Reminder: It’s totally normal to gain weight as you age. After all, thanks to something called responsibilities, you probably aren’t moving around the same way you were younger (read, running up and down a playground all day). Less activity plus the natural loss of muscle mass can both contribute to a slower metabolism as you get older.
But if you’re experiencing sudden weight gain that just doesn’t seem to make sense to you (and it doesn't seem to have to do with normal life changes), then it may be a sign that something odd is going on with your bod. Think: out of whack hormones or other sneaky health conditions that are causing your metabolism to misfire.
Ultimately, you'll need to work with your doc to get a clear explanation for your unexplained weight gain. Before visiting the doc, keep a log of everything you eat as well as your exercise habits (including activity outside of your workouts) for at least a few days if not a week or two, says Melina Jampolis, MD, an internist and physician nutrition specialist based in Los Angeles. Maybe you’re eating more calories now, or you’ve spent weeks sitting down more than usual thanks to a heavier workload.
Your doc can help you get to the bottom of whether any lingering health issues might be causing the weight gain. And there are tons of reasons for unexplained weight gain that have nothing to do with eating more and moving less.
Ahead, a list of conditions that could be causing your sudden weight gain, and how to tell if it’s time to see a doctor.
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.
2. 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 (womp, womp) unexplained weight gain around the mid-section is common, says Dr. Jampolis.
If your menstrual cycles are off, a gyno will likely take a peek at your hormones to diagnose this one.
3. 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.
There’s nothing like a busted night of sleep to make a girl crave sugar and fat (anything to survive at work the next day, right?). That's because missed shuteye does a number on your hunger hormones and metabolism: Sleeping too little raises ghrelin, the hormone that signals it’s time to eat, while lowering your levels of leptin, the hormone that conveys the “I’m full” feeling, says Dr. Jampolis. The result: a totally unsatisfying chow-fest the next day.
Putting off sleep to watch just one more episode? That hour could be contributing to sudden weight gain. A 2018 study in the journal Sleep found that people who slept just one hour more per week lost more fat than those who slept an hour less. The people who slept less lost less—even though everyone in the study ate the same number of calories, proportionate to their weight at the start of the study.
5. 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, diarrhea, 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.
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.
There's a laundry list of both prescription and over-the-counter meds that can trigger sudden weight gain or water retention that shows up on the scale as extra poundage. “Antidepressants—most commonly the selective-serotonin reuptake inhibitors (SSRIs) such as Paxil, Lexapro and Prozac—may affect the appetite center in the brain,” says Rocío Salas-Whalen, MD, an endocrinologist at the Medical Offices of Manhattan.
Meanwhile, beta-blockers (meds that reduce blood pressure) can slow your metabolism, and certain steroids (like prednisone—an anti-inflammatory that causes water retention and an increase appetite) can add on pounds. Even OTC antihistamines like Benadryl, which can disrupt an enzyme in the brain that helps regulate food consumption, can trigger noticeable weight gain, says Dr. Salas-Whalen.
A word to the wise: Don’t stop taking any pills cold-turkey—chat with your doctor, who may be able to find a more waist-friendly substitute.
8. Cushing's disease
A super-rare condition called Cushing’s disease (only 10 to 15 people per million are affected, but 70 percent of those diagnosed are women) causes excess cortisol production and can trigger excessive weight gain just around the abdominal area (the legs and arms usually stay lean) and the back of the neck, says Reshmi Srinath, MD, assistant professor of diabetes, endocrinology, and bone disease at the Icahn School of Medicine at Mount Sinai.
“Cushing’s typically presents with significantly low energy and complications like diabetes, high blood pressure, and high cholesterol. But the telltale sign is very large, red stretch marks on their belly,” she says. If this sounds eerily familiar, talk to your doctor asap.
There’s a reason behind the bloat, and it may have just as much to do with the water you forgot to drink as the food that you ate.
Kristen Neilan, RD, a dietitian at University of Florida Health, says most of us aren’t drinking nearly enough water. That’s because many of us mistake the feeling of thirst for the feeling of hunger. “Confusion, tiredness, and lightheadedness are all signs of even mild dehydration,” she says. Sounds a lot like how we feel when we’re hankering for a snack.
