Therapeutic diets: Food you can use (Proceedings)

Therapeutic diets represent another aspect of treatment of specific diseases in addition to conventional therapy. These diets are designed for one or more diseases and formulated to contain a nutrient composition that may be of benefit in treating these diseases. They are typically fixed-formulation diets and contain better quality ingredients; therefore, they tend to be more expensive. We will take individual diseases, use the 3-step process to identify the characteristics of a diet that might be desirable for managing that disease, and examine examples of commercially available diets.

The American College of Veterinary Nutrition, a specialty college of board-certified nutritionists that are also veterinarians, recommends a two-step process in making nutritional recommendations. The process is iterative in that it should be re-evaluated periodically and changes made as deemed necessary. The first step is ASSESSMENT. During this step, assess the ANIMAL, the DIET, and the FEEDING factors. ANIMAL FACTORS to be assessed include gathering historical information, performing physical examination, body condition scoring, and evaluating laboratory and imaging results if indicated. Gather information on any health or disease-related conditions, medications (including over-the-counter and nutraceuticals/supplements), reason for visit, and other household members. A thorough physical examination is performed and a body condition score assigned. There are 5- and 9- point body condition scoring systems; either can be used. Assigning a body condition score provides more information than body weight alone and takes into account muscle mass and tone.

DIETARY FACTORS include gathering information on dietary intake and inspection of the food, if needed. Take the dietary history from the person that actually feeds the pet(s) asking for type of food, amount fed, frequency of feeding, table food or treats, access to other food (garbage, outside, etc), supplements, and medications (including over-the-counter). If necessary, inspect a sample of the food or send a sample for analysis (i.e. Cornell Animal Health Diagnostic Center, Woodson Tenent Laboratories, EMSL Food and Consumer Products Testing Lab, etc). Pet foods can be purchased in a variety of forms – dry, canned, semi-moist, semi-dry, liquid, and frozen.

Reading the food label is also beneficial. The food label can be roughly divided into a principal display panel and an information panel. The PRINCIPAL DISPLAY PANEL contains information directed towards the consumer including the product name, species for which the food is intended, net weight of product, and descriptive words and/or pictures (e.g. "new and improved", picture of a famous cat, etc). The INFORMATION PANEL contains the important information including ingredient list, guaranteed analysis, feeding guidelines, contact information, and the nutritional adequacy statement. Although often maligned and not as complete as labels for human foods, there is useful information to be found. Ingredients are listed in descending order according to pre-processing weight and names are set by AAFCO (e.g. by-product, etc); this means that ingredients containing moisture that weigh more will be listed first. Unfortunately, this does not give information as to the quality or exact amount of each ingredient; also, different forms of the same type of ingredient are listed separately. Chemical sounding ingredients are typically vitamins, minerals, and preservatives. Feeding guidelines are provided that are suitable for most, but not all, dogs or cats that consume the diet. The manufacturer's or distributer's name and address is required and questions regarding the food should be directed to them; they should be able and willing to provide answers.

The guaranteed analysis provides information regarding the 4 major components of a pet food as percentages of the diet as fed including minimum amount of crude protein, minimum amount of crude fat, maximum amount of crude fiber, and maximum amount of moisture. "Crude" refers to the analytical procedure and does not refer to the quality of the ingredient. Because the guaranteed analysis is in percentage as fed, it is difficult to compare products that differ in composition (e.g. dry product versus canned product); therefore, comparing products on a "dry matter" basis or on a gram per 100kcal basis is preferred. A down-and-dirty rule-of-thumb for comparison is:

