Whether anyone has mentioned this or not, (I didn't read entire thread), it seemed important to note. Vegetable Glycerin, when inhaled, is metabolized by the body and converted into water/carbon dioxide via common action. I don't believe you're getting any calories by vaping VG. I have doubts whether PG would yield caloric intake either.
One interesting side note I discovered:
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The risk of being allergic to vegetable glycerin is very low. The only patient population which may experience problems with metabolism of Glycerol would be diabetics owing to the anabolic hepatic pathway which can convert free Glycerol to glucose(but this would still not be an issue at the levels used in vaping)."
So perhaps this is the only exception although it does not sound like an issue.
More VG Info: Glycerol is one of the most benign organic liquids known to man. It is hype-allergenic, non-carcinigeic, non teratogenic and non-mutagenic. It is metabolized quite easily by a process called beta-oxidation. This process results in the production of CO2 and H2O and is a quite normal, common, and natural catabolic process.
The following is a few excerpts from a study called SIDS initial assessment profile of Glycerol Citation
Glycerol is of low toxicity when injested, inhaled, or in contact with skin
The NOACE for local irritant effects to the upper respiratory tract is 165 mg/m3
Glycerol is of a low order of acute oral and dermal toxicity with LD50 values in excess of 4000 mg/kw bw.
Glycerol has low potential to irritate the skin and the eye
Glycerol is not a skin sensitiser
Glycerol does not induce gene mutations in bacterial strains, chromosomal effects in mammalian cells or primary DNA damage in vitro
Overall, glycerol is not considered to possess genotoxic potential
No effects on fertility and reproductive performance were observed
No further work is indicated by this study, because of the low hazard potential of this substance.
The safety of vegetable glycerin (VG) when inhaled through an electronic cigarette (e-cigarette). Studies on the effect of the inhalation of vegetable glycerin through a personal vaporizer.
). Remember, calories are a measurement of potential heat, and once vaporized we're taking in a heck of a lot less mass than if we ingested the liquid. Also, PG is a pretty darn simple molecule and is metabolized as lactic acid, which is naturally consumed in the process of anaerobic cellular respiration. So nothing harmful there. VG is actually a simple alcohol. Though it shares a common structural backbone with some lipids and triglycerides, it does not actually contribute these to the body when ingested.
