This Is Why You Started Gaining Weight Out of Nowhere

femme laughing and eating ice cream cone

Westend61 / Getty Images

Every size is beautiful, but there's no discovery quite as startling as stepping on the scale and weighing way more than you thought you did (or trying on your favorite pair of pants only to realize that they fit a little tighter than they did the week before) with absolutely no idea why.

Most of the time we can pinpoint our weight gain from, say, an overly indulgent vacation in which we downed a dessert with every meal or a newfound affinity to eat out on the regular. But, then there are those times when we experience unexplained weight gain—the kind of weight gain that seems to show up overnight, out of nowhere, and seemingly for no reason.

"To deal with any third-party conditions that could be causing the weight gain, we need to feel comfortable discussing our experience with our doctor," says New York-based internist Dr. Niket Sonpal. We spoke to Sonpal and registered dietitian Vendana Sheth for tips in terms of dealing with unexpected weight gain, and what might be contributing to the problem in the first place.

Read on to learn the unexpected factors that could be causing sudden, rapid weight gain.

Meet the Expert

  • Niket Sonpal, MD, is a New York City-based board-certified internist, gastroenterologist, and assistant clinical professor at Touro College of Osteopathic Medicine.
  • Vandana Sheth, RD, CDCES, FAND, is a Los Angeles-based registered dietitian nutritionist and author of My Indian Table: Quick & Tasty Vegetarian Recipes.

01 of 14

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. 

02 of 14

Your Medication

Pills on a pink background

Yulia Reznikov / Getty Images

When you gain weight, the first place you look for answers is often your diet or exercise routine, but the culprit can be hiding in your medicine cabinet. Many medications, including those that treat migraines and mood disorders, as well as birth control and steroids, can cause weight gain for a variety of reasons. If you suspect a medication you're taking might be causing weight gain, talk to your doctor to discuss your options. 

03 of 14


Moon Juice SuperYou Daily Stress Management $49

Like with insufficient sleep, stress can cause weight gain because of hormones. "High levels of stress cause our cortisol levels to spike, and this can contribute to weight gain," Sheth says. "Chronically high cortisol levels can disrupt sleep, affect our blood sugars, enhance cravings and lead to more fat storage  especially in the abdominal area." As Sonpal explains, a surge in the hormone cortisol leads to an increased appetite (to fuel your fight-or-flight response).

But stress can be harmful in other ways, too. "Stress has a number of physical effects on your body, but it also has psychological effects that can develop into behaviors that cause weight gain," echoes Sonpal. "Our body and mind respond to this stress in a few ways; one is overeating. When you are stressed, your body starts sounding the fight or flight response, and this can often trigger stress-induced eating."

Exercising regularly is a well-loved solution, as working out not only lowers stress, it also helps with weight loss.

04 of 14

Your Job

If you've had a nine-to-five desk job for a while, you might not suspect it as a reason for weight gain, but the effects of office life on weight go beyond the sedentary nature of it and can compound quickly. Maybe a new project has you working late nights (and, thus, you're not getting enough sleep (see slide one) and super stressed (see previous slide), and/or you're too busy to throw together a healthy lunch, so you're eating more fattening fast food than you realize. Throw in some mindless snacking on the communal food in the kitchen, and a coworker's birthday donuts for the team and the pounds might just start to add up in more ways than one. 

Again, stress can certainly play a role here, as Sheth notes. "Stress is a daily part of our lives," she says. "The key is to practice stress management techniques consistently." She recommends a few strategies that can help: "Eating balanced meals throughout the day, getting a good night’s sleep, doing something physically active—walking, yoga, a virtual fitness class, and incorporating some type of meditation or breathing exercise. You could also consider using apps like Headspace or Calm to help."

05 of 14


woman eating French fries

wundervisuals / Getty Images

Sometimes the reason behind the scale reading a number other than what you expect is your sodium intake. When sodium is the culprit, you haven't gained body fat; your body is just retaining water weight to dilute the sodium. Outside of salt alone, unlikely sources of sodium include plenty of salad dressings and sauces, frozen meals, and bread. If you focus on cutting back on sodium, this form of weight will disappear pretty quickly. 

06 of 14

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. 

07 of 14

Weight Training

Confusingly, you might find that you've gained weight after you start working out more, which happens for two reasons. First, weight training increases muscle mass, and muscle is more dense than fat, so as you lose fat and increase muscle, you might see a higher number on the scale. Second, weight training causes muscle inflammation (the soreness you feel afterward), which means the muscle swells from water retention to protect it. The good news is that although weight training, especially when you're just starting, might cause slight weight gain, it will help you lose inches—which means even if the number on the scale reads slightly higher, your clothes will fit better. 

As Sonpal explains, don't get frustrated if results aren't immediate. "It is not easy," he says. "The first thing I tell patients is, don't put yourself down. There is so much shame associated with weight gain."

08 of 14


HUM base control
HUM Base Control $10

Maybe weight gain isn't the only symptom you've noticed. Maybe you feel tired and weak, too. It's possible that your thyroid gland isn't making enough thyroid hormone, and that's why you've suddenly noticed an increase in weight. Because the hormone regulates metabolism, people found to have underactive thyroids were also found to have lower basal metabolic rates.

