Overfeeding can lead to the number-one nutritional disease, OBESITY. Excessive body weight can increase the risk of liver disease, heart disease, respiratory problems, and constipation. Furthermore, fat cats are at a greater risk of developing diabetes and arthritis. Pet food manufacturers have formulated diets that have fewer calories per gram that may be helpful in treating obese cats.

Feeding dog food to cats is a common error, especially if dogs and cats are in the same household. Dog foods are developed for the nutritional needs of dogs, not cats. There can be serious consequences if a cat's diet is deficient in protein, taurine, niacin, vitamin A, and fatty acids.

Overdosing with vitamin and mineral supplements has been known to cause severe medical problems in cats. Physiological imbalances caused by excess vitamins and minerals can lead to the binding of other nutrients. Overdoses of vitamins A and D are more common than deficiencies of those vitamins, because of unnecessary supplementation of an already balanced diet.

Exclusively feeding meat or fish results in an unbalanced diet and causes related nutritional diseases. Diets containing large quantities of fish can cause yellow-fat disease (steatitis), a result of vitamin E deficiency. Nutritional secondary hyperparathyroidism is usually caused by all-meat homemade diets that are deficient in calcium, thus creating a mineral imbalance in the calcium-phosphorus ratio. The disease most commonly occurs in kittens that are rapidly growing.

http://www.thecatconnection.com/care/feeding.htm