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How to Fatten Up a Dog: 6 Steps to Gain Weight Safely (Vet Answer)

Written by: Dr. Maria Zayas DVM (Veterinarian)

Last Updated on June 11, 2024 by Dogster Team

a dachshund dog looks sick lying on its owner

How to Fatten Up a Dog: 6 Steps to Gain Weight Safely (Vet Answer)


Dr. Maria Zayas  Photo


Dr. Maria Zayas

DVM (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

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It’s easy to fall into the trap of overfeeding your dog, and a majority of a general practice veterinarian’s day includes coaching owners on how to tell if their dog is eating the right amount of food.

With more ready knowledge and resources available about weight loss, what do you do if you think your dog is looking too lean? Maybe you can tell it’s because they aren’t eating or aren’t keeping their food down, but what if they seem fine except that they’re getting skinnier?

Just putting down some more food isn’t always enough to help these pups, so here’s what you should do.

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How to Know If Your Dog Is Underweight

For most dogs, if we’re asking them to gain weight, it’s because they’re underweight. The problem is that even within a breed, there’s no one perfect weight for every dog. Variations not just by sex but also genetic line can lead to upwards of 50-pound differences between dogs of the same sex and breed that are completely normal and expected. We’ve all met Labradors that barely reach our knees and others that look like they could be taller than you if they stand up straight.

The best way to assess a dog’s weight isn’t by their weight but by their body condition score.

The body condition score uses the physical parameters of a dog’s body to tell if they are within an ideal body condition, underweight, or overweight. The scores come in two forms: 1–9 or 1–5.

Here are some things to remember with these scores:
  • The main difference is the 1–5 score allows for half steps, such as an assigned body condition score (BCS) of 3.5, while the 1–9 score only allows for whole numbers.
  • For the 1–5 score, 3 is normal, 1–2 are various levels of underweight, 4–5 are overweight.
  • For the 1–9 score, 4-6 is ideal, 1–3 is under, 7–9 is over.

An ideal BCS score comes from a dog with a visible waist viewed from above or below in which you can just see the end of the rib cage without touching, but each individual rib isn’t readily obvious and countable without touching. If you lose sight of the ribs entirely or the waistline, that dog would have a higher score. If you can count each rib and see the bony prominences of the hips, that dog would have a lower score.

It is important to keep breed variances in mind. Some sighthound breeds are lean by nature and seeing their ribs is normal. For thick-coated breeds, you may not be able to see a dog’s ribs with an ideal BCS, though you can easily feel them with your hands. Some chonkier and meatier breeds, like some Bulldog breeds, may not have a natural waist.

When in doubt, your dog’s examinations with a vet almost always include an updated BCS score. You can learn where your dog is currently scored so you know what that looks like for them, and then track relevant changes, like gains or losses of their waist or rib prominence.

Thin underweight dog
Image By: Peggy und Marco Lachmann-Anke, Pixabay

What to Do for a Dog Not Gaining Weight

As soon as you notice your dog is losing weight, especially if you try to increase their weight unsuccessfully, it’s time to make a trip to the vet’s office. The first step in getting weight onto a dog is finding out why they’re losing it or not gaining it back. Once you do that, here are some ideas on how to get weight onto your dog.


The 6 Steps to Gain Weight Safely

1. Diagnose and Treat the Cause of Weight Loss or Poor Weight Gain

Some medical causes of weight loss, once treated, will rapidly reduce your dog’s weight problems without any other interventions. Do they need to eat upright because of the megaesophagus? Go on a stool softener and intestinal motility agent for megacolon? Did their diabetes just need treatment? Are they eating the wrong diet for their life stage? Did their teeth hurt, and they needed dental cleaning? Fix the issue, and poof, suddenly, the vet is talking about getting your dog to lose weight instead of gain.

Diagnosis may involve a physical exam, bloodwork, X-rays, ultrasounds, or specialized testing, so be prepared for a hunt in some cases to find the cause.

