Gaining Weight for No Reason? Check This Out

If you’re watching your diet and exercising, get a checkup to see if a medical condition may be causing your weight gain.

Two bare feet stepping onto a scale

Medically reviewed in August 2022

Updated on August 9, 2022

You're watching your diet and working out, yet your clothes keep getting tighter. What's the deal? It might be time to see your healthcare provider (HCP).

Some medical conditions can lead to weight gain despite your best efforts. Your HCP can do a physical exam and office tests to determine what could be causing you to put on extra pounds.

One potential culprit: a sluggish thyroid.

The thyroid-weight connection 
About five percent of the United States population aged 12 and older is thought to have an underactive thyroid, called hypothyroidism. Women, people over age 60, and those with other medical issues like diabetes or an autoimmune disease are most likely to develop the condition.

It matters, because your thyroid—the tiny gland right below your Adam's apple—produces hormones that help to control your metabolism. Too-low levels slow down the processes by which your body turns food into energy, so you burn fewer calories. Your HCP can do standard blood tests to check your thyroid hormone levels.

Hypothyroidism can be easily treated with thyroid hormone replacement therapy. It’s usually a tablet that you take by mouth once every day. According to the American Thyroid Association, most people with hypothyroidism lose a small amount of weight (less than 10 percent of their body weight), after starting thyroid medication. Hypothyroidism can cause you to retain extra water and salt, which accounts for much of this weight loss. Because weight gain usually happens gradually and may have many causes, hypothyroidism alone may not be the only cause of your weight gain. The good news is that after you start thyroid medication, you may start to feel better and more able to do activities that help you lose weight.  

 For most people with hypothyroidism, thyroid hormone replacement therapy is a lifelong treatment. Your HCP will re-check your thyroid levels periodically, and adjust your medication dosage to bring your hormone levels up to where they need to be to keep you healthy.

Other causes of unintended weight gain
Though hypothyroidism is the root cause of unintended weight gain for many people, it’s far from the only one. A wide range of medical conditions is associated with extra pounds. For example, other hormone conditions such as polycystic ovarian syndrome and cushing syndrome (which develops when your body makes too much of the stress hormone called cortisol) can also cause unintended weight gain. Hormonal changes related to menopause are a common culprit, as well.

Other causes can include:

  • Fluid buildup or bloating related to menstruation, heart or kidney problems
  • Medications like oral corticosteroids, birth control pills, some mental health medications and some diabetes drugs

Strategies for managing your weight 
Whether or not a medical condition is causing your weight gain, making these key lifestyle changes may help you manage your weight: 

  • Revisit how many calories you really need, since your body’s requirements can change with age and activity level. If you’re getting more than necessary, think about ways to trim your daily calorie intake.  
  • Have you recently quit smoking? Most people who kick the habit gain 4 to 10 pounds during the first six months after quitting. Adding an exercise routine to your quit plan may help you manage your weight and refrain from using tobacco at the same time.
  • Double-check your idea of a normal portion size and consider creative ways to practice portion control.
  • Are you exercising enough? During COVID-19, quarantine and physical distancing measures may have contributed to weight gain related to less exercise and less healthy eating habits.  Find out how much physical activity you should be getting each day. The US Department of Health and Humans Services recommends that adults should get 150 minutes of moderate intensity physical activity each week (like brisk walking) and do muscle strengthening activities (like push-ups or sit-ups) on two or more days each week. Whether it’s a casual activity or a scheduled workout, here’s some quick tips on how to make exercise a regular habit.
Article sources open article sources

Hollowell JG, Staehling NW, Flanders WD, et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002 Feb;87(2):489-99.
National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid). Last reviewed March 2021.
National Institute of Diabetes and Digestive and Kidney Diseases. Cushing's Syndrome. Last reviewed May 2018.
Medline Plus. Weight gain- unintentional. Last reviewed July 19, 2021.
Thayakaran R, Adderley NJ, Sainsbury C, et al. Thyroid replacement therapy, thyroid stimulating hormone concentrations, and long term health outcomes in patients with hypothyroidism: longitudinal study. BMJ. 2019 Sep 3;366:l4892.
American Thyroid Association. Thyroid and Weight. Accessed August 3 2022.
Centers for Disease Control and Prevention. Physical Activity. Last reviewed June 2, 2022.
US Department of Health and Human Services. Physical Activity Guidelines. Accessed August 3 2022.
Zeigler Z. COVID-19 Self-quarantine and Weight Gain Risk Factors in Adults. Curr Obes Rep. 2021 Sep;10(3):423-433.

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