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Sudden Weight Gain: 7 Reasons for Unexplained Weight Gain

Sudden Weight Gain: 7 Reasons for Unexplained Weight Gain

Tripment, Inc
Tripment Health Team

Most people gain approximately 1 or 2 pounds per year from the time they are in their twenties until middle age. Weight gain is completely normal as we age and our priorities and hormones shift. However, if you experience sudden weight gain that does not correlate to a change in diet or exercise, it could be a sign of an underlying condition. 

Causes of unexplained weight gain

In general, you shouldn’t fret too much about a few extra pounds here and there. A thin body isn’t always a happy body, and stressing about it too much could actually cause you to gain more weight — but more about that later. While it’s unlikely that the body you have at 30, 40, and beyond will look exactly like your 20-year-old self, there are certain reasons for unexplained weight gain that could be cause for alarm.

Get checked now

Need a test or a scan to determine the cause of unexpected weight gain?

Your provider can use the diagnostic imaging or lab tests below to help find the cause of rapid weight gain.

What are the symptoms of unintentional weight gain?

Unexplained weight gain can happen for a number of reasons, so there is a wide range of potential symptoms. First and foremost, you would feel like you were gaining weight for no reason. Fluctuations in weight would not seem to correlate with food intake or energy expended. You may also notice some of the following symptoms: 

  • Abdominal pain or bloating 
  • Sweating
  • Heart palpitations 
  • Skin sensitivity 
  • Difficulty breathing 

If you are experiencing symptoms like this, you may wish to talk to your doctor about the types of underlying conditions that could be the source of the problem. He or she may recommend blood tests to figure out the unexplained weight gain.  

1. Medication

One of the first things your provider would probably ask you is whether you are taking any new medications. Weight gain is a common side effect of certain drugs. Some medications can even make people gain a few pounds every month. These medications are frequently used to treat: 

  • Depression 
  • Seizures 
  • Diabetes
  • High blood pressure

2. Sleep deprivation — Insomnia

Poor sleeping habits can also cause weight gain for no reason. Your body works hard to repair and restore balance to its systems when you sleep. Even missing an hour or two of sleep can wreak havoc on your hormones, which is why insomnia is linked to unwanted weight gain. When you don’t get the proper amount of shut-eye, ghrelin levels increase — that’s the hormone that sends hunger signals to your brain. Simultaneously, leptin levels are lowered, which means it takes longer for your brain to receive the message that you’re full. 

3. Quitting smoking

If you’re a smoker, kicking the habit is one of the best health decisions you could ever make. Smoking cigarettes contributes to heart disease, drastically increases the risk for cancer, and causes dozens of other health problems that can be reversed simply by giving up smoking for good. 

However, quitting smoking can also cause weight gain. Nicotine is known to suppress the appetite, so once you lose that steady supply you may find yourself more inclined to snack more frequently. Stress eating is also commonly associated with quitting smoking — luckily, weight gain associated with quitting smoking is generally a temporary problem, and tends to taper off after the first few months.

4. Stress or depression 

Stress causes our bodies to produce cortisol, a hormone responsible for storing fat. This might have made sense for our ancestors, who encountered stress when their bodies were overworked and they didn’t have the luxury of eating three full meals a day. However, we often encounter stress while sitting down and working on our computers all day — definitely not when we need the fat-storing cortisol to kick in. Stress also frequently accompanies anxiety and depression. Coupled with mental health medications that are known to cause weight gain, stress and depression can easily lead to increased weight. 

5. Pregnancy

Weight gain during pregnancy is expected, and is of course vital to ensure the health of the baby. In addition to the weight of the growing baby itself, women’s pregnant bodies also support the placenta and amniotic fluids, as well as a larger volume of blood. Extra weight gain can easily happen in these months, as some women experience cravings for certain foods or may start to stress eat. While many mothers-to-be remain active and can continue exercising throughout the pregnancy, others experience back pain, exhaustion, or other symptoms that may limit movement and cause them to be more sedentary. 

