Contrary to common consent, there is no published evidence that the addition of palatability enhancers to industrially produced foods increases the risk of obesity development in dogs. However, there is such evidence for added fat, which is both a conditional palatant and a concentrated energy source.
It has been stated frequently that palatable foods promote obesity development in dogs. The statement seems logical. Appetizing foods blunt the response to satiety signals, thus causing overeating. Obesity, which is the most common medical disorder in dogs, arises when food energy intake exceeds energy expenditure. The ubiquitous availability of highly palatable commercial dog foods and prevention of canine obesity ostensibly are on bad terms.
In the extremely competitive petfood market, high palatability is essential for commercial success of an industrially produced dog food. For repeated purchase of a particular food, the dog must immediately accept the food. The dog must also enjoy the food obviously so the owner perceives it. A dog pleased with its food makes his or her owner happy. Palatability may be defined as subjective pleasure associated with consuming a certain food and is determined by the food's taste, texture and odor.
There is a wide variety of palatability enhancers, but details on composition and application are not made public by petfood and palatant manufacturers. It is common knowledge that palatability of a dry dog food formula is enhanced conditionally by the addition of liver-based preparations, fats (especially poultry fat), sucrose or yeast products. Dogs generally prefer canned foods over dry foods.
Long-term, liberal consumption of palatable food does not necessarily increase energy intake and induce obesity. Possibly, satiety mechanisms are restored and/or flavor fatigue develops. To find out, dogs given free access to either palatable or less palatable food should be monitored as to body weight and body condition. It should be noted that with different diet formulations, influences other than palatability cannot be excluded. In any event, there is no published evidence that palatants cause additional weight gain, except for supplemental fat.
Two controlled studies, carried out by Romsos et al. more than 35 years ago, indicate that high- versus low-fat diets can induce overweight. This effect occurs within the range of fat content fluctuation in the various types of commercial dog foods, that is any increase between 5% and 28% fat in the dietary dry matter. The high-fat diets increased energy intake, body weight and body fat. It is unknown whether the fat-enriched diets had enhanced palatability, but the two studies underscore that copious fat ingestion raises body fat by a combination of extra energy intake and high efficiency of dietary fat incorporation in adipose tissue.
Details of the two studies are as follows. Young, female beagle dogs, aged two months, were fed ad libitum on canned diets containing either 5% or 18% fat in the dietary dry matter for a period of eight months. The high-fat diet, formulated by isocaloric replacement of corn starch by lard, increased digestible energy intake, body weight and body fat by 14%, 17% and 65%, respectively. Similar effects were seen in adult dogs when tallow was isocalorically substituted for corn starch. The female beagle dogs were aged three years and fed the experimental diets for 25 weeks. The low- and high-fat, canned diets contained 10% and 28% fat in the dry matter. The high-fat diet increased digestible energy intake, body weight and body fat by 13%, 16% and 32%.
Irrespective of the degree of food palatability and dietary fat content, feeding on a fill-the-bowl basis contributes to obesity in many dogs. The message remains unchanged and simple, albeit it difficult to practice: accommodate the amount of food to attain or maintain ideal body condition.