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Is Your Diet Sabotaging Your Thyroid and Metabolism?

Is Your Diet Sabotaging Your Thyroid and Metabolism?

Diet is one of the most influential factors of individual wellness. Unfortunately, dieting can sometimes feel like a pointless and frustrating practice. Many individuals who employ aggressive, overly-restrictive diets experience a quick shedding of pounds only to soon return to their starting weight or even gain weight. The cause of this relapse may be due to disruption of the thyroid.

To avoid the incredibly frustrating and disheartening experience of yo-yo dieting it is important to understand how diet affects thyroid function, how the thyroid impacts metabolism and weight loss, and what can be done to support thyroid function while dieting.

What is The Thyroid?

The thyroid is a small butterfly-shaped gland located in the neck that regulates numerous systems throughout the body. It accomplishes this through the production of various hormones including thyroxine (T4), triiodothyronine (T3), and reverse triiodothyronine (RT3). For the purposes of this discussion, the most important thyroid hormone is T3 because it directly influences metabolic function.

Learn more about the thyroid gland here.

T3 is known as active thyroid hormone because it upregulates cellular function meaning that it gets systems throughout the body moving faster. For example, as levels of T3 increase the metabolism works harder, burns more calories, and provides more energy. Conversely, lower levels of T3 result in a slowing of metabolic action, which contributes to weight gain and fatigue. Sadly, many people are not aware that chronic dieting and overly restrictive diets can reduce thyroid activity and by extension inhibit metabolic function. 

How Can Diet Disrupt the Thyroid?

Diet affects multiple aspects of thyroid function. Research has found that chronic dieting and calorie-restrictive diets can impede thyroid hormone conversion and reduce circulating levels of T3. This can severely cripple the metabolism resulting in more difficult weight loss and even promote weight gain.

To have a positive effect on metabolic function, T3 must be converted from the storage form of thyroid hormone T4. The conversion process requires an adequate supply of an enzyme called Deiodinase type 1 or D1. A deficiency of T4 and/or D1 can cause a significant decline in T3 production and subsequent decrease in metabolic activity – learn more about the importance of deiodinase enzymes here. Calorie restrictive diets promote both physiological and emotional stress, which decreases D1 activity and increase the prevalence of the T3-inhibiting hormone, Reverse T3 – learn more about Reverse T3 here. These two factors reduce T3 prevalence and function resulting in decreased metabolic activity.   

A study published in the American Journal of Physiology, Endocrinology, and Metabolism showed that just 25 days of calorie restrictive dieting caused a notable decline in thyroid function. Participants who dieted showed reduced conversion of T4 to T3 and exhibited a 50 percent decrease in circulating T3. Research shows that a decline of this magnitude translates to a 15 to 40 percent reduction in basal metabolic rate. Such a drop in metabolic activity can devastate your ability to lose weight and also makes it more difficult to maintain current weight.

Calorie restrictive diets put the body in starvation mode, meaning it wants to hang on to as many calories as possible. Studies show that chronic dieting can cause the body to remain in a starvation state for multiple years. Because of this, chronic dieters often have to maintain a reduced caloric intake for an extended period just to remain at their current weight. This is exemplified by a study published in Metabolism showing that individuals who had undergone even moderate weight loss exhibited slower metabolisms than individuals who maintained the same weight for at least a year. Even if individuals weighed the same, those who had lost weight had a metabolism up to 25 percent slower than those whose weight had not changed for an extended period.

These studies may make it appear that effective dieting is impossible. However, if proper care is taken to protect and support the thyroid, dieting can lead to greater overall wellness.

Is Calorie Intake the Key to Effective Dieting?

Popular and trendy diets tend to rely on severe caloric limitations to provide fast results. However, as we now know, this dieting strategy can cause long term damage and actually disrupt thyroid function thereby inhibiting weight lost. If interested in dieting, it is essential that caloric boundaries be set at the appropriate value. If set too high, weight loss will not happen. If set too low, there may be temporary results, but the long-term damage will ultimately eliminate any positive outcomes.

Establishing the correct caloric intake for your individual situation is perhaps the best way of protecting thyroid function and getting your desired results. Appropriate caloric intake depends on many individual patient factors such as activity level, basal metabolic rate, and genetics. Speak with a knowledgeable physician or nutritionist to learn what calorie range is best for you.

Thyroid Dieting Tips

In addition to establishing a healthy caloric intake, there are other ways of supporting thyroid function while dieting. Studies show that thyroid patients are often deficient in important nutrients such as co-enzyme Q10 (CoQ10), Vitamin B12, Vitamin D, and selenium. Getting an adequate supply of these important substances through foods or supplements can help resolve existing deficiencies and improve common problems experienced by thyroid dieters.


  • Found in meat, fish, whole grains
  • Alleviates migraines and headaches, improves energy level, relieves muscle pain and weakness

Vitamin B12

  • Found in meat, fish, dairy products, fortified cereals
  • Improves red blood cell production, promotes neurological function, alleviates fatigue

Vitamin D

  • Produced by the body when exposed to sunlight, also found in oily fish, eggs, fortified cereals, milk
  • Improves absorption of essential nutrients, supports immune function, often beneficial for those with Hashimoto’s Thyroiditis


  • Found in brazil nuts, tuna, lobster, halibut, grass-fed beef
  • Supports neurological function, improves mood, promotes sensations of well-being

Learn more about common nutrient deficiencies in thyroid patients here.

Getting a healthy supply of these substances through foods or supplements helps safeguard against or alleviate common deficiencies found in thyroid patients. Optimizing nutrient intake may also protect against dietary issues that negatively affect thyroid function and impede weight loss.

Keep the Pounds Down by Supporting Your Thyroid

Many fad diets encourage significant caloric limitations to hasten the weight loss process. Unfortunately, such diets tend to provide temporary rewards. Crash diets, chronic dieting, or yo-yo dieting may provide quick results, but they also disrupt thyroid function and metabolic activity. Protecting thyroid function while dieting can be challenging but it is possible. Speak with a dietitian, nutritionist, or doctor familiar with the thyroid to help you create a diet plan the best suits your needs. Safely and effectively reach your weight loss goals by protecting and supporting healthy thyroid function while you diet.


1. Kent Holtorf, MD. “Understanding Local Control of Thyroid Hormones: (Deiodinases Function and Activity) – Dieting.”
2. R. L. Araujo et al. “Tissue-specific deiodinase regulation during food restriction and low replacement dose of leptin in rats.”
3. Leibel RL, Hirsch J. “Diminished energy requirements in reduced-obese patients.” Metabolism. 1984 Feb;33(2):164-70.
4. American Thyroid Association. “Thyroid and Weight FAQs.”

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I just my labs done. TSH with T4 Free. Still Hypo and changed my dose. Hashimoto.

Lady In Black
Lady In Black

A word of caution regarding the Many Forms of B-12…. Only Adenosylcobalamin and Hydroxocobalamin are B-12 forms suited for use by all people. Avoid Cyanocobalamin and Methylcobalamin if you have any DNA SNP issues in your Methylation Cycles (including any of the MTHFR, CBS, BHMT, etc) because these forms can make issues worse! Additionally, stayIng away from Gluten. Gluten is in wheat. Wheat is a food for grazing animals – animals with 4-stomaches for digesting it – not humans. Being aware of what foods you eat and monitoring your health with a food diary is very helpful in learning what… Read more »

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