to digest) are produced and more short-chain fatty acids (SCFAs; which are easier to digest and are more readily available sources of energy which can be used for supporting cell turnover keeping cells, like those found in the GIT, thereby improving GIT health and immune function) are produced. FOS can also impact production of other fatty acids. Malnutrition Malnutrition can be a problem for cats fed non-conventional diets. Cats fed exclusively on raw, freshwater fish can develop a thiamine deficiency. Those fed exclusively on liver may develop vitamin A toxicity. Also, exclusively meat-based diets may contain excessive protein and phosphorus whilst being deficient in calcium, vitamin E, and microminerals such as copper, zinc, and potassium. Energy density must also be maintained relative to the other nutrients. When vegetable oil is used to maintain the energy balance cats may not find the food as palatable. Commercial foods Most store-bought cat food comes in either dry form, also known in the US as kibble, or wet form (canned or in pouches). Some manufacturers sell frozen raw diets and premix products to cater to owners who feed raw. Dry Dry food (8–10% moisture) is generally made by extrusion cooking under high heat and pressure. Approximately 95% of dry pet foods are extruded. During the extrusion cooking process, the meat is first ground up then it is cooked under very high heat and processed so it becomes a powder. The powder is fed into a massive mixer. Once it's in this massive mixer, additional supplements are added; then it's then cooked again under a very high heat to turn it into a dough. The dough is formed so that it can be molded into the form of kibble. The kibble is placed again in high heat to be baked in order to make it stay in that shape. Once the piece comes out, it doesn't smell like meat. Fat may be sprayed on the food after the extrusion cooking process to increase palatability, and other minor ingredients, such as heat-sensitive vitamins, which would be destroyed in the extrusion process, may be added. Dry food is most often packed in multi-wall paper bags, sometimes with a plastic film layer; similar bag styles with film laminates or coextrusions are also used. Dry foods contain high amounts of carbohydrates in order to maintain their shape and structure. Concerns have been raised that there is some association between