There's no minimum amount of carbs you need to eat. Despite what people think, for the most part there's no biological need for carbohydrates. Your body will quite happily fuel itself with fat (either dietary or body) - after all, that's why you store fat, so you have an energy source wherever you go.
It is true that your brain does require glucose to function, but you do not need to eat carbohydrate to get glucose, you can manufacture it yourself from protein. So my advice is always eat the amount of carbs you're comfortable with that deliver the blood sugar goals you're aiming for, which could be anything from 0g to 300g depending on your individual tolerance (although most people probably start to run into trouble before they get to 100g).
Above all, listen to your body. If you're not hungry, then you probably don't need to eat. The human body's pretty good at letting you know when you need or don't need something and I believe the more you trust your body and act on what it wants, the healthier you'll be.