Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Weight and thyroid health are closely linked, but does carrying extra kilos actually trigger hypothyroidism? The thyroid helps regulate metabolism, and research suggests that obesity might raise the risk of developing hypothyroidism, both mild and more severe forms. A study also shows that obesity can influence hormone levels, including those related to thyroid function, which may contribute to an underactive thyroid.
So, what does science really say? Let’s break down the connection between weight and thyroid function and what it means for your health.
Obesity and hypothyroidism often go hand in hand, but the relationship isn’t always straightforward. While hypothyroidism can lead to weight gain by slowing metabolism, research suggests that excess weight may also affect thyroid function.
Studies have found that individuals with obesity tend to have higher thyroid-stimulating hormone (TSH) levels, even when their thyroid function appears normal. This suggests that obesity may influence thyroid hormone regulation, though the exact mechanisms are still being explored.
However, most experts agree that obesity alone doesn’t directly cause hypothyroidism. Instead, weight-related hormonal changes may slightly alter thyroid function, but not to the extent of triggering full-blown hypothyroidism in otherwise healthy individuals.
While obesity may contribute to thyroid dysfunction, other factors are often at play:
Autoimmune disease (Hashimoto’s thyroiditis) – The leading cause of hypothyroidism, where the immune system attacks the thyroid gland.
Iodine deficiency – Iodine is essential for thyroid hormone production, and a deficiency can lead to an underactive thyroid.
Radiation therapy to the neck area – Treatments for cancer can damage the thyroid gland.
Thyroid surgery – Removing part or all of the thyroid can result in hypothyroidism.
Certain medications – Some drugs, including lithium and amiodarone, can interfere with thyroid function.
Congenital hypothyroidism – A condition present at birth due to improper thyroid development.
Pituitary disorder – If the pituitary gland doesn’t produce enough TSH, the thyroid won’t function properly.
Pregnancy – Some women develop postpartum thyroiditis, which can lead to temporary or permanent hypothyroidism.
While obesity isn’t a direct cause of hypothyroidism, it can influence thyroid function in several ways. Take a closer look at the mechanisms behind this connection.
Fat tissue isn’t just a storage unit—it’s metabolically active and can influence hormone production. Excess adipose tissue may disrupt thyroid function by altering the way thyroid hormones are metabolised and circulated in the body.
Leptin, a hormone produced by fat cells, helps regulate appetite and metabolism. However, higher leptin levels, which are common in obesity, can interfere with thyroid hormone production. A study found that excessive leptin may contribute to hypothyroidism by affecting the hypothalamic-pituitary-thyroid (HPT) axis.
Carrying excess weight is linked to chronic inflammation, which may play a role in thyroid health. Certain inflammatory markers, like C-reactive protein (CRP) and tumour necrosis factor-alpha (TNF-α), have been associated with thyroid issues. While scientists are still exploring the connection, keeping a healthy weight could be one way to support your thyroid and overall metabolism.
Insulin resistance, common in overweight individuals, can affect thyroid health. Research shows that people with metabolic syndrome (which includes insulin resistance) often have abnormal thyroid hormone levels. The same research found that those with insulin resistance were more likely to develop hypothyroidism than those with normal insulin sensitivity.
Adipokines are hormones secreted by fat tissue that regulate metabolism and inflammation. In obesity, imbalances in adipokines, such as lower adiponectin levels and higher resistin levels, can negatively impact thyroid function. Studies suggest that these changes may contribute to reduced thyroid hormone activity over time.
While being overweight doesn’t directly cause hypothyroidism, it can contribute to hormonal imbalances that affect thyroid function. This relationship is complex, but research suggests that moderate weight loss can help improve thyroid hormone levels and metabolic health.
If you have hypothyroidism or thyroid issues due to obesity, try the Interval Weight Loss Program. It can do more than just help you lose weight—it also supports your metabolism, thyroid health, and overall well-being. Check out these articles to learn more.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.