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Episode 67: Thyroid And Obesity


Thyroid And Obesity

How is our thyroid function impacted by obesity and weight loss? And, how does fasting affect it? If you’ve been listening to this podcast for quite some time now, you’ve probably heard a lot already about fasting and its benefits in weight loss. However, we have never talked about thyroid function in relation to obesity! Fortunately, one of the listeners reached out to me and asked me if intermittent fasting had any impact on thyroid function. 

So today, join me as I talk about thyroid function it relates to obesity, in addition to the impact of intermittent fasting on the functioning of the thyroid gland itself, if any. 


Key Highlights: 

Tune in to this podcast and learn:

  • The role of the thyroid gland in our body
  • Definition of terms (subclinical hypothyroidism and thyroid-stimulating hormone, etc.)
  • Relationship between TSH levels and BMI
  • Risk of thyroid cancer in obesity  
  • Impact of fasting on thyroid hormone
  • Clinical significance of changes in thyroid levels


What does the Thyroid Hormone Do?

  1. It regulates thermogenesis or body heat production and energy expenditure.
  2. It regulates food intake, and glucose and lipid metabolism.


Definition of Terms:

1. Subclinical hypothyroidism

  • It is a condition with elevated levels of TSH (thyroid-stimulating hormone), but normal levels of thyroid hormones.

2. TSH or thyroid-stimulating hormone

  • It is a hormone that actually stimulates the thyroid gland to produce a thyroid hormone.
  • When the thyroid gland is not producing enough thyroid hormone, more TSH is produced to meet the body’s appropriate thyroid hormone level.

3. T3 or Triiodothyronine

  • It is a type of thyroid hormone.


Major Findings of Different Research Studies:

  1. There is a positive correlation between the TSH levels or the thyroid stimulating hormone levels and the BMI.
  2. Research has shown a decrease in the levels of T3 with fasting and in patients who have anorexia.
  3. Patients with anorexia who have gained weight have also been noted to have an increase in the TSH, while patients with obesity who have lost their weight have been noted to have a decrease in their TSH levels.
  4. There is preliminary data linking obesity with modest increase in the risk of thyroid cancer.


Impact of Fasting on Thyroid Hormone Levels:

1. There is a decrease in T3 levels while fasting. 

2. In one study, two groups (following calorie-restricted diet and alternate day fasting) of people with subclinical hypothyroidism were observed:

  • The 2nd group, who followed the alternate-day fasting, had a decrease in insulin resistance, but the thyroid hormone levels actually were not affected.
  • Weight loss was similar for both groups.

3. The second study involved people fasting for 4 days:

  • There was a drop in T3 levels, but it returned to normal after eating a mixed diet.
  • T3 levels remained low with a high protein diet.

4. Another study observed the changes of thyroid function during Ramadan:

  • There was an increase in the thyroid stimulating hormone levels, but it may not necessarily mean that the patients need to change their medications.

5. The final study focused on the results of eight weeks of time-restricted feeding (16:8 fasting) on basal metabolism, maximum strength, body composition, inflammation, and cardiovascular risk factors on resistance-trained males:

  • T3 levels decreased with time-restricted feeding.
  • No significant change in the thyroid stimulating hormone (TSH) levels



While there is definitely some change occurring in the body with fasting and the type of diet you’re taking with respect to the thyroid hormone levels, there are not enough studies proving the clinical significance of these changes. 

If you notice any changes in your thyroid hormone levels with fasting or you’re experiencing some symptoms that point towards lower functioning of your thyroid gland, do consult your physician.



Dr. Avishkar Sabharwal

“Thyroid hormone level changes with weight in both directions.”

“When we talk about intermittent fasting It is very different from starvation.”

“As with everything in medicine, it isn’t one size fits all.”



Episode 9: Cancer and Obesity


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