Quantifying their own confidence is also something they're not good at, and which the format would prevent them from refusing to do or preceding with a caveat if that's what you'd want of them. Particularly since the response format seems backwards - giving confidence, then carbs estimate, then observations/notes, rather than being able to base carbs estimate off of observations/notes and then confidence estimate off of both of those.

> They'll qualify their answers in English but [...]

That the default user-facing chat as a normal user would use it gives a warning is the key part IMO. I don't think expectations of there being no "wrong way" to use the model can necessarily extend to API usage with long custom system prompt and restricted output format.