Hypothyroidism is usually linked to weight gain, but certain hormone replacement therapy adjustments for hypothyroidism could lead to weight loss.
In this 2024 study, women with additional weight who took levothyroxine, a thyroid hormone replacement medication, experienced weight loss at comparable levels to women with preserved thyroid function. They also displayed lower lipids and lower insulin resistance.
Participants with obesity who took levothyroxine also experienced:
- reduced triglyceride levels
- elevated high-density lipoprotein levels
A 2021 study examining body weight changes in people with hypothyroidism indicates that hypothyroidism causes significant changes in body weight and resting metabolic rate. The study concluded that weight loss from starting levothyroxine treatment was modest and associated more with water loss rather than fat loss.
More research is necessary to highlight the cause of weight loss with hypothyroidism, but levothyroxine therapy may be a factor.
Other factors may affect weight loss, and these may not necessarily be related to hypothyroidism. For example, you may be losing weight due to malabsorption. This means your body cannot absorb nutrients from food. Certain conditions can lead to malabsorption of nutrients, such as:
Hypothyroidism may also lead to decreased levels of hydrochloric acid in the stomach, which could affect the absorption of nutrients, such as iron.
Symptoms of hypothyroidism, such as tiredness and difficulty concentrating, could mask symptoms of an iron deficiency, so you may not realize you have it, or think your treatment for hypothyroidism isn’t working as it should.
If you’re experiencing weight loss with hypothyroidism, contact a doctor or healthcare professional for more in-depth advice.