Is soluble fiber the same as dietary fiber?

A form of, not same: There are many forms of dietary fiber, including cellulose, hemicellulose, gums, mucilages, pectins, etc. Soluble fiber is a type of dietary fiber that dissolves in water (think oatmeal, oatbran). Insoluble fiber doesn't dissolve in water (think wheat bran). They have different chemical and biologic actions.

Dr Namey agreed

There is soluble: Fiber and there is insoluble fiber. Insoluble fiber is more likely to be roughage in the diet. Soluble fiber will tend to absorb toxic substances in the body and retain them to remove those substances in the intestinal tract. Soluble fiber will lower her cholesterol and lower toxic load. Insoluble fiber will provide the roughage to facilitate bowel movements.

Dr Namey and another doctor agreed