My Dog Eats But Does Not Gain Weight, What Is Wrong?

Dogs like Greyhounds have a naturally lean build, so it's really unusual to see them overweight. But if our dog isn't one of these breeds, eating without gaining weight is a reason for concern.

It can simply come down to an imbalance between the amount of energy they get from food and the amount they burn. But other times, eating without gaining weight is a sign of serious diseases that can seriously harm their health. Let's take a detailed look at the main ones.

Your dog's diet

If we notice our dog eats but doesn't gain weight, the first thing to look at is their diet. A newly weaned puppy can't eat the same as a sedentary adult dog or a senior one. Because of this, a dog won't eat the same food throughout their whole life.

Each life stage has different nutritional needs. That's why the diet needs to match our dog's life stage. If we choose commercial food such as kibble, canned wet food, or dehydrated meals, we'll find a wide variety on the market. If we're unsure which to choose, we should check with the vet.

We should also always start by giving the amount the manufacturer recommends:

• Recommended daily food amount for a dog

Depending on whether the dog gains or loses weight, we can adjust the portion. If we choose to feed homemade food, it's essential to consult a vet specialized in nutrition to make sure the menu is properly balanced.

Your dog's physical activity

With a quality diet suited to the amount the dog needs to meet their requirements, they shouldn't have weight problems. If they do, it's time to look at how active the dog is.

Given today's lifestyle, it's much more common to find overweight or even outright obese dogs, as a result of too little activity. But the opposite can also happen. If the dog exercises a lot, the amount of food appropriate for their age and weight might not be enough.

These are dogs that take part in hunting outings or competitions like agility. If this is our case, we should rethink the whole menu, not just increase the amount. Some dog food brands make special products for high-energy-output dogs.

Intestinal parasites causing thinness

First, let's highlight intestinal parasites as one of the reasons a dog might struggle to gain weight even while eating normally. These worms feed off the dog, which is what causes their physical condition to decline. This problem is more common in puppies or in adults weakened for some other reason.

• Everything about intestinal parasites in dogs

We may notice they're thin and have a bloated abdomen. Vomiting and diarrhea or loose stools can also occur. The most severe infestations cause anemia. To avoid this problem, it's essential to deworm the dog regularly, as directed by the vet.

When food doesn't reach the stomach

The esophagus is the tube that carries the food a dog swallows down to their stomach. In the disorder known as megaesophagus, this tube becomes enlarged and, instead of moving food along, it builds up there. The dog eats — in fact, they'll go to their food bowl completely normally.

But in reality, though it can go unnoticed, they regurgitate and re-swallow what they've brought back up. Puppies can suffer from congenital megaesophagus. These puppies will appear malnourished and stunted. It's essential to see a vet. In some cases, surgery may be an option.

When food doesn't agree with them

Sometimes dogs eat normally but lose weight because something is irritating the stomach. This is what happens with chronic gastritis. Dogs may show vomiting as a symptom, but since it happens sporadically, it can go unnoticed.

This gastritis develops as a result of food allergies, ongoing ingestion of irritating things like grass or paper, hairballs, foreign objects, and so on. So even if we don't notice any symptoms, if we do see our dog losing weight, they need to go to the vet.

A damaged stomach, another likely cause

A gastroduodenal ulcer causes damage to the digestive tract. It causes sporadic vomiting that, given how infrequent it is, might seem unimportant to us — unless it contains blood. The dog will eat but will keep losing weight and become anemic. Ulcers often occur in dogs taking corticosteroids.

More common than ulcers are what are known as inflammatory bowel diseases. In these cases the dog eats but loses weight and shows other symptoms such as chronic diarrhea, anemia, and malnutrition.

Malabsorption occurs, meaning that even though the dog eats, even ravenously, they can't absorb all the nutrients they need, or can't properly digest their food. Either way, a vet visit is needed, moving on to a specific diet.

Other common diseases behind this

Digestive disorders aren't the only thing that can cause a dog to eat, even more than usual, without gaining weight. Different systemic diseases can affect the whole body, with weight loss as one of their symptoms. A vet visit is needed.

Here are some of the main ones:

• Exocrine pancreatic insufficiency: the pancreas helps with digestion. If it's not working properly, the nutrients the dog eats can't be absorbed. There are various causes. It's typical for the dog to eat ravenously while still losing weight, and they'll also have diarrhea. This is usually treated with diet and supplements.
• Diabetes: in this condition, insulin production is insufficient. Since insulin's job is to let glucose enter cells, without it glucose builds up in the blood — this is hyperglycemia. The dog's appetite increases at the start of the disease, but they lose weight. They also drink and urinate more. It's treated with diet and insulin injections.
• Dilated cardiomyopathy: this disease causes the heart to enlarge, affecting how it works. The dog loses weight quickly, seems tired, and coughs. Treatment aims to support heart function and manage symptoms.
• Heartworm disease: this disease is caused by worms that settle in the heart, transmitted by a mosquito. Clinical signs depend on how severe the infestation is. The dog tires easily, coughs, loses weight, and has trouble breathing. Treatment is very delicate and is set case by case. Efforts focus on preventing infection by repelling mosquitoes.
• Kidney failure: due to a chronic failure of the kidneys. Sick dogs drink and urinate more, their coat looks poor, they may vomit, and in some cases stop eating. It's treated with diet and appropriate medications based on the symptoms present.
• Cancer: cancer is more common in older dogs. Many tumors are visible as lumps. But when they develop inside the body, symptoms are nonspecific, such as weight loss, vomiting, diarrhea, or constipation. Annual vet check-ups are recommended for early detection.

Bibliography Carlson and Giffin. 2002. Manual práctico de veterinaria canina. Madrid. Editorial el Drac.