Introduction

“Let food be thy medicine and medicine be thy food.” This quote from Hippocrates, referred to as the “father of medicine,” speaks to the importance of nutrition as the foundation for good health. Utilizing an integrative approach in veterinary nutrition allows the veterinary practitioner to tailor a comprehensive nutrition plan for each pet as an individual utilizing current as well as developing knowledge on nutrition and supplements employed for both nutritional and therapeutic purposes. Veterinary nutritionists will rely on conventional nutrition data from the National Research Council (NRC) text “Nutrient Requirements for Dogs and Cats” [1] as a meta-analysis of all the scientific knowledge concerning the nutrition of dogs and cats, the annual Official Publication (OP) from the Association of American Feed Control Officials (AAFCO) [2] for recommendations for commercial pet foods, and the compilation of peer-reviewed scientific research on nutrition and disease condition management for designing optimal nutrition plans. Integrative veterinary medicine, however, may incorporate conventional nutritional strategies for patient management along with evidence-informed practices that are considered alternative or complementary – these may be practices that are based on the best evidence available, even when such evidence does not meet the strictest criteria for efficacy and safety. Pet owners are seeking integrative approaches to pet care with ever higher demand and often for pets with chronic disease states [3, 4]. Although clinical studies on integrative veterinary nutrition are few in number, opportunities exist for integrative practices concerning obesity management, performance nutrition, and nutrition for enhancing physical rehabilitation which may include conventional nutritional knowledge along with the inclusion of strategic nutrients or therapeutic supplements.

Obesity

In 2020, the American Animal Hospital Association declared that pet obesity has become an epidemic [5] and current statistics confirm that >60% of dogs and cats are overweight or obese [6]. In contrast, only 39% of dog owners and 45% of cat owners consider their pet overweight or having obesity [7]. Obesity is associated with an increase in disease risk including joint/mobility disorders, diabetes mellitus, endocrine disease, respiratory disease, cardiovascular disease, liver dysfunction, and even urinary tract disorders [8]. Ultimately, being overweight/obese will lead to a reduced quality of life and a shortened lifespan [8, 9]. Naturally, both pet owners and veterinarians are seeking nutritional or supplemental strategies to help prevent as well as treat overweight/obese body conditions. Assessing body condition and body weight should be an essential part of integrative veterinary practice.

Even though we classify dogs as omnivores, natural feeding studies in domesticated dogs showed that when dogs are given a choice of foods with varying protein, fat, and carbohydrate levels they will choose diets with higher protein and fat content and less carbohydrates (33% of the energy derived from protein, 7% from carbohydrate, and more than 60% from fats). [10] Consistent with cats as true carnivores, similar studies in cats demonstrate they will choose a diet that is 52% protein, 36% fat, and only 12% carbohydrate when allowed to choose their preferred foods [11]. Trends in integrative veterinary nutrition focus on a return to a more “natural” diet often with higher protein/fat content and fewer carbohydrates. These diets may be raw, cooked, air dried, freeze dried, less processed, homemade, commercial, or the standard diet of kibble or canned food marketed to include more “whole food” type ingredients. The term “natural” as defined by the Association of American Feed Control Officials (AAFCO), however, is often unsatisfactory in integrative practice seeking less processed diets as it may also be applied to common highly processed kibble or canned foods. Choosing a “natural diet” does not guarantee that it will be successful in weight management or weight loss, in fact, the macronutrient content and/or energy density of the food may facilitate unintentional overfeeding of calories unless strict portion control is employed. Reducing meal volume may result in a loss of satiety for some pets; which makes calorie restriction difficult. No matter what diet type is employed, ultimately weight loss will require establishing a calorie deficit to induce reduction of body fat stores.

During weight loss, the nutrition plan should utilize diets fortified in nutrients to avoid potential nutrient deficiencies that may occur with food restriction in attempt to limit calorie intake. Research indicates that higher protein diets can spare lean body mass while restricting calories [12, 13]. Both protein and fiber contribute a satiety effect promoting a sense of fullness which may aide in prevention of begging behaviors [14, 15]. In one study, it was shown that a higher protein, medium carbohydrate diet may be a good solution for weight loss as it may preserve lean body mass, improve insulin sensitivity and result in a lower post-prandial glucose and insulin concentration compared to a diet with moderate protein and higher carbohydrate content [16]. Diets with sufficient content of the amino acids leucine and pyridoxine may also encourage lipolysis while maintaining lean tissue mass [17].

