To begin with let’s start with some definitions - from https://www.atcoblueflamekitchen.com/.
Oat groats are the oat grain that has been cleaned and hulled to remove the outer husk. This is the most basic, least processed type of oats, and they’re not commonly found in kitchens.
Steel-cut oats are groats that have been sliced into 2 or 3 pieces but not rolled. Cooking time is about 30 minutes, and they will have a chewy texture when ready to eat.
Rolled oats are groats that have been steamed and flattened with huge rollers to form large flakes. These are sometimes called old-fashioned oats or regular rolled oats. They take about 15 minutes to cook.
Quick-cooking rolled oats are groats that have been cut into several pieces before being steamed and flattened into thinner flakes. They cook in about 5 minutes. Rolled oats and quick-cooking oats are often interchangeable in recipes.
Instant oats are even smaller pieces of rolled oats, cut finer and rolled even thinner so they cook very quickly. These cannot be interchanged with other oats in recipes.
Basically all these oats provide the same health benefits and nutritional content, however the larger oats will be processed slower by the body and so will keep you fuller for longer. Oats contain lots of carbohydrates, along with fat, fibre and protein, which is why they are so filling, but the smaller they are cut, the faster they are digested.
Oats were eaten by paleolithic hunter gatherers about 32,000 years ago, and although many wild species exist only four varieties are widely cultivated today, one only in Ethiopia, one which we see around the rest of the world, and the other two for animal feed.
Why oats are really a superfood is because they contain: riboflavin, niacin, vitamin B6, folate, iron, magnesium and beta-glucan. Beta-glucans are soluble fibers that come from the cell walls of bacteria, fungi, yeasts, and some plants (also barley, sorghum, rye, maize, triticale, and wheat and durum wheat). There is some evidence that they lower the risk for heart disease and help people suffering from diabetes.
Beta-glucans are thought to prevent the body from absorbing cholesterol from food (particularly LDL or 'bad' cholesterol). They might also stimulate the immune system by increasing chemicals that prevent infection. They have anti-inflammatory properties achieved by reducing gene-expression, they have been shown to help heal dry and itchy skin. They can thus possibly help combat a diet high in sugars and saturated fats which are inflammatory.
Ancient oat grinder. traces of oats found on the end of this hand sized pestle rock.