My post earlier in the week was specific for one situation but opens a wider discussion. Are there really differences between OTC foods and "prescription" foods?
The short answer is "Yes, absolutely!"
When I prescribe a specific food for a patient it is common for clients to say "Wow, that's expensive. Isn't there anything over the counter that can do the same thing?" And I certainly understand their concern. Being worried about money and affording food is legitimate, as few of us are wealthy. We do have to watch the cost of feeding our pets, and some of these therapeutic diets are two to three times as much as a "regular" bag of dog food. So I don't take offense when a client brings up to me their financial concerns.
It's hard to make a blanket statement about how all prescription diets are different, and it would take more than a simple blog post to go into the "why" behind each and every one on the market. But I can take a few examples as illustrations.
Foods for kidney disease are specially designed to lower the protein and improve the protein:phosphorous ratio. There are no OTC diets with the right ratio and a low enough protein.
Dogs with recurrent pancreatitis need to be on an extremely low fat diet to help lower the risk of future episodes. OTC diets aren't low enough in fat. In fact, the labels only give maximum and minimum percentages for things like fat, so you can't even tell the exact amount in a food without contacting the manufacturer.
Dogs and cats who have had bladder or kidney stones need to be on a urinary diet that will properly regulate the pH of the urine, lower certain minerals, and promote drinking to ensure dilute urine production. There are no OTC foods that will do all of these things.
Animals with severe food allergies need to be on extremely restricted diets which avoid certain ingredients. Currently most OTC foods don't have significant enough restriction and could cause trace ingredients. Severely allergic animals may need to be on a food that not only limits ingredients but also breaks down the proteins into smaller chains (hydrolyzed) or single amino acids in order to prevent a reaction. There are no OTC foods that process the proteins in those ways.
Like diabetic humans, dogs and cats with diabetes need dietary regulation, especially with a high protein to carbohydrate ratio. OTC diets don't achieve the same ratio and are worse at regulating blood glucose levels.
As you can see from just a few examples there really are significant differences between these prescription diets and what people typically feed their pets. When comparing virtually every therapeutic food there simply are no cheaper foods that achieve the same results. So that cat with kidney failure, the schnauzer with pancreatitis, or the bulldog with food allergies really do need to be eating a food that a client can't get other than through a vet. There are decades of research to show the importance of these foods compared to "normal" pet foods.
The ancient Greek, Hippocrates, is famously quoted as saying "Let food be thy medicine and medicine be thy food." He was referring to using the right kinds of foods as a central part of treating diseases, and no modern doctor would disagree. The same principle applies with pet foods. I have successfully treated many disorders by placing the pet on very specific diets and did not have to give medicine to some of them. Think about that for a moment...what do you think would be better? To give the dog pills twice daily every day for its life, or to feed it a specialized food for the rest of its life? Which is healthier? Which will have fewer side effects? Which will be easier for you and the dog?
Yes, prescription diets are much more expensive than other foods. But pet owners have to stop thinking about them as merely food. They are an essential part of medical treatment and are usually not recommended lightly. Sometimes it comes down to spending $90 per month for a bag of food, or $40 for food plus $60 for medications. Suddenly that expensive food doesn't seem so unreasonable, right?
If your vet recommends an expensive prescription food, it is usually for a very good reason and I recommend following their advice. It is fine to ask if there are other options, but the likelihood is that there are no other comparable OTC foods and you could be delaying or preventing adequate treatment by using a cheaper diet.