8 Common Reasons Why You Could Have Gained Weight So Fast

If you're quickly gaining weight, there are many possible reasons for it.

You know you might put on extra pounds if you regularly skip barre class or keep selecting higher calorie, nutrient-deficient foods when you hit up the office vending machine. But if you haven't changed your eating and exercise habits yet and the number on the scale has suddenly crept up, something more could be going on.

Carrying extra pounds isn't necessarily a problem, of course. But it could signal an underlying medical issue you'll want to address. Maybe it's a hormone condition, a mood disorder, or another factor altering your physiology without you realizing it. The only way to be completely sure of what it means is to consult your healthcare provider. In the meantime, consider these eight health-related reasons that might explain why the scale has soared.

Underactive Thyroid (Hypothyroidism)

Aside from realizing that your jeans are snugger, 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 thyroid hormones. Your thyroid is a master gland controlling many body functions, so when it's not working right, symptoms appear throughout your body.

A major function the thyroid controls is 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, a surgeon and founder of Nusbaum Medical Centers, told 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 number 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 said 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 within weeks.

Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome (PCOS) is another condition caused by out-of-whack hormones. This endocrine disorder is characterized by an imbalance in the sex hormones estrogen and testosterone (women produce testosterone too, though in much smaller quantities than men do). This imbalance leads to irregular periods, acne, and even facial hair growth.

This disorder, which strikes one in 10 women of childbearing age, also disrupts the way the body uses insulin—the hormone responsible for converting carbohydrates into energy, said Dr. Nusbaum. Yep, you guessed it, that means weight gain. When your body becomes insulin resistant, the sugars and starches you consume are stored as fat instead of turned into fuel, explained Dr. Nusbaum.

While there's no cure for PCOS, women who have it can manage their symptoms with lifestyle changes and medication. Your doctor will help you find the method that's right for you.

Mood Disorders Like Depression and Anxiety

Dealing with anxious or sad feelings by mindlessly munching is something almost all of us do on occasion. But either of these mood disorders can make overeating a regular coping mechanism. Dr. Nusbaum gave the example of breaking open a bag of chips, and after three, four, then five handfuls, "you're not even tasting the chips anymore, your taste buds are completely saturated with the flavor, but you're still eating, and you're thinking, Why am I still eating?".

Depression and anxiety can both bring on fatigue, irritability, and a lack of focus. All three can throw you off your game when you work out or lead you to ditch the gym altogether...and pretty soon, pounds pack on.

Reflect on your mood over the past few weeks. If you've been consistently down on yourself, on edge, disinterested in things you usually enjoy, or have had trouble sleeping, consider asking your healthcare provider for a referral to a mental health professional. A therapist can help get to the bottom of what's going on. And proper treatment can help you keep extra pounds at bay.

Perimenopause and Menopause

How the five or so years leading up to menopause—the perimenopausal period—affects you partially depends on genetics, said Dr. Nusbaum. "I joke around with my patients because they'll typically come in saying, 'Holy crap, I'm starting to look like my mother,'" said Dr. Nusbaum. One way to get an idea of the way your body will change during perimenopause and then menopause itself is by asking your mom what changes she noticed in herself. Though your experience could be different than hers, there's a good chance it'll be similar—so if she began gaining weight at this point in her life, it could be the explanation for your weight change.

So once again, hormones are to blame for the extra pounds. "The rapid reduction in the amount of hormones present in your body throws you off-kilter pretty quickly," said Dr. Nusbaum. Lifestyle changes can help, so talk to your healthcare provider for ideas.

Cushing's Disease

Cortisol, nicknamed the stress hormone, is what your body releases in response to overwhelming or dangerous situations, Diondra Atoyebi, DO, a family physician at Piedmont Healthcare in Georgia, told Health. 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, said Dr. Atoyebi. 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, especially in the upper body, is a hallmark sign of Cushing's; 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 healthcare provider will help you determine what treatment best suits you.

Ovarian or Uterine Tumor

In September 2018, Case Reports published a case of a 53-year-old woman in Singapore who had a 61-pound tumor removed from her uterus after showing up at the hospital struggling to breathe. To grow so large, the tumor was likely developing inside her for years. It's an extreme case, but it shows that if left untreated, large pelvic area tumors, such as uterine or ovarian tumors, can distend the abdomen the way excess fat does and send the scale soaring. In the case of the Singaporean woman, the tumor was benign, but others can be cancerous.

In addition to weight gain, symptoms of ovarian or uterine tumors include lower back pain, vaginal bleeding, painful intercourse, and constipation. But these signs are common for other conditions as well, said Dr. Nusbaum, which is why you should always consult your healthcare provider to confirm the root cause of the problem.


Before starting any new OTC or prescription medication, ask your doctor if extra pounds are a possible side effect. Psychiatric medications, especially for depression and bipolar disorder, commonly cause weight gain, said Dr. Nusbaum. "They act centrally on the brain, and while they intend to lower your depression, they inadvertently increase your desire to eat."

Meds that combat high blood pressure can also cause weight gain, Susan Besser, MD, a family practitioner at Mercy Personal Physicians in Maryland, told Health. Another culprit is taking insulin for diabetes, as insulin therapy itself can sometimes cause weight gain. According to the American Diabetes Association, staying active and eating a balanced diet can help you manage the disease without adding excess weight.


If you try to work all day on only four hours of sleep, you'll probably turn to snacking on simple carbs—chips, cookies, candy—to give you quick energy boosts to get through the day. Why does exhaustion trigger cravings like these? Dr. Besser said lack of sleep messes with your hunger-regulating hormones. Levels of ghrelin, a hormone that tells your body it's time to eat, increase after a restless night. At the same time, leptin, the hormone that signals fullness, may plunge. Put the two together, and no wonder your belt feels tight. This doesn't just happen overnight, though. It's persistent insomnia that really adds the pounds up over time.

Sleep deprivation can also affect your decision-making. Let's say you can eat either a banana or a cookie. When you're tired, you become more impulsive, and that impulsivity can coax you into grabbing that food higher in sugar. Sugar is also instant energy, something your body will crave when you're exhausted. A 2018 study published in the American Journal of Clinical Nutrition found that getting more shuteye can mean consuming up to 10 fewer grams of sugar throughout the day.

And while having a cookie isn't going to pack on the pounds, when your habit is to choose sugary foods over more nutrient-dense options, you may find that weight creeping up.

There are many reasons behind gaining weight so fast. From medical conditions to sleep deprivation (which can cause medical conditions), some of the reasons are out of your control. You do, however, have control over what you do about them. See your healthcare provider to investigate the possible cause of the sudden weight gain and get a plan in place for healing.

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