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What Are the Causes of Unexplained Weight Gain?

Helen Akers
Updated Mar 03, 2024
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Unexplained weight gain can result from an underlying medical condition, taking certain prescription medicines, and unintentional lifestyle changes. Thyroid disorders and hormonal changes are common causes of unexplained weight gain. A decrease in physical activity and an increase in unhealthy food consumption is an obvious cause, but in turn, this can occur as the result of mood disorders. Medications used to treat diabetes and prevent pregnancy can also lead to sudden weight gain.

Hypothyroidism, which is a condition that causes the thyroid gland to produce an insufficient amount of hormones, is a leading cause of unexplained weight gain. When the thyroid does not produce sufficient levels of hormones, it can result in decreased metabolic levels. Other symptoms of the condition include prematurely gray hair, dry and itchy skin, acne, and heightened reactions to cold temperatures. Unexplained fatigue is an additional symptom of the disorder, as is increased weight gain occurring mostly in the body's mid-section.

Steroids and certain prescription medications can lead to unexplained weight gain. Birth control pills have been known to cause sudden weight gain in certain individuals. The hormonal changes that these pills induce are thought to be the cause. Insulin that is used to treat conditions such as diabetes may also lead to unexplained weight gain. The disease, as well as its treatment, tends to influence the body's metabolic activity.

Changes in metabolic rate due to the aging process or conditions that directly influence hormone levels can cause sudden weight gain. Individuals who decrease their activity levels and do not adjust their diets accordingly may see unwanted pounds added onto their physiques. Increasing consumption of fat and carbohydrates can result in extra weight for aging individuals or those with a slower metabolism.

Mood disorders might also lead to unhealthy eating habits. While these habits might prove to be temporary, individuals may not be fully aware of their behavior. Depression can cause individuals to use food as a coping mechanism in order to make them feel better or emotionally "full." Anxiety is another related mood disorder that may drive individuals to abuse food to alleviate fear and high stress levels.

Natural changes that come with age, such as menopause, can directly affect hormone levels and metabolic activity. Weight gain tends to occur in the mid-section with these types of changes. Conditions not related to aging might also result in sudden weight gain. Polycystic ovary syndrome, which increases the amount of androgens past normal levels, is one of those conditions. Hormonal treatments can usually resolve these issues, but the weight gain may take some time to go away.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Helen Akers
By Helen Akers
Helen Akers, a talented writer with a passion for making a difference, brings a unique perspective to her work. With a background in creative writing, she crafts compelling stories and content to inspire and challenge readers, showcasing her commitment to qualitative impact and service to others.
Discussion Comments
By Feryll — On Sep 19, 2014

I think stress weight gain and depression weight gain are more common than most people realize. Both of these can lead to you eating more and eating less healthy foods. Stress and depression can also cause you to exercise less. Put these two things together and gaining weight is sure to follow.

By Drentel — On Sep 18, 2014

As I got older the weight gain sneaked up on me. When you're young and active you think you are going to stay that way forever. I thought older people who put on weight just got lazy. Then when I reached my 40s I realized I had become one of those out of shape older people.

The combination of my metabolism slowing down and me spending more time working and less time playing sports added up to more weight and most of it was in my stomach area.

By mobilian33 — On Sep 18, 2014

My sister has a thyroid gland that isn't working like it is supposed to. A few years back she started putting on weight. At first we all thought she was just eating too much and needed to go on a diet. Most people start to put on a few extra pounds when they reach a certain age, so this is part of what we thought was happening.

Then the weight continued to come and she said she was eating less. This didn't make sense to us. We thought she was still eating too much, and we gave her a hard time about the weight gain and not exercising enough because it was a lot of weight and we wanted her to be healthy.

When she went to the doctor they did a special test and saw she had a thyroid condition. You would be surprised how much weight a person can gain in such a short time when there is a thyroid problem.

Helen Akers
Helen Akers
Helen Akers, a talented writer with a passion for making a difference, brings a unique perspective to her work. With a...
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