Many health problems can lead to weight loss, especially in older dogs. This article covers the most common causes of weight loss and when to see a vet.
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Whether your dog is losing weight but eating normally, suffering from a reduced appetite, or even losing weight despite always being hungry, unexpected weight loss is a common cause for concern.
In this article we’ll take a look at the most common causes of weight loss in dogs, why they can cause your dog to lose weight and when it’s time to see a vet.
If your dog is losing weight despite being fed their usual diet, it’s likely there’s a health issue that needs addressing.
For a dog to lose weight, they must be expending more energy than they take in through food. In simple terms, this means they’re either experiencing reduced appetite, struggling to absorb the nutrients they take in, or using more energy than normal.
With the exception of dogs adjusting to a significant increase in activity, weight loss typically indicates an underlying disease process that’s causing one or more of these changes.
A degree of weight fluctuation is normal in healthy animals, but a significant or sustained unexplained weight loss should prompt a vet visit.
This includes slow and steady weight loss over months or even years, which is especially common in older dogs with long-term health issues like chronic kidney disease. While a sudden drop in weight is often noticeable, visually tracking your dog’s weight on a chart can help to identify longer-term trends.
An older dog losing weight should see a vet as soon as possible, as they are more likely to suffer from many health issues and can struggle to regain lost weight. It’s also worth seeing your vet sooner rather than later if you’re noticing other symptoms alongside a dip in weight, such as increased thirst, a change in appetite, lethargy, vomiting or diarrhoea.
Intestinal parasites including roundworms and tapeworms can cause dogs to lose weight. While some dogs may show gastrointestinal signs such as diarrhoea or vomiting, others may only experience weight loss. Their appetite may be increased due to a lack of nutrients or reduced due to discomfort associated with the worms.
Worms may be visible in faeces but they aren’t always easy to spot. A broad spectrum wormer is typically very effective in treating intestinal worms. However, not all products treat all types of worm, so it’s best to seek advice from your vet on the best treatment.
Find out more about parasite treatments in dogs.
Chronic kidney disease, liver disease, pancreatitis and infections can all cause weight loss in dogs. Many of these conditions become more common with age, but chronic diseases can affect young dogs too.
Other symptoms may include reduced appetite, vomiting, diarrhoea and increased thirst, but for some dogs weight loss may be the main concern. Investigating weight loss can help to diagnose these conditions at an early stage. Catching chronic diseases as soon as possible can significantly improve their response to treatment.
Diabetes mellitus is a relatively common hormonal condition in dogs. It’s most common in middle-aged dogs and is typically immune-mediated, meaning it can develop in any dog without a specific cause.
It causes significant weight loss, usually alongside a significant increase in thirst and urination. Affected dogs may also have an increased appetite, develop cloudy eyes and be susceptible to infections. Without treatment, diabetes can be fatal, but most dogs diagnosed at an early stage respond well to insulin treatment.
Addison’s disease (hypoadrenocorticism) can also cause weight loss, alongside waxing and waning gastrointestinal symptoms, weight loss and potentially collapse. Again, this condition is usually manageable with medication, especially if diagnosed at an early stage.
Conditions such as Inflammatory Bowel Disease (IBD) and Exocrine Pancreatic Insufficiency (EPI) affect digestion and reduce the absorption of vital nutrients. Alongside weight loss, other symptoms including vomiting and diarrhoea are frequently seen.
These conditions can be managed effectively with medication, but diagnosis often relies on excluding a number of other potential causes of weight loss.
While dogs of any age can be affected by this, for an older dog losing weight it’s important to try to rule out cancer.
Weight loss is a common symptom of various types of cancer, as nutrients are diverted to tumour growth. Cancers can also interfere with the normal function of organs such as the liver, resulting in other symptoms such as vomiting and diarrhoea.
Seeking veterinary advice is essential for any dog that’s unexpectedly losing weight, but this is especially important for an older dog losing weight over weeks or months.
The early stages of heart disease are unlikely to cause weight loss, but heart failure frequently causes weight loss as a result of muscle loss (cachexia).1 This is caused by a combination of reduced food intake, increased energy use and inflammation.
Dogs suffering from heart failure usually show other symptoms, including exercise intolerance, increased panting, increased breathing rate at rest, coughing or even fainting episodes. Early treatment can slow the progression of heart disease, so it’s best to see a vet sooner rather than later.
