Note that most dietary fiber comes from carbohydrates (fruits, vegetables, grains, legumes, seeds). Fiber is largely carbohydrates (and some proteins) you can't digest. Focus on soluble fiber. You could try a Phyllium supplement. Also important to feed the bacteria in your gut - they need carbs.

Cutting out carbs will drop a lot of water from your system (from my layman's perspective). Drinking more water won't fully replace it b/c of loss of sodium (again, from a speculative standpoint).

How did you get enough fiber without carbs? That seems contradictory.

Not poster, but chia seeds, ground flax meal, unsweetened coconut and cocoa powder are super high fiber sources that are low in net carbs.

I can easily get 40g of fiber with close to zero net carbs per day eating this type of stuff...

black coffee and water in the morning can solve the constipation issue.