Vegetable glycerin (also known as glycerol) is a sugar alcohol used in small quantities as sweetener. It has 60% the sweetness of table sugar (sucrose). For human consumption, glycerin is classified by the U.S. FDA as a caloric macro-nutrient. Vegetable glycerin has a positive heat of solution, feeling warm when ingested. When mixed with sugar alcohols like erythritol which have a negative heat of solution, glycerin counteracts their cooling effect.

Vegetable glycerin acts as a preservative. It's commonly used for alcohol-free liquid extracts called glycerites. Glycerites are normally prepared with 1 part water and 1 part vegetable glycerin. The 1:1 ratio of water to vegetable glycerin ensures that the extract is properly preserved.

Medicinally, in adults, the maximum safe dosage is 120 grams per day (Gilman et al, 1990).

Effects On Enzymes

In vitro tests found that glycerin induces CYP2E1.[2][1] Human CYP2E1 was increased 250-300% after 4-8 hours.[1] The half life of CYP2E1 was also increased 366% (from 3 hours to 11 hours) after treatment with glycerin.[1] These results have yet to be verified clinically in human volunteers.

1. Yang MX, Cederbaum AI.
Glycerol increases content and activity of human cytochrome P-4502E1 in a transduced HepG2 cell line by protein stabilization. Alcohol Clin Exp Res. 1997 Apr;21(2):340-7.; Department of Biochemistry, Mount Sinai School of Medicine, New York, New York 10029, USA.
2. Effects of Purified Glycerol from Biodiesel on Cyp1a1 and Cyp2e1 Expressions in CBA/CA Mice
Szele E, Gombos K, Kovács A, Ember I.; In Vivo. 2011 Mar-Apr;25(2):237-40.; PMID: 21471540
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