"There are decisions we can make every day that lead us on a healthier path, but also understand that age plays a factor," Sonpal says. "Other health conditions like an underactive thyroid can decrease the level at which your thyroid functions." A solid multi-vitamin is a good start, though Sonpal says that seeing a professional is always a good idea if you're concerned about something serious like hypothyroidism: "To deal with any third-party conditions that could be causing the weight gain, we need to feel comfortable discussing our experience with our doctor."

09 of 14

PCOS (Polycystic Ovary Syndrome)

As anyone who has been diagnosed with PCOS will tell you, weight gain tends to be on the lesser end of worries caused by this syndrome. Still, due to the stigmas that surround reproductive health, it's easy to glaze over this symptom. "Women with PCOS have a harder time losing weight and maintaining their weight," Sheth says.

Other signs of PCOS include excess body hair, acne, and irregular periods—and unfortunately, some people go a long time without knowing they have it. There are various treatments available, so just like with hypothyroidism, if you think you might have PCOS seeing a doctor is your best bet.

10 of 14

Quitting Smoking


Duke Harbovitch / Getty Images

We can extoll the virtues of quitting smoking all day, and the good inarguably outweighs the bad in terms of what it does for your health. However, nicotine is a stimulant and an appetite suppressant: two things that lead to weight decrease. When you quit smoking, your metabolism slows to a normal speed and your appetite comes back. Ultimately these are good things, regardless of the added weight.

11 of 14


Depression can be associated with things we've mentioned before, like medication, stress, and your job. But it also effects your weight. There are a couple of reasons for this, not least the fact that depression isn't exactly associated with an increased amount of energy. And unfortunately, a lack of exercise exacerbates depression, too.

"Depression can cause weight gain for a few reasons, but mainly because of those behavioral changes," Sonpal says. "Someone who is depressed may find it hopeless to regularly partake in physical activity, eating may be a source of comfort, and they can get into a vicious cycle of losing hope as they gain weight or start to feel other symptoms of weight gain, like high blood pressure and lack of energy."

Not everyone's depression allows for exercise. In dealing with this particular weight gain symptom, just do what you know is best for you in order to get better, and seek professional treatment.

12 of 14

Digestive Issues

There's been more talk lately about the gut microbiome and what it means for your health—not just your gut health, but the rest of your body, too. The bacteria in your digestive tract can dictate everything from how much acne you have to your weight. An imbalance of good and bad bacteria can lead to sudden weight gain, so you should evaluate the foods you've been eating not just for their general nutritional content but for their probiotic effects. Just taking probiotics can even be a big help!

13 of 14


Hand holding tampon

Megan Madden / Refinery29 for Getty Images

Luckily, it's the kind of thing that's just fixed by waiting it out, but getting your period can cause you to gain a little bit of weight. Not only are you retaining water a bit more, but your hormones are all out of whack. "Hormonal changes can also potentially cause weight gain," Sheth says.

Increases in estrogen and progesterone can cause weight fluctuations, and although it's annoying, the most you can do about it is just wait for it to go away.

14 of 14

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."

Article Sources
Byrdie takes every opportunity to use high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial guidelines to learn more about how we keep our content accurate, reliable and trustworthy.
  1. Patel SR, Malhotra A, White DP, Gottlieb DJ, Hu FB. Association between Reduced Sleep and Weight Gain in WomenAmerican Journal of Epidemiology. 2006;164(10):947-954. doi:10.1093/aje/kwj280

  2. Verhaegen AA, Van Gaal LF. Drugs That Affect Body Weight, Body Fat Distribution, and Metabolism. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Updated February 11, 2019.

  3. Chao AM, Jastreboff AM, White MA, Grilo CM, Sinha R. Stress, cortisol, and other appetite-related hormones: Prospective prediction of 6-month changes in food cravings and weightObesity (Silver Spring). 2017;25(4):713-720. doi:10.1002/oby.21790

  4. Anxiety & Depression Association of America (ADAA). Physical Activity Reduces Stress.

  5. National Institutes of Health. How the body regulates salt levels. Published May 2, 2017.

  6. Laja García AI, Moráis-Moreno C, Samaniego-Vaesken M de L, Puga AM, Partearroyo T, Varela-Moreiras G. Influence of Water Intake and Balance on Body Composition in Healthy Young Adults from SpainNutrients. 2019;11(8). doi:10.3390/nu11081923

  7. Cleveland Clinic. I Just Started Exercising — Why Am I Gaining Weight?. Published March 9, 2020.

  8. American Thyroid Association. Thyroid & Weight. Published 2019.

  9. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). What are the symptoms of PCOS?. Updated January 31, 2017.

  10. Harris KK, Zopey M, Friedman TC. Metabolic effects of smoking cessationNat Rev Endocrinol. 2016;12(5):299-308. doi:10.1038/nrendo.2016.32

  11. National Institute of Mental Health. Depression. Updated February 2018.

  12.  U.S. Department of Health and Human Services Office on Women's Health. Premenstrual syndrome (PMS). Updated March 16, 2018.

Related Stories