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Intermittent fasting (IF) has captured the attention of many seeking a healthier weight and has gained traction over the years as a potentially effective weight loss method.
Fasting involves alternating between periods of eating for nourishment and periods of abstaining from food. This concept is deeply rooted in ancient traditions, with the health benefits of fasting being recognized and documented as early as ancient Greek civilization.
Multiple studies illustrate the benefits of IF beyond weight loss. But does everyone gain the same benefits from IF, especially those living with a chronic medical condition?
In this article, we’ll dive deeper into IF and its science to explore whether IF is safe for those with hypothyroidism.
Intermittent fasting is a practice that involves following a cyclical pattern of eating and fasting. IF isn’t a diet per se where certain foods are restricted. It’s more of a change in your eating patterns that challenges the conventional three-meals per-day schedule.
A person can follow different fasting patterns, with fasting lengths varying between 16 to 48 hours. Some eating patterns split a 24-hour window into periods of eating and fasting, such as the 16/8 method: 16 hours of fasting followed by an 8-hour eating window. Other patterns separate eating and fasting periods by days, like the 5:2 schedule. This eating schedule allows individuals to pick five days a week to eat while fasting on the other two days. In this particular eating pattern, fasting days are non-consecutive, meaning you don’t have to fast two days in a row.
Types of intermittent fasting
The different fasting schedules fall into one of four categories:
- Alternate-day fasting: Simply put, you eat for one day, then fast the next. This pattern is continuously repeated.
- Time-restricted feeding: On this plan, a day’s 24 hours are split into periods of eating and fasting with a food intake window of 8 to 12 hours or less, such as the 16/8 method mentioned above.
- Periodic fasting: This plan cycles between days of eating with occasional, non-consecutive fasting days. The 5:2 method mentioned above is an example of this type of fasting.
- Long-term fasting: This plan features fasting for two or more consecutive days.
During fasting periods, you can drink water, coffee (without cream or sugar), and tea. You may even be allowed restricted caloric intake on fasting days.
People do intermittent fasting for various reasons, including health and religious reasons.
For health purposes, one of the most popular reasons is weight loss. Studies indicate that fasting causes hormonal changes. In the absence of continuous food consumption, these hormonal changes result in the body’s use of fat as energy, thus resulting in weight loss. Remember that if you overeat during eating periods, you are unlikely to lose weight despite fasting.
There are more benefits to fasting than weight loss! Other benefits of IF include the following:
- IF controls inflammation in the body that can lead to chronic medical conditions
- IF boosts metabolism
- IF reduces insulin resistance
- IF improves heart health and brain function
Some people participate in fasting for religious reasons, believing that abstaining from food cleanses the body or demonstrates sacrifice.
While there are health benefits to IF, there are also risks associated with it.
For some, IF may trigger new or previous disordered eating behaviors. IF may also be harmful to those living with certain medical conditions such as diabetes, kidney impairment, or heart disease. For instance, people with diabetes or blood sugar control issues who are fasting may be at risk for low blood sugar levels (hypoglycemia), which can be life-threatening.
In addition, IF is not recommended for:
- Endurance athletes
- Underweight individuals
- Those who are trying to conceive or who are pregnant or breastfeeding
- Individuals at risk for malnutrition, such as those with vitamin deficiencies
Another risk to keep in mind: fasting may also make you feel more irritable or agitated.
Your thyroid is the metabolic powerhouse of the body, and fasting can directly impact its function. An older study showed that fasting decreases thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4). Recent studies have shown similar results.
Before we go any further, let’s review how our body regulates thyroid hormone production.
Thyroid hormone regulation
TSH stimulates your thyroid to make and release two thyroid hormones: T3 and T4. For thyroid hormone to affect your metabolism and keep your body functioning, it must be in its active form, T3. Your body regulates how much thyroid hormone is made through a complex feedback loop.
A thyroid disorder results when a change occurs in the complex feedback loop that regulates your thyroid hormone production. A change in your TSH level either increases or decreases thyroid hormone production. A low TSH level causes increased thyroid hormone production and elevated thyroid hormone levels, as seen in a thyroid condition called hyperthyroidism. In contrast, a thyroid disorder called hypothyroidism occurs when you have a high TSH level and low thyroid hormone production and levels.
