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24 Common Causes Rapid Weight Gain

Common Causes Rapid Weight Gain

If you’ve noticed that the number on your scale is quickly rising or that your clothes have gotten snug, but your eating patterns and activity level haven’t changed, you might want to consider what else could be behind your sudden weight gain.

While there is no specific definition for what is considered rapid weight gain, it shouldn’t be ignored, according to Sharon Orrange, MD, an internal medicine physician at Keck Medicine of USC and associate professor of clinical medicine at the Keck School of Medicine of USC.

Anyone who experiences rapid weight gain that is not due to one of the above causes or that affects their quality of life should see a doctor.

Reasons of Rapid Weight Gain


Certain medications can cause people to gain weight rapidly. According to the Obesity Action Coalition, some medicines can make people gain up to several pounds a month as a side effect.

Medications that might make people gain weight rapidly include some drugs that treat:

  • seizures
  • diabetes mellitus
  • high blood pressure
  • depression and psychiatric disorders

It is essential not to stop taking a medication without discussing it with a doctor first.


When a young woman walks into a doc’s office with unexplained weight gain, the thyroid is the first place most physicians will investigate, says Dr. Jampolis. And for good reason: A whopping one in eight women will develop a thyroid disorder in her life, according to the American Thyroid Association.

That butterfly-shaped gland in the neck is responsible for secreting a hormone that regulates the metabolism, and if you’ve got an under-active thyroid (called hypothyroidism) the metabolism may slow down, triggering weight gain.

Women with hypothyroidism may also suffer from low energy levels or fatigue, dry skin, hair loss, hoarseness, or constipation, says Dr. Jampolis. Notice any of them and you should book a chat with your doc who can check on your thyroid with a simple blood test if necessary.


Obesity has a strong genetic component. Children of obese parents are much more likely to become obese than children of lean parents.

That doesn’t mean that obesity is completely predetermined. What you eat can have a major effect on which genes are expressed and which are not.

Non-industrialized societies rapidly become obese when they start eating a typical Western diet. Their genes didn’t change, but the environment and the signals they sent to their genes did.

Put simply, genetic components do affect your susceptibility to gaining weight. Studies on identical twins demonstrate this very well

Lack of Sleep

Not getting enough sleep has been repeatedly scientifically linked to a significant increase in weight. In one instance, a study published in the journal American Journal of Epidemiology found that women who slept less than six hours a night were more prone to weight gain than women who slept at least seven hours each night.

This is likely due to the effect that insufficient sleep has on the endocannabinoid system, also known as the hormones that regulate appetite; lack of sleep stimulates the ones that tell you you’re hungry. It may also be partially due to the fact that when you’re tired, you’re less likely to exercise or move as much throughout the day. So be sure you’re clocking enough shut-eye, as your late nights might be adversely affecting your waistline.

Menopause Weight Gain

Around menopause, women may gain weight more easily.

“In the early postmenopausal years, we see weight gain and changes in fat distribution,” Orrange says. “The upside is that studies show that increase slows one year after your last period.”

An Underactive Thyroid (Hypothyroidism)

Aside from realizing that your jeans are more snug, have you noticed other body changes—like exhaustion, drier skin, or thinner hair? These are all signs of hypothyroidism, a condition in which the butterfly-shaped thyroid gland in your neck isn’t producing enough of thyroid hormone. Your thyroid is kind of a master gland controlling many body functions, so when it’s not working right, symptoms appear throughout your system.

A major function it controls is your metabolism. “Think of your body as a car. You have an engine, and the thyroid hormone maintains the idling of the engine,” Michael Nusbaum, MD, bariatric surgeon and founder of Healthy Weight Loss Centers, tells Health. “If you’re not producing enough thyroid hormone, your idle gets turned down and you’re not burning as much energy overall.” When your resting metabolism slows, it decreases the amount of calories you burn throughout the day.

One in eight women will develop a thyroid disorder during her lifetime, according to the American Thyroid Association. Dr. Nusbaum says other symptoms to look out for are muscle weakness, constantly feeling cold, bloating, and constipation. If your doctor diagnoses hypothyroidism, you’ll likely be prescribed an oral replacement for thyroid hormone that can alleviate symptoms, including weight creepage, within weeks.

You’re Eating Too Much Salt

Sodium consumption causes your body to retain water, Cheskin says. Water has weight and volume. So if you eat a lot of salty food several days in a row, you may suddenly gain weight, he says.

Restaurant food—and especially fast food—tends to be loaded with sodium. So if you’ve recently filled your days with takeout and restaurant meals, that could account for your abrupt influx of pounds. Keep in mind, however, that plenty of foods you eat at home are sodium motherlodes as well. Bread, sandwiches, cold cuts and cured meats are some of the top sources of sodium in the American diet.

Polycystic Ovary Syndrome

Research shows that as many as one in five women have polycystic ovary syndrome (PCOS) — an endocrine disorder that throws off the balance of reproductive hormones estrogen and testosterone, and can trigger a number of unpleasant symptoms like wacky periods, facial hair growth, and migraines.

