Oats are sold in more forms than any other grain. All of them are high in beta-glucan, a kind of fiber that has special cholesterol-lowering properties. Studies have shown that individuals with high cholesterol have reduced their total level by eight to 23 percent simply by consuming three grams of this soluble fiber per day – the amount you get in one bowl of oatmeal.
Steel-cut oats (also known as Irish or pinhead oats) are whole oats that have been chopped into two or three pieces with steel blades. Uncut, they are known as oat groats. Steel-cut oats and oat groats are the least processed forms available.
Rolled oats are made by steaming the groats, then rolling them, steaming them again, and, finally, toasting them resulting in the familiar thin flakes. Though processed, rolled oats are still a whole grain. The cooking time for steel-cut oats is 20 to 40 minutes, compared to 10 minutes for rolled oats and 45 to 60 minutes for oat groats.
I prefer steel-cut oats because they digest more slowly than rolled ones. Like all other grains in whole or cracked form, steel-cut oats rank lower than rolled oats on the glycemic index (GI), which ranks carbohydrate foods on the basis of how rapidly they affect blood sugar (glucose). The reason for this difference is that it takes longer for digestive enzymes to reach the starch inside the thicker pieces, slowing down their conversion to sugar.
The higher on the glycemic index a food ranks, the more likely it is to cause spikes in blood sugar. Over time, these rapid fluctuations can cause genetically susceptible people (many of us) to develop insulin resistance and metabolic syndrome. Insulin resistance is associated with obesity, high blood pressure, elevated blood fats, and an increased risk of type 2 diabetes.
You can be sure you’re eating a whole grain with a low GI ranking if you have to chew it or can see the grains or pieces of grains. The more your jaw has to work, the better.
Oat bran – the finely ground meal of oat groats’ outer layer – has the health benefits of a whole grain with its high fiber and low starch content. It makes a good addition to other foods, especially baked goods. Despite its short cooking time and smooth texture, it won’t spike blood sugar levels, thanks to its soluble fiber.
While I recommend steel-cut oats, “old fashioned” rolled oats are preferable to quick-cooking ones or instant oatmeal. Those products do not provide whole, intact grains, and some brands of the latter contain partially hydrogenated oils, artificial flavors and colors, or a lot of added sugar and salt.
Because oats have a higher fat content than other grains, they go rancid more easily. For that reason, whether you’re buying oat groats, steel-cut oats, rolled oats or oat bran, buy in smaller quantities, and store these foods in the refrigerator.
Andrew Weil, M.D.
Whitehead et al, “Cholesterol-lowering effects of oat β-glucan: a meta-analysis of randomized controlled trials.” American Journal of Clinical Nutrition, October 15, 2014, doi:10.3945/ajcn114.086108