Treatment of Obesity in Cats and Dogs

Justin Shmalberg, DVM, Diplomate ACVN

This new column explores one of the most common topics in nutrition: obesity. Recent research has better characterized the condition and identified new therapeutic approaches, which are discussed in-depth.

Obesity is a frequently encountered condition in small animal veterinary practice and arguably the most common form of malnutrition.

Weight loss in overweight animals is associated with greater longevity, increased vitality, and reduced pain.¹ Recent research has better characterized the condition and identified new therapeutic approaches.

DEFINITION

Obesity is commonly defined either mathematically or descriptively. Table 1 identifies mathematical definitions; alternatively, obesity is described as a clinical condition characterized by excessive accumulation of body fat that leads to pathology or impaired function.

PREVALENCE

Estimates suggest that at least 25% to 30% of dogs and cats in industrialized countries are obese. The prevalence of overweight animals warrants clinical efforts aimed at treatment and prevention of this nutritionally responsive disease.

IDENTIFICATION

The body condition score (BCS) provides an objective measurement for assessment of nutritional status; both 5-point and 9-point scoring systems (Figures 1 and 2) have been validated for veterinary use by advanced techniques that determine body composition.

Figure 1. The 5-point body condition score scale, courtesy Hill’s Pet Nutrition (hillsvet.com); visit todaysveterinarypractice.com (Resources) to download this scale and the Hill’s Pet Nutrition Body Fat Index (BFI) Risk Charts. The current 5- and 9-point scales do not account for pets with body fat > 47%; the BFI Risk Charts account for pets with up to 75% body fat.

Figure 2. The 9-point body condition score scales, courtesy Nestle-Purina and available at todaysveterinarypractice.com (Clinical Resources).

When used appropriately, BCS permits calculation of ideal body weight (BW), a value necessary for estimating any overweight animal’s caloric intake for weight loss. Table 2 describes how to calculate ideal BW in dogs. BCSs also identify obesity in cats; however, mathematical equations are generally unnecessary, as most cats should weigh between 3 to 5 kg when lean.

An educational component may be required when explaining an animal’s BW to its owner, as owner disagreement can be common when veterinarians identify an overweight patient.²

RISK FACTORS

Risk factors for canine and feline obesity are outlined in Table 3.

CONSEQUENCES

Caloric restriction increases lifespan in a number of species, and obesity has a negative association with longevity in humans and dogs.

Dogs

A lifetime feeding study in Labrador retrievers showed that:³

1. Lean dogs live, on average, 1.8 years longer than obese dogs.
2. Radiographic and clinical signs of osteoarthritis (OA) were detected earlier, and were generally more severe, in the group fed ad libitum compared to energy-restricted control dogs.

A reduction in spontaneous activity associated with OA likely further decreases energy expenditure, contributing to an obesity–arthritis cycle. Conversely, recovery from orthopedic injury, such as cranial cruciate rupture managed with or without surgery, is improved with concurrent weight loss.⁴

Other pathologies associated with canine obesity include respiratory diseases (eg, tracheal collapse), cardiovascular disease, and insulin resistance.^5,6

Cats

The effect of feline obesity on longevity has not been confirmed. However, obesity is associated with diabetes mellitus (see Diabetes Mellitus in Obese Cats), hepatic lipidosis, dermatologic diseases (eg, alopecia, epidermal scaling), various gastrointestinal disorders, and feline lower urinary tract disease.⁷ A link with OA is expected, although this is less well studied than in dogs.

PATHOPHYSIOLOGY

The pathophysiology of obesity is related to a number of hormones secreted by adipose tissue, known as adipokines. The mechanical consequences of excess fat accumulation are intuitively understood, but only recently have the metabolic and hormonal consequences been better described.

Leptin is produced by fat cells and, in normal individuals:

• Suppresses appetite
• Increases energy expenditure.

