Calorie-restricted diets can be counterproductive for people with hypothyroidism because they slow down metabolism. Intermittent fasting has a less negative impact on metabolism as it enables the body to access stored energy.
Because intermittent fasting improves insulin resistance and reduces inflammation, it may be even more beneficial for people with hypothyroidism.
Losing weight with hypothyroidism is a struggle. The metabolism is slow and the body doesn’t want to spend energy. Unfortunately, calorie-reduced diets just make it worse.
Is intermittent fasting any different?
Before answering this question, let’s take a closer look at the thyroid’s role and why it is so crucial for weight regulation.
The thyroid is a small butterfly-shaped gland located in the front neck. It’s the master regulator of energy metabolism (1).
It does so with the help of hormones: Triiodothyronine (T3), Thyroxine (T4), and TSH (thyroid-stimulating hormone). T3 and T4 are produced by the thyroid, TSH is produced by another organ: the pituitary gland.
These two organs regulate thyroid function by a neat interplay, which you can compare with a home’s central heating system. The pituitary gland is the thermostat that is set to a certain temperature. The thermostat sends signals (TSH) to the heater (the thyroid) to turn on or off (to produce more or less T4).
T4 is the major form and is long-lasting. It is converted into active T3, which is the hormone that affects cells and, thereby, regulates metabolism.
The pituitary gland measures the concentration of T4 in the blood. If T4 is too low, it secretes TSH. TSH then stimulates the thyroid to produce more T4.
If T4 is too high, the pituitary gland produces less TSH, and the thyroid’s T4 release goes down (2).
Read more about intermittent fasting and hormones here.
In hypothyroidism, the thyroid is not active enough and does not produce enough thyroid hormones. Because thyroid hormones regulate energy metabolism, hypothyroidism leads to a decrease in energy expenditure (3). For this reason, people with hypothyroidism feel sluggish and lack energy–the body is in energy-saving mode.
An unwanted consequence of hypothyroidism is weight gain. As the body spends so little energy, it’s very hard to maintain weight or lose weight, despite reduced caloric intake.
Two important markers to diagnose hypothyroidism are T3 and TSH. T3 tends to be too low with hypothyroidism. And because the thyroid is not producing enough hormones, the pituitary gland increases its TSH production. Hence, TSH is usually too high in people with hypothyroidism.
Losing weight with hypothyroidism is a struggle. You’re usually advised to consume fewer calories to lose weight, but even in healthy people, this works only short term. Your body has to work economically. The less you eat, the less energy your body can spend. For this reason, metabolism can slow down on calorie-reduced diets, making it harder to lose weight (4).
This problem is even more pronounced in people with hypothyroidism. The metabolism is already slow, and reducing calories worsens the situation.
Intermittent fasting is, however, different from the typical calorie-reduced diet. It enables the body to access stored energy (5). Because we all have plenty of stored energy (in the form of body fat), there is no energy shortage once we can assess this energy. Hence, the slowing down in metabolism and energy expenditure is usually not an issue with intermittent fasting—when practiced correctly.
There are not many studies assessing the effect of (intermittent) fasting on hypothyroidism. In one study, prolonged fasting led to a decrease in T3. But this was only temporary. As soon as the probands ate, T3 was back to normal (6).
In another study that assessed the effect of Ramadan fasting on thyroid hormones, fasting had no effect on these hormones (7). During Ramadan fasting, people only eat between sunset and sunrise, for one month. So, it is a kind of intermittent fasting, though eating at that time is not ideal. Even people with hypothyroidism don’t have to increase their thyroid medications, which is another sign that Ramadan fasting does not negatively affect thyroid function (8).
There is another reason why intermittent fasting can be beneficial for hypothyroidism–it reduces insulin resistance (9). People with hypothyroidism are often insulin resistant and insulin resistance can worsen hypothyroidism (10).
A common cause of hypothyroidism is Hashimoto’s disease, an autoimmune condition where immune cells attack and destroy thyroid cells. Chronic inflammation is thought to play an important role in autoimmune conditions, and reducing inflammation can help (11).
Because intermittent fasting reduces inflammation, it is potentially beneficial for people with Hashimoto’s (12).
Intermittent fasting can potentially help with hypothyroidism and does not present the typical problems of calorie-reduced diets.
Nevertheless, you should approach intermittent fasting carefully with hypothyroidism. Start with a mild form of intermittent fasting, such as 12/12 fasting, and eat three meals per day. Make sure that these meals are nourishing and provide enough calories. You don’t necessarily have to reduce calories when practicing intermittent fasting. You rather go through cycles of fasting and feasting.
If you feel well with this way of eating, you can slowly increase your daily fasting time. You may then notice that you automatically eat less without feeling hungry–that’s a good sign that many people will experience when intermittent fasting.
Be sure to work together with your GP as thyroid medication dosages may need adjusting and thyroid hormones should be closely monitored.
Intermittent fasting has many health benefits. There is not much research on intermittent fasting with hypothyroidism, but it can potentially help.
In fact, in our intermittent fasting community for women only, we have many members with hypothyroidism, and they successfully lost weight with intermittent fasting. You can join the community here to get all the support you need.
1. Armstrong M, Asuka E, Fingeret A. Physiology, Thyroid Function. StatPearls. 2021.
2. Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. StatPearls. 2021.
3. Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. Lancet. Sep 23 2017;390(10101):1550-1562. doi:10.1016/S0140-6736(17)30703-1
4. Van Gaal LF, Vansant GA, De Leeuw IH. Factors determining energy expenditure during very-low-calorie diets. Am J Clin Nutr. Jul 1992;56(1 Suppl):224S-229S. doi:10.1093/ajcn/56.1.224S
5. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. Oct 2017;39:46-58. doi:10.1016/j.arr.2016.10.005
6. Azizi F. Effect of dietary composition on fasting-induced changes in serum thyroid hormones and thyrotropin. Metabolism. Aug 1978;27(8):935-42. doi:10.1016/0026-0495(78)90137-3
7. Sulimani RA. The effects of Ramadan fasting on thyroid functions in healthy male subjects. Nutrition Research. 1988/05/01/ 1988;8(5):549-552. doi:https://doi.org/10.1016/S0271-5317(88)80076-9
8. Sheikh A, Mawani M, Mahar SA. Impact of Ramadan Fasting on Thyroid Status and Quality of Life in Patients with Primary Hypothyroidism: A Prospective Cohort Study from Karachi, Pakistan. Endocr Pract. Oct 2 2018;24(10):882-888. doi:10.4158/EP-2018-0038
9. Albosta M, Bakke J. Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians. Clin Diabetes Endocrinol. Feb 3 2021;7(1):3. doi:10.1186/s40842-020-00116-1
10. Gierach M, Gierach J, Junik R. Insulin resistance and thyroid disorders. Endokrynol Pol. 2014;65(1):70-6. doi:10.5603/EP.2014.0010
11. Mikos H, Mikos M, Obara-Moszynska M, Niedziela M. The role of the immune system and cytokines involved in the pathogenesis of autoimmune thyroid disease (AITD). Endokrynol Pol. 2014;65(2):150-5. doi:10.5603/EP.2014.0021
12. Wang X, Yang Q, Liao Q, et al. Effects of intermittent fasting diets on plasma concentrations of inflammatory biomarkers: A systematic review and meta-analysis of randomized controlled trials. Nutrition. Nov - Dec 2020;79-80:110974. doi:10.1016/j.nut.2020.110974
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