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Feline obesity: What happens when cats get fat?

Feline obesity, an increasing concern for cat owners, can have profound health implications for our feline friends. A recent study from the University of Illinois Urbana-Champaign has shed light on the repercussions of overeating in cats, particularly focusing on their digestive system and gut microbiota.

Feline obesity in the U.S.

As a starting point, it’s alarming to realize that approximately 60% of cats in the U.S. are overweight. Such staggering figures can lead to a plethora of health issues for these animals, including diabetes and chronic inflammation.

Ample research has been dedicated to feline weight loss. However, the opposite end of the spectrum – the impacts of weight gain – has been left relatively unexplored.

Kelly Swanson is the study’s co-author and an authoritative voice in the realm of animal sciences. She emphasizes the importance of understanding the “metabolic and gastrointestinal changes that occur as a result of overeating and weight gain in cats.”

Investigative methodology

The comprehensive study consisted of 11 adult spayed female cats. After setting a two-week baseline on standard dry cat food consumption, the felines were given the liberty to eat as they wished. Regular collection of blood and fecal samples, combined with monitoring their physical activities, was carried out.

Swanson highlighted that upon the commencement of overfeeding, cats significantly upped their food consumption, leading to weight gain. Their body condition score (BCS), a scale analogous to the human BMI, shot up to a worrying 8.27 from 5.41 in just 18 weeks, marking them 30% overweight.

Digestive insights into feline obesity

Close analysis of fecal output, gastrointestinal transit time, digestive efficiency, and microbiota bacterial composition was undertaken over the study’s 20-week span.

Swanson explained, “As cats ate more and gained weight, gastrointestinal transit time was reduced, and so was digestive efficiency.” An increased food intake meant that the digestive system processed the food more rapidly. This led to decreased nutrient extraction.

Furthermore, a significant alteration in the gut microbial composition was observed. Contrary to overweight humans, the abundance of the beneficial Bifidobacterium bacteria increased in cats. Meanwhile, Collinsella, associated with pro-inflammatory diseases, reduced. This interesting observation underscores the intricate association of certain bacteria with weight gain.

Swanson emphasized the importance of the discovered change in the gastrointestinal transit time. She suggests it could help explain future shifts in pet microbiomes.

Another observation pointed to increased fecal output as food consumption grew. Essentially, more eating resulted in more excretion. Additionally, fecal pH levels dipped. This metric indicates a more acidic stool, which Swanson correlated with reduced digestibility and increased food intake in humans.

Activity levels remain unchanged

Despite the weight gain, the researchers were intrigued to find no consistent change in the cats’ activity levels when suffering from feline obesity. But Swanson cautioned that individual cats and their specific environments could yield different results. This depends, most importantly, on the interaction levels with their owners.

Feline obesity implications

Recognizing the metabolic and gastrointestinal changes in cats can arm owners with knowledge for better prevention and treatment plans. Additionally, Swanson’s subsequent research indicates that restricted feeding can facilitate safe weight and fat loss.

Encouragingly, after the weight gain study concluded, the 11 cats were successfully returned to their standard weight through restricted-feeding diets. This offers hope to pet owners. With the right interventions and a better understanding of our pets’ digestive systems, we can ensure a healthier, happier life for our feline companions.

The first study, “Effects of overfeeding on the digestive efficiency, voluntary physical activity levels, and fecal characteristics and microbiota of adult cats,” is published in the Journal of Animal Science.

The second study, “Effects of weight loss and feeding specially formulated diets on the body composition, blood metabolite profiles, voluntary physical activity, and fecal metabolites and microbiota of overweight cats,” is also published in the Journal of Animal Science.

More about cats and feline obesity

House cats, or domestic cats, have graced human households with their adorable purring sounds for thousands of years. Revered for their elegance and mystery, they have secured their place as one of the most popular pets worldwide.

Origins of the domestic cat

The origin of domestic cats traces back thousands of years, and their journey from wild predators to household companions is a fascinating tale of symbiosis with humans.

Wild Ancestors

The direct ancestor of domestic cats is believed to be the African wildcat (Felis silvestris lybica). These wildcats roamed various regions of Africa, Europe, and Asia.

Domestication Process

The domestication of cats is thought to have begun around 9,000 years ago. As humans transitioned from nomadic lifestyles to settled agricultural communities, they stored surplus grain. This surplus attracted rodents, which in turn attracted wildcats.

Over time, a mutually beneficial relationship formed. The wildcats reduced the rodent population, protecting the grain, while humans provided a steady source of food in the form of the rodents.

