Sounds reasonable. Can you explain why "acetone breath" only happens to some of the faster, and never (AFAIK) more than once per fast, or other than in the beginning? If it was as simple as you describe, it should be very consistent or completely random.
p.s: I don't see anyone mentioning toxins before you did
I think it depends on how much glucose and carbohydrates you're getting in your diet. Your body needs a minimum level to survive (eg. for brain function) and if it doesn't get it, it converts fat. So if you're on a low carb diet, but getting at least that bare minimum, you won't get ketosis. Something like that, anyway.
You were the one who started it:
> your body is finally getting rid of some stuff it should have gotten rid of
Sounds like woo-woo toxin theory to me. There are fat-soluble toxins, but I doubt they'd be enough to make you sick or smell bad.
> I think it depends on how much glucose and carbohydrates you're getting in your diet.
Let me rephrase the question, as apparently it wasn't clear:
Most instances of fasting (specific time + specific instance) do not get acetone breath at all.
Some instances of fasting do get acetone breath, but if they do, it's usually only for a couple of days near the beginning of the fast (usually starting around 2nd day and ending before the 4th day), even if the fast goes on for 3 weeks.
Your explanation does not seem to make this dichotomy possible - it seems to imply an all-or-nothing situation (for a specific instance). Can you extend your description to accommodate this observation? [Note: based on personally collected set of anecdotes - I couldn't find any rigorous collection of this data]
> Sounds like woo-woo toxin theory to me.
I specifically avoided "toxins" in this reply (but not in others) because toxin theory is not well defined, and can thus easily be ridiculed to death. If you define it more properly, (e.g. caffeine "detox"), it is exactly as described, it does make you feel sick. Technically, caffeine is poisonous (as is alcohol) - it's just that in small doses, we as a specie seem to like the effect it produces.
I'm not sure what you mean by an "instance", but there will likely be variations in how quickly people respond to metabolism, and also depends on what you're eating during the fast.
One possible mechanism is that the muscles of the people fasting are more able (either through genes or exercise) to burning fat, meaning that you need to convert less fat into glucose. I'm not a biochemist (I've mainly read Good calories, bad calories plus various primal/low carb blogs) but it seems pretty straightforward (fat -> fatty acids -> acetyl-CoA -> ketones): http://en.wikipedia.org/wiki/Ketosis
Feeling sick on a caffeine detox is likely to just be withdrawal, and/or the "low-carb flu".
p.s: I don't see anyone mentioning toxins before you did