A fill is when the doc injects normal saline,which is basically sterile salt water,into the port or hole,where your lap band is.by doing this,he can make the opening that your food goes through smaller,or if you become undernourished, loosen,the opening.Whey is a powder with alot of protein in it that you can put in your liquids-there are different flavors,and some of the powders are natural,which means they will not change the taste of the liquid(skim milk,water,etc) but might change the consistency. I put one or two scoops of chocolate whey in the blender and add skim milk and blend well-it's really good.the strawberry flavor is good too.Hope this helps!Mary