As far as I am aware, there is no set amount of carbs you need to have with Metformin. I am 40g a day or less, others are much higher. As far as I am concerned, your carb levels will be dictated by how much pancreatic function you have. If like me, you have very little you will need to have low carbs, if your pancreas is not so bad, then you will tolerate more. I have never ever had tummy trouble with Metformin and I am on the bog standard ones 500mg twice a day. I did however suffer from a decimated appetite when I first started them, but that is long gone, and I am fine now. I have also lost 90 pounds in weight since March.