How to help a dog gain weight

We’ve talked about overweight dogs, now let’s talk about what to do if your dog is underweight, which we know is just as worrying. There are a number of reasons why your dog might be underweight, and it can be a struggle to get the weight back on. Some dogs are naturally more lean than others, but sudden weight loss is something to pay attention to. 

Before you change your dog’s diet, the first thing you need to know is whether your pup is truly underweight or not.

To help figure it out, we’ve pulled together some of the common reasons behind weight loss, how to tell if your dog is underweight, what to look out for and how you can get your pup to gain weight healthily. All advice in this blog is backed by my professional insights as a nutritionist. If you’re at all concerned about your dog’s weight, it’s always best to speak to your own vet.

Key takeaways

• The Body Condition Score (BCS) and hand test are effective methods to assess whether your dog is underweight or not.
• If you think your dog is underweight or your dog is not eating, take them to your vet. This can rule out any underlying medical conditions before you adjust their diet.
• Increase your dog’s food gradually and feed them smaller but more frequent meals. This can help with digestion and allow your pup to gain weight slowly and steadily.
• Choose food that is high in protein, healthy fats, and calories. Nutritious meals with 1-2 extra treats are ideal.
• Track your dog’s weight gain by weighing them weekly and recording their progress.

Table of contents

How to tell if your dog is underweight
Why is my dog underweight?
When to speak to your vet
How to help a dog gain weight safely
What to feed an underweight dog
How much should I feed my dog to help them gain weight?
How to track your dog’s weight gain

How to tell if your dog is underweight

It’s not nice to think about underweight dogs, but it always helps to know what that looks like. If your dog is underweight, you’ll be able to see prominent hip, rib and spinal bones. The waist will also be noticeably narrow when you look at them from above. Think of it this way, depending on how pronounced the bones are, the more underweight the dog is. In a healthy dog, a small amount of rib, hip and spine showing is normal. But if you’re in any doubt, always speak with your vet so you know what’s healthy for your individual dog. You can also check out our guide here.

Body Condition Score (BCS) & the hand test

The Body Condition Score test is a way to evaluate fat and muscle coverage to see if your dog is underweight, obese, or healthy. The scale starts at 1 which represents emaciation, and goes up to 9 which represents obesity. If your dog falls between 1-3 then they are classified as underweight and will need more nourishment and calories. A healthy BCS score is around 4-5.

There are two ways to check your dog’s BCS, one is through a visual BCS chart and the other is through the hand test.

The hand test involves using your hand to assess your dog’s weight. If you put your hand into a fist and feel your knuckles, this is what an underweight dog’s ribs may feel like. If you lay your hand flat on a surface and feel your knuckles again, this is what a healthy dog’s ribs should feel like, as they have a thin layer of fat covering them. If you turn your hand over to the palm side and run your finger over it, this is what an overweight dog’s ribs may feel like.

If in doubt, visit your vet who can assess your dog’s BCS score accurately.

Why is my dog underweight?

A tricky start in life

Maybe you recently adopted your dog from a shelter and they’re not in the best condition. Unfortunately not all dogs have the best start in life. Sometimes they need a helping hand to gain weight.

Picky eater

The belief that dogs will eat anything isn’t always the case. Some dogs are fussy with their food and sometimes turn their nose up at what they’re offered. If you feed lots of treats and table scraps, it could be that they’re holding out for something better.

Sickness

Illness or an upset stomach can affect your dog’s appetite and cause them to lose weight. Other health issues like dental disease, injuries and arthritis can also cause weight loss. Chewing and standing up might be too uncomfortable to eat, which can put dogs off their food. If they skip just a meal or two from an upset stomach, there’s usually nothing to worry about. But if it keeps happening and your dog is losing weight, it’s time for a vet visit.

Stress

Just like humans, stress can cause our dogs to pass up on food. Stressful events like a new baby in the home, a new environment or separation anxiety can all be a bit overwhelming.

