People with the highest fiber intake had ~80% greater chance of living long & healthy life out of all other dietary factors looked at.

other factors including total carbohydrate intake, glycemic index, glycemic load, and sugar intake. Successful aging was defined as including an absence of disability, depressive symptoms, cognitive impairment, respiratory symptoms, and chronic diseases including cancer, coronary artery disease, and stroke.

The gut is a major source of inflammation and also the major regulator of the immune system. Fermentable fiber feeds the beneficial bacteria in the gut which then prevents them from being forced to cannibalize the gut barrier (which causes inflammation) and it allows them to produce signaling molecules (short chain fatty acids) which make the immune system better. Also, many foods that contain fiber such as vegetables and fruits also have many important micronutrients and other plant compounds that play a role in successful aging. For more on the importance of fiber in successful aging watch my interview with the authors of The Good Gut, Drs. Justin and Erica Sonnenburg: https://youtu.be/gOZcbNw7sng