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As awareness of the pet obesity epidemic increases, more pet owners are familiar with disease conditions associated with the condition. Owners today more quickly understand the increased risk of diabetes, arthritis, and cancer posed by excess fat. Less known are the effects of excess fat on lung function.

Research in humans has described lung changes and decreased lung function in obese patients. Similar research in pets has only recently begun. Although the research has not been able to explain the exact changes that impact lung function in animals, weight loss seems to have the same positive effect found in human patients.

A recent study in the Journal of Veterinary Internal Medicine documents this improvement.

The Cause of Decreased Lung Function with Obesity

You may know or have watched overweight individuals panting or experiencing shortness of breath after simple tasks like bending over or walking a short distance. These individuals often have increased heart rates during these tasks. Most attribute this difficulty to the bulk of fat and its effect on the diaphragm when bending or the increased load when walking. Researchers think the problem is more complex and includes changes in the elasticity of the lung and chest tissues that restrict ventilation.

A proven method for assessing lung function in overweight patients is the 6-Minute Walk Test. It is a non-stressful method for testing the severity of lung dysfunction or function improvement with weight loss.

The 6-Minute Walk Test

The test is simple. Patients merely walk at a voluntary pace for 6-minutes. Heart rate, respiration rate, and blood oxygen levels are sampled before, during and after the walk. The total distance walked in 6-minutes is recorded.

Repeat tests allow evaluation of decreased or increased lung function based on weight gain or loss. The test has been shown to be as effectively useful in dogs. The researchers in the above study used the 6-minute walk test on obese Beagles.


The Study on Obese Beagles

Two groups of Beagles were examined in the study. One group of nine were dogs, volunteered by their owners, that had been obese for a substantial period of time. Only six of these volunteers completed the experiment.

In the second group, six normal-weight laboratory dogs were fed to the same level of obesity as the volunteer dogs.

The experimental design was to investigate differences between chronic obesity and acute (sudden) obesity on lung function. Both groups were then put on a calorie restricted, weight loss program. The 6-minute walk test was performed periodically until all dogs achieved their target body conformation score (BCS) of 5/9. A BCS of 5/9 represents a dog’s individual, ideal body weight.

The results were in line with human research. As the dogs lost weight, their resting heart rate and respiratory rate decreased and their 6-minute distance increased. Panting during the walk and during recovery from the walk were also observed but not measured. Equally fascinating is that the dogs did not have to reach their target BCS before improvement was documented. 

The researchers hypothesized that the fast weight gain of the laboratory dogs would have less impact on lung function. In fact the dysfunction was equal for both groups, suggesting that obesity immediately impacts lung function and the heart needs to compensate for the decreased lung function by increasing heart rate and blood circulation.

Another interesting finding was that chronically obese volunteers took twice as long to achieve their ideal BCS. The researchers had no answers for this finding but I suspect it is a result of the biological adaptations that occur with obesity to maintain that state in the face of calorie restriction.

The findings of this research do not surprise me. The most common observation made by owners of my weight loss patients is the immediate increase in energy. These comments are common after only 2-3 weeks of dieting.

Dr. Ken Tudor

Image: Fabio Alcini / Shutterstock

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