Cats with temperaments that were more tolerant of human presence had an advantage in this scenario. Over generations, natural selection favored these less aggressive wildcats, leading to a population of cats that were more amenable to living in close proximity to humans.

Archaeological Evidence

The first concrete archaeological evidence of domesticated cats dates back to around 7500 BCE. An ancient burial site on the island of Cyprus contained the remains of a cat alongside a human.

This discovery was particularly significant because cats are not native to Cyprus, suggesting that humans brought them to the island. This close association in burial indicated a special bond between the cat and human, a sign of early domestication.

Spread and Evolution

As civilizations grew and trade expanded, cats traveled with humans, making their way to various parts of the world. Their utility as pest controllers, combined with their companionship, made them indispensable. Over time, due to factors like geographic location, climate, and human preferences, different cat breeds with distinct characteristics emerged.

Genetic Studies

Modern genetic studies have further pinpointed the African wildcat as the ancestor of domestic cats. A 2007 study published in the journal Science analyzed the DNA of domestic cats and identified a lineage of Felis silvestris lybica from the Middle East as the likely progenitor of today’s house cats.

The domestication of cats is a testament to their adaptability and the enduring bond they’ve formed with humans. From wild hunters in ancient landscapes to beloved household pets, cats have firmly cemented their place in human history and hearts.

Physical characteristics

House cats, also known as domestic cats (Felis catus), possess a unique set of physical characteristics that distinguish them from other members of the feline family. Here’s an overview of their physical features:

Size and Weight

Domestic cats typically weigh between 6 to 16 pounds, though this can vary with breed and diet. They are generally small to medium-sized animals. However, cats afflicted with feline obesity can be several times that average weight.

Body Shape

Most house cats have a sleek and muscular build, which provides agility and strength. Their bodies are built for stalking and pouncing, reminiscent of their wild ancestors.

Fur and Coat

Domestic cats come in a variety of coat lengths and patterns. This includes short-haired, long-haired, and hairless varieties. Common patterns are solid, tabby, calico, bicolor, and more. Their fur can be soft and silky or dense and plush, depending on the breed.


Cats can be found in a wide range of colors including white, black, brown, gray, orange (often referred to as “ginger” or “marmalade”), and cream.


A cat’s eyes are large and usually almond-shaped. They possess a third eyelid known as a nictitating membrane. Eye colors vary and can include green, yellow, blue, and copper. Some cats even have heterochromia, where each eye is a different color.


Cats generally have upright ears that are pointed at the tip. Some breeds, like the Scottish Fold, have a unique folded ear appearance.


Cats have long, sensitive whiskers on their cheeks, above their eyes, and on the back of their front legs. These whiskers, or vibrissae, help them navigate their surroundings and detect nearby objects, even in the dark.


A cat’s tail is long and flexible, aiding in balance, especially during high-speed chases or when climbing. The tail can also express a cat’s mood—raised when happy, twitching when irritated, and puffed up when frightened.

Paws and Claws

Cats have retractable claws, allowing them to keep them sharp for hunting and climbing. They typically have five toes on their front paws and four on their rear paws. Some cats, due to a genetic mutation, might have extra toes and are known as polydactyl cats.


Domestic cats have sharp, pointed teeth designed for gripping prey and tearing meat. They have 30 teeth in total: 12 incisors, 10 premolars, 4 canines, and 4 molars.


A cat’s nose is typically small and moist, with a unique pattern of ridges and bumps, akin to a human’s fingerprint.

While domestic cats may share many of these general physical characteristics, individual breeds might possess distinct features, making each cat truly unique in its appearance.

Behavior and habits

Despite domestication, house cats retain many behaviors of their wild ancestors. They are natural predators. A simple play session with a string or toy mouse often reveals their innate hunting instincts. Cats also engage in territorial behaviors, marking their space with scent glands on their cheeks and paws.

Health and nutrition

For a house cat to thrive, it needs a balanced diet. This usually consists of commercial cat food that meets their protein and taurine requirements.

If owners aren’t careful, they may end up with a cat that suffers from feline obesity. Regular veterinary check-ups ensure they remain free from diseases and receive necessary vaccinations.

Cats and human bonds

Over time, cats have become more than just pest controllers. They’ve morphed into cherished family members, offering companionship and often helping reduce stress in their human counterparts. The purring of a cat can soothe nerves, and their playful antics provide endless entertainment.

In summary, house cats, with their rich history and dynamic personalities, continue to captivate the hearts of many. Their blend of independence and affection makes them an ideal pet for households around the world.

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