However, both humans and dogs develop leptinemia when overweight, possibly due to leptin resistance. Adverse effects from high circulating leptin have not yet been fully described in dogs.⁶

Adiponectin, a more frequently studied adipokine:

• Increases insulin sensitivity by increasing skeletal muscle glucose uptake and decreasing hepatic production of glucose.⁸
• May also increase fatty acid oxidation and reduce inflammation.⁹
  Increased adiposity appears to be inversely correlated with serum adiponectin levels. Research has found that:
• 20% of obese dogs develop metabolic abnormalities characterized by increased insulin and decreased adiponectin levels¹⁰
• Weight loss reverses hypoadiponectinemia¹¹
• In other studies, however, no changes in adiponectin levels were found before or after weight loss in dogs.¹²

Hypoadiponectinemia consistently occurs in obese cats,⁸ which may explain why they have more severe insulin resistance and increased predisposition to NIDDM.

A number of other adipokines that create a chronic mild inflammatory state in obese individuals have been characterized in humans and laboratory animals. This may contribute to obesity’s documented adverse effects.⁹ Hormones, such as TNF-alpha and C-reactive protein, are elevated in some obese dogs, and decrease after weight loss.¹²

Future investigations and therapies are likely to focus on the hormonal components of excess adipose tissue.

OBESITY INTERVENTIONS: EXERCISE

Active dogs, as measured by pedometers, have lower BCSs than inactive dogs.¹³

Paired with Therapeutic Diet

A recent study demonstrated that active dogs fed a therapeutic diet formulated for weight loss used approximately 25% more energy than inactive dogs, while achieving 2% weight loss weekly.¹⁴ Each 1000-step interval was associated with an approximately 2% increase in daily energy expenditure. Other studies suggest that, for each km traveled, caloric expenditure increases by approximately 2 kcal/kg0.75.¹⁵

Underwater Treadmill Therapy

Underwater treadmill therapy has been part of a successful weight loss program in combination with owner education, a high-protein low-fat diet, and owner-supervised exercise.¹⁶ A recent study demonstrated that a healthy dog, walking at a normal pace in elbow-height water for 30 minutes daily, would use 2.5% more calories per day (eg, 25-kg dog consuming 1000 calories daily uses 25 additional calories).¹⁷

Therefore, exercise, unless performed over extended distances, is unlikely to cause weight loss without concurrent restriction of caloric intake.

OBESITY INTERVENTIONS: MEDICATION

Dirlotapide (Slentrol, zoetis.com), a selective microsomal triglyceride transfer protein inhibitor, is licensed for treatment of obesity in dogs. It prevents lipoprotein formation in the enterocyte, increasing intracellular concentration of lipids, which is thought to increase circulating levels of the hormone PYY, a satiety signal that acts on the hypothalamus. While the complete mechanism of action of dirlotapide is unclear, appetite reduction is most likely responsible for weight loss.

In clinical and field trials, dogs given dirlotapide:²¹

• Were not fed any specific diet; owners were asked to make minimal dietary changes before starting the drug
• Lost weight at a rate of approximately 0.74% to 1.4% per week, which is consistent with rates observed for caloric restriction associated with therapeutic weight-loss diets
• Demonstrated some adverse reactions including, but not limited to, gastrointestinal signs and elevated alanine transaminase and aspartate aminotransferase
• Regained some weight during an 8-week monitoring period following discontinuation of the drug.

The starting dose for dirlotapide is 0.05 mg/kg (0.01 mL/kg) PO Q 24 H for 14 days. Refer to the product insert for further dosing instructions.

OBESITY INTERVENTIONS: NUTRITION

Caloric restriction is considered the primary treatment of small animal obesity. However, reduction in volume of food and number of treats fed is often a significant barrier for owners.

Protein

High-protein diets are recommended during the weight loss period. Animals have well defined amino acid requirements; providing additional protein can prevent possible deficiencies of taurine or other amino acids. In addition, high-protein diets preserve lean body mass during weight loss.²²

Recent research has shown that:^23-25

• A high-protein diet (≈120 g/Mcal) allowed cats to consume about 10% more calories to achieve the same degree of weight loss as those fed a lower-protein alternative (≈90 g/Mcal).
• Cats fed a high-protein diet consumed a higher number of calories than those on a lower-protein diet and better maintained their weight following weight loss.
• Cats fed ad libitum on a high-protein diet (≈120 g/Mcal) showed an increase in daily energy expenditure. This effect may be due to a principle called dietary thermogenesis, in which different energy substrates have different energy costs associated with metabolism.
• High-protein diets may increase palatability of reduced-calorie diets, as cats typically prefer protein to fat and carbohydrate.