6. Distracted eating — Fast food

Sudden changes can impact the way we eat — a new job can leave you scrambling for spare time, or moving to a different town can completely upend your daily routine. When priorities suddenly shift, we often sacrifice healthy eating habits in favor of saving time. Picking up fast food meals rather than preparing food at home, or even skipping meals altogether, can upset your metabolism and impact how you gain weight.

7. Diseases or conditions that cause weight gain

Sudden, unexpected weight gain can also be a symptom of an underlying condition, or the onset of disease. If you have symptoms that match one of the following conditions, schedule a time to talk to your primary care provider soon to determine if you have a disease that may cause weight gain. 

Thyroid disorder

Your thyroid gland is responsible for producing hormones that regulate your metabolism. If your thyroid does not produce enough of these hormones, you may have a condition called hypothyroidism. This causes your metabolism to slow down, which typically results in sudden weight gain. Other symptoms of hypothyroidism include hair loss, dry skin, and fatigue. Thyroid disorders are relatively common — it’s estimated that up to 12% of the population experiences problems with thyroid function at some point in their lives. Luckily, most thyroid disorders are easily treated. 

Cushing's disease

This rare disease is caused when the body produces an excessive amount of cortisol. One of the most easily recognized symptoms is sudden weight gain in the abdominal area. Low energy, the appearance of large red stretch marks on the abdomen, diabetes, and high cholesterol are also symptoms of Cushing’s disease. 


Weight gain with cancer typically doesn’t happen until the later stages, when tumors are large enough to cause a noticeable difference in weight, or when stress on the organs cause fluid to build up in the abdomen. However, sudden unexpected bloating and weight gain coupled with pain, the need to frequently urinate, and changes to the menstrual cycle could be signs of ovarian cancer. 

Other cancers can also cause weight gain, as tumors grow and spread throughout the body. It’s important to talk to your doctor about sudden changes you experience in your body as soon as you notice them, in order to catch diseases like cancer in their early stages. 


Weight gain from Type 2 diabetes is most often linked to a diet high in sugar combined with a sedentary lifestyle. People who have Type 2 diabetes usually have much higher levels of insulin than normal, which also leads to abdominal weight gain. 

Perimenopause or menopause

Once a woman reaches menopause, her estrogen levels start to drop. This can trigger weight gain, as well as the other hormonal and metabolic changes that typically occur during this time. 

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a fairly common hormonal issue for women who are within their childbearing years. It’s due to a hormonal abnormality that can cause not only weight gain, but also excessive hair growth, acne, and infertility. 

Heart failure

Gaining 2-3 pounds in a 24 hour period or 5 pounds in a week could be a sign of a very serious condition — heart failure. This type of weight gain is caused by rapid fluid retention, and is typically marked by swelling in the abdomen, ankles, feet, and legs. If you experience this type of swelling in combination with dizziness, breathlessness, coughing, and loss of appetite, contact your doctor immediately. 

Kidney problems

Your kidneys remove waste from your body. If they are damaged, they may not be able to function properly, and waste can build up in the form of fluid retained in the tissues. If you experience weight gains with joint pain, muscle cramps, fatigue, and foamy urine, talk to your doctor about your kidney health. 


When healthy liver tissue is replaced by scar tissue, you have a condition called cirrhosis. This can cause fluid to build up quickly in your abdomen. If you have an enlarged, painful abdomen, swollen ankles, and difficulty breathing, discuss your liver health with your provider. 


This rare condition is a result of overproduction of growth hormone by your pituitary gland — sometimes due to a benign tumor pressing on the gland. The most obvious symptoms are enlarged hands and feet, excessive sweating, achy joints, and a suddenly deeper voice. 


Dehydration can cause weight gain in a roundabout way — when we don’t drink enough water, we often mistake symptoms of dehydration for symptoms of hunger, and we reach for a snack instead of fluids. Being properly hydrated is also necessary for your metabolism to function normally. 

Get checked now

Need a test or a scan to determine the cause of unexpected weight gain?

Your provider can use the diagnostic imaging or lab tests below to help find the cause of rapid weight gain.

When to see a doctor

As you can see, there are many reasons why you could be experiencing rapid, unexpected weight gain. The only way to get to the root of the problem is to consult with a trusted provider, who can diagnose the issue and help you develop a treatment plan. 

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