The greatest problem associated with feeding pets in the developed world is obesity. Obesity occurs when energy intake exceeds expenditure, and however complex the metabolic derangements associated with obesity may be, the quintessence remains that an owned animal that is obese has been allowed access to an amount of food that is excessive. Too little emphasis has been placed on the human variables that influence the development of obesity and its management, and some recent studies have illustrated the need for a much deeper understanding.
Risk Factors for Obesity
Several studies have reported risk factors, which differ widely between studies. For instance, the provision of ad lib feeding was a risk factor for feline obesity in some studies, whilst in others it was either not significant or protective.1,2 Similarly, the feeding of scraps to dogs was weakly protective if fed frequently in one study, but increased the risk if fed infrequently.3 However, it appears true that no particular feeding practice is a strong risk factor for cats, whilst dogs are less accurate at regulating intake, and ad lib feeding cannot be considered a sensible approach. For both cats and dogs, the most consistent risk factors for obesity other than age are neutering, low activity, and owner underestimation of their pet's body condition. The conflicting results between studies are caused by differences in sampling strategies, survey questions, geography, and sample populations. Nonetheless, when specifically asked, there is a consistently strong association between owner underestimation of body condition and obesity.
Low activity decreases energy expenditure and, therefore, if food intake remains the same, weight gain will result. However, this statement requires that food intake remains the same for it to be true. Food intake is surprisingly accurately matched to fluctuations in energy expenditure in normal animals; thus for inactivity to lead to obesity, there still needs to be dysregulation of food intake. Alternatively, for activity to prevent obesity, there has to be an effect of activity on the regulation of food intake. Although not studied mechanistically in either dogs or cats, it is likely that inactivity is associated with inappropriately high intake, and that intake does not quite match the increased requirements of certain amounts of activity. Thus sustained, "regular activity" decreases the risk of obesity. The amount and type of activity necessary have not been defined.
Most animals can regulate food intake appropriately within a wide range of energy densities, and a high-energy density per se is not predicted to lead to obesity. However, when changing from one energy density to another, there is much better compensation when changing to a low-density food than when changing to a high-density food. Thus, when switched from a high- to low-energy density food, a cat or dog might lose weight briefly, then adapt and put it back on to restore its original mass. However, when switched from a low- to a high-energy density diet, there is a period of over-intake, weight gain, followed by a normalisation in energy intake, but not a compensatory decrease to lose the weight gained.7 This emphasizes that most mammals have evolved in an environment where access to nutrients is limiting, and the evolutionary drive is to be efficient at securing food. There has not been evolutionary pressure to protect against obesity; thus there is much more accurate defense against energy deficiency than energy excess. This probably explains the effect of feeding scraps to dogs.
Modern pet foods are frequently blamed for increasing the prevalence of obesity, and thus the common perception is that obesity prevention can be solved through formulation of a magical, "ideal diet." As an animal eats "the ideal diet," it would receive satiety signals at exactly the right point in a meal to meet its energy requirements for that period. Certainly some dogs consuming a high-fiber and high-protein diet will consume less energy than when fed either high protein or high fiber alone, despite comparable palatabilities.8 However, long-term trials that have allowed true ad libitum access to food have not been conducted. Thus no diet, including the large number of diets marketed as "low energy density," has been shown to reduce the risk of obesity.
The Human Factor
Owners ultimately have control over the intake of their pet, and thus our efforts should be directed toward assisting owners to feed the correct amount. It really is that simple. Feeding guides provided by pet food companies are the bane of their existence. A good manufacturer is expected to provide a feeding guide with their food, but the challenges are considerable, since resting energy requirements (RER) vary by at least ± 25%, and the energy requirement for "normal" activity varies such that the maintenance energy requirements (MER) range from 1.1–2x RER (excluding working or sporting dogs). Although the majority of animals lie within a few percentages of the mean, even a few % excess will lead to significant body fat accumulation in the long term. Even if an owner knew the exact requirements of their pet, if they use a measuring cup to measure the food, they may inadvertently measure as much as 80% more than intended.9 To make matters worse, the amount owners feed is influenced by the size of the food bowl and scoop used to dispense dry food.10 So, the exact amount of food an animal needs is not known; animals of the same weight can vary enormously in their requirements; a neutered animal is unable to regulate its food intake normally; and there is great inaccuracy in the normal methods of food allocation. Thus, the emphasis from veterinarians must shift from the dietary factors, to feeding to an "ideal" body condition, or to maintain an established ideal weight.
If an owner does not perceive his or her cat as overweight, he/she will not be motivated to reduce the cat's calorie intake. Unfortunately, owners are unreliable in assessing body condition. Underestimation of the body condition of their pet by owners is a common risk factor for obesity and was the strongest explanatory independent risk factor for obesity in cats in a study in New Zealand, and this has been confirmed in Scotland and France.2,4,11 Owners with overweight dogs underestimate their dog's BCS, although as the BCS increases, the odds of underestimation decrease (Courcier et al.).12 In the UK, owners underscored their dogs when judged overweight, but had better concordance when very obese.13 In that study, it was also found that in most cases, the dog's obesity had been discussed with a veterinarian, but they still underscored their dog.
