Almost all pet weight loss diets have a reduced protein and fat content per unit weight; therefore, something else needs to take up the space in the ingredient recipe. So the pet food manufacturers added fiber to bulk up the diet so the dog would "feel full" on a lower caloric density diet. (There are surely some human psychological factors at work here, too, because every pet owner wants the pet to have the satisfaction of a “full tummy”.) The dog's suggested meal portion would be satisfyingly large in quantity but would be less "calorie dense."
Not a good idea, as it turns out, for a meat-eating animal such as a dog or cat. Case, Carey and Hirakawa in their book Canine and Feline Nutrition, published by Mosby and Sons, 1995, state "Diets that contain increased levels of indigestible fiber and reduced levels of protein are not recommended for weight loss or for long-term weight maintenance of sedentary dogs and cats. If a diet is simultaneously high in indigestible fiber and low in fat and/or other nutrients, it is possible that long term feeding may result in nutrient deficiencies in some animals". Those last two sentences explained why I was seeing so many patients eating reducing diets that were developing dry, itchy, flaky skin and had coats that were coarse and greasy and lacked luster.
Remember that an ounce of fat has twice the calories of an ounce of protein or carbohydrate. Many weight-reducing diets for pets contain increased amounts of carbohydrate from corn, barley, wheat and rice in place of the calorie dense fats. And since dogs and cats convert protein to energy much more efficiently than humans, many weight loss diets have reduced protein levels -- and the protein ingredients are replaced with even more carbohydrate.
An added bonus for the manufacturer is that carbohydrate ingredient sources are generally less expensive than sources of fat and protein. So, intuitively, it seems to make sense that pet weight loss diets should have less fat and protein and more carbohydrate. And over the last twenty-five years that is precisely how weight loss diets for dogs and cats have been constructed.
The conclusion that came to me is this: Most weight loss diets for pets are carbohydrate based, and that's precisely why they're not working.
What You Should Know About Carbohydrates
Biology rules! I believe carbohydrate is the dominant nutrient driving the success or failure of a weight loss diet formulation for dogs and cats. Here's why: Ingested carbohydrate stimulates insulin secretion from the pancreas every time the dog or cat consumes substances such as corn, wheat, barley, sugar, sucrose, rice, potatoes, fruits, vegetables or pasta.
But insulin, just like other chemicals in the body, does exactly what it is supposed to do. And one of those tasks is to promote the conversion and deposition of extra dietary carbohydrates (those not needed immediately for the day's energy consuming activities) into reservoirs of glycogen in the muscles and liver. Once those reservoirs are full, extra glycogen is directed by insulin chemistry to be modified a bit and deposited into the major energy reservoir called adipose tissue -- or fat.
To simplify, continuous exposure to excess carbohydrate for the day's activity and metabolic needs results in conversion of the excess carbohydrate into fat. The same statement is not so true regarding excess protein ingestion.
What You Should Know About Protein
An interesting and important fact of protein metabolism is that if the dog or cat consumes more protein on a daily basis than needed for metabolic processes, energy needs, and tissue building and repair, the extra protein is excreted by the kidneys and not stored as fat. Unlike extra carbohydrate calories that are stored as fat, protein surplus is essentially eliminated from the animal's body.
What You Should Know About Fat
Decreasing the fat content of weight-reducing diets to achieve a less calorie dense product may not be wise. It has been my unbiased observation that a large percentage of dogs and cats consuming these diets end up with dry, flaky and itchy skin, coarse and greasy coats, and even cracked nails and pads. They start overweight and stay overweight! Add some high quality fats and protein to theses diets and the undesirable conditions disappear within three weeks.
Not very scientific, I admit, but neither is increasing the carbohydrate content of a diet in place of high quality protein and fat in an effort to reduce a dog or cat's fat reservoir!
Weight management in pets involves more than dietary considerations. Domestic pets don't have to chase down their meals these days so they inherently experience less exercise and acquire more food with less energy output than their wild predecessors. Human and animal behavior modification is an absolute necessity if a dog owner is to successfully reduce the dog’s body weight to an optimum level.
David Kronfeld, DVM, PhD., until he passed away was a specialist in veterinary nutrition at Virginia Tech, University in Blacksburg, VA. He pioneered scientific studies in animal nutrition. He has said, "In my experience, the only worthwhile weight loss programs are life-style oriented -- more exercise and less food, that is, a lower intake of a diet of the highest quality."
Twenty-five years ago I was a proponent of cereal based, low fat, reducing-diets for body weight management in dogs and cats. When I observed that in a substantial majority of cases these diets simply did not do what they were intended to do, and in some cases actually resulted in the opposite of what was expected, I rethought what made sense from a natural and biological standpoint.
I now recommend to dog and cat owners whose pets are overweight but healthy (no thyroid or other metabolic disorders) that they feed controlled portions of a diet composed of high quality protein sources, moderate percentages of high quality fat, and low carbohydrate. Add exercise to the recipe and the weight reducing results are excellent and predictable.
Image: Derek Gavey / via Flickr