Cats with myocardial disease may be optimally conditioned or may be under- or overconditioned depending on severity and chronicity of the disease. Obesity results in blood volume expansion with elevated cardiac output, increased plasma and extracellular fluid volume, increased neurohumoral activation, reduced urinary sodium and water excretion, tachycardia, abnormal systolic and diastolic ventricular function, exercise intolerance, and systemic arterial hypertension.3 This may result in progression of the disease. Likewise, cachexia may occur with myocardial failure. Cachexia associated with heart disease or failure results in negative nitrogen and energy balance.^4,5 The pathogenesis of cardiac cachexia is multifactorial involving increased sympathetic tone, increased tumor necrosis factor and interleukin-1 levels, decreased physical activity with an increased resting energy requirement (RER), decreased tissue perfusion, venous congestion, and adverse effects of medications. Decreased nutrient intake and possibly increased nutrient losses (e.g., potassium loss with diuretic therapy), and loss of body weight (and more importantly, lean body mass) occurs resulting in an inability to respond to medical therapy and an increase in morbidity and mortality.

Cats have a dietary requirement for taurine because they have limited ability to synthesize it from cysteine and methionine, and because it is used exclusively for bile acid conjugation. Taurine deficiency results in dilated cardiomyopathy in predisposed cats (Fig. 21.1). The mechanism of heart failure in taurine-deficient cats is poorly understood. Taurine may function in osmoregulation, calcium modulation, and inactivation of free radicals.² Other factors are likely involved as many cats fed taurine-deficient foods for prolonged periods of time fail to develop myocardial dysfunction. Additionally, there is an association between taurine and potassium balance.⁶ Inadequate potassium intake may induce significant taurine depletion resulting in myocardial dysfunction. Male cats may be more prone to developing taurine deficiency–associated myocardial failure than female cats, or male cats may be more prone to developing clinical signs at higher plasma taurine concentrations.⁷

Dietary thiamine deficiency was associated with cardiomyocyte atrophy and congestive heart failure in one cat that also developed hepatic lipidosis and poliencephalomalacia.8 L-carnitine is a conditionally essential nutrient involved with transport of long chain fatty acids from the cytosol into the mitochondria where they undergo beta-oxidation for energy production. L-carnitine deficiency has been associated with dilated cardiomyopathy in some dogs;⁹ however, this has not been reported in cats.

There is a large body of evidence supporting beneficial effects of omega-3 fatty acids for both primary and secondary prevention of cardiac disease in people. There is also increasing evidence for use of omega-3 fatty acids in dogs with heart disease. Benefits of omega-3 fatty acid supplementation with heart disease include antiinflammatory and antiarrhythmic effects on maintaining muscle mass and controlling arrhythmias. Omega-3 fatty acids may have a positive effect on myocardial energy metabolism, endothelial function, heart rate, blood pressure, and immune function. In a study of cats with hypertrophic cardiomyopathy (HCM), however, plasma concentrations of omega-3 fatty acids were higher in cats with cardiac disease than in healthy control cats.¹⁰ Additionally, among cats with HCM, there were no differences in plasma fatty acid concentrations, and no association between left atrial dimension and fatty acid concentrations. Omega-3 fatty acid supplementation is unlikely to have benefits in cats with HCM.

Restriction of sodium intake is often recommended with heart disease; however, it may not be necessary until later in the course of the disease. Sodium restriction should occur concurrently with chloride restriction as chloride salts of sodium have more effect on blood pressure and plasma volume than nonchloride sodium salts.¹¹ Salt sensitivity has not been documented to occur in cats. In a study of healthy cats, high dietary sodium chloride intake was not associated with hypertension or with myocardial dysfunction.¹² Hypokalemia and hypomagnesemia are associated with arrhythmias, decreased myocardial contractility, and muscle weakness. Additionally, inadequate potassium intake may be associated with taurine deficiency.

In a study of cats with HCM evaluating six commercial diets (three canned and three dry formulations), there were some differences among the groups including biomarkers of myocardial function; however, most echocardiographic parameters were not different suggesting that diet may influence some variables in cats with HCM.¹³ There are commercial therapeutic diets that are suitable for cats with cardiovascular disease. Dietary recommendations for cats with cardiac disease are designed to optimize body condition:

Some cats require feeding of frequent small meals due to decreased appetite. Pharmacological appetite stimulation (Table 21.1) or assisted feeding using feeding tubes may be required. Additional nutrients that may be beneficial include coenzyme Q10, which is required for energy reactions and is an antioxidant, and other antioxidants, which may decrease oxidative stress with dilated cardiomyopathy. There are no studies documenting the most effective dose for coenzyme Q10 in cats; however, 20–30 mg/day appears reasonable.

