According to healthline, oats are nutrient-dense whole grains that are rich in soluble fiber and a good source of protein, vitamins, minerals and antioxidants. And, gluten-free (check to package though). Old fashioned oats, quick oats and steel-cut oats all have similar nutritional content. Steel cut oats have a slight edge on fiber. Instant oatmeal is the least nutritious as packages often contain added salt and sugar.