There is a dangerous myth that continues to play out in veterinary world about senior pets (especially cats) needing less protein as they get older. Not only has this myth (made popular in the 1930s) been debunked countless times, but formulated Veterinary Senior Formulas only ensures that your older cat lives an incredibly painful and hazardous last few days, months, or years.
As we've mentioned countless times before, energy requirements sharply and progressively increase in older cats, starting at the age of just 10 years old. In addition, older cats require higher amounts of protein so they can continue to maintain protein reserves compared with younger cats. Since older cats metabolize protein at a much slower rate, they need more of it in order to satisfy their energy requirements.
Dr. Mark Peterson from feline-nutrition.org explains that ”[t]he initial biochemical reactions by which energy is derived from carbohydrates, fats, and proteins are different. However, all three macronutrients eventually go through a final common pathway for energy generation called the citric acid cycle". Glucose derived from carbohydrates is first oxidized through the glycolysis pathways to yield pyruvate and then acetylene-CoA. Fats are initially oxidized to acetyl-CoA by the beta-oxidation pathway which then enter the citric acid cycle and subsequently generate ATP". Protein synthesis is maximized, excess amino acids can be used for energy by undergoing transamination and deamination. Proteins are present in EVERY LIVING CELL. In the skin, hair, cartilage, muscles, teeth, tendons, ligaments. Unlike fat or carbohydrates, protein cannot be stored in the body as much as muscle protein itself. As Dr. Peterson explains, "In animals fed diets containing more protein than is needed, the extra protein is metabolized and used for energy.”
Now, your cat, as a strict carnivore, has evolved to depend on protein as a major energy source. Their dietary composition is one of high protein and fat but low carbohydrate. Cats have a much higher protein requirement than other species like dogs and humans. When most omnivores ingest a diet high in protein, the "activities of the amino acid-catabolizing enzymes in the liver increase to cope with the higher flux of amino acids".
Omnivores can accommodate to low protein diets because they can lower the hepatic activity of these catabolic enzymes. By contrast, cats have a very limited ability to down-regulate these hepatic catabolic enzymes when fed a low-protein diet.
This limited metabolic flexibility in cats likely represents an evolution where an abundant supply of protein was always available (example: streets cats who continuously hunt for food). It is only when cats are fed a diet high in carbohydrates and low in protein, that conditions and health problems arise because that would never happen in the wild.
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