Intestinal parasites

Making sure your dog is dewormed regularly is really important, as parasites like roundworms or tapeworms can cause your dog to lose weight. This is usually only in severe cases where they’ve had worms for a long time. Your dog may also have bouts of diarrhoea, feel weak and seem constantly hungry.

Over exercise

Too much exercise can lead to unnecessary weight loss as your dog might be consistently burning more calories than they’re taking in. For spritely pups that are naturally energetic and always on the go, this can also cause weight loss. Especially with breeds from working lines, like Springer Spaniels and Collies.

Phobias

Dogs can be a bit sensitive when it comes to feeding time. If something previously spooked your pup around meal times or in the place they eat, they might refuse to eat. Dogs can also go off their food long term if they’ve been seriously unwell, even if they used to gobble down that same food before.

Certain breeds

Just like some breeds are more prone to weight gain, some breeds can struggle to keep the weight on. Sight hounds are a classic example, like Greyhounds, Salukis and Lurchers.

You should see a vet if your dog is eating like normal but isn’t putting on weight, or has sudden weight loss. There may be an underlying medical reason which would need attention.

When to speak to your vet

If your dog isn’t gaining weight or has unexplained weight loss, it’s important to visit your vet to rule out any medical conditions.

Here are some red flags to watch out for:

• Sudden weight loss
• Ongoing diarrhoea or vomiting
• Lethargy
• Loss of appetite

How to help a dog gain weight safely

Increase calories gradually

To help bulk out your dog, firstly you’ll want to choose a quality dog food for weight gain. This will give your dog the right balance of calories and nutrients, so they gain those extra pounds steadily and safely. Sudden increases in food can cause digestive issues, so small and measured increases is the way to go.[1] The best dog food to gain weight will also consider your dog’s age, breed, activity levels, metabolism and more to ensure they get everything they need into their body. However, if your dog does have tummy troubles, it’s important to get to the root cause of the problem first, as a simple change in diet is unlikely to help long term.

Feed smaller, more frequent meals

Give your dog more opportunities to eat throughout the day. Measure out your dog’s daily allowance of food and split it up into 3 or 4 smaller meals. If your dog has low appetite or a fast metabolism, smaller meals more often can help them gain weight over time.

Make food more appealing (without creating bad habits)

For those picky eaters pooches, try making the food more appetising by adding a tasty wet food topper. This will give that added moisture and flavour, along with a few extra calories. Try to avoid using human foods to tempt your fussy pup, as this could make their pickiness worse and even cause tummy upset. You could also try warming their food up and adding in different textures to make their food more appetising.

Offer extra treats in moderation

If your vet has confirmed that your dog’s underweight and needs feeding up, you can give your dog a couple of bonus treats each day to ramp up their calorie intake. Test out a few options to see what kind of treats your dog goes bananas for. Carrots covered in peanut butter (xylitol free) are a good start. Most dogs love peanut butter! Or maybe some cream cheese in a treat toy. My go to is offering a cooked egg, as these are highly digestible and provide high quality calories. When it comes to additional treats, always be cautious with this approach as you don’t want your dog filling up on treats and side stepping their proper meals. This could make your pup’s diet unbalanced and deficient in key nutrients. An extra treat or two a day is the best way to go.

Choose working dog food or puppy food

High-performance or working dog food is a type of dog food that is higher in protein and fats, used to provide nourishment for athletic, working, and underweight pups. If your dog is underweight, they may benefit from working dog food, or puppy food, which is also high in calories and protein. It may be best to add one portion of this to your dog’s diet first before completely switching to these foods. It’s also important to seek advice from your vet before adjusting your dog’s diet.

If you go to your dog’s profile on Tails.com, you can update your dog’s weight and change their BCS to underweight, which means your next order will be higher in calories. You can also speak to our customer service team who can do this for you.

