Can I trust my health insurer?

This is typically the attitude of sales personnel to make the sale (and achieve targets) wherein they over-commit to the prospect. Please note that in the event of a claim in future, invariably this fact will get recorded in the case sheet and drugs may be administered to control diabetes. This, when mentioned on the discharge summary (which is a medico legal document and therefore such details have to be disclosed) will lead to repudiation of the claim. As per the terms of all policies, the insurance cover/claim is liable to be repudiated/cancelled in case of intentional non disclosure of facts or misrepresentation. I will strongly advise you against with-holding any such information while purchasing an insurance policy. Such matters should be reported to the senior management of insurance companies to ensure that insurance is not sold through misrepresentation.