The use of a body condition scoring chart, such as that developed by Laflamme (1997), may be a useful tool in establishing a body condition benchmark.14 However, one study has suggested that even when owners of overweight cats are shown silhouettes of cats ranging from emaciated to obese, many chose the silhouette of a cat that was considerably thinner than that of an objective independent assessor.15 This suggests that a number of psychological approaches may need to be in place to change an owner's perception of his or her pet's body condition.
In the Netherlands, there is an association between canine and human obesity, but not feline obesity, that appears to be explained by the amount of time spent walking with the dog.16 A similar positive relationship between the weight of dogs and their owners has been demonstrated in other European countries.3,17 It seems highly likely that this finding can be extrapolated across cultures. Socioeconomic class seems to be an important factor in the development of canine obesity. The risk of obesity in dogs is also associated with owner income in the UK, whereby those in the highest income bracket are much less likely to have obese dogs.18
An owner's perception of their pet's body condition will be influenced not just by their understanding of what constitutes "normal," but also what is "healthy." An owner is unlikely to ascribe the definition of "obese" to their pet if they do not associate that with disease. In a recent phone survey of pet owners in the US and Australia, 356 of 1104 (32%) of owners in USA and AUS reported their pet was overweight or obese.19 However, only three of those owners (0.8%) believed it was a health problem. Owners of obese dogs were more likely to believe that exercise and balanced dog nutrition were less important than were owners of normal-weight dogs.3 Social contagion is likely to be an important factor for the appearance of obesity as a contagious, infectious disease in humans when viewed from an epidemiological pandemic. Similarly, owner perceptions - and perhaps veterinary perceptions - might be shifting toward acceptance of obesity as a normal state. Thus, educational strategies to address owner perception must educate owners on what is normal and what is unhealthy.
Weak intentions to feed appropriately are associated with pets being overweight. Owners who believe they lack knowledge of appropriate feeding behaviour and that feeding appropriately is unimportant are less likely to intend to feed their dogs appropriately, whereas owners who believe they have control over feeding appropriately are more likely to hold strong intentions to do so.20 The more owners value exercise, the more likely they are to hold strong intentions to exercise their dogs, whereas the more owners think that exercising their dogs is hampered by barriers such as time, dislike of exercise, and little access to appropriate areas, the less likely is their intent to exercise their dogs appropriately. To increase an owner's motivation for exercise, it is important not just to increase their awareness of the health benefits, but to assist them in overcoming the perceived barriers. Improving feeding and exercising behaviours in owners requires modification of both their beliefs and intentions.
In an online survey of more than 30,000 cat owners in New Zealand, it was found that there were significant associations between how an owner perceives their cat, what type of information was important to them, and what food they routinely fed. In addition, an owner's description of how fussy their cat is was strongly correlated with their choice of food. Owners for whom objective, veterinary-sourced information was important, and who had a strong attachment with their pet were more likely to feed premium diets purchased at a veterinary clinic. Owners with a strong attachment, but for whom the perception of what their cat liked most was more important than objective information, were more likely to feed multiple flavours of canned food and to describe their cat as fussy. Although these latter clients were still highly motivated and attached to their cat, they are probably less likely to adhere to strict dietary recommendations, and they need to be motivated in very different ways to other clients.
When veterinarians were recently surveyed in Australia as to what they considered the "cause of obesity" in dogs was, 36% replied dietary factors (e.g., overfeeding 12%), 21% cited insufficient exercise, and 34% said it was human related. Of those that cited "human factors," 11% related the factor to exercise such as the sedentary or overly busy lifestyle of owners, but only 3% thought the owner perception of ideal weight was an important factor.21 When asked what their preferred management strategy for obesity was, the most popular were: 1) instruct owner to reduce food, 2) reduce treats, 3) change to a low energy diet, 4) natural remedies, and 5) obesity clinic. Owners saw veterinarians as the preferred source of help for weight-loss help by owners. However, it seems that the majority of animal health professionals recommend simple nutritional management and nothing else. It is now well known that successful prevention and management of human obesity require multifaceted management strategies that change the environment in a way that causes sustainable behavioural changes in diet and exercise habits.22 It is clear that we need a similar approach.
A simple consult-room observation that an animal is overweight and advice to reduce its intake will not lead to weight loss. Offering low-energy dense foods and generic information is equally unlikely to prevent or manage obesity. We need to make owners believe that obesity is a health issue and that healthy feeding and appropriate activity require informed, active engagement by them. We need to understand that an owner's current feeding practice gives us a clue as to which multifaceted weight management strategy is most likely to be successful. One size does not fit all.
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