Fasting and your thyroid
Now, back to the study results.
As mentioned, an older study showed that fasting decreases TSH, T3, and T4. T3 rapidly returned to normal levels once fasting ended.
A more recent study evaluated the effects of alternate-day fasting in healthy people. Compared to the control group, those who alternated 36 hours of zero-calorie intake with 12 hours of unlimited eating showed lowered levels of T3. Yet, overall thyroid function was not impaired.
Another study conducted in 2020 compared the weight-loss efficacy of alternate-day fasting versus daily calorie restriction in adults with subclinical hypothyroidism. After six months, results showed a similar body weight decrease by both alternate-day fasting and calorie restriction. There was a significant difference, however. Alternate-day fasting reduced insulin resistance more than calorie restriction. TSH and free T4 remained unchanged.
Lastly, a recent review explained that T3 levels drop drastically within the first 24 hours of fasting. However, multiple studies showed that TSH levels remained unchanged despite this drop. And your TSH level has to either increase or decrease to affect thyroid hormone production.
In summary, fasting may affect your thyroid hormone levels, but the clinical significance is unknown.
Hashimoto’s thyroiditis is a thyroid autoimmune disorder, the number one cause of hypothyroidism in the U.S. An autoimmune thyroid disorder means your immune system mistakenly starts attacking your healthy thyroid cells. As a result, thyroid cells are damaged or destroyed, affecting thyroid hormone production and causing chronic inflammation.
One of the primary goals of treating Hashimoto’s is to reduce the amount of inflammation in your body. And IF may be able to help with that by:
- Improving gut microbiome: Research shows that your gut microbiome plays a role in your thyroid function. And changes to your gut microbiome can change how your thyroid functions. IF may help restore your microbiome by promoting the growth of beneficial gut bacteria, thus indirectly helping to manage thyroid disorder symptoms.
- Reducing oxidative stress: Oxidative stress occurs when you have more free radicals than antioxidants. Free radicals cause damage to your cells, while antioxidants prevent this damage from occurring. Oxidative stress is common in those with autoimmune disorders, so efforts to reduce it can lessen symptoms. Alternate-day fasting can increase protective proteins, further reducing oxidative stress.
- Lowering inflammatory biomarkers: Those living with an autoimmune disorder tend to have high levels of inflammatory biomarkers, indicating an inflammatory process is occurring in the body. One study showed that inflammatory biomarkers in those with autoimmune disorders decreased during and after Ramadan – a religious holiday that involves fasting from sun-up to sundown for a month – compared to initial levels before the fast. As a result, inflammation decreased, improving autoimmune disorder symptoms.
It is important to note while IF will not cure Hashimoto’s, hypothyroidism, or other chronic medical conditions, it may help reduce the severity of these conditions.
If you live with hypothyroidism or Hashimoto’s, you may take thyroid hormone replacement medication to help manage your symptoms. These medications help restore your thyroid hormone levels to a normal range. In turn, this helps correct TSH levels.
Experts aren’t entirely clear on how IF affects your thyroid medication dose, but it may in some cases. Another study of the effects of Ramadan on thyroid function showed that TSH levels exceeded normal levels after the Ramadan fast. Because of this, thyroid hormone medication doses needed to be increased.
When TSH levels are too high, you may develop symptoms of hypothyroidism, including:
- Weight gain
- Depression and anxiety
- Brain fog
- Dry skin
- Hair loss
- Cold intolerance
If following an IF plan, it’s essential to report any new or worsening symptoms to your healthcare provider. They can check your TSH level and adjust your dose if needed.
If you are considering IF for health benefits or religious reasons, talk to your thyroid care team first. As we discussed, IF isn’t for everyone, and you want to ensure you do it safely. Your plan may include checking your thyroid function more frequently while fasting, especially if you take thyroid hormone replacement medications.
If you choose Paloma Health for your hypothyroidism care, your care team will include not only an expert thyroid practitioner, but you’ll also have the option to work with our thyroid nutritionist. Working closely with a nutritionist allows you to create a customized eating plan to optimize your thyroid health. This may include identifying dietary triggers, reversing nutritional deficiencies, and weight loss. Are you interested in adding a nutritionist to your healthcare team? Set up an appointment with one today.