Is Coke Zero bad for someone in a diabetic family?

It is bad,because in fact it contains aspartame which makes someone gain fat more than sugar, and healthy weight is very important for a diabetic. So if someone drinks lots of it, it can be bad. And I know this for a fact as my ex husband was diabetic and it is his doctors that told us after he gain a lot of weight even by cutting sugar. How was eating everything no sugar added (which mostly contains all aspartame)