What Breaks a Fast
What breaks a fast?
This is an eternal question that confuses many and sparks endless debates. The simplest answer is: it depends. It depends on what your fasting goals are, how deep into fasting you are and what is the quantity of food we are talking about.
Technically, the most accurate way to measure this would be by wearing a CGM (continuous glucose monitor) while ingesting food. Anything we eat raises our insulin levels to some extent. Insulin is a hormone that clears glucose from the bloodstream and shuttles it to cells and tissues. Sugars trigger the most insulin response, starchy carbs a bit less, and fibrous carbs even less. Protein intake triggers some insulin response as well, and consuming fats has the smallest effect. There are other factors to determine whether we are in a fasted or fed state, but insulin is the dominant one.
If your aim is fat oxidation (or fat burning), better body composition, improved cognitive function, stabilised blood sugar levels, lower triglycerides levels, better hunger control and a more stable mood then consuming liquids with no calories is the way to go (i.e. tea or coffee). Even a small amount of healthy fats can be ok if you are in a very low glucose state (for example after 12 or more hours into a fast). All this can be achieved on a daily regimen of 16 hour fasting windows and even on an alternate day fasting protocol.
However, if you are only a few hours into a fast, almost anything you eat will break your fast.
If your aim is to maximise autophagy (cell recycling), cell rejuvenation, bring all the life-extension pathways to their maximum potential, then longer, water only fasts would be recommended. This means either a weekly 24-hour fast or maybe a 3-5 day fast every three months. Ideally, only water and electrolytes (mainly salt and magnesium) would be consumed, although some research suggests that polyphenols in tea can help with that process as well.
If your aim is to improve mental resilience then any form of delayed gratification will work.
So there you go. Everything can break a true fast, but it’s very contextual. The key thing to understand is that the body doesn’t operate in ones and zeros. It’s a scale. It is very dose- and timing-dependent. You can be three days into a fast and eat a peanut. That doesn’t mean you have to start from scratch to achieve the full five days of fasting. Since you are in a state of deep glucose depletion that peanut probably won’t break the fast. But if you are fasting after a big meal, even a single peanut can break your fast.