Fiber One bars are not the best snack bars to eat on a keto diet. This is because they are generally lower in calories and fat and contain around 12–20 g of net carbs, which is more likely to break ketosis.
Additionally, Fiber One bars don't contain much fat — most varieties provide only about 6 g per bar. Because a keto diet is characterized by very low carb, high fat foods, Fiber One bars do not meet most of the requirements.