Causes For Unexplained Weight Gain

Weight gain and fatigue are common problems that nearly all people face. It may be due to stress or lack of sleep, but unexplained weight gain and fatigue may be symptoms of an underlying health condition needing treatment.

However, there may also be some non-specific symptoms, and most diseases could manifest them, so it may be challenging to get the precise cause. If you are a healthy eater that sleeps on time but still has unexplained weight gain and fatigue, you need to consult with a doctor to understand why it is happening.

Overview of Unexplained Weight Gainunexplained weight gain


Unexplained weight gain happens when you put on weight without the increase in your food consumption while not decreasing your physical activity. It comes into notice especially when you are not trying to gain weight. It is usually due to abnormal growth, pregnancy, constipation, or fluid retention. 

This condition can be rapid, continuous, or periodic. Periodic weight gain includes frequent weight gain and loss. For instance, women usually go through unexpected weight gain and gain fatigue during their menstrual cycle. Long-term unexplained weight gain is generally because of some pregnancy symptoms, which last for nine months.

Rapid weight gain can be because of the side effects of medications. Most of the time, this condition is harmless. But some indications experienced with rapid weight gain may signal a medical emergency.

What Are the Causes of Unexplained Weight Gain?

As mentioned earlier, there may be various possible reasons for sudden weight gain. Let us take a deep look.


unexplained weight gain

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In women, periodic weight gain is due to the menstrual cycle. Women may go through water retention and bloating around their period. Changing levels of progesterone and estrogen can cause weight gain. Generally, women may gain a few pounds.

This weight gain happens when the menstrual time ends for the month. It usually reappears the following month after the menstrual period comes again, and sometimes during ovulation.


unexplained weight gain

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When you are gaining weight, the first place you look for answers is often the diet or exercise routine, but the cause of it may be hiding in the medicine cabinet. Many medicines, those that treat migraines and mood disorders and birth control, and steroids, can result in weight gain for various reasons. If you think that a medicine you’re taking might be causing weight gain, talk to your doctor to discuss your options. 

Polycystic Ovary Syndrome

unexplained weight gain

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Polycystic Ovary Syndrome, also known as PCOS, happens due to the imbalance in reproductive hormones in women. In PCOS, weight gain or weight loss is typical because it leads to insulin resistance. It occurs when the body is having difficulty pulling glucose from the bloodstream and converting it into energy.

The body then needs to create more insulin to keep the average blood sugar level. Over time, the body starts to overproduce insulin for maintaining blood sugar levels normal, which potentially leads to weight and diabetes type 2.

People with PCOS may also experience fatigue. There are also other symptoms, such as:

  • High cholesterol
  • Missed menstrual period
  • Depression
  •  Hair growth on the face, chest, abdomen, and arms.

There is no treatment for PCOS, and you can control the symptoms with medications. Your doctor may prescribe you diabetes medication such as metformin to lower insulin and blood glucose levels. You can opt for other treatment options: birth control pills, IVF, and hormone therapy with progesterone.

Cushing’s Disease

unexplained weight gain


Cushing’s disease is an endocrine disorder where there is an excessive amount of stress hormone cortisol in the body. The production of cortisol is triggered by releasing the adrenocorticotropic hormone (ACTH) from the pituitary gland. When a tumor happens in the pituitary gland, it causes the gland to secrete too much ACTH and increase the production of cortisol.

Unexplained weight gain is usually the initial sign of the condition. Too much cortisol can change the amount and distribution of body fat, making a person’s face round and leading to weight gain around the midsection and upper back and accumulation of fat between the shoulders. People with this disease also get severely tired.

Surgery, radiation, or chemotherapy will need to be done to remove the tumor from the pituitary gland. Hormone-inhibiting medication may also be prescribed to reduce the level of cortisol in the body.

Weight Training

unexplained weight gain


You may see that you are gaining weight after working out; it happens for two reasons. First, weight training enhances muscle mass, and muscle is more dense than fat. So when losing fat and increasing muscle, you may see the increased number on the scale. 

