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What is Intermittent Fasting and Is It Safe for Thyroid Patients?

What is Intermittent Fasting and Is It Safe for Thyroid Patients?

Dieting with a dynamic or unique strategy has become a popular practice. This has been facilitated by the impressive range of diet plans developed and honed over the past few years.

Currently, one of the most popular diet plans is intermittent fasting. This weight management strategy revolves around limiting caloric intake to a specific period of time and then fasting for the remaining hours to support a longer period of ketosis or fat burning. When done correctly, intermittent fasting provides excellent results. But is it safe for those with a thyroid condition? Knowing the basic principles of intermittent fasting, how it supports healthy weight loss, and how it affects the thyroid is important for dieting safely.

The Basics of Intermittent Fasting

Studies have found a number of impressive benefits associated with intermittent fasting including effective and sustained weight loss, increased insulin sensitivity, better stress response, reduced oxidative stress and inflammation, and greater longevity. At its basis, intermittent fasting involves extending the time between meals, or any caloric consumption, to allow the body to enter a state of ketosis. During ketosis, the body begins utilizing fat stores to maintain bodily function. This is different than a starvation state where the body attempts to hold on to and store as many calories as possible.

There are many different approaches to intermittent fasting. Perhaps the most popular method is by following a 16/8 schedule for eating. This requires fasting for 16 hours each day, 14-15 hours for women, while allowing 8-10 hours to consume a healthy number of calories. When intermittent fasting, as with any diet, it is important to eat a well-balanced collection of nutrients while not exceeding healthy caloric intake. This plan simply confines consumption to a specific time frame.

In addition to the popular 16/8 plan, there are others such as the 5:2, where one restricts their diet to 500-600 calories for two days out of the week while eating normally during the other five. Some practice a 24 hour fast where they eat nothing for one to two days out of the week. Regardless of the schedule, weight loss requires healthy food choices and not binging on junk foods during the allotted eating periods.

Intermittent Fasting and The Thyroid

The primary impact of intermittent fasting, regarding thyroid activity, is on the body’s circadian rhythms and blood sugar balance. These two factors play an important role in thyroid function, specifically among those with hypothyroidism and Hashimoto’s thyroiditis.

The thyroid relies on the body’s internal clock known as the circadian rhythms. This cycle regulates hormones, influences digestion and nutrient absorption, maintains immunity, and influences insulin release and stress response. Those with an autoimmune thyroid condition such as Hashimoto’s, typically experience diminished circadian activity. For example, TSH levels, dictated by circadian rhythms, increase during the night and decrease during the day. A study found that hypothyroid children experienced a TSH increase averaging 22% during the night while typical children saw a TSH increase of 124% during the same time period. It is believed that this increase in TSH is an important part of proper thyroid function.

Some have found that the standard 16/8 plan for intermittent fasting may actually be beneficial for those with hypothyroidism. Consuming the bulk of your calories during daylight hours, supports healthy regulation of the circadian cycle, thereby improving TSH activity. Therefore, if a thyroid patient wants to follow an intermittent fasting diet is best that they schedule their 8-hour eating window during daylight hours.

Following a 16-hour fast can help reduce sugar and insulin levels thereby supporting hormone activity. Furthermore, the compacted consumption of calories during daytime hours helps calibrate diurnal, or daytime, circadian rhythms. Eating primarily at night and fasting during the day may cause the body to start acting as though day is night and vice versa. Therefore, extended fasts of 24 hours or more may disrupt circadian rhythms thereby impeding thyroid function. Because of this, it is often best for thyroid patients to limit fasting periods to be less than 24 hours.

Concerns About Intermittent Fasting with Hashimoto’s

Hashimoto’s thyroiditis is a thyroid autoimmune disorder that is a leading cause of hypothyroidism. Some believe that intermittent fasting can be beneficial in treating Hashimoto’s due to the similar benefits it provides for hypothyroid patients. Although this may be true in some cases, it is important to be cautious with intermittent fasting as a Hashimoto’s patient.

Long gaps without eating may cause blood sugar levels to plummet and exacerbate adrenal fatigue associated with Hashimoto’s – learn about the thyroid-adrenal connection here. Extended fasts of 24 hours or more followed by binge eating and subsequent blood sugar spikes can have a significant impact on Hashimoto’s patients. The resulting insulin surge can trigger increased levels of cortisol along with suppression of luteinizing hormone and follicle stimulating hormone in the pituitary. These are important regulatory hormones for women. Other issues may also develop such as poor liver detoxification, inhibited T4 to T3 conversion, resistance at thyroid hormone receptor sites, and immune dysfunction resulting in greater inflammation. These factors can cause significant worsening of Hashimoto’s.

Most Hashimoto’s patients do not have stable enough adrenal function, blood glucose levels, or circadian balance to safely engage in intermittent fasting. However, those who have reached a point of adrenal and blood glucose stability may benefit from shorter fasting periods. That being said, it is essential that they maintain appropriate blood glucose levels and avoid insulin surges by only skipping at most one meal per day.

Staying Safe while Fasting

Intermittent fasting can be a powerful weight loss and wellness tool if used appropriately. However, it is important to implement it safely and ensure that any preexisting condition such as hypothyroidism or Hashimoto’s will not be worsened by it. Fasting should not be attempted by pregnant women, those with eating disorders, diabetics, and individuals with hypoglycemia or adrenal fatigue. Furthermore, fasting should only be done by adults. Always speak with a physician before beginning an intermittent fasting regimen. If you are hypothyroid or suffer from Hashimoto’s, you may need to stabilize various factors such as blood sugar and adrenal function before fasting. Intermittent fasts can provide many benefits but, as with all diet plans, it is important to implement them safely.


1. Fasting and Thyroid. Dr. Sara Solomon.

2. 6 Popular Ways to Do Intermittent Fasting. Healthline.

3. Intermittent Fasting and Hashimoto’s. Hashimoto’s Healing.

4. Intermittent Fasting as a Therapy for Hypothyroidism. Perfect Health Diet.

5. What Is Ketosis? WebMD.

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1 year ago

Hi do I have to take my thyroid medication during the 8 hour window? Or can I take it at 4 a.m. [my usual time] during the 16 hour window [fasting]

1 year ago
Reply to  Arlene

I just take it like in the mornings as I usually do, fasting or not. To my knowledge it shouldn’t interfere with anything as long as it’s taken with water, but I’m not a doctor or anything I just haven’t experienced any problems with doing so

Linda Galli
Linda Galli
1 year ago

I have been doing the Intermittent fasting for 11 days. I am able to do 14 hr fasting. When I go for the 15 or 16 I get dizzy. I am now re-thinking my food list I have eaten my normal foods the first week, then started changing some of the items to be more dense nutrition . From this point on I will make sure the meals are with in the AIP protocol to avoid items that will cause issues. I need to drop about 50 lbs and this is working , slowly but a steady loss. Staying healthy is more important than a diet. So I will keep a close eye on my Hashimotos. Good dense nutrition and good sleeping habits, Getting on a strict schedule and not cheating.. I have tried everything else with no weight loss. this seems to be working. I have lost 8 lbs in 11 days. That is amazing to me. I will stay on the 14 hour fast and 10 window to eat. My fast starts at 7 pm and ends at 9 am, The only thing I take is my suppliants around 9 pm before bed time, I do take my thyroid meds at 5 am. No calories and just with water. So most of my fast is during my sleeping hours. Just have to avoid food after my 7 pm meal. I have had a few 15 hour days when I get busy in the morning. I will probably keep it between 14 and 15 depending on my daily activity. Good luck with your quest. I am working hard on mine.

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