Psyllium husk is a grey area. Pure psyllium is mostly indigestible fiber with very few usable calories, so plain versions barely affect a fast, but sugar-sweetened fiber products break it.
| Calories | ~0-10 kcal per serving |
|---|---|
| Breaks a weight-loss fast? | Partial |
| Breaks ketosis? | No |
| Breaks autophagy? | Partial |
| Insulin impact | Minimal |
Psyllium husk is soluble fiber that the body cannot digest for energy, so plain psyllium provides almost no usable calories and does not spike insulin or blood sugar. In that sense it barely touches a fast and can help with regularity and appetite. The complication is the product: many fiber supplements are sweetened with sugar.
Plain, unsweetened psyllium husk powder is close to fast-safe. Sweetened fiber drinks like the sugar versions of Metamucil contain real sugar and calories that break a fast. Choose the sugar-free or plain version and mix it with water.
A teaspoon of plain psyllium in a large glass of water is the usual amount and stays close to a fast.
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