• For dry foods – add 10% to nutrient of interest AF

      o Ex. 21% protein AF = 21 + (21 × 0.1) = 21 + 2.1 = 23% protein DM

•For canned foods – multiply nutrient by 4

      o Ex. 5% protein AF = 5 × 4 = 20% protein DM

The nutritional adequacy statement must be included and is designed to ensure that the product, when fed as the sole source of nutrition, is complete and balanced for one or more life stages, including how this adequacy was verified. The four recognized life stages by AAFCO are pregnancy, lactation, growth, and adult maintenance, and nutritional adequacy can be determined by feeding trials or by calculation. The calculation method involves determining the amount of nutrients in the diet and comparing to AAFCO nutrient profiles for that/those life stage(s). Feeding trials are performed by feeding the diet to the animals in that/those life stage(s) following AAFCO protocol. Feeding trials, while not perfect, provide indirectly information on bioavailability of nutrients and is preferred method for validation of nutritional adequacy. Therapeutic diets, supplements, and treats often do not carry a nutritional adequacy statement. Therapeutic diets are formulated for specific non-healthy conditions, which are not recognized by AAFCO and for which no nutrient profiles exist (e.g. renal failure, liver failure, etc); they usually carry a statement such as "intended for intermittent use" or "use only under the supervision or direction of a veterinarian". Snacks and treats are not formulated or intended to be the sole source of nutrition; therefore, they are not required to carry a nutritional adequacy statement.

FEEDING FACTORS to be assessed include how the nutrition is provided and must take into account owner and animal factors. Simply filling a bowl within reach of the animal is not enough; the appropriate diet must be provided in the appropriate amount. Obesity is the most common nutritional disorder of dogs and cats and, in part, is due to overfeeding. "One cup" of food refers to the amount of food contained in one 8-ounce measuring cup. Ask specifically for the size of the cup used and the size of the bowl that is filled up. Many owners feed free choice – "drive-by feeders" - without regard to amount. The amount of energy required by the pet can be determined using one of two formulae:

Linear: [(30 x BWkg) + 70] and Exponential: 70 x (BWkg0.75)

This provides the RESTING ENERGY REQUIREMENT and this result is multiplied by a life stage or activity factor depending on the individual.

The second step is FORMULATION AND INITIATION OF A FEEDING PLAN. The nutritional plan is formulated based on the assessment phase and initiated. It is important that this plan is re-evaluated periodically (iterative process) and adjustments made based on what is found during assessment. Recommendations for the feeding plan are made based on life stage and physiological or pathological condition of the pet as well as the life style of the owner. Working within the constraints placed by the owner helps to ensure compliance; otherwise, recommendations will not be followed. There is no "one best" diet available for healthy pets or for pets that suffer from a disease. Oftentimes, many options exist including homemade diets.

Gastrointestinal disease

In general, diets designed for treatment of gastrointestinal disease are usually either highly digestible and "bland" or contain increased levels of fiber. Additional diets utilizing novel proteins or hydrolyzed proteins may be used. Diets may also be formulated for or contain ingredients to aid in management of dental disease. "intestinal Diets" contain highly digestible and consistent ingredients. Usually they contain single ingredients that are highly refined, and are lower in fiber, although some contain soluble fiber that may be beneficial. "Restricted- and Moderate- fat diets" may or may not contain additional fiber. Dietary fat is more digestible and more energy dense than dietary carbohydrate and protein; however, some animals cannot tolerate dietary fat at a level found in adult maintenance diets. "Fiber Enhanced Diets" contain 7-25% fiber, usually insoluble fiber; therefore, they are more 'bulking'. Some of these diets do contain soluble fiber. Soluble fiber increases intestinal content viscosity, delays gastric emptying, slows transit time, is fermentable, and may bind toxins and bile acids. "Gluten- and Gliadin-free foods" are diets that do not contain these compounds. Gluten and gliadin are found in flour when cereal grains are processed, specifically wheat, barley, rye, buckwheat, and oats. Gliadin, a polypeptide, is responsible, in part, for gluten-sensitive enteropathies, such as that found in Irish Setters; however, gluten and gliadin are not thought to be important in most other gastrointestinal diseases. "Elimination Diets" include diets containing novel proteins or hydrolyzed protein. A protein is only "novel" if the animal has not consumed it previously; therefore, it is important to acquire a good dietary history, if possible. This includes treats, snacks, and flavored medications. Because proteins with molecular weights over 18,000 Daltons are incriminated as being antigenic, modification of proteins to compounds having lower molecular weight may be of benefit. Protein modification is a process that alters the physical characteristics of protein molecules, presumably reducing the antigenicity and rendering them less able to elicit an immune response. By reducing the average weight of the protein molecule, this process can result in a protein that may be truly hypoallergenic. To be effective, it must reduce the molecular weight of the protein below 18,000 Daltons. These "Protein Hydrolysate" diets appear to be effective as elimination diets, and they have the advantage of being complete and balanced. These diets may be used long-term, but cost more. "Dental Diets" are also available to control plaque and dental disease. These diets either contain added ingredients, such as hexametaphosphate or micro-cleansing crystals, or have a fiber arrangement that provides a 'shearing' effect to scrape tartar and plaque. The Veterinary Oral Health Council (http://www.vohc.org/) maintains a listing of products that have achieved VOHC Seal of Acceptance.