Oral disease occurs more commonly in older cats, usually associated with systemic disease; therefore, oral disease may be related to systemic effects of those disorders and to nutritional imbalances due to those disorders or to difficulty in eating. In one study, severity of periodontitis in cats was positively associated with age, bodyweight, total globulins, alanine aminotransferase activity, and IgG concentration, and negatively associated with albumin, hemoglobin, hematocrit, and aspartate aminotransferase activity, suggesting potential systemic effects of periodontal disease in cats.14 Historical information should include diet, eating behavior, and access to toys, foreign bodies, etc. A complete oral examination should be performed, which may require sedation or anesthesia, in addition to a physical examination evaluating for systemic disease.

Several dietary factors have been implicated with oral disease. Food texture and composition can directly affect oral cavity health through:

Claims of dry food being better for prevention of dental plaque than moist foods are unsubstantiated in dogs;¹⁶ however, one study suggested that eating a dry food was associated with better oral health in young and adult cats.¹⁷ There are no data to support the notion that natural diets and foods are better for oral health than commercial foods. Dietary texture can be modified by increasing fiber content with a size and texture that promotes chewing and mechanical cleansing of teeth.^16,18,19 Dental treats do not offer an advantage over dry foods; however, some contain hexametaphosphate, a calcium chelator, which may decrease calculus formation although data are contradictory.^20,21 Hexametaphosphate has not been evaluated in cats. Many oral diseases are inflammatory in nature and modification of the inflammatory process may be beneficial. Antioxidants, vitamins E and C, and selenium may be beneficial, but data are lacking in cats. Nutritional deficiencies, such as calcium, and vitamins A, B, C, D, and E, are associated with oral cavity disease, but these deficiencies occur uncommonly (see Chapter 20: Nutritional Disorders).

Nutrition has been implicated as a cause of feline tooth resorption. Acid-coating of foods has been suggested, but not proven, to cause tooth resorption.^22–24 Dry food may cause microfractures predisposing teeth to infection and inflammation; however, this is unproven. Increased dietary vitamin D has been implicated in tooth resorption. Evidence to support this assertion includes correlation between cats with tooth resorption and increased blood levels of 25-hydroxyvitamin D and histologic comparisons of the effects of excessive intake of vitamin D with the effects of bone resorption.^22,25 Although a direct effect of vitamin D has not been proven, there is some evidence for active vitamin D signaling in the pathophysiology of tooth resorption^26,27 although other data refute this.²⁸

Feeding a dental health diet that carries the Veterinary Oral Health Council (http://www.vohc.org/) seal for plaque control may be beneficial for cats that are prone to periodontal disease. Additional recommendations for diets to prevent or control dental disease include these nutrient levels:

Clinical signs associated with nutritional abnormalities include a sparse, dry, dull, and brittle hair coat that epilates easily, slow hair growth, abnormal scale accumulation, alopecia, erythema, crusting, decubital ulcers, and slow wound healing.31 Other clinical signs may be present with nutrient-deficient dermatoses (see Chapter 20: Nutritional Disorders). For more information on skin diseases, see Chapter 25: Dermatology.

Inadequate energy intake is associated with keratinization abnormalities, depigmentation, changes in epidermal and sebaceous glands, and increased susceptibility to trauma. Protein deficiency is associated with similar clinical signs. Essential omega-6 fatty acids include linoleic acid (>0.5% on a DMB) and arachidonic acid (>0.02% on a DMB).32 Omega-3 fatty acids can supply part of the omega-6 fatty acid component. Clinical signs of essential fatty acid deficiency include scaling, matting of hair, loss of skin elasticity, dry and dull hair coat, erythema, epidermal peeling, otitis externa, and slow hair growth. Certain mineral deficiencies may affect the skin (see Chapter 20: Nutritional Disorders). Copper deficiency is associated with loss of normal hair coloration, decreased density or lack of hair, and rough or dull hair coat. Many dermatologic conditions may occur with zinc deficiency and respond to zinc supplementation. Dietary phytate binds zinc, resulting in clinical signs of deficiency including erythema, alopecia, and hyperkeratosis. Certain vitamin deficiencies may affect the skin. Vitamin A deficiency is associated with skin lesions and focal sloughing of skin. Vitamin E deficiency occurs in cats in association with steatitis. Clinical signs include erythema and keratinization defects. Vitamin E–responsive dermatoses include discoid lupus erythematosus, systemic lupus erythematosus, pemphigus erythematosus, sterile panniculitis, acanthosis nigricans, dermatomyositis, and ear margin vasculitis. Dermatologic conditions also arise from adverse food reactions (see Chapter 20: Nutritional Disorders).³³