Mixed signals aren’t the only only possible culprits behind your unexplained weight gain. “Adequate hydration increases mitochondrial function—what that basically means is that it increases your metabolism,” says Neilan. Without enough water, your cells can’t do their thing (namely, convert your food into energy) quickly and efficiently.
10. Ovarian cancer
In rare cases, an expanding belly is the result of an ovarian tumor and fluid buildup associated with it, says Sanaz Memarzadeh, MD, PhD, a gynecologic cancer surgeon at UCLA Health. “Patients come in with abdominal bloating, and their usual pants are not fitting,” she says. “Sometimes the tumor 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.
11. You quit smoking
Smoking can often act as an appetite suppressant, so when you quit, the cravings can hit strong. Pouya Shafipour, MD, a weight-loss specialist at Paloma Health, explains that smoking can lead to a rise in dopamine, the neurotransmitter responsible for instant pleasure. It's the same kind of pleasure you get when you eat a sweet snack, like ice cream.
Quitting smoking causes that dopamine level drop, but your cravings for it still remain, and this craving for a dopamine hit can sometimes lead to eating something satisfying, and more than usual. "When one quits smoking, the body still has cravings for dopamine and often people get this craving from excess intake of refined sugar and starch (i.e., candy and other starchy snacks) and gain weight," says Dr. Shafipour.
To counteract the lower levels of dopamine once you quit smoking, it's important to engage in other behaviors, like exercise or meditation, that help release feel-good endorphins and also provide a nice distraction and healthy new habit.
Type 1 and type 2 diabetes both require insulin management in order to keep blood sugar levels regulated. In people with type 1, the pancreas essentially isn't producing enough insulin, so those that have it need to regularly insert themselves with the hormone. Insulin allows the body to absorb glucose (or sugar) and use it for energy.
Type 2 diabetes is associated with insulin resistance from a poor diet, a sedentary lifestyle, and unhealthy eating behaviors. That can usually contribute to weight gain in itself, explains Dr. Shafipour. Type 2 diabetics have a higher baseline insulin level which by itself causes more weight gain, typically around the belly," says Dr. Shafipour.
But an increase in insulin from external hormone treatments can also lead to weight gain. Insulin lets glucose into your blood cells so that it can be stored for energy, but if you're eating more calories than your body needs, your cells will take what they need leaving the remaining glucose to be stored as fat.
To counteract weight gain, it's important to closely monitor your diet and avoid eating too much fast food or foods high in refined sugar, Dr. Shafipour says.
13. Other cancers
Most cancers in their early stages will result in weight loss, instead of weight gain, unless it's a cancer that causes the release of cortisol, like a tumor in the adrenal gland.
However, as cancer progresses it can cause weight gain. "This weight gain can be due growth of the size of the tumor itself or [if it spreads] to other organs like the liver, which can cause fluid build-up in the stomach or the stomach cavity," says Dr. Shafipour.
But don't be too alarmed, as this is usually a worst-case scenario. Most cancers will cause other symptoms that may cause you to see a doctor while it's still in an early stage.
When should I see a doctor for sudden, unexplained weight gain?
First, you should take a look at what your lifestyle's like. If your diet is poor, it's normal to gain between a half a pound to a pound of weight a week. Your menstrual cycle can also caught your weight to fluctuate between four and five pounds depending on what stage of your cycle you are.
But when is weight gain a cause for concern? If you're gaining one to two pounds or more a week, and you don't see the numbers going down, then it might be time to see a doctor. "If one notices that they're gaining weight rapidly, one to two pounds a week, and it's not related to menstrual cycle, poor sleep, anxiety or depression, or snacking or overeating, then they should probably see their primary care physician, who will do a thorough history and physical as well as some appropriate laboratory work-up to find the causes of weight gain," says Dr. Shafipour.
A doctor can work with you to determine whether an underlying condition is determining your weight gain, and find appropriate remedies to help you maintain a weight that makes you feel good.