Diets selected for weight management should be evidence based and should be higher protein, higher fiber, and formulated for caloric restriction with higher nutrient levels. Diets should be fed in a calorie controlled manner to create a calorie deficit promoting a safe rate of weight loss at around 1–2% body weight per week. Co-morbidities should always be considered during diet selection in case contraindications are present that require limiting protein, fiber, or other select nutrient levels in the diet.

Spay/Neuter

Spaying and neutering are advocated for virtually all dogs and cats; however, this intervention does have potential consequences on body weight. It is in fact the largest risk factor for obesity in dogs and cats [18, 19]. 85% of dogs and 93% of cats are spayed and neutered [20]. Spaying and neutering will increase appetite even within three days of the procedure while decreasing metabolic rates up to 30% in dogs and 24% in cats [21–23]. Recognizing that most of our veterinary patients are or will be spayed and neutered mandates that diets recommended should consider weight management and obesity prevention as a priority.

L-Carnitine

L-carnitine is a nutrient that may offer benefits during weight loss. Carnitine serves as an essential cofactor in the transfer of long chain fatty acids within cells from the cytosol into the mitochondria where they will undergo beta oxidation in production of energy. Increasing intakes of dietary L-carnitine may promote the oxidation of long chain fatty acids [24]. Lower blood carnitine concentrations were found in overweight dogs compared to lean dogs in two studies [25, 26]. This finding could indicate a carnitine insufficiency related to spontaneous adiposity and altered lipid metabolism in overweight dogs. A carnitine supplemented diet was shown to support weight loss and improve body condition [27]. L-carnitine may also support muscular function during exercise. In one study, supplementing L-carnitine had positive benefits in Labrador retrievers for activity intensity, body composition, muscle recovery, and oxidative capacity [28]. Currently, optimal L-carnitine dosing for weight management or support of muscle mass is not known; however, multiple therapeutic weight loss diets include this nutrient.

Omega 3 Fatty Acids

Regulation of energy expenditure occurs through uncoupling proteins located in the mitochondria. Novel therapies could target these molecules for prevention and treatment of obesity in animals. As polyunsaturated fatty acids play a role in regulating gene expression of uncoupling proteins, the omega-3 fatty acids can enhance their expression. The results of a single unpublished grade II study suggests that increased consumption of dietary omega-3 fatty acids may be beneficial in overweight dogs subjected to caloric restriction [29]. Further studies are needed, however, to define the role and benefit of omega-3 fatty acids in weight loss in addition to optimal dosing.

Obesity is well known to create a state of inflammation and heightened state of oxidation within the body, for both humans as well as dogs [30–32]. Cats fed a diet enriched in omega-3 fatty acids when obese were found to have less insulin secretion and were postulated to have a lower risk of developing diabetes mellitus [33]. In dogs, the omega-3 fatty acids eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) may reduce the overall inflammatory state as they reflect increased adiponectin and decreased leptin. Current evidence suggests a positive, dose-dependent relationship between omega-3 fatty acid intake and circulating levels of adiponectin [34]. Supplementing EPA and DHA in diets may be a strategy to reduce inflammation in the body associated with obesity.

Other Nutraceuticals Used for Obesity Management

Low grade evidence, defined as that extrapolated from clinical opinions, descriptive studies, studies in other species, pathophysiology justifications, or reports by expert committees exists for other nutraceuticals for weight management including DHEA (use limited due to toxicity), pyruvate, amylase inhibitors, conjugated linoleic acid, phytoestrogens, diacylglycerol, chromium, and vitamin A supplementation [35]. Use of these supplements, however, cannot be recommended without further research.

Performance Nutrition

For the working dog or canine athlete, genetics, inherent behavior, and musculoskeletal conformation are the major determinants of performance; however, nutrition and training play key roles in maximizing outcomes. Nutritional studies are lacking for dogs enrolled in agility, field trials, and detection work, and thus, much information is derived from data collected in studies on endurance dogs (sled dogs) and sprinting dogs (racing greyhounds). In general, energy intakes must increase to meet demands from activity and modifications of the nutrient composition of the food and feeding schedule accordingly may improve performances.

