For Weight Control and the Nutritional Management of Fiber Responsive Diseases. Excess weight, diabetes and digestive troubles can cause real problems for your cat. Feeding the right food can help your pet live a healthier lifestyle. Prescription Diet w/d Feline cat food, with its fiber rich formula, may be useful as a nutritional aid for cats with fiber responsive diseases such as diabetes mellitus, colitis, diarrhea, constipation, and to help manage overweight cats, including those with struvite urolithiasis. The nutritional formulation of Prescription Diet w/d may also be useful for pets with a variety of conditions.