Thyroid Function and its Effect on Weight Loss

Thyroids have a lot of control over the body, especially overall metabolism and resting metabolic rate (how many calories you burn per day at rest). For this reason, many people attribute their inability to lose weight to thyroid function.

We are all familiar with energy balance for weight loss—to lose weight, you must have a negative energy balance, which means you expend more energy than you consume. However, if your thyroid is not functioning optimally and your metabolic rate is low, you may experience difficulties losing weight because your body does not expend energy effectively. This may lead you to be in a state of caloric maintenance or surplus, thus preventing you from losing weight.

What I want to emphasize is that you cannot break the laws of thermodynamics—you can lose weight if you’re in a caloric deficit, however for those with thyroid issues this may not be that easy. However, there are ways to approach it.

In this blog, we’ll talk about the thyroid’s role in the body, symptoms of hypothyroidism and hyperthyroidism, and how to optimize your approach to weight loss if you do struggle with either thyroid disorder.


Thyroid Overview

The thyroid gland, which is in the neck, consists of two lobes. It produces two hormones: triiodothyronine (T3) and thyroxine (T4). Ultimately, the thyroid controls and regulates metabolism in the body.

How are T3 and T4 released?

It’s a process with several players involved.

  1. The hypothalamus releases thyrotropin releasing hormone (TRH).

  2. TRH stimulates the release of thyroid stimulating hormone (TSH) which is released from the pituitary gland.

  3. TSH then goes to the thyroid gland and allows for the release of T3 and T4.

What happens after T3 and T4 are released?

T3 and T4 attach to proteins (carrier proteins, specifically) which are transported through the bloodstream. From there, they continue their journey to the cells, where they detach from the protein and do their job of regulating metabolism of the cell.


Hypothyroidism and Hyperthyroidism

Hypothyroidism and hyperthyroidism can be diagnosed by medical professionals through blood work that measure TSH. If you are experiencing the symptoms of either hypo or hyperthyroidism, a screening for thyroid function may be something work talking about with your PCM.

How to Optimize Thyroid Function

When someone suspects their inability to lose weight is due to thyroid issues, they are referring to hypothyroidism. If properly diagnosed, medication is given to the individual to control the thyroid function. However, it is not the only thing that should be done to help. Other factors that need to be addressed are the three pillars of overall health and wellness: nutrition, exercise, and lifestyle.

Logically if you have hypothyroidism, you should be able to add in thyroid hormones and experience desired weight loss results. However, that is NOT the case. There are initial results that are favorable (described below) but there is not drastic body composition changes from utilizing just these medications. The studies with exogenous thyroid hormones demonstrated the following results:

  • Exogenous T4 treatment [1]

    • Results: decrease in body weight and increase in resting energy expenditure HOWEVER fat mass was unchanged, and weight loss was primarily due to excess water loss in the body.

  • Exogenous T3 treatment [2]

    • Results: For hypothyroid patients, there was weight loss of about 2kg (4.4 lbs) in 6 weeks, but it stalled after that.

Let’s say you do have hypothyroidism/hyperthyroidism, and want to optimize your health in addition to the medication prescribed by your doctor, the following things should be considered in your approach:

  • Optimize your sleep. Aim to get quality sleep every night and aim for 7-9 hours. Recovery is essential.

  • Do not decrease your caloric intake drastically. We have mentioned in various blog posts that nutrition is all about creating a solid foundation through a sustainable approach. If you restrict your calories drastically, you inevitably put your body through excess stress and will experience a decrease in T3/T4 hormones.

    • One study by Hulmi, et al. [3] showed that women who competed in physique sports, such as bodybuilding, has a significant decrease in T3/T4 hormones due to their excessive caloric restriction and extremely low body fat. This further resulted in lethargy and menstrual cycle irregularity. It usually takes about 3-4 months for thyroid levels to return to baselines if body fat was too low or excessive measures for weight loss were taken.

  • Fill your days with whole foods as much as possible. Whole foods are the way to go to optimize your vitamin, mineral needs however that does not mean you only have to eat whole foods. Keep a good balance that is best for you but prioritize whole foods and keep most of your foods in that realm.

  • Do not cut out food groups. We recommend you do not cut out all fats or all carbs out of your diet. Instead, keep a good balance of all three macronutrients in your nutrition approach- carbs, fats, and protein.

  • Exercise regularly. Aim to exercise regularly, to include strength training and conditioning.

All the steps we encourage you to take are things we speak about regularly for overall health and wellness. If you experience thyroid issues, we encourage you to speak with your doctor, as well as develop the habits of living a healthy life. Many times, results do not come overnight, but with consistency and adherence, you will feel better and see the results you want.



1.     Mullur, R., Y.Y. Liu, and G.A. Brent, Thyroid hormone regulation of metabolism. Physiol Rev, 2014. 94(2): p. 355-82.

2.     Celi, F.S., et al., Metabolic effects of liothyronine therapy in hypothyroidism: a randomized, double-blind, crossover trial of liothyronine versus levothyroxine. J Clin Endocrinol Metab, 2011. 96(11): p. 3466-74.

3.     Hulmi JJ, Isola V, Suonpää M, Järvinen NJ, Kokkonen M, Wennerström A, et al. The Effects of Intensive Weight Reduction on Body Composition and Serum Hormones in Female Fitness Competitors. Front Physiol. 2017 Jan 10;7.