The World Health Organization states that worldwide obesity has nearly tripled since 1975, that most of the world’s population now lives in countries where obesity and being overweight is linked to more deaths than being underweight.
These statistics reflect animal obesity concerns too. In 2020, 78% of veterinary professionals highlighted to the PAWS report that they had seen an increase in pet obesity over the last two years. Obesity has remained a top concern of veterinary professionals since we collected data for the first PAW Report in 2011, and it has been consistently highlighted as one of the top 5 welfare issues facing dogs, cats, and rabbits in the UK. Despite this, in 2020, only 14% of dog owners, 18% of cat owners and 10% of rabbit owners reported their pet to be overweight or obese.
This is mirrored by a 2021 study from the Royal Veterinary College (RVC) that revealed the scale of the overweight epidemic in dogs in the UK, with 1 in 14 dogs recorded by their vets as overweight each year. Breed and other factors also contribute to increased risk of obesity. According to some studies, Pugs, Beagles, Golden Retrievers and English Springer Spaniels are at higher risk. Being middle-aged and neutered were also found to be a risk factor for dogs; alterations to sex hormones following neutering are thought to result in several behavioural changes, including increased appetite and decreased physical activity, which contribute to the risk of obesity.
Alarmingly, in another study in a UK sample of 154 brachycephalic dogs, 57% were overweight or obese. It is noteworthy that rising popularity and ownership over the past decade of the Pug, French Bulldog, and Bulldog, has been at the heart of the growing concerns about brachycephalic health issues in dogs.
Furthermore, it is estimated that between 39 and 52 per cent of cats in the UK are overweight or obese. The prevalence of overweight or obese pet rabbits is estimated to be as high as 35%, depending on the study.
Health and obesity
It is documented in humans that obesity is a risk factor in several diseases, and similarly obesity carries severe welfare risks for companion animals.
Obesity is a complex condition that may be caused by a combination of factors. These factors include, but are not limited to, genetic, environmental and lifestyle, metabolic, iatrogenic, socio-demographic and owner factors. Obese dogs have shortened life spans and reduced quality of life; it has also been associated with higher frequencies of conditions including osteoarthritis, breathing problems, heart disease, diabetes and certain types of cancer. One study found that obesity was the third most common disorder in brachycephalic (flat faced) dogs. Furthermore, obesity has been associated with increased risk of hyperadrenocorticism, hypothyroidism and urinary tract disease, urinary incontinence, cruciate disease.
Obesity in rabbits also carries consequences, including osteoarthritis, pododermatitis, hepatic lipidosis, atherosclerosis, insulin resistance, and increased risk of post-anaesthetic complications.
Obesity in cats is a major risk factor for diabetes mellitus and has also been associated with other disorders such as an increased risk of other diseases, such as lower urinary tract disease, dermatoses, oral cavity disease, and lameness.
“We can be obese but remain healthy.”
It has been suggested that being fit might attenuate some of the adverse consequences of obesity. In some human literature we are seeing that some people, despite raised BMI and obesity, appear to remain healthy – not exhibiting the normal issues cardiovascular disease risks relating to obesity. There is limited evidence that high cardiorespiratory fitness (CRF) might mitigate the detrimental effects of excess body weight on cardiometabolic health. Researchers worldwide are investigating this phenomenon – examining genes, animal models, and humans to understand more. The researchers are also working to define metabolically healthy obesity.
What influences this?
As for many other phenotypes, genes and environmental factors both influence adiposity and cardiorespiratory fitness. The heritability of both obesity and cardiorespiratory fitness might be up to 50%, leaving environmental factors such as diet and exercise routine to explain the rest. Among environmental factors, regular physical activity and, particularly, that of vigorous intensity have shown to be the most effective in improving cardiorespiratory fitness.
In the late 1990s, some studies provided first evidence for what was later known as the ‘Fat but Fit paradox’. These studies demonstrated that all-cause and cardiovascular disease mortality risk in obese individuals, as defined by body mass index (BMI), body fat percentage or waist circumference, who are fit (cardiorespiratory fitness level above the age-specific and sex-specific 20th percentile) is not significantly different from their normal-weight and fit counterparts (the theoretically healthiest group possible).
A study investigating the concept suggested that, although physical activity partly mitigates the detrimental effects of overweight/obesity on cardiovascular disease risk, we still know that obesity, especially severe/morbid obesity, is a major health problem for people. Focus on exercise and a healthy diet are important public health goals, however it should be noted that focus should not be placed exclusively on losing weight/fat, but also on increasing cardiorespiratory fitness, since a medium–high cardiorespiratory fitness level may attenuate the adverse consequences of obesity on health.
Excess body weight is still associated with a marked increase in the prevalence of major risk factors, as reflected by approximately two-, five-, and four-fold higher odds for hypercholesterolaemia, hypertension, and diabetes among active but obese individuals compared with their inactive peers with normal weight.
This is looking at cardiovascular health… which is not comparable in many animals
These studies looking into the ‘fat but fit’ paradox focus on cardiovascular health, and for good reasons. Cardiovascular disease is a leading cause of death worldwide, accounting for 45% of all deaths (>4 million) in Europe and prevalence in UK has remained constant at around 3% in England and 4% in Scotland, Wales, and Northern Ireland.
The aetiology of CVD in animals and humans is relatively incomparable: humans commonly experience coronary heart disease, atherosclerosis and atheroma commonly linked to obesity, whereas dogs are represented with degenerative valve disease and acquired cardiomyopathies, and in cat’s cardiomyopathies are most prevalent, with specific risk factors making some individuals more predisposed to specific disease processes. Given this limited evidence we need to continue to work with the current information we have available. Obesity in animals is a risk factor for several health issues and increased mortality, even if you believe they are healthy it is still important to work towards an appropriate body condition score in your dog, cat or rabbit and maintaining good musculature.
We shouldn’t let our companion animals get overweight
There is limited evidence to support the theory in humans of the ‘fat but fit’ paradox, and even less so in animals. Studies we have are currently focusing on cardiovascular diseases, which is not comparable in many of our companion animals. As our animals’ advocates and caregivers, and commonly the person providing for their nutritional needs (unless they scavenge or hunt), it is our responsibility to ensure their health and welfare needs are met.
Of course, bodies that are underweight or ideal weight may also have health issues; skinny isn’t always synonymous with healthy – but at least we are not adding a preventable issue to our animal’s risk factors by allowing them to become obese (unless we have a genuine health reason for weight gain, such as hypothyroidism). Common health issues can be made worse, or even be caused by obesity – we must work to keep our companion animals at a healthy weight.