PCOS can also muck up the way your body uses insulin (the hormone that helps turn sugars and starches into energy), which means unexplained weight gain around the mid-section is common, says Dr. Jampolis.

If your menstrual cycles are off, a gyna will likely take a peek at your hormones to diagnose this one.


Research has shown repeatedly that insufficient sleep is one of the main causes of weight gain. Changes in sleeping cycles can affect your eating patterns as well as your mood and then you often overeat. One study completed in 2013 shows that people deprived of sleep who ate more carbs to meet their energy needs could put on weight.

Quitting Smoking

Some people gain weight initially when they stop smoking tobacco products. Experts believe that this occurs both because nicotine suppresses appetite and because withdrawal symptoms may include stress, which can lead to overeating.

Research has shown that 1 kilogram (kg) is the average weight gain in the first month after quitting cigarette smoking. The majority of a person’s weight gain seems to occur during the first 3 months after quitting smoking, with the rate of weight gain appearing to slow down by the 6-month mark.

However, changes in weight as a result of quitting smoking can vary depending on the person. The same research found that 16 percent of people lost weight in the first year of not smoking while 13 percent gained over 10 kg.

Heart Failure

Rapid weight gain or swelling in particular areas of the body can be due to fluid retention and may be a sign of heart failure.

According to the American Heart Association, a weight gain of more than 2–3 pounds (lb) over 24 hours or 5 lb in a week could be a sign of heart failure.

However, it is vital to note that a person’s weight usually fluctuates by a few pounds over the course of a day. If their weight returns to normal and they do not have additional symptoms, the temporary increase could be due to normal bloating and fluid retention.

If blood is flowing slowly to and from the heart, it affects the function of other major organs in the body. As a result, fluid collects in the tissues, which causes weight gain and swelling.

People may experience weight gain with swelling in the:

  • stomach area
  • ankles
  • legs
  • feet

Other signs and symptoms of heart failure include:

  • fluid collecting inside the lungs (pulmonary edema)
  • frequent coughing
  • feeling breathless when resting
  • dizziness or confusion
  • loss of appetite
  • difficulty sleeping or lying flat

If people are experiencing any of these symptoms alongside rapid weight gain or unexplained swelling, they should seek medical attention.

Depression or Anxiety

When you’re stressed, you’re thrown into fight-or-flight mode and get a surge of adrenaline, along with a heavy dose of the hormone cortisol, which is supposed to help you restore energy reserves and store fat. Because, hello, you just sprinted three miles from a tiger (okay, dramatic example)—you’re starving.

The problem? Lots of us get chronically stressed sitting at our desk all day or just living a crazed life, says Dr. Jampolis. When your cortisol levels stay elevated for a prolonged period, then your body continues storing fat, which can lead to weight gain.

If you’ve persistently felt down in the dumps or anxious, have trouble sleeping, feel fatigued, or you’ve lost interest in the stuff that used to make you tick, talk with an MD or mental-health pro who can make suggestions for getting back on track if stress seems to be the culprit behind your sudden weight gain.

Engineered Junk Foods

Heavily processed foods are often little more than refined ingredients mixed with additives.

These products are designed to be cheap, last long on the shelf and taste so incredibly good that they are hard to resist.

By making foods as tasty as possible, food manufacturers are trying to increase sales. But they also promote overeating.

Most processed foods today don’t resemble whole foods at all. These are highly engineered products, designed to get people hooked.

Water Retention

Like with sodium, water weight isn’t fat, but it can tip the scale and make you feel heavier. Though it might sound counter-intuitive, the solution to clearing that water weight is to drink more water. The reason your body seems to be holding on to the water weight is because you’re not drinking enough fluids, so it thinks it has to store the water it doesn’t have in reserve.


Bloating is usually marked by a sensation of abdominal fullness, pressure or tightness, and your abdomen may appear swollen.

“It’s important to sort out whether a patient is really experiencing weight gain — pounds on the scale — because often, they are complaining about abdominal bloating or tight pants, and that’s very different,” Orrange notes.

“Bloating is commonly reported in people with irritable bowel syndrome and is handled much differently than weight gain,” she explains. Constipation, lactose intolerance and premenstrual syndrome are other possible causes of bloating.

Cushing’s Disease

Cortisol is nicknamed the stress hormone, Diondra Atoyebi, DO, family physician at Piedmont Healthcare in Georgia, tells Health; your body releases it in response to overwhelming or dangerous situations. But when your system makes too much cortisol over an extended period of time, you can develop Cushing’s disease. One unpleasant side effect: abnormal fatty deposits in the abdominal area and around the face.

If you’re taking long-term steroids, you’re more likely to develop Cushing’s disease, Dr. Atoyebi says. The condition can also be brought on by tumors on the pituitary gland in the brain, which triggers an uptick in the production and release of adrenocorticotropic hormone—the catalyst that signals the adrenal glands to produce cortisol.

