Nutrition is an important part of disease management, even though few disorders can be cured solely with diet. The interaction between illness, health, and nutritional status is multifactorial and complex. The nutritional requirements of many sick dogs and cats are qualitatively the same as those of healthy ones; however, they differ in the amounts required—certain nutrients may be needed in greater amounts or may need to be restricted.
Adverse Reaction to Foods in Nutrition in Disease Management in Small Animals
Food reactions are classified using specific terminology:
An adverse reaction to a food is a clinically abnormal response to any type of food ingested.
Food intolerance is a type of adverse reaction that does not involve the immune system, eg, food poisoning.
A food allergy is a type of adverse reaction that does involve the immune system, eg, colitis or atopic dermatitis.
Dogs and cats with food allergies usually have GI clinical signs (eg, vomiting, diarrhea, or both) or a pruritic skin condition, especially in the regions of the ears, rear, and feet in dogs and around the neck and face in cats. The prevalence of true food allergies relative to atopy and flea allergies remains relatively low. Some dogs and cats with nonseasonal pruritus are having an adverse reaction to food.
Unfortunately, food allergy cannot be differentiated from food intolerance, and skin testing for food allergies is unreliable. Blood and saliva testing for food allergies are also unreliable ways to diagnose food allergies in dogs and cats. Hence, given all the possible etiologies and limited diagnostics available, any animal suspected of having an adverse reaction to food should undergo a food trial.
The length of time needed for a food trial depends on the condition being managed. Food trials for adverse reactions to food associated with clinical signs involving the GI tract should continue for 2–4 weeks, whereas food trials for clinical signs involving dermatologic conditions should continue for 8–12 weeks.
During a food trial, the only item fed should be a single novel protein source or a hydrolyzed protein diet. A careful dietary history must be obtained from the pet owner before selecting the type of diet.
If the owner elects to feed a commercially prepared food, several products are available for dogs that use single novel protein sources (eg, kangaroo, venison, rabbit, duck, or fish). Commercially available diets available for cats use protein sources consisting of rabbit, duck, venison, and lamb. Fish is not a novel option for most cats.
Most importantly, the formulation of whatever product or diet is fed must be fixed to ensure that the ingredient composition is consistent from batch to batch. These products are more expensive not only because of their unique and limited sources of protein but also because of the quality control procedures required to ensure fixed formulations and to eliminate cross-contamination with previous production batches of different foods.
An alternative diet option for use in dogs and cats with suspected adverse reactions to food is a hydrolyzed protein diet. Protein is the most common nutrient associated with adverse reactions to food because it is needed to bridge two IgE molecules together to cause the release of histamine. The protein in hydrolyzed diets is broken down into smaller peptide fragments that are too short to bridge two IgE molecules.
Although hydrolyzed diets are helpful in many dogs and cats with adverse reactions to food, they are expensive, and the extent of protein hydrolysis among diets also varies. In addition, some animals with allergies to the protein sources in these diets may still react to the typical hydrolyzed protein diet, depending on the level of hydrolysis. The choice between a novel protein diet and a hydrolyzed diet should be individualized for the patient and owner, in coordination with their veterinarian.
Homemade diets are also possible using the same protein sources suggested above (or other ingredient sources the owner wants to test), and they have pros and cons.
Currently, beef, chicken, and dairy products are the most common food allergens in dogs, whereas beef, fish, and dairy products are the most common food allergens in cats. However, dogs and cats can develop an allergy to any protein in the diet. On average, there is no price advantage in making a homemade diet over using commercially prepared foods; in fact, formulating a homemade diet containing hydrolyzed protein is both very difficult and expensive.
The trial diet should be exclusively fed for the recommended length of time, and all treats, snacks, and table foods eliminated unless they are made of the exact same ingredients as the trial diet or contain a hydrolyzed protein source. All chewable medications and supplements must be eliminated from the trial diet, because most contain the same protein and additive ingredients as pet foods and treats.
Other treatments such as hyposensitization and flea control are necessary in animals with concurrent disease. Testing various suspect ingredients by reintroducing them to the diet one at a time followed by recurrence of clinical signs is affirmation of an adverse reaction to that ingredient. Dietary ingredients reintroduced may reproduce clinical signs as early as 12 hours after ingestion but can take as long as 10 days. Lifelong treatment is dietary avoidance, which may be difficult if the offending ingredients are not positively identified.