2. Calorie Rich Diet

Sometimes even after we find the cause and treat it, these dogs are expected to still struggle to gain weight and will need more help. Some severe diseases may not ever be fully controlled with treatment, and others, like cancer, may continue to cause weight loss no matter what we do. Nervous dogs may do okay other than their weight, and it’s more reasonable to focus on their diet than it is to place them on daily anxiety medication.

For these dogs, you’ll want to explore diets that help with weight gain. One of the things I’ll tell my clients is to place their adult dog onto a puppy diet. Each commercial diet for dogs in the US will have an AAFCO statement on the bag that certifies which life stage the diet was formulated for. It may say things like for puppies, pregnant or lactating dogs, adults, seniors, and growth.

There’s also a common statement that you might find on the back of your dog’s food bag if you check, which is “formulated to meet the needs of all life stages” or something similar. AAFCO has two main life stage categories: adult maintenance and growth and reproduction, and if a diet meets the requirements for growth and reproduction, it may be marketed as good for all life stages.

The reason to know all this is that by purchasing a diet with one of these statements, you’ll know it has a nutrient profile that is appropriate and safe for your dog but is purposefully calorie dense and formulated to encourage weight gain. While it’s intended for puppies or pregnant or lactating female dogs, it’s a great tool for choosing a diet for a dog that needs to gain weight as well. A great example of this is Purina Pro Plan’s Performance All Ages Diet.

man checking dog food label
Image By: BearFotos, Shutterstock

3. Spice Up the Diet

In addition to targeting a more calorie-dense diet for your dog, you’ll need to assess how well your dog is eating what you’re offering. Dogs with dental pain may need soft food. Picky eaters may only like certain kibble shapes, canned diets, or specific flavors. Dogs under the weather may need you to use some tricks to entice them to eat.

Warming up fresh or canned diets makes them more fragrant and appetizing. Mixing high-reward treats, lean meats, gravy toppers, warmed wet food mixed into kibble, or anything else they love can encourage them to eat more and help support weight gain.

4. Feed More Meals

When feeding more, it may be more useful to feed more meals throughout the day than to offer a larger meal. Larger meal sizes increase the risk of bloat for large breed dogs. They may also fail to properly digest and therefore absorb nutrients from larger meals. Frequent smaller meals throughout the day are more likely to support good digestion and a willingness to eat just a little more each meal.

underweight young puppy eating from a green bowl
Image Credit: Janis Petranis, Shutterstock

5. Food-Based Enrichment Activities

Why waste play time with your dog when you can use that as yet another opportunity to fatten them up? Instead of offering stuffed toys to chew on, you can give them food-related toys and activities instead. Filling a Kong with pumpkin puree, peanut butter, dog cheese sprays or other loved fillers can give them a fun way to eat more. For dogs who need more of a challenge, you can freeze the Kong and its contents before giving it to your dog.

Lick mats and sniff mats can also keep them occupied pulling out food. Sometimes having to work for it encourages their appetite.

There are also endless puzzle toy options now that you can hide food inside. You can try just treats or put high-calorie items like hot dog pieces inside to further support weight gain. Slowing your dog down as they get their treats can also allow you to give them more without causing an upset stomach.

6. Medication

The last option available is for dogs that have a poor appetite. You can reach out to your veterinarian to ask about appetite stimulant medication; there are a couple of options to see if they would be a good fit for your dog. They aren’t miracle workers, and some types are expensive, but when they work, they can be a lifesaver.

a shih tzu dog being checked by two vets
Image Credit: KongNoi, Shutterstock


Why Might a Dog Fail to Gain Weight?

You’ve noticed your dog is starting to look lean, and you’re worried about them. You’ve been putting down more food for them, but it’s just getting worse. What could be going on?

1. There are lots of reasons a dog might struggle to maintain weight.

If they’re going through a stressful event or are anxious by nature, they can burn more calories and tend to run lean. If they are also picky eaters, this trouble can compound itself with them becoming chronically underweight.

