do collagen peptides break a fast？

This is exactly how we approach our marketing. We get this question daily.
We explicitly position our hydrolyzed collagen as a “keto-friendly, fast-extending” supplement. Because a standard 10g serving is only about 35-40 calories with zero carbs, we tell our customers that mixing it into black coffee won’t spike their blood sugar. It keeps them satiated longer without ruining the metabolic benefits of their intermittent fasting routine. It’s all about setting the right expectations on the label.

Scientifically, it depends on the goal of the fast.
If a consumer is fasting for strict autophagy (cellular cleanup) and gut rest, then yes, collagen peptides absolutely break the fast. Collagen is pure protein, and amino acids stimulate the mTOR pathway, which immediately halts autophagy. However, if they are fasting strictly for weight loss and blood sugar management, pure peptides cause almost zero insulin response, making them highly acceptable for a “dirty fast.”