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7 reasons for weight gain in dogs and cats

It happens to many of us. One day you look at the scale or try on that favorite pair of pants and realize you’ve put on some weight. Well, while our pets may not be squeezing into a pair of skinny jeans, they are susceptible to weight gain, too.

While a few extra pounds on a human may not be anything to stress over and oftentimes can easily be managed, that’s not necessarily true for our pets. For them, weight gain, especially when it happens very quickly, may indicate an underlying illness. Extra weight also makes them more susceptible to health issues like arthritis, heart disease, breathing difficulties and can reduce their life expectancy by more than two years. As such, it’s important to pay attention to your pet’s diet and to monitor their weight. If you’re noticing changes, it’s time to understand some of the common reasons for weight gain in dogs and cats so you can put them back on the path to a healthy weight.

1. Overeating

Overeating can occur for a number of reasons, but in most cases, it’s the pet parent who needs to make some changes. For example, a pet who’s free fed—or has unlimited access to food throughout the day—is likely to overindulge and can become overweight. Too many treats can also lead to a situation where your pet is being overfed.


Measure portions based on the food packaging’s instructions. If your pet remains at an unhealthy weight, ask your veterinarian to help set up a feeding schedule and recommended portions for your pet based on their unique needs. Keep in mind that treats should only make up 10 percent of your pet’s normal diet. If you’re exceeding that, it’s time to cut back.  

2. Diet Problems

A pet who’s overfed table scraps, eats poor quality food or whose diet is inappropriate for their age, breed and lifestyle may have resulting weight problems. For example, a senior dog who eats food formulated for a younger canine might be consuming too many calories. Since senior dogs are less active, an older dog on a high-calorie diet will likely pack on the pounds.


Visit a Petco store for a nutrition conversation or speak with your veterinarian about the best foods to feed your dog based on their specific needs. Fresh foods from brands like JustFoodForDogs or Instinct, for example, are minimally processed and allow you to provide your pet with all the nutrition they need.

3. Lack of exercise

Like people, our pets require daily movement to stay healthy. How much varies based on breed, age and size, but your veterinarian can help you establish an exercise plan.


Exercising with your pet helps them stay healthy and bond with you at the same time. Going on walks and hikes together can be an easy way to get active (for both you and your dog!), while visits to dog parks or dog-friendly beaches help your dog socialize while simultaneously getting in some exercise. It’s also important to provide your pet with interactive toys that help stimulate them mentally and physically. For cats, interactive toys like teasers and wands are easy and fun ways for them to get their daily exercise. Dogs, on the other hand, often enjoy games of fetch and can benefit from a dog walking service if you’re often away from home or have restricted mobility.

4. Age

Older pets can gain weight for a number of reasons, including slowing metabolism, lack of exercise, improper diet and underlying health issues.


Switching up their exercise routine to lower intensity activities like slower walks or swimming is a great way to ensure they get their exercise in a way that is more comfortable for them. Providing supplements for your older dog or cat can help improve joint performance and get them moving more comfortably. Feeding your pet senior-specific foods—available for both dogs and cats—also helps ensure they get the nutrients their body needs at this life stage.

5. Hormones and changes

Your pet is likely to go through many hormonal and lifestyle changes throughout their life, and their weight can be impacted by these changes. Spaying and neutering, for example, can decrease hormones and metabolic rate, making it easier for your pet to gain weight, and aging itself can also impact hormones and cause metabolic changes.


Take note of changes in your pet’s life and set up an appointment with your veterinarian to discuss and have them examine your pet. They will be able to help come up with a recommended approach to keeping your pet at a healthy weight that may include a new food or modified activities.

6. Predisposed breeds

Certain breeds—generally smaller or lower energy breeds are more prone to gaining weight, and being affected by it, more quickly. While an increase of 1-5 pounds may seem like nothing too serious, to a small breed dog that should only weigh 5-25 pounds, it is an increase of 20% of their body weight! To put it in perspective, that would be like asking an average adult that weighs 150-200 pounds to carry an additional 30-40 pounds around with them all day, everyday.


While there’s not much you can do about your dog’s breed, you should always be proactive about monitoring your pet’s weight. Providing a breed-specific food—like those offered by Royal Canin—that cater to their particular needs, could help, but always be sure to also consult with their veterinarian for other recommendations.

7. Health issues

Underlying health issues can make your pet gain weight or make it difficult for your dog or cat to get as much exercise as they need. Thyroid issues can also cause weight gain, which will need to be monitored and addressed.


If you notice a drastic change in your pet’s weight, check in with your veterinarian. Stay up to date with annual visits to catch any issues that crop up before they become a problem, and pay attention to symptoms like lethargy, loss of appetite and depression that could mean your pet is experiencing an underlying health issue.

It’s important to remember that a dog or cat’s ideal weight is a combination of many factors, including their size, age and breed. You should consult your veterinarian to determine a healthy weight range for your pet and check in with them during their annual or semiannual wellness visits to confirm that all is well. And while it may be possible to address a pet’s weight issues simply by shifting around some lifestyle factors, like changing their diet, providing more interactive toys and getting out to exercise more, your veterinarian will be able to offer more recommendations and tips based on your pet’s exam results.

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