Updated: Jan 19
Does fiber break a fast if you're using Intermittent Fasting? Yes and no. The answer comes down to what your goal is with Intermittent Fasting and what type of fiber you're using. Today, we're breaking down the details of fiber and Intermittent Fasting.
Does Fiber Break a Fast?
If your goal with Intermittent Fasting is improved gut health and motility, then yes, fiber will break a fast. Complete abstinence from food and drinks (except for water) is required to stimulate the Migrating Motor Complex and clean out the left behind food and bacteria that typically lead to bloating.
If your goal is weight loss with Intermittent Fasting, then fiber on its own will NOT stimulate an insulin response and therefore will NOT break a fast. One of the main perks of Intermittent Fasting is that it naturally allows for lower levels of insulin during the fasted state, which then triggers the fat burning process, called lipolysis.(1) However, here is where we get into some tricky territory of the different forms that fiber can take.
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Fiber supplements can come in a variety of forms. For example, the popular fiber product, Metamucil, typically contains the sugar maltodextrin. Even though the fiber (psyllium husk) in Metamucil will not break a fast, the maltodextrin will. Therefore, Metamucil will break a fast. On the other hand, pure psyllium husk does not contain any added ingredients and therefore will not break a fast (at least, if weight loss is your goal).
If you are using a fiber supplement while Intermittent Fasting, it's crucial that you first check to see the other ingredients included to determine if it will break a fast AND to determine what your goal with Intermittent Fasting is.
If your goal is weight loss and your fiber supplement does not contain anything other than fiber in the ingredients, then this should be fine during your fasted state. However, if your goal is maximizing gut health with Intermittent Fasting, then you'll want to aim for the fiber supplement during your eating window.