10% phosphatidylethanolamime) daily for 2 months, relative to the placebo treatment of 500mg soy oil, reduced total cholesterol (42.60%) and LDL-C (56.11%) without influencing HDL-C or triglycerides relative to baseline.^[2]

May have cholesterol reducing properties, but limited human evidence and the mechanism does not appear to be unique (being common to soluble fiber in general)

6.1. Immune cells

7 days of dietary intake of soy lecithin at 2g/kg () has been noted to increase macrophage phagocytic activity in rats by aroud 29% without influencing alloxan-induced diabetic rats;^[4] this is thought to be secondary to phosphatidylcholine, as macrophages cultured with PC in vitro have been shown to have altered function towards lymphocytes.^[15]

In diabetic rats without effect on macrophages, lymphocyte count has been noted to preserved in diabetic rats given concavalin A (mitogen) relative to nondiabetic rats given concavalin A (and 92% greater than diabetic control); nondiabetic rats given soy lecithin has a suppression of lympchyte activity by approximately 35%.^[4]

7.1. Absorption enhancement

A brand name delivery system known as Phytosome®, which plays on the ability of soy lecithin (being phospholipids) to enhance delivery of hydrophobic/lipid soluble drugs or nutrients^[16][17] with an overall stoichiometry in the range of 1:1–1:3 between the active and the phospholipid formulation aid.^[18] The mechanisms underlying the absorption enhancement appear to be in part due improving their dispersion in the intestinal fluids and in part due to chaperoning molecules into enterocytes via forming complexes.^[16] It seems that, relative to liposomes the reduced concentration of phospholipids allows a greater amount of phytochemicals to be integrated into the phytosome and as such phytosomes using soy lecithin can carry more substrate than an equal amount of liposomes.^[18]

This has been used to enhance absorption of Boswellia Serrata,^[19] Curcumin,^[17] Silymarin (from Milk thistle),^{[17][20][21][22]} Grape seed extract,^[17] and green tea catechins.^[17] Elsewhere, it has enhanced chemical resistant of resveratrol during simulated digestion (ex vivo).^[23]

Some pharmaceuticals, such as Naproxen^[24] also benefit from soy lecithin delivery.

Soy lecithin is used as an agent to increase intestinal bioavailability of some other agents (may not apply to all agents)

Soy lecithin phospholipids have also been used in immunological endeavours, as the nanoparticles formed from soy lecithin phospholipids can facilitate antigen uptake by antigen presenting cells (APC)^[25] and thus lower the antigen payload required for a desired effect.^[26]