Anti-hairball diets for Cats?

Special diets to avoid hairball contain high levels of fibre, which increases the amount of water held in the digestive tract. This helps to keep the swallowed hair soft and moist and so aid in its expulsion; there is potential for creating a problem here.

In many cats, water metabolism is critically balanced. They may not drink much water, for example because they don't like the smell of the chlorine in tap water. They may not go outside to drink if the weather is cold or wet. There is also a growing tendency to keep cats indoors permanently. Increased secretion of water into the gut will lead to a tendency to produce a more concentrated urine and this may predispose to health problems.

I do not know if the pet food companies which make hairball diets have investigated this and will have taken avoiding action. A healthy system means that the cat will not over-groom. Also the cat will not ordinarily shed hair which can be swallowed.