Dog losing weight but still eating? Causes and warning signs

If your dog is losing weight even though you haven't changed anything about their food or exercise, have them examined by a vet soon – if vomiting, diarrhoea, unusual thirst, lethargy or loss of appetite come with it, don't wait. Possible reasons range from too little energy in the bowl and problems with the teeth, digestion or parasites to diseases such as diabetes. Only once the cause is clear do you gradually increase the food amount towards the target weight.

This article is about unintentional weight loss. If, on the other hand, you want your dog to slim down on purpose, you'll find everything you need in our guide Helping your dog lose weight: a diet plan.

A dog that is slowly losing weight often still seems fit for a long time. So what matters is what else comes along with the weight loss.

Straight to your vet or an emergency service

• Your dog is drinking and peeing noticeably more and seems lethargic and weak, is eating poorly or breathing heavily. In diabetes, these can be signs of a metabolic crisis called ketoacidosis – an emergency.
• They're vomiting, seem listless and weak or have abdominal pain – possibly together with diarrhoea. This is what severe inflammation of the pancreas (pancreatitis) can look like, for example.
• They've stopped eating altogether. How long you can wait, depending on age and size, is explained in our guide Dog not eating: reasons and a self-check.

Have it checked soon, even if your dog seems fit

• They're losing weight even though they're eating normally or even more.
• They keep getting diarrhoea or have it for a longer time, or their stools are pale, soft and unusually plentiful.
• They're drinking more than usual.
• Eating is difficult for them, for example because their teeth or mouth hurt.
• Their back, shoulders or hips feel bonier than before – a sign of muscle loss.
• They're a puppy. Puppies should be growing and putting on weight; if a puppy loses weight, have them seen soon.

The nutritional assessment guidelines of the AAHA, the American Animal Hospital Association, give you a point of reference: there, unintentional weight loss of more than 10% of body weight counts as one of the risk factors that should be investigated more closely. For a 20 kg dog, that's 2 kg; for an 8 kg dog, 800 g. This mark isn't a waiting period: if other symptoms come with it, go sooner.

Weighing your dog regularly helps you notice weight loss in the first place. Especially with long fur, you won't see a few hundred grams less.

A dog loses weight when they take in or can use less energy than they burn. Sometimes there's something simple behind it, sometimes a disease. This overview doesn't replace an examination, but it helps you sort your observations before you see the vet.

Too little energy in the bowl

The most harmless cause is a calculation that no longer adds up: a new food with fewer calories per 100 g, more exercise than before or a second dog who eats some of the food too. Even among dry foods, typical values range from roughly 330 to 400 kcal per 100 g – what counts is the figure on your packaging. Compare the daily amount with what your dog needs, and let the calculator work out the figure: work out your dog's calorie needs.

When eating hurts: teeth and mouth

The AAHA guidelines explicitly list dental disease as a nutritional risk factor. A dog who is in pain when chewing may eat less than what goes into the bowl. A look at the mouth and teeth is therefore part of the check-up.

When the food isn't absorbed: digestion and gut

Typical signs of a problem with digestion or absorption in the gut are diarrhoea and weight loss, even though the dog is eating well or even more. But the absence of diarrhoea doesn't rule out a serious gut disease. Possible causes include chronic inflammation of the gut, infections, parasites such as hookworms or Giardia, and tumours in the gut such as lymphomas. A faecal test for parasites is therefore part of the check-up.

Exocrine pancreatic insufficiency (EPI) plays a special role: the pancreas produces too few digestive enzymes, so the food isn't broken down properly. Affected dogs often eat a remarkable amount and still lose weight, they have diarrhoea, and their stools are usually pale, soft and bulky and can smell unpleasant. In German Shepherds, Rough Collies and Eurasiers, the most common cause is a wasting away of the enzyme-producing tissue, and they usually develop it as young adults. In other breeds, long-standing inflammation of the pancreas is more often behind it. EPI is diagnosed with a blood test, and with the right treatment, affected dogs usually put weight back on quickly.

Metabolic and general diseases

With diabetes mellitus, increased thirst, frequent peeing, a bigger appetite and weight loss are typical signs. The disease often develops gradually, so it's easy to overlook at first. It's diagnosed through raised sugar levels in the blood and urine.

Many other general diseases tend to come with a poor appetite. Heart and kidney disease or cancer can also lead to muscle loss, known as cachexia – even in dogs that eat normally. Which values are checked is decided by the vet based on the examination and your dog's history.

