Your rice, pasta and potato portions at each meal should be about the size of a standard tennis ball. If you tend to eat more than that at one meal, just cut back at another. 2. Pasta, bread and rice aren't the only carbs. Vegetables, fruit and even dairy foods also contain carbs. But grains tend to pack more than these other foods (although some starchy veggies like potatoes, corn, peas and butternut squash are relatively high in carbs, too).