Adjust exercise (build muscle, don’t burn fat)

When it comes to exercise for underweight dogs, it’s all about quality over quantity. It may be a good idea to cut down on longer endurance runs, and switch to shorter activities that also build muscle. You could also introduce mental stimulation sessions in the form of brain games or training to brush up on those skills. 

What to feed an underweight dog

Underweight dogs need more protein and healthy fats, as part of a healthy, balanced diet. You may be tempted to give your dog lots of treats to increase their calories, but this isn’t ideal. Some extra treats can help, but your dog needs a diet that’s nutrient dense, easy to digest and focused on high-quality protein and healthy fats. This is why we suggest working dog food, increasing their portion size or providing smaller yet more frequent meals. [2]

How much should I feed my dogs to help them gain weight?

We recommend increasing your dog’s portion size by 10% [3], and then re-weigh them in one week’s time. If they’ve not gained any weight, you could increase by a further 10% and re-weigh them after one week. If they’re eating but haven’t gained any weight, there may be a medical problem that needs veterinary attention. Remember that a slow and gradual pace is ideal when adjusting your dog’s diet.

How to track your dog’s weight gain

When adjusting your dog’s diet for weight gain, it’s important to track and monitor their progress. It’s best to do weekly weigh-ins and photos to assess your dog’s weight gain. You can also refer to the BCS visual chart and the hand test over time to reassess your pup. Remember that slow and steady progress is ideal.

Supporting healthy weight gain

Overall, if you suspect your dog is underweight, the best course of action is to speak with your vet who can assess your pup and tell you how you can help your dog gain weight healthily. Before you adjust your dog’s diet, it’s important to rule out any health issues and assess their body condition which is why seeking professional guidance is a key step.

Once you’ve decided to change your dog’s diet, make sure to increase the calories safely by increasing their portion by 10% and weighing them in a week’s time to track progress. Make sure to also do weekly weigh-ins, take photos, and jot down your dog’s weight every week to monitor their progress and make sure they’re gaining weight in a slow and gradual way.

Here at Tails.com, our nutritional specialists can update your dog’s BCS to underweight which means you can be offered dog food that’s higher in calories. Speak to our customer service team or you can do this yourself in your online dashboard.

FAQs

How long does it take for a dog to gain weight?

Depending on your dog and their lifestyle, on average a dog can gain between 1 to 5% of their body weight per week. This varies significantly on your dog’s activity levels, age, and other factors.[4]

Why is my dog eating but not gaining weight?

If your pup is eating but isn’t gaining weight, it may mean your dog has an underlying medical condition that needs attention. Gastrointestinal diseases, poor nutrition, and dental problems could be the reason, so it’s important to visit your vet to rule them out.[5]

Is it bad if my dog is underweight?

When a dog is underweight it can increase their risk of muscle loss, a lowered immune system, and poor coat quality, so it’s important to seek professional advice and adjust your dog’s diet if needed to get them to a healthy weight.[6]

Can stress cause weight loss in dogs?

Stress can be a reason why your dog isn’t eating as much, resulting in weight loss. If you think your dog stops eating, take them to your vet.[7]

Should I give treats to help my dog gain weight?

You can offer them 1-2 more treats per day to help increase their calories and coax them into eating, but it’s important to be cautious with this approach so they don’t only eat treats and not nutritious meals.

Sources

[1] ‘What type of food should I feed my dog?’ Blue Cross
[2] ‘What’s the Best Dog Food for Weight Gain?’ PetMD
[3] ‘Strategies to Help Your Malnourished Dog Gain Healthy Weight’ Houndsy
[4] ‘Understanding How Fast Can Dogs Gain Weight: A Comprehensive Guide for Pet Owners’ Houndsy July 2025
[5] ‘Is Your Dog Losing Weight? Common Causes and When It’s Time for a Vet Visit’ PetMD
[6] ‘Your dog’s body shape’ PDSA
[7] ‘Why Is My Dog Not Eating? Causes and What To Do’ PetMD