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Can Crash Dieting Cause Hypothyroidism?

Find out why restricting calories may not be right for your thyroid health.
Can Crash Dieting Cause Hypothyroidism?
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Crash dieting is a way of quickly losing weight by dramatically limiting how much you eat. A crash diet is any form of eating that restricts, eliminates, or “cleanses” the body of essential calories and nutrients.

Metabolism describes the chemical process in the body that determines how much energy you use each day. When you lose weight, your resting metabolic rate (RMR) also slows, as less energy is needed to maintain essential bodily functions. When you drop your calorie count too low, you stress your body as it adapts to the perceived threat of starvation. Your body slows down to the rate at which it burns calories to conserve energy. This slowed metabolism means you burn fewer calories per day.

This process is called “metabolic adaptation.”

Impact of crash dieting on the body

The stress that your body experiences when you severely limit calories or follow a crash diet can be counterproductive and harmful to body processes and functions in the long term.

The Obesity Action Coalition notes some of the risks associated with crash dieting, including:

Gallstone production: The gallbladder stores bile that helps our bodies break down fat from our foods. When weight loss is rapid (for example, 3 pounds or more per week), it can lead to an overproduction of bile, which causes stones to form. These stones can grow quite large and cause severe pain and illness.

Loss of lean body mass: When a large amount of weight is lost quickly, there is always a risk that some of that weight comes from lean body mass, namely muscle. A reduction in muscle also contributes to a lowered metabolism and reduced physical strength. 

Nutritional deficiencies: Every day, we need a baseline level of nutrients from food, including protein, fats, vitamins, and minerals. When you crash diet, you are severely restricting your body from taking in and absorbing these vital nutrients, which can lead to nutritional deficiencies. The thyroid gland is highly nutrient-dependent, and poor nutritional status is one of the root causes of thyroid dysfunction.

Psychological and mental impacts: It is important to mention that prolonged dieting can lead to psychological effects such as depression, emotional distress, and irritability. In addition, some studies have shown that because those who diet choose to ignore hunger cues and signals, it may lead to binge eating behaviors. That feedback loop between starvation, binge eating, and then reducing eating again will not only prevent weight loss goals from being achieved mindfully, but it will also negatively impact someone’s mental health.

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Effects of a low-calorie diet on thyroid function

Because the thyroid controls much of our body’s metabolism processes, it is crucial to discuss the impact of low-calorie crash diets on thyroid function and health.

A study published in the International Journal of Obesity studies a group of obese women over 18 weeks. All the women ate a 1200-calorie per day diet for the first four weeks. Participants were then split into two groups. Half the participants ate a very low-calorie diet of 400 calories daily for eight weeks before returning to the 1200 calories/day diet. The remaining half stayed on the balanced deficit diet of 1200 calories for 18 weeks.

Both groups experienced a change in the active thyroid hormone triiodothyronine (T3). Participants who ate a very low-calorie diet saw a more significant T3 decrease of up to 66%. Participants who ate a balanced deficit diet saw a reduction in T3 of up to 40%. When these participants reintroduced more calories into their daily diet, they saw an increase in T3.

The study demonstrated that restrictive dieting reduces T3, causing the metabolism to slow and weight loss to become more challenging.

Restrictive dieting or dropping entire food groups from your diet also deprives your body of critical nutrients, which can stress your immune system. The more dietary pressure you put on yourself, the more likely you are to experience inflammation. In turn, inflammation can worsen your autoimmune reactions or further interfere with your thyroid function.

Weight loss tips for people with hypothyroidism

One of the most frustrating symptoms of an underactive thyroid is weight gain or increased difficulty in weight loss. The best type of diet for people with hypothyroidism takes your unique health situation into account and is sustainable for you in the long run.

Ahead are some tips for healthy weight loss with hypothyroidism.