Carbohydrate & Fat

Modifications in carbohydrate and fat concentrations are variable in therapeutic weight-loss diets. Fat is often reduced since it provides over 2 times as many calories by weight as carbohydrate or protein. However, essential fatty acids are required and fat cannot be reduced below a certain threshold. Carbohydrate and protein are commonly both increased in a diet when fat is reduced.

Fiber

Fiber is added to increase both volume and weight of a food, while minimally affecting its caloric content. It is the most controversial nutrient modification for obesity because studies examining rates of weight loss or satiety have had mixed or poorly-controlled results.²²

• Insoluble fiber, like cellulose or peanut hulls, is eliminated in the feces and increases fecal volume, which can be negatively perceived by some owners. Diets with large amounts of insoluble fiber may reduce food consumption in cats.
• Soluble fiber, generally fermented by intestinal bacteria, is employed in other weight-loss diets.
• Crude fiber percentage on most product labels refers to insoluble fiber, while total dietary fiber (TDF) reported by some companies better reflects both soluble and insoluble fiber sources.

A recent study in obese dogs demonstrated that a high-protein, high-fiber diet (103 g protein, 97 g TDF/Mcal) produced greater weight loss (1% vs 0.7%/week) than a high-protein, moderate-fiber diet (104 g, 56 g TDF/Mcal).²⁹

Moisture Content

Diets formulated for weight loss may increase moisture content of canned diets during extrusion to increase food volume during caloric restriction.

High-moisture diets reduced ad libitum caloric intake of cats in 1 study,³⁰ while another showed no intake difference during the weight loss period. The latter study did show that weight regain was significantly reduced.³¹

It has been hypothesized that some animals find canned food more palatable, but this likely depends on pre-existing preferences.

Additional Ingredients

Weight-loss diets occasionally incorporate ingredients purported to improve the efficiency of weight loss.

• L-carnitine has been suggested to help increase weight loss and preserve muscle mass.²² It is responsible for transporting acyl groups from fatty acids into the mitochondrial matrix, and may also increase muscle mass.
• Fish oils are a source of the polyunsaturated fatty acids EPA and DHA (omega 3). Some limited work examined the effect of EPA on preventing the decrease of adiponectin and increase in insulin seen in obese cats.⁸
• Other diets provide increased antioxidants, conjugated linoleic acid, chromium, and other nutrients, but there is limited information supporting use of these compounds.

REBOUND WEIGHT GAIN PREVENTION

After the weight loss period, it is suggested that nearly 50% of dogs regain more than 5% of BW in a “rebound” phenomenon; dogs maintained on a weight-loss diet gained less than those switched to maintenance diets.³⁴

Reduction in energy expenditure, after target weight is achieved, has been observed in dogs and cats.

• Cats: One study found that energy expenditure decreased 19% compared to baseline expenditure during weight loss, and was decreased 12% after weight loss.³⁵
• Dogs: The energy expenditure needed to maintain post-loss BW was found to be only about 10% greater than that needed for weight loss.³⁶
  Therefore, dogs and cats may require an energy-restricted high-protein diet after ideal weight is achieved, and dietary management for treatment and subsequent prevention of obesity is likely lifelong.

BCS = body condition score; BW = body weight; DM = diabetes mellitus; NIDDM = noninsulin-dependent diabetes mellitus; OA = osteoarthritis ; TDF = total dietary fiber

References

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Justin Shmalberg, DVM, Diplomate ACVN, is a clinical assistant professor of integrative medicine at University of Florida College of Veterinary Medicine. His service specializes in the incorporation of nutrition, rehabilitation, hyperbaric oxygen therapy, and acupuncture with conventional care; he holds certifications in acupuncture and herbal medicine. Dr. Shmalberg’s research interests include nutritional oncology, sports and rehabilitative nutrition, evaluations of new small animal dietary trends, and the safety and efficacy of Chinese herbal products. He received his DVM from University of Wisonsin-Madison. Dr. Shmalberg completed an internship in veterinary acupuncture at University of Florida along with a residency in small animal clinical nutrition.