In cats with dermatologic disease, the quality and quantity of the diet fed including treats, snacks, and table food should be evaluated. A complete and balanced diet may be made incomplete or unbalanced when fed with other food stuffs. Homemade diets must be evaluated carefully.34 If a nutritional deficiency is suspected, con­sideration should be given to changing the diet to a better quality one. With suspected adverse food reaction, diet change should be considered (see Chapter 20: Nutritional Disorders). If a specific nutrient deficiency is identified, the diet can be changed to one that is not deficient, and the deficient nutrient can be supplemented. Zinc is supplemented for zinc-responsive dermatoses (zinc sulfate 10–15 mg/kg/day by mouth; zinc methionine 2 mg/kg/day by mouth). Vitamin A is supplemented for vitamin A responsive dermatoses (tretinoin topically, every 12–24 hours; isotretinoin orally, 1–3 mg/kg/day; etretinate orally, 0.75–1 mg/kg/day).

Fatty acid supplementation is often recommended for managing inflammatory skin disease. Cats have limited capacity to convert 18-carbon long-chain fatty acids to 20-carbon long chain fatty acids due to low activity of delta-6-desaturase.³⁵ It is 20-carbon long-chain fatty acids that are incorporated into cellular membranes and subsequently metabolized to prostaglandins, leukotrienes, and thromboxanes. To alter levels of these cytokines in cats, it is necessary to supplement 20-carbon long-chain fatty acids. Insertion of omega-3 fatty acid (eicosapentaenoic acid [EPA]) into cell membranes results in production of cytokines of the odd-numbered series (e.g., prostaglandin E3, leukotriene B5) in place of the even-numbered series of cytokines (e.g., prostaglandin E2, leukotriene B4) produced from omega-6 long-chain fatty acids (arachidonic acid). These odd-numbered cytokines promote less inflammation and are more vasodilatory than the even-numbered cytokines. When supplementing omega-3 fatty acids to cats, they must receive 20- and 22-carbon fatty acids due to limited ability to convert 18-carbon to 20-carbon fatty acids. The 20-carbon omega-3 fatty acid is EPA and the 22-carbon omega-3 fatty acid is docosahexaenoic acid (DHA). Oils derived from marine life are high in EPA and DHA. Oils derived from plant life, such as flaxseed and borage, contain primarily 18-carbon fatty acids which limits their conversion to the required 20-carbon fatty acid and their effectiveness in managing inflammation.³⁶ There are no data on effectiveness of omega-3 fatty acids in managing inflammatory skin diseases in cats.³⁷

Obesity is the most important nutritional disease of cats. At prevalence rate estimates of up to 40%,38–40 obesity must be considered a significant hazard to cats. Increased emphasis on pet health and preventative health programs makes obesity prevention an important aspect of health maintenance programs in dogs and cats. Treatment for obesity varies from frustrating to rewarding and evaluating and prescribing for successful, long-term weight loss and maintenance usually requires management of multiple, interrelated patient and client factors. Diagnosis of disease secondary to obesity and the major task of client education and motivation is the provenance of the veterinarian.

Obesity is a condition of positive energy balance and excess adipose tissue accumulation with adverse effects on quality and quantity of life. Obesity literally means increased body fatness, but measurement of fat fractions of body composition is difficult in practice. Therefore, obesity can be defined as body weight that is 15% to 20% greater than ideal weight due to the accumulation of body fat.⁴¹ Negative health manifestations often begin at this level of weight excess and are a virtual certainty at 30% over ideal weight. Associated health risks include musculoskeletal and cardiovascular disease, diabetes mellitus, hyperlipidemia, hepatic lipidosis, higher incidence of cancer, possible anesthetic and surgical complications, decreased heat tolerance and stamina, and reproductive problems. Obesity is a proinflammatory condition and adipose tissue is an active endocrine organ that produces cytokines called adipokines.^42–44 This may explain in part the association of obesity with inflammatory conditions such as osteoarthritis (OA).