Energy and Performance

Exercise relies on energy production or specifically ATP produced from substrates such as carbohydrates, fats, or protein. The energy available in any particular diet is reported as kilocalories (kcal) or kilojoules (kJ) per cup and will be available on packages or in product guides. The National Research Council (NRC) has established energy requirements for dogs based on the available scientific research (130 x metabolic body weight MBW = [(kg body weight)^0.75] [1]; however, active dogs will require more calories depending on the type of exercise or work performed. Racing greyhounds have been reported to require a minimal increase (5–10% more) while endurance dogs require much more (up to an eight fold increase) [36]. Other factors to consider affecting energy needs include ambient temperature, thermal stress, and terrain traversed. The increased energy needs during such activities may not be recognized by owners, making underfeeding a potential issue especially if participating in multiple-day events. Conversely, overfeeding or overtreating is a concern, especially in events with frequent rewards for behaviors. Increased food intake will also increase fecal mass and needs for defecation, which can negatively affect performance.

Nutrients for Energy: Fats and Carbohydrates

Animals performing at maximal speeds immediately during exercise (sprinting) will deplete ATP reserves quickly and then rely on easily accessible energy from glucose generated via glycogenolysis from glycogen stores (liver, muscle). Fatty acid oxidation begins within minutes but does not peak until after 30 minutes or longer. Dogs may utilize either fats or carbohydrates during longer duration, lower intensity exercise. Earlier studies have shown that dogs perform equally well on diets containing almost no carbohydrate (1 g/1000 kcal) as compared with two diets with increasing carbohydrate content in moderate-intensity working sled dogs [37, 38]. In general, dogs participating in longer duration, endurance type activities will benefit from higher fat intakes with up 50–70% of calories (metabolizable energy (ME)) from fats and then only 10–15% of calories from carbohydrates [36, 39]. In times of extreme demand, fats may be utilized to provide even up to 85% of ME calories [36]. It is important to note that acclimation is needed even over several weeks’ time to a higher fat diet to avoid adverse gastrointestinal consequences (steatorrhea) and the diet is only fed for a limited time. Sprinting dogs such as racing greyhounds may benefit from diets with carbohydrate content between 30–50% of ME calories which is similar to many commercial kibble foods available [40]. It is important to note that many canine athletes are more likely intermediate between these and perform for a shorter duration and intensity, thus diets chosen for these dogs should reflect the intensity and duration of performance. Those participating in longer duration endurance might incorporate more fats and those with sprinting activities could utilize more carbohydrates.

Meal timing may optimize availability of nutrients and it is recommended to feed the canine athlete at least four hours prior to exercise, one meal with in two hours post-exercise and then, if needed, small amounts during exercise for longer events. The largest meal should be after exercise has been completed. Providing sufficient water throughout the event and after is essential to prevent dehydration and facilitate normal heat dissipation/cooling during events [41].

Protein for the Working Dog

Proteins (amino acids) are not stored within the body as other nutrients; rather they are oxidized for energy, incorporated into tissue protein, or converted to fatty acids/glycerol then stored as adipose or glycogen. Amino acids will contribute only a small amount of energy (5–15%) during exercise which is derived from the branched chain amino acids (leucine, isoleucine, and valine). Animal protein sources (meat, organ tissues) have the highest content of essential amino acids and the highest digestibility. Dietary protein will help maintain muscle mass and total body proteins, serum albumin, and hematocrit [36]. Based on studies in sled dogs, it has been recommended to feed performance dogs diets that contain approximately 30% protein (metabolizable energy; 70–80 grams protein/1000 kcal) from highly digestible animal based protein [40]. Plant-based proteins exclusively fed may not be sufficient, as dogs fed on a diet of soy protein versus fish or meat-meal based diets had decreased hematocrits and increased red cell fragility after three weeks of feeding according to one study [42]. Endurance athletes will require more protein for exercise (30%+ protein ME or higher) while diets selected for sprinting or intermediate athletes are sufficient with at least 24% protein (ME calories; 60 grams protein/1000 kcal).

Dietary Fiber in the Working Dog Diet

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