Causes of Unexplained Weight Loss

At some point in our life, most of us have often experienced some unintentional or unexplained weight loss. While weight loss, unexplained or not, is generally welcomed by most of us, there are certain causes behind this that may prove to be dangerous. This is why it is important to always pay attention to unexplained weight loss. Losing over five percent of your body weight within just six to seven months, especially if you are not trying to lose weight, can point towards several underlying causes such as thyroid issues, infections, to even cancer. If you are not actively trying to lose weight, then you must consult your doctor to find out the causes of unexplained weight loss. Let’s a take a look at some potential causes that may lead to unexplained weight loss.

What is Unexplained Weight Loss?

To begin with, it is first important to understand what is defined to be unexplained or unintentional weight loss. Unexplained weight loss is typically defined as a loss of about 10 pounds, roughly five percent of the body weight, over a time period of six months to a year. This weight loss happens without you actively following a regime to lose weight or without even trying to lose weight. This should also not coincide with the start of any exercising program or routine that could possibly explain the reason behind losing weight.

This weight loss, though, may occur due to changes in appetite, or due to the fact that your body is using certain nutrients differently, indicating, again, an underlying problem within such as a change in your metabolic rate or an underlying tumor.

So what can be the potential causes of unexplained weight loss?

Causes of Unexplained Weight Loss

Causes of Unexplained Weight Loss


An overactive thyroid, also known as hyperthyroidism, is a condition where your thyroid gland starts making too much of the thyroid hormone. The thyroid hormones are responsible for controlling several functions in the body, particularly your metabolism.

When you have an overactive thyroid, you will start burning up calories faster than usual, even if you maintain a healthy appetite. This often causes unintentional weight loss.

Some of the potential causes of hyperthyroidism could include:

Some other symptoms of hyperthyroidism include:

  • Anxiety
  • Irregular or fast heartbeat, or both
  • Fatigue
  • Lighter than normal periods in women
  • Hand tremors
  • Heat intolerance
  • Sleeping disorders

Hyperthyroidism can be treated depending on the severity of your condition and also on your age with the use of anti-thyroid medications, surgery, beta-blockers, as well as radioactive thyroid.

Muscle Wasting or Muscle Loss

A condition known as muscle wasting or muscle loss can also cause unexpected weight loss. Characterized by unnatural muscle weakness, you may also find that one limb looks smaller than the other in this condition.

It’s important to consider the fact that the human body is primarily composed of fat mass and fat-free mass. This comprises bone, muscle, and of course, water. This is why when you lose muscle, you end up losing weight as well.

But how does muscle wasting happen? While there are many causes for this condition, one of the most common cause is when you don’t use a particular muscle set for a prolonged period of time, it starts losing mass.

Some of the other possible causes of muscle wasting include:

This condition is commonly observed in people who have desk jobs, are bedridden, or do not exercise. However, muscle loss is a reversible condition and it can be treated with proper nutrition and exercise.

Rheumatoid Arthritis (RA)

RA is perhaps one of the more common causes of unexplained weight loss, after hyperthyroidism. RA is an autoimmune condition in which your immune system turns against your joints and starts attacking the lining that is present between the joints. This causes inflammation and pain. Over a period of time, chronic inflammation can boost your metabolism, making you lose weight.

While the exact cause of RA remains unknown, some of the common symptoms of RA include pain and swelling in the joints. Generally, it has been observed that the disease affects the same joints on both sides of the body. When you suffer from this condition, your joints tend to feel very stiff, preventing you from moving for long periods of time. This can range from an hour to more in some severe cases.

When you don’t move for prolonged periods of time, it can also cause muscle loss, another potential cause of unexplained weight loss.

Medications such as corticosteroids, biologics, disease-modifying anti-rheumatic drugs, and even Janus associated kinase inhibitors are being used to treat RA. However, there is no cure for this condition.


Unexpected weight loss may also be caused by type 1 diabetes. In this condition, your immune system starts attacking your pancreatic cells that manufacture insulin for the body. When there is no insulin, your body is unable to utilize glucose that is required for energy, thus causing high levels of glucose to build up in your blood. This is what is known as high blood sugar or high blood glucose.

Your kidneys are responsible for getting rid of the unused glucose in the body through urine. However, when glucose or sugar is flushed out of the body, so are the calories. Loss of calories leads to unexpected weight loss.

Type 1 diabetes can also cause symptoms such as:

  • Fatigue
  • Frequent urination
  • Dehydration
  • Increases hunger and thirst
  • Blurry vision

The treatment of type 1 diabetes includes regular monitoring of your blood sugar levels, taking insulin, having a healthy diet pattern, exercise, and maintaining an overall healthy lifestyle.

Inflammatory Bowel Disease

If you are losing weight unintentionally, it could also be a sign of inflammatory bowel disease (IBD), a term used to describe many types of chronic inflammatory diseases of the digestive tract. The two most common types of IBD include ulcerative colitis and Crohn’s disease.

IBD causes chronic inflammation in the body, putting the body in a catabolic state. This means that the body is perpetually in a state that uses up energy.

Furthermore, IBD also causes disruption in many hormones of the body, particularly ghrelin, which is the primary hunger hormone, and leptin, which is the hormone that signifies satiety. This causes a drastic reduction in appetite, followed by weight loss.

Some other symptoms of IBD include:

Consuming certain types of foods is likely to trigger the symptoms of this condition and you may eventually become quite hesitant about eating anything.

IBD is treating with medication and nutritional support. In some rare cases, surgery may also help.

Other Causes of Unexpected Weight Loss

There are many reasons that cause unexpected weight loss. While some reasons are quite serious, others may be more of a nuisance. One must also consider that in the elderly (people over the age of 65 years), one of the most common causes of unintentional weight loss is usually found to be cancer, followed by psychiatric and gastrointestinal conditions.

Some other common causes of unexpected weight loss may include:

  • Endocrine Conditions: Apart from hyperthyroidism, there may be other endocrine conditions that may cause weight loss. These include diabetes, Addison’s disease, and even hypothyroidism, or an underactive thyroid.
  • Infections: When your body is infected by any kind of bacteria, virus, or parasite, and an infection follows, you will end up losing weight. Infections such as tuberculosis, endocarditis (an infection of the heart valves), and even HIV/AIDS, can cause weight loss.
  • Cancer: Weight loss is often one of the first noticeable signs of cancer of the blood such as lymphomas and leukemias. It may also be a sign of solid tumors such as colon cancer, lung cancer (particularly adenocarcinoma of the lung), pancreatic cancer, and ovarian cancer. Studies have found that nearly 40% of people who were diagnosed with cancer, experienced unintentional weight loss as the first symptom and it was continuing at the time of their diagnosis.
  • Heart failure
  • Kidney failure
  • Smoking
  • Problems with the intestines: Peptic ulcer disease, pancreatitis, celiac disease, Crohn’s disease, and ulcerative colitis, can all cause weight loss
  • Neurological disorders: Conditions such as Alzheimer’s disease and Parkinson’s disease can cause weight loss


Every now and then your body weight tends to fluctuate. However, if you notice that you are consistently losing weight without any change in your daily habits and routine, then there might be an underlying condition responsible for weight loss. If you notice a five percent loss in your weight over a period of six months to a year, then you should consult your doctor at the earliest.

Also Read:

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 28, 2023

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