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Why Am I Gaining Weight: A look into Thyroid Disorder


Are you a woman in your late 20s and one day, to your surprise realize you’re 15 pounds heavier without having made any changes to your diet or exercise routine? Are you a 50-something menopausal woman who is 20 pounds heavier compared to 10 years ago?

You ask yourself, IS IT MY THYROID? The simple answer is maybe, but most likely not.

Weight gain is a common, but  very complex medical issue.  A study of over 4000 normal weight men and women 30-59 years old conducted over a span of 30 years, showed that after 30 years, more than 50% were overweight, and that 30% of women and 25% of men were obese.  That is mind boggling!

So why do people gain weight?

Pregnancy, oral contraceptives, and menopause contribute a lot to  weight gain as women get older.  Excess weight gain during pregnancy leads to difficulty losing weight after delivery. Some women do gain weight when they start birth control but not all. Most women gained on average around 6.4 lbs. and have a 5.7 cm increase in waist circumference within 6 years of menopause.  In men, the transition from an active lifestyle in their teens and early 20’s to a relatively sedentary lifestyle when they hit their 30s is usually the culprit for weight gain.

The availability of cheap, palatable and energy dense foods that started being produced in the 1970s, genetic predisposition, sleep deprivation and smoking cessation have all been shown to lead to weight gain.

  • Sleep deprivation decreases serum leptin, the hormone that makes you eat less, and increases serum ghrelin, the hormone that increases appetite.
  • On average, people gain 8 to 10 pounds after quitting smoking.
  • Medications like anti-depressants, anti-psychotics, lithium and anti-seizure have also been associated with weight gain.

Although there are other “hormonal” causes of weight gain like hypothalamic obesity, Cushing’s syndrome, PCOS and growth hormone deficiency, hypothyroidism (an underactive thyroid gland) is the most common endocrine disorder that can lead to weight gain.  

Although it is true that thyroid hormone regulates metabolism, there is a complex relationship between thyroid disease, body weight and metabolism, which means the thyroid alone does not determine weight gain.  The weight gain associated with hypothyroidism because of decreased metabolic rate is modest, on average ranging between 5 to 10 pounds. Massive weight gain however is rarely due to just an underactive thyroid. The cause of weight gain in hypothyroid individuals is complex and usually not connected to excess fat accumulation. The main cause is usually due to excess accumulation of salt and water.

The treatment of hypothyroidism will lead to modest weight loss, usually less than 10% of body weight. When the thyroid level has been normalized, the ability to gain or lose weight is the same as those without a thyroid problem. Trying to give more thyroid hormone in order to lose more weight is usually ineffective and should not be attempted. It will  just lead to unpleasant symptoms of too much thyroid hormone and can lead to heart problems and loss of muscle and bone tissue.

It is human nature to want to have a simple and easily treatable condition like underactive thyroid to blame our weight gain on. However, we need to look deeper at other factors when we fail to lose weight, even after treating the hypothyroid condition.


Florence I. Celzo-Vista, MD, is an Endocrinologist and earned her Medical Degree at University of the Philippines College of Medicine in Manila, Philippines. She completed her Residency in Internal Medicine at the Cleveland Clinic Foundation in Cleveland, OH and Fellowship-training in Endocrinology at Henry Ford Hospital in Detroit, MI. Dr. Celzo-Vista is Board Certified in Internal Medicine, Endocrinology, and Diabetes & Metabolism. She’s seeing patients in Middletown and Warwick.