Food allergy

A food allergy is an immunological reaction to a food component, typically protein, although there is speculation that certain products of food processing may induce a reaction. Not all adverse food reactions that dogs and cats experience have an immunological basis and so not all problems associated with diet are 'allergic' in nature. Nutritional management includes changing the diet. This can be done by feeding a "Novel Protein" or "Protein Hydrolysate" diet or by changing form of diet.

Liver disease

Protein restriction is necessary when hyperammonemia is present; however, it need not be restricted if hyperammonemia is not present. If hyperammonemia is present, then a "renal failure" diet may be fed. Recently, diets formulated for use in liver disease have become available. These diets contain high bioavailable protein, added antioxidants, carnitine to aid in fat metabolism, soluble fiber, and are low in copper.

Exocrine pancreas

Usually a low fat (and perhaps high fiber diet is used). Examples include the "Restricted- and Moderate-fat diets" and "High Fiber Diets". They are particularly useful when pancreatitis is associated with hyperlipidemia.

Obesity

These diets tend to be "High Fiber Diets" that contain fewer calories or "Metabolic Diets" for cats. "High Fiber Diets" are designed for weight reduction and are balanced to the lower energy intake that induces weight loss. These diets are not maintenance diets; however, there are "Weight Maintenance Diets" that are less restricted in fat and contain less fiber than the "High Fiber Diets" that can be used for weight maintenance in an obese-prone pet. "Metabolic Diets" are diets formulated for cats that contain less carbohydrate and more protein than typical adult maintenance cat foods. This formulation promotes utilization of peripheral adipose tissue as well as decreasing pancreatic insulin secretion.

Diabetes mellitus

The goal of dietary management of diabetes mellitus is to decrease insulin requirements while maintaining adequate blood glucose control and clinical signs of hyper- and hypo-glycemia. Achieving ideal body condition and weight benefits animals with type 1 and type 2 diabetes mellitus; therefore, nutritional management may be directed at weight reduction, at least initially. Dogs almost always suffer from type 1 diabetes mellitus; however, cats may be affected with either type 1 or type 2 diabetes mellitus. Some cats may have their insulin dosage decreased or discontinued or may not require insulin with adequate weight loss using either a "High Fiber" or "Metabolic" diet.

Osteoarthritis

There are several diets marketed for management of osteoarthritis in dogs. These diets are less calorically dense and so contain lower levels of fat. Additionally, they contain a lower n6:n3 ratio than maintenance foods, and may contain glucosamine, which is a Chondromodulating agent. It appears that the higher n3 fatty acid content is the primary benefit of such diets. In managing dogs and cats with osteoarthritis, achieve optimal body condition and weight; therefore, weight reduction may be required before switching to a "Joint Diet".

Cancer

Diets formulated for managing patients with cancer are calorically dense containing increased levels of protein and certain amino acids, such as arginine. Additionally, a low n6:n3 ratio may be beneficial. Certain types of lymphoma appear to utilize carbohydrate rather than fat; therefore, feeding a higher fat (and hence more calorically dense) and lower carbohydrate may be beneficial. Additional anti-oxidants may also help, although there is controversy about using a higher n3 and anti-oxidant diet in patients undergoing radiation therapy. Perhaps most important in patients with cancer is to keep them eating and to maintain optimal body condition, regardless of formulation of diet.

