A full serving (3 scoops) will give you significant portions of protein and dietary fiber (as well as nutrients) so that your shake is truly a meal replacement. However, people who are not used to a high-fiber diet would benefit from starting out with less than a full serving so that their digestive system can adjust to all the new fiber over a week or two. The body will benefit from the protein and nutrients in a partial serving– and the microbes in the intestines will be happy that new fiber is being introduced!