Do peptides break a fast?

Different story for GLP-1s (tirz, sema) — those directly affect insulin and glucose. But "breaking a fast" with them isn't really a meaningful concern because the entire point is metabolic signaling. Fasting logic doesn't really apply.

Caloric load from a 250mcg BPC dose is effectively zero. Insulin response from a small peptide that isn't a GLP-1/insulin analog is minimal to none. You're fine, BPC doesn't break your fast in any meaningful way.

GH secretagogues (ipamorelin, CJC, tesamorelin) are a hot debate for fasting. Some people say the ghrelin agonism "breaks" a fast in a hormonal sense. Most agree it doesn't break it in the autophagy/metabolic sense. But if you're doing an mTOR-off fast for longevity reasons, a GHRH/ghrelin pulse is going the opposite direction.

good distinction. just BPC for me for now.

Goal is fat loss + eating discipline. 16:8. So yeah, BPC is fine. thanks.

As always: define the goal of your fast. For 16:8 body comp, peptides are basically irrelevant to the fast. For a deep autophagy fast, different conversation.

Interesting question: worth noting most of the "breaks a fast" arguments online are pop-physiology with very thin primary sources. Strict calorie definition is ~0. Hormonal definition is squishy and depends who you ask.

BPC literally doesn't trigger insulin or mTOR meaningfully, so if your goal is fat loss and autophagy during the fast window you're fine. The people saying peptides "break" a fast are usually conflating hormonal signaling with actual metabolic breaks, which is lazy. Test your fasting glucose and insulin if you're really worried about it, otherwise you're overthinking.