Wheatgrass is sold in many forms, including Juice Powder and Whole Powder. The main argument around the difference between Wheatgrass Juice Powder and Wheatgrass Whole Powder seems to be around the presence or absence of fiber.
Fiber is the portion of plants that cannot be digested by the human digestive tract and is classified as soluble and insoluble. Oats, beans, dried peas, and legumes are major sources of soluble fiber whereas wheat bran, whole grain products, and vegetables are major sources of insoluble fiber, meaning it does not dissolve in water.
Cellulose is a type of insoluble fiber, and it is the main constituent of plant cells. When eaten, cellulose passes through the gastrointestinal tract relatively intact.