Obesity in Nutrition in Disease Management in Small Animals
Obesity is the most common nutritional health problem in dogs and cats, and obesity-associated health risks continue to increase. Obesity is the excessive accumulation of adipose tissue—for dogs and cats, > 20% above ideal body weight. Dogs and cats 10%–20% above ideal body weight are considered overweight. It is estimated that > 50% of dogs and cats in the US seen by veterinarians are overweight or obese.
Obesity occurs when energy intake exceeds energy expenditure. Risk factors for developing obesity include the following:
lack of exercise
breed predisposition (breeds with an increased risk include Labrador Retrievers, Miniature Schnauzers, Dachshunds, Shetland Sheepdogs, Cocker Spaniels, Beagles, Basset Hounds, and Cairn Terriers)
increasing age (metabolic rate decreases with age as lean muscle mass decreases and fat mass increases
neutering
certain endocrine disorders
certain drugs, such as corticosteroids and phenobarbital
Health problems associated with obesity include decreased life expectancy, impaired quality of life, chronic inflammation, pulmonary and cardiovascular problems, exercise and heat intolerance, joint and musculoskeletal problems (eg, arthritis), compromised immune function, pancreatitis (dogs), diabetes mellitus and hepatic lipidosis (cats), and increased morbidity and mortality during and after anesthesia.
Adipose tissue was long considered metabolically inert, and its primary role in disease was attributed to stress on the joints caused by increased weight bearing and increased workload on the heart. However, it is now known that adipose tissue is not inert but rather a major endocrine organ that produces adipokines. The expression, production, and release of many adipokines are increased in obesity, which results in persistent low-grade inflammation and increased oxidative stress that play a role in many chronic diseases, such as osteoarthritis and diabetes mellitus.
Treatment for obesity should include both short- and longterm goals. Short-term goals are to lose weight and reach an ideal body condition score. The longterm goal is to maintain an ideal body condition score. Both of these goals require modification of behaviors that resulted in the dog or cat becoming overweight. Recommendations for lifestyle changes should be made in the context of maintaining the owner-animal bond. If this is ignored, owner compliance is unlikely. If giving treats is an important owner-pet interaction, providing the owner with low-calorie treat options is important. Most treats are not complete and balanced, so they should be restricted to < 10% of the total caloric intake to avoid causing nutrient imbalances.
The most successful weight loss programs include a combination of caloric restriction and exercise. The first step is to obtain a thorough diet history, followed by calculating the caloric intake appropriate to induce weight loss. Determining 60% of maintenance energy requirement (MER) for dogs and 70% of MER for cats is one way to calculate starting caloric intake for a weight management program. Regardless of the formula used, the calculated caloric intake is only a starting point and may require modification based on response.
The next step is to decide on a diet for the weight loss program. Maintenance diets are generally not recommended for weight loss programs, because they are formulated to meet the nutritional needs of moderately active adults. Restricting caloric intake using maintenance diets may result in inadequate intake of some nutrients, and one study documented numerous nutritional deficiencies when maintenance or over-the-counter weight management diets were fed in a calorically restricted fashion to induce weight loss.
Therapeutic weight loss diets are formulated to be restricted in calories while providing other nutrients in appropriate amounts. Adequate protein levels are important in any weight loss diet chosen. Most diets formulated for weight loss also have other nutrient modifications, including increased levels of dietary protein and fiber, as well as supplemental L-carnitine. It is better to divide total daily caloric intake into multiple meals rather than one large meal.
The next step is to decide on a rate of weight loss; a reasonable goal is loss of ~1% of body weight/week. If the animal is losing weight at a slower rate than that chosen but is doing well otherwise and the owner is satisfied, then it may be best to allow weight loss to continue at the slower rate. The animal’s weight should be monitored every 2 weeks and the program modified if needed based on response. Any weight loss is good weight loss, and celebrating successes with the owner helps maintain motivation.
Obese cats undergoing weight loss are at increased risk of developing hepatic lipidosis. Cats must continue to consume adequate calories and nutrients. If a cat does not like the weight loss diet chosen, then an alternative should be found. Starvation is never a safe or humane way to cause weight loss.