Surprisingly, even significant dental problems are relatively unlikely to cause weight loss in dogs. The pain associated with dental disease can be severe but is usually chronic, meaning many dogs are stoic and simply learn to live with it.
However, occasionally dental disease can either become so severe, or worsen rapidly enough, that it causes a noticeable change in a dog’s appetite. This can contribute to weight loss, but your vet may recommend testing to rule out other, more common causes of weight loss.
If you’ve been in significant pain in your life, chances are you didn’t feel like eating much. Unfortunately, it can be challenging to pick up on the signs of pain in dogs. While acute pain is often obvious, pain associated with chronic conditions like arthritis is insidious, and often written off as ‘normal’ age-related slowing down.
Pain doesn’t cause weight loss in all dogs, but is something to discuss with your vet if your dog’s appetite is reduced and no other cause is identified.
An increase in activity can help dogs to lose weight, but doesn’t usually cause drastic weight loss, or result in a dog being underweight.
Young, working breed dogs are an exception to this. It’s not uncommon for very high energy dogs working for long periods of time to struggle to maintain a good weight. If you suspect this applies to your dog, it’s still worth seeing your vet to discuss their nutrition and rule out health concerns.
It’s vital for your dog’s health to feed them a complete diet, with the right balance of all the nutrients they need.
The energy density of dog foods varies, so if you switch diets it may take time to work out exactly how much of the new diet your dog needs to maintain their weight. It’s important to remember that feeding guidelines on pet food packaging are just that: guidelines. Depending on your dog’s activity levels and metabolism, they may need more or less than the recommended amount.
It’s also important to ensure your dog is getting enough food for their activity level. If you increase their activity, you’ve switched who’s feeding them and they’re getting smaller scoops, or another pet is pinching their food, they’re likely to lose weight.
Finally, the effect of stress and anxiety is easy to underestimate. While some dogs may clear their bowl regardless, for more anxious or less food-motivated dogs, stress can significantly reduce their appetite.
Dogs may be stressed by major changes like moving house, or even relatively minor changes like the noise from building work next door. If you think your dog’s weight loss may be stress related, your vet can advise you on ruling out other conditions and helping to manage their anxiety.
Unexpected weight loss in dogs can be a sign of various underlying health issues, some of which may be serious. With early diagnosis and appropriate treatment, these conditions can often be either cured or managed effectively, keeping your dog healthier and happier for longer.
Various conditions could cause your dog to lose weight despite eating normally. If they’re not up-to-date with their worming treatments, your vet may recommend ruling out intestinal worms first. However, other conditions such as diabetes can cause your dog to lose weight without a reduced appetite, and can cause severe illness if left untreated.
If you find yourself thinking, “my dog is losing weight but eating normally. Should I be worried?” it’s best to see your vet as soon as possible. They can fully assess your dog and work with you to plan the best course of action.
It can be difficult to know when to see your vet about your dog losing weight. Tracking your dog’s weight visually can help you to spot long-term trends, assess your dog’s normal level of weight fluctuation and visualise how significant any drop in weight is.
Normal weight fluctuation for dogs is often quoted as up to 5-10%, so any weight loss over 10% should prompt a vet visit. You should also see your vet if you’ve noticed your dog losing weight rapidly over a short period of time, even if they’ve not lost 10% of their weight.
It’s worth noting that some dogs may lose muscle mass despite their weight not dropping significantly. Conditions such as heart failure, hormonal disorders and arthritis may cause your dog to lose muscle but maintain their weight, at least temporarily, due to other factors like fluid retention. If you notice your dog’s body changing, it’s worth seeking advice from your vet.
Gradual weight loss is common even in healthy older dogs. However, in many older dogs weight loss indicates an underlying health issue - so how can you tell the difference?
Normal weight loss in older dogs is typically very gradual, and shouldn’t be associated with other symptoms like gastrointestinal upset, increased thirst or lethargy. Arthritis is a common cause of both weight gain, due to reduced activity, and weight loss as muscle is lost and appetite is reduced.
It’s best to discuss the possibility of an underlying condition with your vet, as early management of health issues in older patients can significantly slow their progression. Your vet can also advise on the best nutrition for your older dog, as they often benefit from a senior or geriatric diet with higher energy density and more easily digestible proteins.
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Slupe, J.L., Freeman, L.M. and Rush, J.E. (2008), Association of Body Weight and Body Condition with Survival in Dogs with Heart Failure. Journal of Veterinary Internal Medicine, 22: 561-565. https://doi.org/10.1111/j.1939-1676.2008.0071.x
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