10 Underlying Medical Issues That Can Lead To Sudden Weight Gain

While most of us have been conditioned to think otherwise, the truth about weight gain is that it's not always a problem or an indicator of poor health. However, there are times when sudden and unexplained weight gain might be dangerous for health and long-term wellbeing. Being in tune with what's "normal" for your body, whether that's weight, smell, or the amount of hair you lose in the shower, is an important way to gauge your health over the long term.

As a certified health coach, I work with clients on connecting with their bodies and understanding how certain foods, behaviors, and hormonal changes can interfere with their abilities to maintain health, happiness, and confidence long-term. Sometimes weight gain can occur for no clear reason, and while changes in body size and weight happen constantly, it can be frustrating to feel at a loss of knowledge. Further, these changes could be indicators of medical issues that merit attention from a doctor.

Look for these 10 causes of sudden weight gain and how they can affect your overall health and wellness. By identifying the potential cause of the weight gain, you'll be better able to determine if it's a sign of a medical issue, and talk to your doctor about how to feel more like yourself again.

1. Your Thyroid Is Out Of Whack

If your thyroid is unable to produce enough thyroid hormone — which could indicate that you might have hypothyroidism, Graves, or Hashimoto's disease — then weight gain is rather common and can be harmful to your health if not treated appropriately, Marcelle Pick, OB/GYN NP said on Women To Women, the site of a women's health clinic. If you notice swelling in the neck (a "goiter") or other symptoms, such as fatigue, depressive mood, irregular bowel movements, and irregular body temperature, seek a physician for a diagnosis.

2. You're Taking Birth Control

Experts at Mayo Clinic share that birth control might lead to extra fluid retention depending on brand, dosage, and hormonal levels. It may take your body a few cycles to adjust to a new birth control brand, so be patient (unless, of course, you're experiencing other symptoms that get in the way of your daily functioning). If you're still experiencing extra fluid retention after three cycles, talk to your doctor about finding a weight-neutral prescription.

3. You're Not Getting Enough Nutrients

If you are not properly absorbing nutrients or consuming balanced meals, it can mess with your metabolism, explains running coach and personal trainer Susie Lemmer, over email with Bustle. For instance, vitamins A, D, E, and K are fat-soluble and must be consumed with healthy fats to be absorbed by the body. If you eat vegetables without a healthy fat, your body won't reap the benefits. Pair healthy fats, such as avocado, olive oil, fish, and nuts, with meals to get in all the nutritional aspects.

4. You're Having A Depressive Episode

Numerous studies have found that depression can lead to changes in appetite and metabolism that can cause weight gain. In an interview with Live Science, University of Alabama at Birmingham Professor Belinda Needham, PhD, explained that this link may be due to the stress hormone cortisol. "Cortisol acts as a support for the body’s fight-or-flight system," Joyce Faraj, PhD, RDN, CDN, a nutritionist at Mountainside, a substance use recovery center, tells Bustle. "When we are in a constant state of stress, cortisol can affect our body composition by upregulating gluconeogenesis, that is, the creation of blood glucose through breakdown of muscle, leading to a state where more muscle is broken down and visceral fat is accumulated."

5. You're Working Out Too Much

While working out benefits the body, as it boosts endorphins to make us happier, more creative, more productive, and balances our blood sugar levels to prevent diabetes and heart disease, too much training can cause our bodies to store fat, thanks again to the stress hormone cortisol. "When you start working out, especially for strength training, tiny muscle tears and fluid retention can lead to increased weight," Faraj says. "These microscopic muscle tears occur during weight lifting and are part of the muscle-building process. When this occurs, muscles swell and retain fluids for a few days, and is a normal part of the recovery process."

6. You Have Bacterial Overgrowth

Sometimes bad bacteria (different from our typical microbiome) can grow inside the gut, leading to bloat, fatigue, irregular bowel movements, and weight gain. Roughly 60% of our immune system resides in the gut, certified healthy lifestyle coach Liz Traines tells Bustle, so when there's an overgrowth and imbalance within it, it can throw our bodies and hormones out of whack. "Poor digestion and even slow bowel movements can lead to sudden weight gain," nutrition coach Darin Hulslander tells Bustle. "Low fiber, dehydration, certain medications, or even a lack of healthy gut flora can lead to poor digestion and constipation. A probiotic can assist with this," Hulslander adds.

7. Your Work Schedule Has Shifted

If you've noticed a change in work schedule or travel, you might find yourself with diminished sleep or irregular cycles. Plus, if your travel is international, the jet lag can really take a toll on the body, according to a study published in the journal Cell. Not getting adequate sleep can interfere with our hormones, predominantly cortisol and the hunger hormones, ghrelin, and leptin, which can enhance cravings and overeating.

"Shorter sleep is associated with lower leptin and higher ghrelin," Faraj tells Bustle. "Less sleep also leads to decreased leptin secretion, which is an appetite suppressant. These differences in leptin and ghrelin are likely to increase appetite... Another contributing factor may be that when we’re tired we tend to put in less effort to make healthy food choices or we may also be more sedentary as a result of increased fatigue."

8. Your Electrolytes Are Imbalanced

If you're not drinking enough fluids during the day (think water or juice), or are eating too many salty foods, you might experience water retention and bloating. "A high sodium meal can cause you to store some excess water," says Hulslander.

Another reason for this imbalance? Drinking so little water you're dehydrated. "Dehydration, which is very common during working out, can also lead to water retention as part of our survival mechanism," Faraj says. "Therefore, maintaining good hydration can help fight water retention caused by dehydration."

9. It May Be Due To A Tumor

If you gain weight around your belly, as opposed to your lower body, it could signal a larger problem at hand. Sometimes an extended stomach can be the result of a tumor, such as an ovarian tumor, as Howard Eisensen, M.D., director of Duke University's Diet and Fitness Center, told Shape. It's worth checking with a doctor to rule out any possible tumor diagnoses, especially if you're experiencing pain.

10. You Have Insulin Resistance

If you do any Googling on this subject, you might come up against the phrase "insulin resistance." This symptom, which basically means your body doesn't process the hormone insulin the way it should, is a precursor to diabetes, and is manageable.

"Insulin resistance ... is in large part a result of chronic inflammation," Faraj says. "In an inflammatory state, fat cells may grow, and this growth pulls in cells from the immune system leading to increased proinflammatory signals and decreased anti-inflammatory signals." In order to manage a diagnosis of insulin resistance, try to manage your exposure to inflammatory foods or stressors, such as processed foods.

While most weight gain is not dangerous, some weight gain — especially if it's sudden, painful, or out of the norm for your body — can be dangerous for long-term health and wellbeing. If you notice something off with your body's normal functioning, talk to your doctor to rule out any serious complications. It's always worth a second check if you notice any abnormalities or discomfort.

This post was originally published on September 29, 2016. It was updated on June 18, 2019.