Is My Pet Overweight? Causes, Health Risks and Safe Weight Loss (A Vet's Guide)

Carrying extra weight is the most common health problem I see in otherwise healthy dogs and cats, and it is also one of the few we can actually reverse. This is a practical guide to why pets gain weight, what it does to their body, and how to take it off again safely.

To be honest: this is one of the harder conversations I have in the consultation room. Nobody overfeeds their pet out of neglect. It happens out of love, a little at a time, and because we see our own animal every day we rarely notice the change. Surveys in several countries suggest that around half of all dogs and cats are above their ideal weight, and most of their owners would describe them as normal.

How to tell if your pet is overweight

The number on the scale means little on its own, because ideal weight varies enormously between breeds and individuals. Vets use a body condition score from 1 to 9, where 4-5 is ideal, and every point above 5 corresponds to roughly 10% excess weight. You can do a simplified version at home:

• Ribs: You should feel them easily under a thin layer of fat, about like the back of your hand. If you have to press to find them, there is too much padding.

• Waist: Seen from above, there should be a visible waist behind the ribs.

• Tummy tuck: Seen from the side, the belly should slope upwards from the chest towards the hind legs. In cats, look for a swinging fat pad under the belly.

• Behaviour: Tiring quickly on walks, heavy panting, reluctance to jump or climb stairs, or a cat that no longer manages to groom its back are all common signs.

Why pets become overweight

In the vast majority of cases the explanation is simple: more calories go in than the body uses. The interesting part is why that happens so easily.

• Portions measured by eye. A scoop or a cup is surprisingly inaccurate. Feeding guides on the bag are also only a starting point, and are often generous for a calm, neutered indoor pet.

• Treats, chews and table scraps. These are the calories nobody counts. For a 5 kg cat or a small dog, one slice of cheese is the equivalent of a full meal for us.

• Free-feeding. A bowl that is always full works for some cats, but many will eat out of boredom.

• Neutering. After neutering, energy needs drop by around a quarter while appetite tends to increase. If the portion stays the same, weight gain is almost guaranteed.

• Age and activity. Older and less active pets need less food. So do pets recovering from injury or surgery.

• Breed and genetics. Labradors, Golden Retrievers, Beagles, Pugs, Cavaliers and Dachshunds are overrepresented. Many Labradors and Flat-coated Retrievers carry a gene variant that makes them genuinely hungrier than other dogs. It is not a lack of character, in the dog or in you.

• Several people feeding. In many households the pet gets breakfast twice.

Sometimes there is a medical reason. An underactive thyroid (hypothyroidism) and Cushing’s disease can both cause weight gain in dogs, and medications such as corticosteroids and the epilepsy drug phenobarbital increase appetite considerably. That is why a weight-loss plan should start with a check-up rather than just a smaller bowl.

What excess weight does to the body

Fat is not just passive storage. It is an active tissue that produces hormones and inflammatory substances, which is why obesity affects far more than the joints. In a well-known lifetime study of Labradors, the dogs that were kept lean lived on average almost two years longer than their heavier littermates, and developed arthritis and other chronic diseases later in life. Two years is a lot in a dog’s life.

The problems I most often see linked to excess weight are:

• Osteoarthritis and joint pain. More load on the joints plus more inflammation. This easily becomes a vicious circle: pain leads to less movement, which leads to more weight.

• Cruciate ligament rupture and back problems, especially in breeds that are already predisposed.

• Diabetes. Overweight cats have several times the risk of developing diabetes. In dogs, obesity causes insulin resistance and makes existing diabetes harder to control.

• Breathing problems and heat intolerance. Particularly serious for flat-faced breeds and dogs with tracheal collapse, and a real risk factor for heatstroke in summer.

• Higher anaesthetic and surgical risk. Dosing is harder, breathing is poorer, and surgery takes longer.

• Pancreatitis in dogs, and urinary tract disease in cats.

• Skin and coat problems. Overweight cats in particular cannot reach to groom themselves, leading to matted fur and skin infections.

• Fatty liver (hepatic lipidosis) in cats. An overweight cat that suddenly stops eating can become critically ill within days. More on that below, because it matters for how you diet a cat.

How to help your pet lose weight safely

• Start at the vet. Rule out medical causes, get an accurate starting weight and body condition score, and agree on a realistic target weight and a daily calorie allowance.

• Weigh the food in grams. Use a kitchen scale, every day. This single change is often enough to get things moving.

• Consider a veterinary weight-loss diet. Simply feeding much less of the regular food can leave your pet short of protein, vitamins and minerals - and permanently hungry. Weight-loss diets are lower in calories but higher in protein and fibre, so your pet keeps muscle and feels fuller.

• Keep treats under 10% of daily calories, and take them out of the daily ration rather than adding them on top. Pieces of the regular kibble work well for training. Many dogs are happy with carrot, cucumber or green beans. Never grapes, raisins or onion.

• Make meals last longer. Slow-feeder bowls, puzzle feeders and scattering kibble in the grass all help. For cats, several small meals and food puzzles mimic natural hunting behaviour.

• Increase activity gradually. For an overweight dog with sore joints, several short walks are better than one long one, and swimming is excellent. For cats, two or three play sessions of five minutes a day make a real difference.

• Get the whole household on board. One person in charge of the food, a note on the fridge, and an agreement about treats. Most weight-loss plans fail because of the feeder nobody knew about.

NOTE: Never crash-diet a cat. A cat that eats far too little, or stops eating altogether, can develop fatty liver disease, which is life-threatening. Weight loss in cats should always be slow and planned with your vet, and a cat that has not eaten for more than a day should be examined.

How fast should the weight come off?

Slow and steady. As a rule of thumb I aim for 1-2% of body weight per week in dogs and about 0.5-1% per week in cats. For a 30 kg Labrador that is 300-600 grams a week, so reaching a target of 25 kg will take several months. That is completely fine. Faster weight loss costs muscle, and the weight tends to come back.

Weigh your pet every two to four weeks, preferably on the same scale and at the same time of day. Most clinics will let you drop by to use theirs for free. If nothing has happened over two consecutive weigh-ins, the ration needs adjusting, usually by around 10%, in consultation with your vet. Plateaus are normal and do not mean the plan has failed.

The short version

• You should be able to feel the ribs and see a waist. If not, your pet is probably carrying too much weight.

• Excess weight shortens life and drives arthritis, diabetes, breathing problems and surgical risk.

• Start with a vet check, weigh the food in grams, count the treats, and move a little more every day.

• Aim for slow, steady loss, never starve a cat, and weigh in every two to four weeks.

The reward is usually visible long before the target weight is reached. Owners often tell me after the first couple of kilos that they have got a younger dog back. That is the part that makes this conversation worth having.