Written by Christine Richmond

If you found yourself gaining weight in 2020, you’re not alone: A study of 7,753 adults found that nearly one-quarter of those surveyed did, too. [1]

Of course, if you asked those folks why they gained weight, the culprits would probably be easily identifiable. Calorie-dense foods, glasses of wine, and Netflix binges supplied temporary comforts in a year filled with isolation, chaos, and fear.

But what if your diet was (relatively) clean, you exercised regularly, and the number on the scale still continued to climb?

First things first: Make sure that the part about your diet is true. Studies show that most adults tend to underestimate the number of calories they’re consuming. [2,3] Your best bet is to make sure you’re following a balanced diet.

If your diet hasn’t changed recently, there might be something going on with your health. Here are a few common reasons why the number on the scale could be creeping up.

Weight Gain Culprit #1: You’re Older Than 30

Starting at around age 30, your metabolism naturally slows down. According to Harvard University, it also means you lose about 3 to 5 percent of your muscle mass each decade. [4]

That’s important, because muscle burns more calories than fat, even when you’re at rest [5]. This is why “what you ate and the exercise you did in your 20s to keep slim isn’t working anymore,” [6] explains Kathryn Boling, M.D., a family physician at Mercy Medical Center in Baltimore.

One solution for combatting the hands of time? Strength training. A study in the Journal of Translational Medicine found that lifting weights (particularly heavier ones, for six or fewer repetitions at a time) resulted in an increased calorie burn—even once the workout session was over. [8]

Weight Gain Culprit #2: You’re Going Through Menopause

The hormonal changes that accompany perimenopause and menopause can have a significant impact on your weight, studies show [9]. That’s because, as your body produces less estrogen and progesterone, [10] you’re more likely to put on pounds, especially around your waist. [11]

“The average weight gain for a woman going through menopause is roughly 15 pounds,” explains Dr. Boling. [6] This won’t come as a surprise, but research has shown that moving more and eating less can help combat menopausal weight gain. [9,10,11]

Check your hormones now.

Weight Gain Culprit #3: You’re on a New Medication

An often overlooked—yet very common—cause of weight gain? Your prescriptions. [12]

“Across the board, there are tons of medications that can cause weight gain,” says Boling, including antihistamines, antidepressants, antipsychotics, and beta-blockers. “Talk to your doctor to see if there’s something else you can take instead that might be less likely to cause weight gain.” [6,12] Be sure to not discontinue any medication you’re taking before consulting with your doctor.

Weight Gain Culprit #4: Your Sleep Schedule Is Out of Whack

Whether it’s insomnia or sleep apnea, if you routinely don’t get a good night’s sleep, you might have more trouble maintaining a healthy weight. [13]

Research has shown that sleep deprivation can cause you to have less leptin (the hormone that suppresses hunger), more ghrelin (the hormone that stimulates appetite), and a higher body mass index. [13] This could mean that your diet has subtly become more carb- and sugar-heavy without you even realizing it. “It can be an insidious, slow change over time, so you may not notice,” Dr. Boling says. [6]

If you have trouble falling asleep or staying asleep, talk to your doctor about your options (they may suggest lifestyle changes, medication, or a combination of the two). As for sleep apnea—a condition in which your breathing is interrupted multiple times throughout the night—it’s sometimes common to not realize you have it. But if left untreated, sleep apnea can increase your risk of health problems like heart disease and type 2 diabetes. [15]

A few telltale signs you may have sleep apnea: drowsiness during the day and loud snoring at night. Your doctor can order a sleep study to determine whether you have sleep apnea. [15,16]

Weight Gain Culprit #5: You Might Have a Hormonal Disorder

Is your weight gain (especially at the waist) coupled with acne, irregular periods, and excess hair growth? A hormonal disorder affecting women of reproductive age, called polycystic ovary syndrome (PCOS), could be to blame. [17]

Women with PCOS tend to be insulin resistant, which means that their blood sugar levels are too high (which also increases the risk of developing type 2 diabetes). That spike triggers your body to store extra belly fat, Boling explains. [6,17] Take a hormone test now.

If your doctor suspects you have PCOS, you’ll likely get a pelvic ultrasound to check for cysts. While there’s no cure for PCOS, it’s treatable. Talk to your doctor to learn more. [18]

Weight Gain Culprit #6: You Have an Underactive Thyroid

One commonly undiagnosed hormonal disorder, known as hypothyroidism, means your thyroid gland (located in the front of your neck) isn’t making enough hormones. [19] “Your thyroid runs your metabolism,” explains Dr. Boling, so if it’s underactive, you might start gaining weight. [6,19]

Dr. Boling tests her patients’ thyroids at their yearly physicals, but not all primary care doctors do. Keep in mind that it’s unlikely that weight gain would be your only symptom if you had an underactive thyroid—you could also notice issues like hair loss, dry skin, constipation, sensitivity to cold, and depression.

Simple blood tests can confirm whether your thyroid hormone levels are off. If you do have an underactive thyroid, your doctor may prescribe a supplemental thyroid hormone. [6,9]

Take a thyroid test now.


  1. Flanagan EW, Beyl RA, Fearnbach SN, Altazan AD, Martin CK, Redman LM.
    The Impact of COVID-19 Stay-At-Home Orders on Health Behaviors in Adults
    Obesity (Silver Spring) 2020 Oct 11:10.1002/oby.23066

  2. Brian Wansink
    Solve & Share
    Why do Overweight People Underestimate How Much They Eat?

  3. Treadmill Reviews
    Perception vs. Reality: Chain Restaurant Foods

  4. Harvard Medical School
    Harvard Health Publishing
    Preserve your muscle mass

  5. Mayo Clinic
    Metabolism and weight loss: How you burn calories

  6. Kathryn Boling M.D.
    Mercy Medical Center

  7. Mercy Medical Center
    Kathryn A. Boling, M.D.

  8. Paoli A, Moro T, Marcolin G, Neri M, Bianco A, Palma A, Grimaldi K.
    High-Intensity Interval Resistance Training (HIRT) influences resting energy expenditure and respiratory ratio in non-dieting individuals.
    Journal of Translational Medicine 2012 Nov 24;10:237

  9. Kapoor E, Collazo-Clavell ML, Faubion SS.
    Weight Gain in Women at Midlife: A Concise Review of the Pathophysiology and Strategies for Management
    Mayo Clinic Proceedings 2017 Oct;92(10):1552-1558

  10. Mayo Clinic

  11. Harvard Medical School
    Harvard Health Publishing
    Winning the weight battle after menopause

  12. University of Rochester Medical Center
    Health Encyclopedia
    When Your Weight Gain Is Caused by Medicine

  13. Taheri S, Lin L, Austin D, Young T, Mignot E
    Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index
    PLOS Medicine December 7, 2004

  14. Mayo Clinic
    Diagnosis and Treatment

  15. Mayo Clinic
    Sleep Apnea
    Symptoms & Causes

  16. Mayo Clinic
    Sleep Apnea
    Diagnosis and Treatment

  17. Centers for Disease Control and Prevention
    PCOS (Polycystic Ovary Syndrome) and Diabetes

  18. Mayo Clinic
    Polycystic ovary syndrome (PCOS)

  19. U.S. National Library of Medicine
    Medline Plus