The pathogenesis of obesity is multifactorial and is more than just “too much energy in and not enough energy out.”⁴⁵ There are genetic, sex, and environmental influences. Apartment dwelling, inactivity, middle age, being male, of mixed breeding, neutering, and certain dietary factors, such as dry food, are associated with being overweight.^39,40,46,47 Ovariohysterectomy has been shown to result in energy requirements that are 25% lower than National Research Council recommendations for cats; therefore, it is important to monitor body weight and body condition score (BCS) in cats after neutering as label feeding guidelines may be excessive, resulting in obesity.⁴⁸ In male cats, neutering has not been shown to change energy expenditure; however, food intake increases may result in weight gain.⁴⁹

The pet owner’s contribution to the problem may be significant and must be understood and addressed. In one survey of over 18,000 dog and cat owners in Australia and the United States, almost one-third of owners reported their pet as overweight or obese, but less than 1% felt that obesity was a health problem.⁵⁰ In another study of 120 German owners of indoor cats, questionnaire responses of owners of normal body weight cats were compared to responses from owners of overweight cats.⁵¹ Owners of overweight cats were more likely to watch the cat eat and gave in more frequently when the cat begged for food.⁵² Owners of overweight cats were less likely to spend time playing with the cat, and appeared to have a different relationship with their cat, being more likely to anthropomorphize and consider the cat a substitute for human companionship. Showing owners the BCS of their cat improves their perception and understanding of obesity.⁵³ However, unlike obese dogs, obesity in cats was not related to body mass index of owners in the Netherlands.⁵⁴ While dietary carbohydrate has been implicated in the pathogenesis of obesity in cats, feline obesity is more influenced by dietary fat intake.^55–57

Diagnosis of obesity is the first step in managing the disease. Determining whether a cat is overweight is not difficult; however, accurately determining the degree of overweight and the cat’s ideal weight is challenging. Many owners underestimate their cat’s body condition and veterinarians may overlook obesity. Documenting body weight in the medical record is important as veterinarians may be part of the problem. In one study, medical records dramatically underreported overweight and obesity in cats when BCS results were compared to reported diagnoses.⁴⁰ For example, the prevalence of obesity defined by BCS in the population studied was 6.4% compared to 2.2% when defined by a recorded diagnostic code in the medical record. In addition to recording the body weight, it may be helpful to calculate the percentage change in weight since the last visit and compare it to a similar weight gain in a person. For example, an 8.8 lb (4 kg) cat that has gained 1 lb (0.5 kg) has increased its body weight by approximately 12%; this is equivalent to a 14 lb (6.3 kg) weight gain for a 120 lb (54.5 kg) person. A morphometric method has been published for estimating body fat content as well.⁵⁸

Body condition and muscle condition scoring provides additional information concerning the appropriateness of the cat’s body weight to its overall condition.^{39,45,59–66} There are several BCS systems available; the most widely used are 5-point and 9-point scales (Table 16.2).^{45,61–64,66,67} In both scales, the middle value (3/5 or 5/9) is considered optimal condition where the cat has 15%–25% body fat. Lower values on the scale are degrees of undercondition (cats having 2/5 or 3/9 have 5%–15% body fat, and cats having 1/5 or 1/9 have <5% body fat) while higher values on the scale are degrees of overcondition (cats having 4/5 or 7/9 have 25%–35% body fat, and cats having 5/5 or 9/9 have >35% body fat).⁶⁸ As additional data are generated, it likely revisions of the scales will occur.⁶⁸ Muscle condition scoring assesses muscle mass and tone.⁶⁹ Evaluation of muscle mass includes visual examination and palpation over the temporal bones, scapulae, lumbar vertebrae, and pelvic bones. Decreased muscle mass may increase morbidity and mortality associated with disease.⁷⁰

Dietary Factors

In order to achieve loss of weight to ideal body weight, a change in diet is necessary. Feeding less of the same food is usually unsuccessful because the cat is used to eating the diet, it does not induce a shift in metabolism, and it may induce deficiencies and predispose to hepatic lipidosis. There are two dietary strategies for inducing weight loss in cats:

1. 1. Increased fiber/high carbohydrate diets that contain:
   
   
   
   1. a. Carbohydrates <40% on a DMB. Simple sugars and starch are avoided.
      
   2. b. Fiber 7%–18% on a DMB. Use of a fiber source with high water-binding capacity may be beneficial.72
      
   3. c. Fat <15%–17% on a DMB.
      
   4. d. Protein 30%–55% on a DMB.
      
   5. e. Food form: semimoist foods should be avoided. Canned foods may facilitate weight loss better than dry foods.
   
   
2. 2. Increased protein/low carbohydrate diets that contain:73
   
   
   
   1. a. Carbohydrates <20% on a DMB. Simple sugars and starch are avoided.
      
   2. b. Fiber <5% on a DMB.
      
   3. c. Fat 12%–25% on a DMB.
      
   4. d. Protein 30%–55% on a DMB.
      
   5. e. Food form: semi-moist foods should be avoided. Canned foods may facilitate weight loss better than dry foods.74,75

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