When you eat fiber, your body produces bile to digest it. Because it's hard to digest, you produce more bile. Bile is made from cholesterol, so a high intake of fiber directly reduces cholesterol levels. If you believe high cholesterol levels increase cardiovascular disease risk, then increasing fiber decreases cardiovascular disease risk which is the largest killer of Americans.

Another major benefit of fiber is that is slows down the breakdown of long-chain carbohydrates because you dilute them with long-chain cellulose carbohydrates that our body can't breakdown. This slows their absorption into the blood thus smoothing out sugar entry and subsequent insulin increases. Insulin sensitivity is a major health issue, typically showing up as diabetes and other metabolic disorders.