Most previous weight-loss studies examined the effect of dietary caloric restriction (5
) and drug therapy (4
) and, whilst there have been occasional studies examining lifestyle factors (7
), this remains an understudied area in canine obesity management. It is noteworthy that the overall rate of weight loss in this study (1.5% SBW/week) was faster than the rates reported in previously published clinical reports using client-owned dogs with naturally occurring obesity. For instance, Saker and Remillard (25
) summarized 2 canine weight-loss studies, using a low-calorie diet, with an overall reported rate of weight loss of 0.75%/week (25
). In a more recent study, a mean rate of weight loss of 0.85%/week was achieved, using a similar high protein weight-loss diet to the current study with a similar degree of caloric restriction (60% MER at TBW) (9
). Furthermore, in clinical trials using dirlotapide for weight loss, an expected weight loss of ~0.75%/week was reported (4
Thus, the current preliminary results suggest that either including exercise sessions with an underwater treadmill or active client motivation, or both, may improve rate of weight loss. Nonetheless, many limitations exist, most notably the fact that the study was retrospective and did not include a contemporaneous control group for comparison. Making comparisons with the results of historical studies can be unreliable, in that both client and animal populations may vary, there may be differences in diet composition, and in the strategies used for weight management. A second limitation of the study is that it was not possible to determine whether the benefit was the result of the exercise strategy, or client education, or both. Interestingly, a previous trial demonstrated that owner attendance at educational seminars had a limited effect on the outcome of weight loss in dogs (7
). These findings may suggest the exercise component was key; however, a prospective, randomized controlled trial would provide more reliable results and, in fact, such a study is currently underway.
All clinical cases received an intensive exercise program, with regular sessions on an underwater treadmill in addition to other activities commonly undertaken in weight-loss programs (such as regular lead walking). Over the course of the study, a gradual increase in exercise capabilities was noted for the dogs, in that session speed, session duration, and total distance walked all increased significantly. As seen in , the pattern of response differed for the parameters assessed: session duration increased in the first month of the program, but did not increase thereafter. This may partly relate to the fact that the dogs needed some training before they became completely accustomed to treadmill exercise, but it may also reflect that the session time was limited (up to 30 min). Thus, to increase overall activity further (in terms of distance travelled and hence energy expenditure) session speed would need to increase. In contrast to session duration, more gradual increases in session speed and total distance covered were seen over the course of weight loss. Again, this may partly relate to training and experience with the treadmill. However, given the subjectively gradual nature, other factors may also be involved including the fact that there may have been improvements in fitness levels as the weight program progressed and activity increased.
It is difficult to gauge the effect that the treadmill exercise itself would have had on energy expenditure since this was not directly measured. Energy expenditure during exercise is complex, with greater expenditure occurring with weight-bearing modalities, and with high intensity activity (27
). With an underwater treadmill, the reduced joint-loading (due to the buoyancy effect of water) would serve to reduce energy expenditure, but this, however, would be counteracted by water resistance (due to water viscosity), and by altering the treadmill speed to allow the intensity to be varied during a session. Resistance training has been shown to increase resting energy expenditure and increase muscle mass (28
), thereby contributing further to energy expenditure by increasing MER. However, the main advantage of using an underwater treadmill is to avoid excessive joint loading, which is helpful for obese animals with orthopedic disease, such as with the American pitbull in the current study.
With respect to exercise, previous studies have demonstrated benefits in human weight-loss programs. First, physical activity can contribute to negative energy balance in patients on caloric restriction, and thus improve the rate of weight loss (10
). The degree of energy deficiency, however, is minor in relation to the effect of caloric restriction: it is estimated that walking for 5 km/d only increases daily energy requirements by 7% (29
). Given that the treadmill exercise that each dog received was not equivalent to such exercise, it is perhaps surprising to note the difference in rate of weight loss. Another possibility is that exercise may affect appetite, as suggested by previous studies (30
). A final possibility is that providing more formal exercise may have indirectly improved outcome by improving owner compliance; in this respect, the commitment required to attend regular exercise sessions may improve owner dedication to the program as a whole. This may, in part, be related to the other known effects of increasing exercise, namely that improvements in fitness can be seen even very early on during the weight management regimen; compliance is likely to be better when owners can see rapid benefits in quality of life. Further studies would be required, however, to determine the exact reasons for how exercise improves outcome in weight loss.
In summary, although the findings are preliminary in nature, the results suggest that introducing a formal exercise plan, involving standardized exercise on a treadmill, and active client education may improve the rate of weight loss whilst on a conventional weight-loss regimen. These findings should prompt further studies to determine the optimal strategy for exercise during weight management regimens in dogs.