Get tested for hypothyroidism

The first step to treat hypothyroidism is proper diagnosis. Many labs look only at thyroid-stimulating hormone (TSH) to assess thyroid health. Paloma’s practitioners also believe measuring free T3, free T4, and thyroid peroxidase (TPO) antibodies is critical. Understanding what’s happening with your thyroid function is the first step to optimize thyroid function and improve overall health. Work with a trustworthy doctor to optimize your thyroid hormone replacement treatment to support healthy weight loss.

Replace low-calorie with nutrient-rich foods

Generally, we think about a diet as removing foods. However, considering what foods we add may be even more critical. Consider following a sustainable diet that doesn’t deprive or starve your body of essential nutrients. With a lot of talk of elimination diets, it’s easy to get caught up in removing triggering foods without correcting nutrient deficiencies. Your body needs adequate levels of minerals like selenium, iron, and zinc to convert T4 into T3. This conversion is critical to thyroid function and positively affects metabolic function. Work with a knowledgeable thyroid nutritionist to determine your nutritional status and develop a thyroid diet plan that removes dietary triggers and replaces them with healing, nutrient-dense foods.

Manage your stress

Aside from the stress of crash dieting on your body, managing stress related to work, family, and life is also necessary. Too much stress can throw the endocrine system out of balance by disrupting the regular production of thyroid hormones. Remember to prioritize the basics, like sufficient sleep and daily movement. Sleep and movement are proven to alleviate stress and support successful weight loss efforts. It might also be helpful to take part in a social support group or find a buddy so you can support one another in your unique experiences. Ask a friend to cook healthy meals together once a week, take part in community events such as exercise groups or classes, or sign up for classes at your local dance studio so you can also have some fun while doing something good for your mind, body, and soul.

Don’t forget about movement

Sustaining weight loss requires a balance between food intake and physical activity. Combining dietary therapy and physical activity is vital to achieving and maintaining weight loss. We urge you to work with a certified and experienced professional such as a physical therapist or trainer to help you not only build a feasible physical activity routine but also do it safely to avoid mental exhaustion or bodily injury.

A note from Paloma

If you feel frustrated by your weight loss challenges and aren’t seeing results despite your best efforts to do everything right, it’s time to call in reinforcements! Professional guidance from physicians, nutritionists, and health coaches who are well-versed in supporting patients with hypothyroidism can help you overcome weight loss obstacles. Schedule a free call with one of our care advisors to decide if a Paloma Health membership is right for you.

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Jacques J. The Risks of the Crash Diet. Obesity Action Coalition. Published 2014.

Memon AN, Gowda AS, Rallabhandi B, et al. Have Our Attempts to Curb Obesity Done More Harm Than Good? Cureus. 2020;12(9). doi:

Social support: A necessity for weight loss. Mayo Clinic Diet. Accessed April 2, 2024.

‌Mohan V, Joshi S. Pros & cons of some popular extreme weight-loss diets. Indian Journal of Medical Research. 2018;148(5):642-647. doi:

Wadden TA, Mason G, Foster GD, Stunkard AJ, Prange AJ. Effects of a very low calorie diet on weight, thyroid hormones and mood. Int J Obes. 1990 Mar;14(3):249-58. PMID: 2341229.

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Neeyaz Zolfaghari

Holistic Nutritionist and Nourishment Coach

Neeyaz Zolfaghari is the founder of Unspoken Nutrition, a nutrition and lifestyle brand dedicated to helping others find and create harmony with their daily habits to support their wellbeing and ‘health’. Her journey began over a decade ago, when she was diagnosed with two autoimmune diseases. Knowing what she learned from her upbringing, Neeyaz turned to nutrition as the first pillar of her healing. As her body began to heal on a physical level, she began to learn how our minds, bodies and souls are all innately connected.  

Now as an Integrative Nutritionist and Patient Advocate, Neeyaz offers the people she works with the support, guidance, and tools they need in order to live a fulfilled life. While Neeyaz initially endeavored to make a difference at the individual level, her vision grew to embrace broader community impacts. She is currently pursuing her Masters in Public Health, serving as a testament to her unwavering commitment to instigate change on a grander scale.

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