2. Parasites are a classic reason for a dog to lose weight despite eating well.

Intestinal parasites, in particular, will steal nutrients the dog would otherwise absorb themselves. It isn’t uncommon for GI parasites to cause vomiting or diarrhea as well, which further interferes with nutrient access for the dog.

Rhodesian Ridgeback dog sick with vet
Image Credit: Zontica, Shutterstock

3. Similar to parasites but scarier, cancer can also cause rapid weight loss that you can’t seem to turn around.

Cancer cells have a higher metabolic rate than regular ones, meaning they’re burning through calories like it’s their job, because it is. Some dogs may not show other signs of illness, and some may develop a poor and dull hair coat, lethargy, chronic vomiting or diarrhea, and maybe even visible masses.

4. Other systemic diseases can also lead to weight loss in dogs.

Sometimes this is because they can cause muscles to atrophy, like with chronic kidney disease. Other times illness can make a dog feel dumpy which can lead to anorexia, vomiting, or diarrhea, such as with diabetes or Addison’s disease. There are many types of diseases that can link back to loss of appetite, nausea, or diarrhea, and any of them can therefore cause indirect weight loss.

5. Some dogs lose weight because they aren’t on the proper diet.

Nutrient deficiencies can cause illness which may put a dog off their food, but diets for the wrong species or stage of life can also be the culprit. Puppies eating an adult-only diet are likely going to fail to gain weight. Dogs with a food allergy eating a diet with their allergen in it may chronically do poorly.

dog not eating its food
Image Credit: Daria Lixovetckay, Shutterstock

6. Always remember some breeds already just run lean.

These dogs, if faced with any of the above, will fall underweight faster than other breeds and may have a smaller tolerance for changes or being ill. If these dogs are in an especially active part of their year, such as the warmer months, they may cyclically fall underweight, so you may need a plan for fattening them up only as needed.

7. Some dogs are born with or develop anatomical abnormalities that keep them from digesting food properly.

A condition called megaesophagus will keep food from efficiently making it to the stomach and the intestines, and they will instead chronically regurgitate their food. These dogs almost always present to their vet underweight and ravenous. On the opposite end of the body, a megacolon can cause an accumulation of stool that doesn’t pass efficiently. As these dogs become constipated, they can go off food or even start vomiting, and this condition is often linked to nutrient absorption problems in the intestines also.


How to Know If Your Dog Is Gaining Weight

Now that you have a plan in place to fatten up your dog, how can you best go about tracking weight gain?

For dogs, it isn’t recommended to weigh them more than once weekly unless otherwise advised by your veterinarian. Furthermore, you’ll want to track progress on a monthly schedule instead of anything shorter. Dogs can go through appetite cycles that are several days long, where they eat very little for a couple of days but then make up the calories a couple of days later. You’ll save yourself a lot of stress if you look at weekly, or even better, monthly trends instead of the minutiae.

When weighing your dog, you have a few options, but be sure to use the same scale every time. Most veterinary clinics will let you swing by the clinic to use their dog scale, which is especially helpful for large dogs. You can purchase a large dog scale to keep at home also as there are several affordable options. When able, you can also weigh yourself on a bathroom scale, then weigh yourself holding your dog, and then subtract out your weight to find your dog’s weight.

It’s also a good idea to familiarize yourself with one of the BCS scoring systems and score your dog weekly or monthly to help you track their weight as well. Keeping a journal of this data can also track daily appetite, signs of illness, treatments, and the response to different interventions you try.



Fattening up a dog can be a more serious undertaking than you’d think, but luckily, there are many ways to go about it. Always start with a vet visit to get to the bottom of what’s going on and treat any underlying issues. Then, for dogs that need more help, you can use this list to help find the best ways to get more calories into your dog. Make sure you track their changes and have an idea of what normal looks like for them if they reach it, and keep their veterinary team informed on their progress.

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Featured Image Credit: Leka Sergeeva, Shutterstock

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