— By Dr. Perry Jameson
One of the most common problems of pets that are brought to me (Perry Jameson) is weight loss. The reason for this is almost any disease process can result in loss of weight.
To figure out the cause for any problem, I like to break down the issue into groups that make it easier for Mom and Dad — and me — to understand. So for weight loss, I break it down into the following three categories: not eating enough calories, not absorbing the calories eaten and increased metabolism (using more calories than you eat).
- Not enough calories
Finding out if a pet is eating enough calories is not as easy as it sounds. In my home, we have multiple pets. I feed them all at the same time. So I make the assumption if they are showing up for a meal, they are eating normally. This is not a good way to assess food intake.
For many diseases, there will be a gradual drop in what they eat. If the change is small enough each day, even a more attentive pet owner than me may not notice. The best way to assess for changes is to isolate them from other pets while they eat and to measure the amount.
Last week, a 14-year-old dog was brought to me for weight loss. In questioning Mom and Dad, they related to me that he was eating everything they were feeding him and appeared normal otherwise.
About six months prior, they had changed his diet. I told them to start offering him more food. He has already gained 3 pounds. They were inadvertently starving him as the new diet had less calories per cup than his previous food.
- Not absorbing calories
To absorb calories, the food must be broken down into a small enough size to cross over the cell walls into the blood or lymphatics, which are small thin channels similar to blood vessels that collect and carry tissue fluid (called lymph) from the body to ultimately drain back into the blood stream.
In some pets, they will not produce enough pancreatic enzymes to adequately digest their food. So even if they are eating plenty, it cannot be absorbed. Depending on the degree of enzyme deficiency, the stool may be normal looking to watery diarrhea.
If there is inflammation or cancer of the intestinal wall, this may prevent absorption of calories even if digested properly. Inflammatory bowel disease is the most common condition resulting in malabsorption. This is where there is inflammation of the intestinal wall without infection. We do not understand what happens to turn the immune system on. It may be a reaction to something in the food or an inappropriate response to the normal bacteria that live in the intestines. Regardless, the inflammation prevents adequate calorie absorption.
Lymphoma is the other most likely cause of malabsorption. This cancer can show up almost anywhere, and when the intestines are involved, decreased caloric absorption is a result. Unfortunately, we cannot cure this in pets but they often respond well with few side effects to chemotherapy.
Biopsies are required to diagnose intestinal disease. We can obtain these both surgically or endoscopically.
Surgery allows for larger samples and for samples from anywhere along the GI tract to be obtained so we are almost guaranteed to get the answer. The drawback to surgery is it's harder on the pet and is not an outpatient procedure.
The other option is endoscopy. This can be done as an outpatient and since there are no incisions, there is no discomfort afterward. The drawback is the samples are small and only a portion of the intestines can be sampled.
- Increased metabolism
Increased metabolism is where the pet is eating adequate calories and absorbing them completely but is still losing weight. The most common cause in cats is hyperthyroidism. These cats often have an insatiable appetite with marked weight loss.
Heart failure may result in weight loss as well. The heart is a powerful muscle that requires calories to function. If it is working harder than normal, it will use more calories. These pets also will be in heart failure. So not only will they be losing weight, they will have trouble breathing.
Unless you are trying to get your pet to lose weight, weight loss is not normal. The sooner you find out the cause, the more likely for a better outcome.
