I have a bariatric lap band, since 2005, and must also supplement my diet with powdered protein supplements. The brand I am advised to use by my bariatric surgeon is UNJURY (
http://www.unjury.com/) and I have been using it daily for 12 years.
At home, I have the protein powder in plastic containers. While traveling or on Camino, I am able to obtain the powder in Chocolate, Strawberry and Vanilla, in individual serving packets. When I travel to Santiago to work for a month at the Pilgrim Office, I pack several large containers, as it is cheaper that way. However, the containers are clumsy, I would NOT even think about bringing them on a Camino.
The UNJURY dissolves well in water and tastes very good. The protein is whey based and each packet contains 20 grams of protein. It does contain an artificial sweetener. But unflavored / unsweetened UNJURY is also available for cooking and mixing. I must use a minimum of 2 servings per day, in addition to any protein I can locally source. So, I plan on two packets (2 x 20 gm) daily.
To use the powder with my water carrying system, I have my favorite collapsible funnel (see it here):
http://www.amazon.com/Silicone-Collapsible-Foldable-Funnel-Light/dp/B00RY5L11G/ref=sr_1_4?s=home-garden&ie=UTF8&qid=1519825660&sr=1-4&keywords=Mini+Collapsible+Funnel&dpID=318f%2BuyJl1L&preST=_SX300_QL70_&dpSrc=srch
The collapsible funnel enables placing the protein powder into any water bottle. In the morning, I add a single serve coffee packet with hot tap water to use to jump start me, until I can get proper coffee at a cafe / bar down the trail. I mix the second to use later in the morning, or early afternoon if I am able to get other food based protein, like the excellent tortilla pie served across northern Spain.
Two weeks of protein powder packets, in assorted flavors, plus the funnel, weigh about one kilo. Each packet weighs about an ounce. The good thing is that the weight diminishes as you walk further.
Finally, to save weight, I always send a supply down the road to Ivar to hold, see Services by Ivar at Santiago, here in the forum. This way, I have a resupply on arrival to tie me over until I return home.
Hope this helps. If you have more questions, send me a private conversation.