Collagen may have a use as a supplement, but most definitely not as a substitute for whey or any other source of complete proteins. The reason is that collagen lacks the essential AA tryptophan. That's why collagen's DIAAS score is zero. For the purpose of muscle maintenance or growth, collagen is absolutely useless.

It may have its applications in other conditions such as osteoarthrits, but you need to keep in mind that the term collagen describes different types with different structures, compositions, and origins, which lead to different properties and potential effects.

The subject of collagen supplementation would justify dedicating an entire post to it. Your question has motivated me to take that subject on my to-write list. Thanks for that, Kornelia.

Your question about insulin resistance:

there are two aspects to your question, and I'm not sure which one you have in mind: the sugar added to protein powders, or the insulinotropic effect of protein in general?

The first one is easy to answer: Make sure your protein supplement contains as little sugar as possible. I use a whey powder that has around 10 grams of sugar per 100 grams of dry powder. That's acceptable given the amount of supplement I take.

The second aspect is a little more complex. Protein intake acutely stimulates insulin production, thereby lowering blood sugar. But in a chronic high-protein diet insulin resistance may result. Not for everyone, and we need to differentiate whether high-protein intake is accompanied by resistance exercise or not.

I have written an article about that subject (https://medium.com/illumination-curated/how-to-safely-transform-dietary-protein-into-healthy-longevity-a2a54f96cb17)

It appears that the branched-chain amino acids (BCAA) play a crucial role in this context. While their reduction confers certain health an longevity benefits, they are required for athletes who also live healthier lives than non-athletes. This paradox probably resolves with the inclusion or exclusion of exercise.