Convalescence

Diets designed to promote recovery from surgery and illness are highly digestible, and contain increased amounts of protein and fat. Additionally, they tend to have a homogeneous consistency. This allows them to be used more easily through feeding tubes. Several of these diets are also marketed as dry formulations.

Heart disease

These diets tend to be sodium-restricted and calorically dense to minimize cardiac cachexia. These diets may also contain higher levels of taurine and carnitine, which have a role in certain types of cardiovascular disease.

Urinary tract disease

There are many different diets formulated for management of different forms of urinary tract disease.

Chronic renal failure: "Renal Failure Diets" tend to be slightly to markedly reduced in protein, reduced in salt, restricted in minerals, and contain alkalinizing agents. Many diets also contain an n6:n3 fatty acid ratio of 5:1, which may be beneficial in renal failure. These diets also contain a higher fat content than adult maintenance foods, which increases the caloric density. At least one diet has been shown to be beneficial in slowing progression of IRIS stage 2-3 renal failure in dogs and cats.

Urolithiasis

Several types of stones are amenable to medical dissolution including struvite, urate, and cystine; however, calcium oxalate uroliths cannot be dissolved.

Struvite – Dissolution

Diet is low protein, magnesium, and phosphorous, and acidifying. Only 1 diet has published data on its use as a dissolution diet.

Sterile struvite – Prevention

Similar composition to dissolution diet, but not to the extreme. Most cat foods are designed to prevent struvite uroliths (that is, they are acidifying); however, there are specific "Struvite Preventative Diets" available, and many are designed for prevention of calcium oxalate. In dogs, struvite uroliths almost always form because of a bacterial urinary tract infection with a urease-producing organism; therefore, while "Struvite Preventative Diets" are available for use in dogs, they are unnecessary and do not prevent infections that cause struvite stones to form.

Calcium oxalatre

Are not able to be dissolved. Diets are either restricted in protein and minerals, or high in fiber. Most induce alkaluria. Inducing a diuresis, either with diet or by drinking, is beneficial in many dogs and cats. Approximately 20-35% of cats with calcium oxalate uroliths have idiopathic hypercalcemia. Some of these cats appear to respond to consuming a "High Fiber Diet" with supplemental potassium citrate.

Urate

Urate uroliths form either secondary to a congenital liver disease (e.g. portosystemic shunt or microvascular dysplasia) or to an inherited disorder of uric acid metabolism (e.g. Dalmatians and English bulldogs). In animals with portosystemic shunts, correcting the shunt is often all that is required. If the congenital liver disease is not amenable to surgical correction, then feeding diets restricted in protein that are alkalinizing and induce a diuresis may help with clinical signs of liver disease and prevent urate uroliths. In dogs and cats without liver disease, restricting dietary purines and inducing alkaluria and diuresis may be useful in dissolving and preventing urate uroliths. For dissolution in dogs, administration of the xanthine oxidase inhibitor, allopurinol, is also required.

Cystine

Cystine uroliths form due to an inherited defect in renal proximal tubule reabsorption of cystine (and often other amino acids). Cystine uroliths tend to form in acidic urine. Management of cystine uroliths involves decreasing dietary protein (restricting amino acid intake) and inducing alkaluria and diuresis. For dissolution of cystine uroliths in dogs, administration of a 'chelator' such as 2-MPG or D-penicillamine is also required.

There are many resources available including

The ACVN (http://www.acvn.org)

Angell Memorial: 617 / 522 – 7282

Michigan State: 517 / 432 - 7782

Ohio State: 614 / 292 – 1221 http://www.vet.ohio-state.edu/nssvet.htm

Tufts University: 08 / 839 – 5395 ext 84 696

UC Davis : 530 / 752 – 1387 www.vmth.ucdavis.edu/vmth/services/nutrition/nutrition.html. http://www.ucvmc-sd.vetmed.ucdavis.edu/nutrition.cfm

University of Missouri: http://www.vmth.missouri.edu/clin_nu.htm

University of Tennesse: 865 / 974 – 8387, utvns@utk.edu