Most people don’t set out to make their pet overweight. It happens the way a lot of problems happen in real life: gradually, quietly, and with good intentions. A few extra treats. A little less activity. A busy season. A pet that looks “cute” with a round belly. Then one day you realize your dog can’t jump into the car like he used to, or your cat is grooming less, or your pet is breathing harder after a short walk. And by the time it’s obvious, it’s usually been building for a long time.
I’m going to be direct because I’m a veterinarian and because I care about outcomes. Excess body fat is not just a cosmetic issue. It is a medical problem that affects comfort, mobility, organ function, and lifespan. It also makes almost every other condition harder to manage. If your pet is overweight and develops arthritis, they hurt more. If they need surgery, anesthesia is riskier. If they become diabetic, regulation is harder. If they have breathing issues, the extra weight makes it worse. And if they’re a cat, obesity can set them up for one of the most dangerous emergencies we see: hepatic lipidosis, or fatty liver disease, especially if they stop eating.
Let’s start with the “why.” Fat is not inert. It’s metabolically active tissue. It produces inflammatory signals. It changes hormone balance. It affects insulin sensitivity. It puts extra load on joints and the heart. It changes how the body handles heat. It can even alter how medications distribute in the body. That’s why I take it seriously even when a pet is acting “fine.” Many overweight pets act fine until they don’t.
Now I want to talk about something that doesn’t get enough attention in cats: hydration. Cats are not small dogs. They are built differently. Their ancestors evolved as desert-adapted hunters, and cats are naturally conservative with water. Many cats have a low thirst drive compared to dogs. In the wild, they would get a lot of their moisture from prey. In our homes, many cats eat dry food as a major part of their diet, and some cats simply do not drink enough water to make up the difference.
Chronic mild dehydration in cats can contribute to urinary issues and kidney stress over time, but it can also play a role in weight gain in a more indirect way. When a cat is not well hydrated, they may feel “off” in subtle ways—less energetic, less playful, less inclined to move around. Activity matters for weight, especially in indoor cats. A cat that is slightly under-hydrated day after day may not feel like chasing toys, jumping, or engaging the way they would if they felt better.
Here’s the part that surprises a lot of cat owners. Sometimes what looks like hunger is actually a hydration problem. Cats are designed to get a lot of their water from what they eat. In the wild, prey provides moisture along with calories, so cats never developed the strong thirst drive dogs have. Put that same biology in a modern home with mostly dry kibble, and some cats will ‘look for hydration’ by eating. That’s one reason adding wet food or improving water access can help both hydration and weight.
There’s also a behavioral piece. Cats are excellent at training humans. If a cat is bored, under-stimulated, or mildly uncomfortable, they may seek interaction. Many owners respond to that interaction request with food because it’s easy and it works quickly. The cat learns that “I feel something I don’t like” or “I want attention” leads to eating. Over time, that pattern can become a major driver of calorie intake.
Hydration and satiety are connected too. Wet food has more volume per calorie because of the water content. A cat can eat a physically satisfying portion of wet food with fewer calories than an equivalent “small scoop” of dry food. Dry food is calorie dense. It’s easy to overfeed without realizing it, especially if you free-feed. A cat can consume a lot of calories quickly, and because the meal is not bulky, they may still act hungry. That doesn’t mean dry food is “bad” in every situation, but it does mean we have to be honest about how easy it is to overdo it.
So what do I recommend for cat hydration and weight management? First, make water access easy and appealing. Many cats prefer wide bowls so their whiskers don’t touch the sides. Many prefer fresh water away from their food. Some prefer running water, and a cat fountain can be a game-changer. Second, talk to your veterinarian about incorporating wet food, even if it’s partial. Sometimes a mixed feeding plan is the most realistic approach. Third, measure food. I know that sounds obvious, but “I just pour some in” is how cats gain weight. Fourth, increase activity in ways that fit your cat. Short play sessions count. Food puzzles count. Even moving the food bowl to a different location so the cat has to walk and “hunt” a little can help.
Now let’s shift to dogs, because dog obesity has its own set of drivers and one endocrine condition that people ask about frequently: hypothyroidism.
Hypothyroidism in dogs occurs when the thyroid gland is not producing enough thyroid hormone. Thyroid hormone influences metabolism, skin and coat health, and energy level. A hypothyroid dog often gains weight more easily, not necessarily because they are eating more, but because their metabolic rate is lower and they may be less active. Common signs include weight gain, lethargy, heat-seeking behavior, a dull coat, hair thinning (often on the trunk or tail), recurrent ear or skin infections, and sometimes a “tragic” facial expression due to skin changes. Not every overweight dog has hypothyroidism, but it is on the list of things we consider when the story fits.
This is where I want to correct a misconception. Many people assume that if a dog is overweight, it must be a thyroid problem. In reality, the most common cause of obesity is still excess calories relative to activity. Treats, table scraps, free-feeding, and underestimating portion sizes are the usual culprits. Hypothyroidism is real, and it matters, but it is not the default explanation for every overweight dog.
When we suspect hypothyroidism, we don’t guess. We test. Thyroid testing can be nuanced, and interpretation matters, especially if a dog has other illnesses or is on certain medications. If the diagnosis is confirmed, treatment is typically straightforward: thyroid hormone replacement. When properly treated, many dogs have improved energy, improved coat quality, and an easier time losing weight—though they still usually need a controlled diet and appropriate exercise. Medication is not a free pass to keep feeding the same way. It’s a tool that makes the plan work.
Whether we’re talking about cats or dogs, the practical path forward is similar. We start with an honest body condition score. We set a realistic target. We measure food. We reduce treats or switch to lower-calorie options. We increase activity in a safe way. And we recheck progress. Weight loss should be gradual. Rapid weight loss is dangerous in cats and can be unhealthy in dogs as well.
If you take one thing from this column, let it be this: fat pets are not just “a little chubby.” They are carrying a chronic medical burden. The good news is that weight is one of the conditions we can improve dramatically with consistent, boring, effective steps. And if there is an underlying issue—like hypothyroidism in a dog, or chronic dehydration contributing to low activity and overeating patterns in a cat—we can address that too.
If you’re not sure where your pet stands, ask at your next visit. We can tell you if your pet is at an ideal weight, mildly overweight, or in a danger zone. We can help you build a plan that fits your life. Your pet doesn’t need perfection. They need you to notice, decide it matters, and take the first step.
MJ Wixsom, DVM MS is a best-selling Amazon author who practices at Guardian Animal Medical Center in Kentucky (GuardianAnimal.com). She has volunteered at Saipan Cares, learned to dive while in Saipan, and is a donor supporter of CNMI Sinlaku recovery efforts.
Editor’s note: The views and opinions expressed in this op-ed are those of the author and do not necessarily reflect the views of NMI News Service or its staff. All assertions are the sole responsibility of the writer. To submit an op-ed for consideration, email your piece to brad.ruszala@nminewsservice.com.