Weight gain is a hallmark sign of Cushing’s, but other symptoms include discolored stretch marks, acne, and fragile skin. Depending on the cause, Cushing’s disease can be treated in a variety of ways. If you have Cushing’s disease, your doctor will help you determine what’s best.

Small Intestinal Bacterial Overgrowth (SICO)

The gut relies on good bacteria to function well (probiotics, anyone?), but there’s also bad bacteria chilling in your digestive tract. When that balance of good to bad gets thrown off, small intestinal bacterial overgrowth (SIBO, for short) can take place, triggering extra gas in your GI tract along with bloating, abdominal pain, diarrhoea, and — you guessed it — sudden weight gain.

Docs aren’t entirely sure how SIBO may trigger those extra pounds, says Dr. Jampolis, but treatment for SIBO typically includes antibiotics to treat the bacterial overgrowth, according to the U.S. National Library of Medicine.

Lack of Physical Activity

True, excessive exercise can lead to obesity and weight gain, but not indulging in physical activity can harm the body. It can result in cardiovascular diseases, hypertension, type 2 diabetes, and hypercholesterolemia. Physical activity promotes improved sleep cycles, increased capacity to do daily chores, and better mental and bone health. Combining physical activity with a healthy diet plan can help maintain a healthy weight.

Kidney Problems

Sudden weight gain or swelling in the body could be a symptom of kidney disease, such as kidney failure or nephrotic syndrome, which is damage to the kidneys.

If the kidneys are not functioning correctly, the body may retain fluid, resulting in weight gain. Damaged kidneys are not able to remove waste and fluids from the body properly, so these build up in the tissues.

Swelling due to kidney problems usually affects the legs, ankles, or feet.

Other symptoms that may indicate a problem with the kidneys include:

  • fatigue
  • not urinating very much
  • urine that looks foamy
  • itchiness
  • loss of appetite
  • muscle cramps
  • joint pain
  • headaches
  • difficulty concentrating or confusion


If people experience rapid weight gain and their abdomen looks enlarged, this may indicate cirrhosis.

Cirrhosis is a condition in which scar tissue replaces healthy tissue in the liver, and it can cause fluid to build up in the abdominal cavity. This abnormal buildup of fluid is called ascites.

Other symptoms of cirrhosis include:

  • swollen ankles
  • breathing difficulties
  • abdominal pain

If people are already having treatment for ascites, they should contact their doctor if they gain more than 2 lb a day for 3 days in a row.


The transition period to menopause (a.k.a. perimenopause, which can start in women as early as their mid-30s, but usually starts in your 40s) triggers hormones like estrogen to rise and fall unevenly, which can cue weight gain in some women, says Dr. Jampolis. (Other signs of perimenopause include irregular periods, hot flashes, mood swings, and a change in your libido—symptoms your doc can usually suss out with her eyes closed.)

Compound perimenopause with the other inevitable body changes that happen with age (like a loss of muscle mass and increase in body fat), and it may feel like the scale’s tipping fast. Talk to your doctor to manage “the change” in stride.


Insulin is a very important hormone that regulates energy storage, among other things.

One of its functions is to tell fat cells to store fat and to hold on to the fat they already carry.

The Western diet promotes insulin resistance in many overweight and obese individuals. This elevates insulin levels all over the body, causing energy to get stored in fat cells instead of being available for use.

While insulin’s role in obesity is controversial, several studies suggest that high insulin levels have a causal role in the development of obesity.

One of the best ways to lower your insulin is to cut back on simple or refined carbohydrates while increasing fiber intake.

This usually leads to an automatic reduction in calorie intake and effortless weight loss — no calorie counting or portion control needed.

An Undiagnosed Medical Condition

Unfortunately, some reasons for sudden weight gain can be a bit more insidious. We’ve discussed hypothyroidism, PCOS, and depression, all three of which are serious conditions, but there are a litany of conditions associated with rapid weight gain that require immediate medical attention. These include tumors, Cushing disease, and Type 2 diabetes.

“If you experience sudden weight gain, consider meeting with a registered dietitian nutritionist to better understand your nutritional needs to identify what needs to be adjusted,” Sheth says. “Ensure that you have a realistic action plan and one that is sustainable.”

Ovarian Cancer

In rare cases, an expanding belly is the result of an ovarian tumour and fluid buildup associated with it, says Dr. Sanaz Memarzadeh, a gynaecologic cancer surgeon at UCLA Health. “Patients come in with abdominal bloating, and their usual pants are not fitting,” she says. “Sometimes the tumour is so large it can cause dissention of the abdomen,” says Dr. Memarzadeh.

Women are more likely to be diagnosed with ovarian cancer after menopause. But it’s important for women at every age to look out for this symptom, as well as feeling full too quickly, pain in the lower stomach area, and extra pressure on the bladder. See your doc if the bloating persists, especially if your family has a history of ovarian cancer.

Causes Make You Gain Belly Fat

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