Underweight dogs require careful feeding and attention to restore them to their ideal weight. Underweight dogs do not receive enough nutrients and calories from their diet, and their bodies are in “starvation mode.” An underweight dog is consuming glucose reserves stored in his liver, has slowed his metabolism and is often consuming his own fat reserves to maintain his energy needs.

Causes of Underweight Dogs

Underweight dogs are much less common than overweight dogs in developed countries, but pet owners may still have to deal with a malnourished dog. Dogs may be underweight if they have been strays, or have roamed away from home for an extended period of time.

Medical conditions can result in underweight dogs. Underweight dogs may be suffering from cancer, anemia, pancreatitis (inflammation of the pancreas) or kidney failure. A bowel obstruction due to ingesting foreign matter can also result in malnourishment.

Dental problems can also result in underweight dogs. A dog experiencing pain from tooth decay or gum disease may avoid eating, resulting in unhealthy weight loss.

Veterinary consultation is essential before treating underweight dogs: the problem may be more than a lack of food.

Signs Dogs are Underweight

Severely underweight dogs are pitiful sights. Their ribs can be counted by sight. A healthy dog’s ribs are covered by a thin layer of fat and detectable by running a hand along his side.

A healthy dog has pinkish-red gums. Underweight dogs often have pale or grey gums due to anemia. Anemia may be caused, in turn, through blood loss or accidental ingestion of rat poison.

Underweight dogs also have poor muscle tone and significant loss of both fat tissue and muscle mass. Injuries take extra time to heal and a general lack of energy is noted. Veterinary examination may reveal abdominal pain, metabolic disorders or reproductive disorders.


Underweight dogs are also often dehydrated, especially if they were starving on the streets. To determine if a dog is dehydrated, gently pull on the skin at the base of the neck. A properly hydrated dog’s skin will quickly settle back into position. A dehydrated dog’s skin will “tent” and not settle back quickly. Severe dehydration may require treatment with intravenous fluids.

Refeeding Syndrome

The biggest risk when treating underweight dogs is feeding them too much, too fast. Underweight dogs faced with food will eat as much as they can, which often results in a condition known as “refeeding syndrome.”

Refeeding syndrome results in a number of serious and even life-threatening symptoms, including:

  • damage to the heart muscle
  • heart rhythm irregularities
  • muscle cramps
  • muscle weakness
  • red blood cell rupture
  • respiratory failure
  • seizures.

Feeding Underweight Dogs

To avoid refeeding syndrome, underweight dogs should be fed small meals every six hours, instead of one or two large meals a day. Small amounts of highly digestible puppy food or growth food are recommended. Poor quality dog food often lacks the nutrients underweight dogs require.

Even when feeding underweight dogs a high quality, high protein dog food, nutritional supplements are essential. A malnourished dog should receive vitamin and mineral supplements with every meal.

Veterinarians may recommend supplements that include omega-3 and omega-6 fatty acids. Supplementing the amino acid arginine is also recommended for underweight dogs.

The nutritional requirements for underweight dogs vary depending on the size, malnutrition and health of each dog. Consult with your veterinarian to determine both the size of meal servings and the best vitamin supplements for the dog.

Underweight Dogs: The “Shrunk Stomach” Myth
One popular belief holds that starvation shrinks a dog’s stomach. This is incorrect. Underweight dogs’ stomachs often have extremely sensitive stretch receptor muscles, which send a signal of fullness to the brain. The stomach has not shrunk; the dog receives a “full” signal even if only a small portion of food is eaten. After three to seven days of feeding underweight dogs, the stretch receptor muscles become less sensitive and send more appropriate signals to the brain.