Generally, beans have more soluble fiber than oatmeal. However, some types of beans cooked in a particular way have less soluble fiber than oats. Similarly, processed oatmeal products have less soluble fiber than unprocessed oats.
There are approximately 40,000 bean varieties, but people consume only a small percentage of these that are mass produced. The amount of soluble fiber in each bean variety is as variable as the beans themselves. A cup of fresh, cooked green beans, for example, have 1 gram of soluble fiber; 1 cup of dry oatmeal has 4 grams of soluble fiber. Oatmeal typically doubles in size when cooked, so 1 cup of cooked oatmeal has 2 grams of soluble fiber.
The average amount of soluble fiber in oatmeal that has been processed into sweet snacks, such as crisps and squares, is roughly 1.3 grams per cup. A cup of dried, cooked lima beans has 7 grams of soluble fiber. A cup of roasted soybeans has roughly 14 grams of soluble fiber, but 1 cup of wax beans has less than 1 gram of soluble fiber, even less than 1 cup of oatmeal crisps.
Higher amounts of soluble fiber potentially support cardiovascular and gastrointestinal health. Soluble fiber forms a gel when it absorbs water. This gel slows the emptying of the stomach and, in turn, digestion, which creates a sensation of fullness for longer periods and possibly stabilizes blood sugar. Soluble fiber also interferes with the absorption of dietary cholesterol, which helps to lower low-density lipoprotein.