Grilled Sweet Potatoes With Rosemary. Sweet potatoes are naturally low in fat and calories, high in fiber and anti-oxidants. The Center for Science in the Public Interest ranks them #1 in nutritional value among vegetables. They have a lower glycemic index than white potatoes, which makes them a healthier choice. They are, however, fairly carbohydrate-dense, so they do affect the glycemic load of any meal in which they appear. Bottom line: Eat them in moderation.