Second, weight training causes muscle inflammation or soreness, meaning that your muscle swells from water retention for protection. The good part is that weight training, especially when you are a beginner, may cause slight unexplained weight gain that will help you to lose some inches. This means that on the scale, numbers are high, but your clothes will fit better.


unexplained weight gain


Depression is a mood disorder where sadness affects your ability to function in daily life. People with depression frequently go through chronic fatigue. It may also be the side effect of commonly used antidepressants because depression medication contains a chemical that provides a soothing and relaxing effect on the user.

If you have depression, you may also experience changes in your appetite and either lose or gain weight regardless of the diet. Centers for Disease Prevention and Control stated that roughly 43% of people with depression are obese, and those people are more likely to become obese than those without depression. Sudden weight gain is a noticeable side effect of many depression medications, specifically selective serotonin reuptake inhibitors (SSRIs).


unexplained weight gain

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It happens when the menstrual period stops and the ovaries no longer produce estrogen and progesterone. It usually happens after you reach the age of 45. A woman will reach menopause when they have not had a period for one year.

During women’s menopause, the period that leads to it, estrogen levels start to drop, and this hormonal shift begins to slow down the metabolism. Even if someone continues to have a healthy diet, they are more likely to gain weight.

Fatigue is common in those with menopause because estrogen and progesterone are both essential for sleep. Estrogen plays a part in the metabolism of serotonin and other neurotransmitters that affects our sleep.


unexplained weight gain

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It is a sleep condition that makes it difficult to sleep. It can also cause you to wake up early. When you do not get sufficient sleep due to insomnia, you will naturally become tired and experience fatigue. However, this sleep problem is also linked with weight gain and obesity.

According to research, sleep deprivation affects the body similarly to activation of the endocannabinoid system. It is a critical player in your brain regulation of energy levels and appetite. When participants with sleep deprivation had higher eCB levels in the afternoon and lasted longer than when they had a whole night’s rest, this happened around the same time that they reported increased hunger and appetite.

Insomnia is also associated with other conditions which cause unexpected weight gain and fatigue, such as depression. It is amongst the diagnostic criteria of major depressive disorder. It is estimated that 90 percent of people with depression have insomnia or daytime drowsiness.

Also Read: What is A Clear Liquid Diet? What To eat And What To Avoid

Heart Failure

unexplained weight gain


Rapid weight gain or swelling in some areas of the body may be due to fluid retention and can be a symptom of heart failure. According to the American Heart Association (AHA), a weight gain exceeding 3 pounds over 25 hours or 5lb in a week can be a sign of heart failure.

However, it is essential to note that a person’s weight usually fluctuates by a few pounds over a day. If their weight returns to standard and does not have additional symptoms, the temporary increase could be due to average bloating and fluid retention.

If blood is flowing slowly to and from the heart, it will affect the function of other significant organs in the body—resulting in the fluid collection in the tissues, which causes weight gain.

People may go through weight gain with swelling in the:

  • stomach area
  • Ankles
  • Legs
  • Feet

How to Treat Unexpected Weight Gain?

unexplained weight gain


There are various methods to treat unintentional weight gain. The best method would be depending on the condition’s cause. 

If the problem is hormonal balance, the doctor may prescribe you medicines to balance the hormone level. The medicine also depends on the affected hormones. These medications are typically for long-term use.

If the unexpected weight gain is due to the medications, your doctor may change the current medicine and prescribe an alternative.


Dealing with sudden or unexplained weight gain and fatigue can be difficult, especially when you don’t know the precise cause. Not knowing what is happening to the body can be scary, but it is essential to be patient. Being in control of your health is the best method to address new or worsening symptoms.

When going through unexplained weight gain and fatigue, it is critical to address the issue as soon as possible so that any underlying health condition is treated accordingly. You can enjoy your life with an illness with an appropriate diagnosis, attitude, and treatment.

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