How many calories are in a serving of oatmeal?

One cup of cooked steel-cut oatmeal contains 300 calories and 4 grams of fat. One cup of cooked rolled oats has the same number of calories with 5 grams of fat. One packet of instant oats contains 100 calories and 2 grams of fat.

Steel-cut oats are the least processed of all oatmeal varieties and are basically coarsely chopped oat groats. Rolled oats, also known as old-fashioned, are oats that are steamed, then rolled flat. Instant oats are precooked, then dried and packaged.

Oatmeal contains both soluble and insoluble fiber. Soluble fiber absorbs water in the digestive tract, and helps to decrease LDL, or "bad" cholesterol as part of a healthy diet. Insoluble fiber stays in the stomach for a long time, providing a sense of fullness and preventing overeating. In addition to fiber, oatmeal contains thiamin, magnesium, phosphorus, zinc, iron, selenium and manganese.