How can I safely help my dog gain weight?

The right approach depends on why they are underweight in the first place, so it is best worked out with your vet rather than simply increasing food, which will not help if there is an underlying medical cause reducing how much your dog absorbs or wants to eat.

Is it normal for some breeds to look thinner than others?

Yes — naturally lean, athletic breeds like sighthounds can look thinner than a stockier breed while still being a perfectly healthy weight, which is exactly why body condition scoring by feel matters more than comparing your dog's shape to another breed.

My puppy looks thin — is that a problem?

Growing puppies can go through lankier phases as different parts of their body grow at different rates, but a puppy who is not gaining weight steadily overall, or seems weak or lethargic, should be checked by a vet rather than assumed to be a normal growth phase.

Is my dog underweight?

You can get a good sense of whether your dog is underweight by feel rather than a scale: you should be able to feel the ribs easily under a thin layer of fat, see an obvious waist from above, and see a clear tuck where the belly rises up behind the ribcage. If the ribs, spine or hip bones are sharply visible with no covering at all, that points towards underweight rather than lean.

How to actually check

Run your hands along your dog's ribcage with light pressure — you should feel the ribs without having to press hard, but they should not be sharply visible or feel like there is nothing over them. Look down at your dog from above and you should see a visible narrowing at the waist behind the ribs.

From the side, there should be a clear upward tuck where the belly rises towards the back legs, rather than a straight line from chest to hips. A dog who fails all three checks towards the thin side — prominent bones, no waist visible because there is no fat to lose, an exaggerated tuck — is more likely to be genuinely underweight than simply lean.

What commonly causes it

A dog can be underweight simply because they are not being fed enough for their size and activity level, which is the most straightforward cause to fix once identified. Working and very active dogs in particular can need more food than owners expect to maintain a healthy weight.

Underlying health issues are another common cause — dental pain making eating uncomfortable, parasites, digestive problems that prevent proper nutrient absorption, or a range of other conditions that reduce appetite or the body's ability to use the food eaten. This is exactly why persistent unexplained weight loss needs a vet's involvement rather than just more food.

When to see a vet

Any unexplained weight loss, or a dog who is eating normally but still losing weight, warrants a vet visit rather than assuming more food will fix it. A vet can rule out or identify a medical cause and advise on a genuinely appropriate plan for your individual dog.

If your dog is simply lean rather than losing weight, and you are unsure which side of that line they fall on, a vet or veterinary nurse can check their body condition score accurately at a routine visit, which is a more reliable read than trying to judge it yourself.

Common questions

How can I safely help my dog gain weight?: The right approach depends on why they are underweight in the first place, so it is best worked out with your vet rather than simply increasing food, which will not help if there is an underlying medical cause reducing how much your dog absorbs or wants to eat.
Is it normal for some breeds to look thinner than others?: Yes — naturally lean, athletic breeds like sighthounds can look thinner than a stockier breed while still being a perfectly healthy weight, which is exactly why body condition scoring by feel matters more than comparing your dog's shape to another breed.
My puppy looks thin — is that a problem?: Growing puppies can go through lankier phases as different parts of their body grow at different rates, but a puppy who is not gaining weight steadily overall, or seems weak or lethargic, should be checked by a vet rather than assumed to be a normal growth phase.

Sources

Written against guidance published by UK veterinary and welfare organisations. Always confirm specifics with your own vet.

Written by Matt Garnett, who runs Giddy Pets and is a lifelong pet owner — not a vet. This is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your animal. How we write these guides.