There should be fiber - at least the guides to keto I've consulted all emphasize dark leafy greens. Certain ones are sub 2g carbs per serving net, so one could theoretically max out their daily with 12 servings of such vegetables. I agree that people moderately exercising and above would be foolish to restrict themselves to 25g carbs daily. However, it works as a tasty jumpstart to dropping water weight assuming you get just enough protein to not consume muscle.