specialized carnivores. Nutritional analysis shows that cats evolved to feed on prey and must ingest certain specific nutrients from animal tissues that may be deficient or absent in other foods. The protein requirement of cats is much higher than that of dogs, and they also need more arginine, sulfur-containing amino acids and certain B vitamins. The main way for wild and stray cats to obtain food is hunting, and prey is also their main food source. Prey provides energy and nutrients, just as the ingredients in a formula provide energy and nutrients. If the prey completely meets the cat's nutritional and energy needs, the cat will survive. Otherwise, it may result in difficulty for the individual or the species to survive. This greater or lesser reliance on luck and chance to obtain prey does not mean that the cat's physiology is only capable of accepting this diet. The nutritional needs of cats can be met equally well by scientifically formulated commercial cat food or home-made food. Nutrients can be divided into two categories. “Essential” nutrients must be provided by the diet because the body cannot synthesize enough of these nutrients. The “non-essential” nutrients are also required by the animal, but the body can synthesize sufficient amounts of these nutrients on its own as long as there are enough precursors, such as many non-essential amino acids (e.g., alanine, glutamine, tyrosine, etc.) and glucose. Glucose is an important source of cellular energy. Although it is physiologically indispensable, it does not require additional direct intake from food because it can be produced by amino acid conversion.

Carbohydrates.

Differences in the nutritional composition of hunter-gatherer and commercial pet foods, particularly the carbohydrate (CHO) content, have led some people to believe that commercially available dry foods may not be suitable for cats. Some studies have suggested that CHO may increase a cat's risk of diabetes or obesity and therefore should not be in a cat's diet. Most cats really don't need carbohydrates from their diet. The same applies to dogs, humans, and most mammals. However, since glucose is extremely important for survival, there are multiple mechanisms within organisms to ensure its continuous supply at the cellular level. Dietary CHO can be used as a direct source of glucose; in the absence of CHO, proteins can produce glucose through gluconeogenesis. Similar to humans, cats regulate hepatic gluconeogenesis in response to physiological needs and adjust the rate of protein oxidation in response to protein and CHO intake, as long as minimum protein requirements are ensured. Therefore, when dietary protein is insufficient, CHO acts as a “protein saver” to reduce protein consumption. Cats have some special characteristics in carbohydrate metabolism, such as a lack of sweet taste receptors, a lack of glucokinase, and relatively low digestive enzyme activity. Despite this, cats are able to efficiently digest and metabolize CHO.

Several studies have shown that the digestibility of CHO in commercial and experimental cat foods typically exceeds 80-90%, comparable to canine performance. Although cats lack glucokinase, their abundant hexokinase is fully capable of supporting carbohydrate metabolism. Normally, cats are not limited in their ability to metabolize carbohydrates, but may metabolize them at a slightly slower rate than dogs. The kinetics of hexokinase metabolism in cats is closely related to their dietary habits of eating small amounts of food several times a day, a habit that is independent of carbohydrate intake. It has been suggested that a high-carbohydrate diet may lead to persistent hyperglycemia, which can lead to “beta-cell failure” and diabetes mellitus. Although a high-carb diet may be followed by an increase in postprandial blood glucose, studies have shown that healthy cats only become hyperglycemic when the diet is more than 50% CHO and very low in protein (about 22%). Even in this extreme case, the elevated blood glucose levels were well below the threshold for “glucose toxicity”. Epidemiologic data do not support a high-carbohydrate diet (e.g., dry food) as a risk factor for diabetes. Rather, obesity and physical inactivity are the major risk factors for feline diabetes. Therefore, although a low-carbohydrate diet may be advantageous in the management of diabetes in cats, there is no evidence to suggest that carbohydrate intake is a direct causative factor for diabetes.

Protein.

Cats' protein requirements are much higher than those of dogs and most other animals, making how much protein cats should consume and their ability to adapt to a low-protein diet controversial. Early studies had concluded that cats were unable to reduce levels of proteolytic metabolism and gluconeogenesis, but later studies have shown that this conclusion is not correct. Cats' protein metabolism can be flexibly regulated according to the ratio of protein to CHO in the diet and blood glucose levels, and they are able to adapt to different diets as long as their protein intake is adequate. A daily intake of 2.5 g protein/kg body weight is sufficient to maintain nitrogen balance in cats. However, several studies have questioned whether maintaining nitrogen balance is sufficient to achieve optimal health in a given species. Chronic low-protein diets, while maintaining nitrogen balance, may weaken immune function and make animals more susceptible to disease, environmental stress or parasites. To maintain lean body mass (LBM) or normal protein metabolism, dogs and cats require two to three times the protein intake needed to maintain nitrogen balance. Adult cats need about 34% of their daily caloric intake from protein (equivalent to 5 g/kg body weight per day) to maintain lean body mass and overall health. High protein diets play an important role in weight management in cats, helping to lose fat while maintaining lean body mass and helping to reduce the risk of weight regain. Cats need amino acids rather than having to get their protein from meat. These essential and non-essential amino acids can come from a variety of sources. The notion that cats cannot digest or utilize plant-sourced proteins is not valid because regardless of the source, proteins are broken down into amino acids during metabolism, and the body is unable to differentiate whether a particular amino acid is from an animal protein or a plant protein.

While plant proteins, such as soy, corn, wheat gluten or rice gluten, are not sufficient to provide all the essential amino acids a cat needs and therefore cannot be used as the sole source of protein, plant proteins are well digestible and a good source of many amino acids. Properly cooked and used in conjunction with other sources of amino acids, plant proteins can be used as part of a cat's complete and balanced nutrition.