Is Intermittent Fasting Bad For Your Hormones?

I get asked about many types of diets, but intermittent fasting (IF) is probably the most frequent.  And I get it, the idea of not having to worry about food does sound kind of nice, but if the goal is to fix a hormone imbalance or support long term health, fasting isn’t the answer.  Can it help with temporary weight loss for some?  Yes, but it often leads to even more weight gain, cravings, and blood sugar dysregulation.  Let’s break down the main arguments for fasting below. 

IF Is What Our Ancestors Did

Our ancestors had much more scarcity with their food than we do, which meant we had to evolve to deal with the lack of food and uncertainty of when or where their next meal would come.  Different seasons like winter also brought their challenges limiting particular foods or not having food at all.  Back in those times, there wasn’t access to grocery stores or restaurants.  Most of us, on the other hand, have food readily available around the clock.  While our ancestors lived off of the land (hunting and gathering), we, for the most part, rely on the convenience of shopping for food at a nearby grocer, convenience store, fast-food chain, or dine-in restaurant.  Our ancestors’ lack of readily available food gave them no other choice than to stretch out the time between meals.

Don’t get me wrong; I understand the thought process of fasting being more natural because it’s what we evolved doing; however, our modern-day life is filled with chronic stress without much relief.  When we were forced to IF as we evolved, there wasn’t constant stress all day long from work, technology, the media, chemicals, our environment, etc.  There was intense stress like getting food, being attacked by animals, etc. then long periods of rest.  We very rarely rest in today’s society, which makes fasting much less appropriate. 

IF Reduces Inflammation

Fasting increases cortisol, our stress hormone, which is anti-inflammatory in the short term but adds to inflammation in the long run.  This increase in cortisol leads to blood sugar dysregulation (see below), which leads to more insulin and more inflammation.  For women already dealing with hypothyroidism and Hashimoto’s, the added stress of excessive cortisol is only going to worsen their conditions.  The increase in cortisol will also lead to inefficient thyroid function.  Cortisol lowers TSH in the short term, but in the long run leads to poor conversion of the thyroid hormone T4 to T3 (the active form), which impairs thyroid function. Continuously high levels of cortisol lead to us being in a chronically stressed-out state.  What happens when the human body is under chronic stress?  Inflammatory responses.  So, while there may be an initial anti-inflammatory benefit, the opposite occurs if followed for an extended period.  

What would happen if we reduced more inflammatory foods in our diet day-to-day instead of adding in fasting?  Or possibly add nutrients that counteract stress?  Magnesium is crucial for helping the body deal with stress and also for recovering from it. ⁣Magnesium-rich foods include spinach, leafy greens, banana, avocado, and plantains. Other sources are Epsom salt baths and magnesium oil spray. When sodium and magnesium levels are unbalanced, it can lead to dysfunction in the body’s adrenal glands and the ability to respond to/handle stress. ⁣

  • High ratio of sodium to magnesium = fast adrenal activity and higher stress⁣
  • ⁣Low ratio of sodium to magnesium = slow adrenal activity and fatigue⁣

IF Allows You To Live Longer

The main reason fasting helps us live longer is that certain nutrients (like polyunsaturated fats and methionine) are restricted in the diet.  Another big reason fasting helps to support our long term health is because it reduces our exposure to chemicals and heavy metals.  But again, why not just be mindful of the foods we are eating and the chemicals in our environment?  Supporting thyroid health and metabolism through nutrition and lifestyle is much more helpful for long term health than adding another stressor.  

Our metabolism is what connects all of the systems of the body.  It is the sum of all of the body’s processes, providing energy to your body to support all operations.  It occurs within the cells and feeds every part of the body.  Metabolism is how you sustain life.   When metabolism is slow, everything else slows down.  If correcting metabolism is all you have to do to improve your quality of life and achieve longevity, would you do it?  It seems simple enough, right?

IF Improves Metabolic Function 

Negative.  Fasting leads to downregulation in our HPT axis (hypothalamus-pituitary-thyroid axis).  TSH or thyroid-stimulating hormone is decreased during fasting, which is typically a good thing, but the conversion of inactive thyroid hormone (T4) to active thyroid hormone (T3) is reduced during fasting.  This means less T3 for your cells.  Every cell in our body has a thyroid hormone receptor, which means every system is impacted by thyroid dysfunction. 

When we fast, such as when we are asleep, our bodies rely on our stored glucose to sustain our bodily functions until we eat again.   Once the body has used all of the stored glucose, it turns to muscle protein and breaks that down for energy during more extended periods of fasting.  When we break down protein (whether it’s from our muscle tissue or our diet) and turn that into glucose for energy, it’s like using an alternative fuel source.  Think of using a generator to power your home–you can only use certain appliances simultaneously, and things are typically a bit slower.  Our bodies are the same way when using fat and protein as a fuel source.  It also makes us use glucose less efficiently and can lead to feeling like you don’t tolerate carbohydrates in your diet well in the future. 

IF Balances Blood Sugar

Because IF leads to more cortisol production, this leads to blood sugar imbalance.  We end up using up stored glucose in our liver, which usually helps balance our blood sugar whenever it drops (especially throughout the night while we are technically fasting).  This leads to more cortisol production and stress for the body and pushes us further into dysregulation.  Even Chris Kresser, a well respected functional medicine doctor who often preaches the Paleo diet, explains in this post why fasting isn’t suitable for everyone, specifically those with blood sugar issues.  In his article Intermittent Fasting, Cortisol, and Blood Sugar, Kresser discusses how often there is a combination of both high blood sugar and low blood sugar as a result of IF.  If an individual is already struggling with an imbalance of blood sugar, IF will not be their cure-all.  In fact, he recommends that they eat more frequently.  Most people cannot use fasting regularly.  The majority have too much stress and already have blood sugar dysregulation.  Adding in fasting when you have hormone problems is like adding fuel to the fire.  If we want healthy hormones, we need a healthy thyroid.  Considering how fasting impacts thyroid function and metabolism, it doesn’t make sense to use fasting for hormone health. 

What does this all mean?  EAT!  I want to normalize regularly eating throughout the day.  I know IF is touted with a million benefits, but many can be achieved long term without fasting.  Eat breakfast and then eat when you are hungry.  Focus on meals balanced with protein, fat, and carb.  Avoid extreme diets.  Some individuals practice intermittent fasting (IF), and it works for them, that’s great.  Not everyone is that lucky.  This article is for individuals struggling with hormone health and want a sustainable nutrition approach to help with that.  Want more nutrition myth busting? Check out the first episode of the Are You Menstrual? Podcast, in which we talk about the dark sides of today’s trendiest diets.

Amanda Montalvo

Amanda Montalvo is a women's health dietitian who helps women find the root cause of hormone imbalances and regain healthy menstrual cycles.

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