Muscle loss in old age

Even healthy older dogs have less muscle than young ones; this is called sarcopenia. The remaining muscles also work less well, so the dog becomes weaker and recovers more slowly from illness or surgery. But because the same muscle loss can also be caused by disease, you shouldn't simply put it down to age. What changes about feeding in later life is covered in our guide Senior dogs: gently adapting their diet.

The scales show you that something is changing. Whether your dog is too thin is shown by the Body Condition Score (BCS) on the 9-point scale of the WSAVA, the World Small Animal Veterinary Association. 4 to 5 out of 9 is ideal; scores of 1 to 3 mean underweight:

How to check for yourself:

1. Ribs: Place both hands flat on the sides of the chest and stroke back and forth with light pressure. At ideal weight, you can feel the ribs under a thin layer of fat. If you can feel them with no padding at all, or can even see them, the BCS is 3 or lower.
2. Waist: Look down at your dog from above. A waist behind the ribs is what you want to see. A very pronounced waist with protruding pelvic bones suggests underweight.
3. Back and pelvis: Run your fingers along the spine in the lower back and feel the pelvic bones. If the tops of the vertebrae are visible and the pelvic bones stick out, your dog is too thin.

With medium-length to long fur, looks can easily deceive – then the only thing that helps is feeling with your hands.

Checking the muscles: the Muscle Condition Score

The BCS assesses fat. For muscle, there's the Muscle Condition Score (MCS), which the nutrition guidelines also recommend. It distinguishes between normal muscle and mild, moderate and marked muscle loss. You can assess it yourself by feeling along the back, head, shoulders and hips. The muscles to the left and right of the spine usually waste away first – so that's where you start.

The two scores aren't directly linked. A dog can be overweight and still be losing a lot of muscle; conversely, a slim dog can have normal muscle. A healthy dog that eats too little mainly loses fat; a sick dog, by contrast, mainly loses muscle. So if your dog is getting bonier along the back and hips even though the ribs are still well padded, tell your vet. Muscle loss that's spotted early is easier to treat.

More food is only the second step. If a digestive disorder or disease is behind it, your dog will keep losing weight despite bigger portions – dogs with EPI often eat a remarkable amount already. Once the vet has found or treated the cause and set a target weight, here's how to go about it:

1. Calculate the requirement at the target weight. The starting point is the calorie requirement your dog would have at their target weight. An example for an adult, neutered, normally active dog: they weigh 9 kg and their target weight is 10 kg. To maintain 9 kg, they would need around 580 kcal a day; at the target weight, around 630 kcal. With a dry food containing 360 kcal per 100 g, that's about 175 g instead of 160 g. The calorie needs calculator gives you the figure for your dog – as a starting point, because dogs differ a lot.
2. Increase in small steps. Raise the amount over several days, not from one day to the next. If you spread the daily amount over two to three meals, each individual portion doesn't suddenly get much bigger.
3. Work with the figure on the packaging. What counts is the kcal per 100 g stated on your food, not the feeding recommendation for a different product.
4. Weigh regularly. Once a week, ideally on the same scales, at the same time of day and before a meal. Small dogs are easiest to weigh by weighing yourself first on your own and then with your dog in your arms. Every few weeks, also check the BCS and muscles.
5. Adjust together with your vet. How quickly your dog should gain weight and when the amount gets adjusted is something to discuss with the vet. Once the target weight is reached, feed the amount that maintains it.
6. Keep the muscles in mind. Exercise helps maintain muscle. How much of it is right is something to clear with your vet first – especially for older or ill dogs.

Dog too thin: do home remedies help?

There's no home remedy that fixes the cause. Some well-meant tips do more harm than good:

• Leftovers from the table: Large amounts of table scraps are considered a common risk factor for inflammation of the pancreas. The nutrition guidelines also list snacks, treats and table scraps as a risk factor as soon as they make up more than 10% of daily calories.
• Simply doubling the portion: If the problem lies in digestion, more food won't help. And without doing the maths, you won't know how much energy is really being added.
• Lots of extra protein for the muscles: When it comes to maintaining muscle, more protein isn't automatically better. What's right depends on your dog's age and health.

What helps instead is unspectacular: a balanced complete food in the amount that suits the target weight, weekly weighing and a little patience. Whether a different food makes sense depends on the cause – that's for the vet to decide.

Once the cause is clear and you're cooking for your dog yourself, the DoggoMeal app calculates recipes with gram amounts to suit their weight and target weight – including when they need to put weight back on. Get the app.