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Do I Need to Put My Cat or Dog on a Diet?

Do I Need to Put My Cat or Dog on a Diet?

Written by Dr. Aisling O'Keeffe MVB CertSAM ISFMCertAdvFB (United Kingdom)

Everything you need to know about how to assess your pet’s weight, if they need to be on a diet and if so, how to start the process.

As pet owners, it can be hard to know if our pets are the correct weight. Are they underweight or overweight, do they need to be put on a diet? With so much information out there nowadays, it can be confusing. But don’t worry, in this article, we’ll discuss everything that you need to know including how to assess your dog/cat’s body condition, the calories they should be consuming, and how to put them on a diet if they need it.

Is My Pet Overweight?

First of all, you need to assess if your cat or dog is the correct weight. This can be a confusing task, particularly if they’re long-haired as all that fur can hide a lot. As vets, we usually judge a dog or cat’s weight based on a few factors such as their weight in kg/lbs and their body condition score.

A body condition score (BCS) is a method to assess body fat in pets. It is ranked from 1-9, with 1 being emaciated and 9 being clinically obese. Dogs and cats should usually be ranked around 4-5 to be at a healthy weight. You can check your dog or cat against this BCS at home if you’re comfortable with how to interpret it. The body condition score will mainly focus on the fat on your pet’s ribs and how easy or hard it is for you to feel them. For example, if you’re finding it very difficult to feel your pet’s ribs it’s likely that they’re carrying too much weight.

It will also discuss their waist or a lack of a waist. In dogs, this is very easily seen by looking down on them and assessing if their waist tucks inwards after the end of their ribcage. It can be a little bit more difficult in cats as their waist might not be as obvious. Cats that are carrying extra weight will usually have abdominal distension with fat deposits and a large fat pouch, or a primordial pouch as it’s correctly named.

If you’re unsure of how to assess your pet’s BCS don’t fret. Schedule an appointment with your veterinarian who will score your pet for you and discuss the results with you. Pets that have high body condition scores may need to go on a diet. Your vet may want to rule out potential medical conditions first depending on your pet’s case, such as hypothyroidism or osteoarthritis.

How Many Calories Do Pets Need?

So now that you’ve assessed your pet’s body condition score, you’ll know if they’re the correct weight they should be. If they’re overweight or obese, they’ll need to go on a diet to lose weight. In order to start putting them on a diet, we need to know how much they should be eating on a daily basis. I would recommend talking to your vet or a veterinary nutritionist about this.

This is calculated by assessing their resting energy requirements (RER), the energy they use in their body for functions such as breathing or eating. The calculation for this is as follows:

RER = BW(kg)0.75 X 70

This involves multiplying their body weight in kg (to the power of 0.75) by 70. This is then multiplied below by their life stage factor to get the daily calories they need.

MER = RER X life stage factor

The life stage factor are factors that will affect how many calories your pet needs. Let's talk about this in more detail now.

What Factors Affect Calorie Requirements?

Not all dogs or cats will require the same calories, even if they’re the same size. This will depend on a few factors that affect how many calories they burn daily. Factors that affect this include;

  • Activity levels
  • Neutered status
  • Pregnancy and feeding
  • Age
  • Breed

For example, pets that are exercising a lot, pregnant/feeding or growing will require more calories than pets that are sedentary or neutered. The life factor numbers reflect this;

Neutered adult

=1.6 x RER

Intact adult

=1.8 x RER

Inactive/obese prone

=1.2-1.4 x RER

Weight loss

=1.0 x RER for ideal weight

Weight gain

=1.2-1.8 x RER for ideal weight

Active, working dogs

=2.0-5.0 x RER

Puppy 0-4 months

=3.0 x RER

Puppy 4 months to adult

= 2.0 x RER

Your vet or a pet nutritionist can help you calculate this. Essentially, you will judge your pet’s weight and their lifestyle when considering how many calories to feed them. For example, a thin cat that is feeding kittens will need extra calories in their diet, like in our Mousse Pate for Mama & Kittens range here.

If you’ve calculated that your pet is eating more calories than they need and they’re overweight, the next step is putting them on a diet.

How to Put Your Pet on a Diet

Now that you’ve looked at your pet’s body condition score and their caloric requirements, you may realise that they’re overweight and have been eating too much. Don’t worry, this is a very common problem in the pet world, you aren’t alone. The first step is getting your pet on the right track to lose weight and be the healthiest version of themselves.

Food Portions

Start by checking how much food they should be eating. You can do this by checking their daily calorie allowance against the calorie content of the food they eat (e.g. how many calories are in a certain amount of the food they eat). This will be visible on the tin of our pet foods and we include a handy feeding guide that goes on the size and weight of your pet. To feed them the correct portion, I’d recommend using this guide or weighing their food on a weighing scale.

Don’t forget that treats and table scraps count towards their daily calorie allowance! Many owners forget to include these. If you’re trying to put your pet on a diet, I would recommend cutting out all treats and extra food if possible. This will make it easier to monitor your pet’s food intake. You can use pieces of their actual food as treats instead or use low-calorie treats and subtract these from the daily calorie allowance.


Along with controlling their food portions, exercise plays an important role in weight loss along with improving heart health and building muscle. Many pets that are overweight are less active or sedentary. For dogs, start getting them out on their walks one to two times daily. Don’t overdo it initially, increase their walks by 5 minutes to start and go from there. If your pet is suffering from mobility or health issues, check this with your vet first as increased exercise may not be suitable for them.

In terms of cats, some are extremely active while others like to relax. You can increase your cat’s activity levels by introducing play sessions with their favourite toys. Puzzle feeders and feeding balls are a great way to feed your cat as it makes them eat slower and work for their food.

Exercise is a great way of burning extra calories for pets trying to lose weight. Always introduce this slowly if pets aren’t used to it and consult your veterinarian if they have any pre-existing conditions before starting their exercise regime.

How Much Weight Should I Expect My Pet to Lose?

Pets should lose weight gradually over the course of several months. Monthly weight checks are recommended to ensure that your pet is on track with their diet.

The Association of Pet Obesity Prevention, recommends that dogs lose 3-5% of their body weight per month while cats are recommended to lose 1-3% of their body weight (0.25kg) per month.

It’s important that weight loss isn’t too rapid, as this may cause your pet to lose too much weight or become unwell. Consistency and patience are key to weight loss success.

Effects of Obesity in Pets

Sometimes we may need to remind ourselves why our pet's diet is so important and why we need to persevere. Pets that are overweight or obese are at increased risk of developing certain diseases/conditions such as;

  • Chronic inflammation
  • Diabetes and insulin resistance
  • Osteoarthritis
  • High blood pressure
  • Kidney disease
  • Respiratory disease
  • Cancer

I’m sure you’ll agree that we want to avoid the conditions on the list above for our pets. Being at the correct weight will keep our pets healthier for longer and can increase their life expectancy.


It can be difficult to know if our pet is at the correct weight and if we need to put them on a diet. Using a body condition score, we can assess if they’re carrying extra weight and calculate their daily calorie needs accordingly. By weighing out their food and using portion control, cutting out excess treats and table scraps, and introducing some exercise we can help them to safely lose weight and be healthier.

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