[001sky]

"from my understanding it's not thought to contribute to metabolic problems in reasonable quantities"

Xylitol is quite toxic to some animals, such as dogs tho.

http://www.vcahospitals.com/main/pet-health-information/arti...

edit: this snippet maybe worth highlighting

In both humans and dogs, the level of blood sugar is controlled by the release of insulin from the pancreas. Xylitol does not stimulate the release of insulin from the pancreas in humans. However, when non-primate species (e.g., a dog) eat something containing xylitol, the xylitol is quickly absorbed into the bloodstream, resulting in a potent release of insulin from the pancreas. This rapid release of insulin results in a rapid and profound decrease in the level of blood sugar (hypoglycemia), an effect that occurs within 10-60 minutes of eating the xylitol. Untreated, this [canine] hypoglycemia can be life-threatening.

[jerf]

That doesn't help much, though. There's all kinds of things that are toxic to one species and not another, even just in Mammalia, and everything that anything anywhere ever eats is definitely not good for some other species.

[001sky]

The mechanism of toxicity (in dogs) is specifically relevant. There are multiple studies showing that artificial sweeteners in general are unhealty -- the body recognizes them -- and takes a variety of actions as a result.

Clearly these reactions in some cases may be simply performance related (see: http://www.gssiweb.org/Article/sse-118-carbohydrate-mouth-ri...). Whilst others can be catastrophic (see: xylitol in dogs).