Hi,
When my father was diagnosed St. III (colon cancer) in 1998, I also put him on protein shakes, along with vitamins in addition to his chemo. He actually gained weight.
Not sure what kind of protein you have your father on, but check the label & see how many grams of protein are in each shake.
The brand I put my father on is called MetRx. I have absolutely no connection with this company. I just found it to be the best nutrition wise. My Dad is a diabetic so I needed something without added sugar.
MetRx delivers 38 grams of whey protein in each shake when mixed with water. Mix it with skim milk and you just upped the protein by another 16 grams. Plus it's loaded with vitamins and minerals.
Body builders typically use this product.
I bought it at my local CVS store. But you can find it at GNC and other health food stores. It comes in premeasured pouches of 12 shakes in a box for about $27.
I mix Dad's shake in a blender at night, put it in the fridge for his breakfast. It continues to thicken & he says it tastes just like a rich thick Chocolate shake.
I hope this helps. May God bless you and your family.
Miss Kate