Is Intermittent Fasting Bad For Your Hormones? These Are The Pros & Cons

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The research surrounding intermittent fasting (IF) is super exciting; it's been shown to increase autophagy (also known as cellular repair), decrease inflammation, and heal the gut. Sounds awesome, right? Intermittent fasting is one of my favorite tools, and I recommend it to many of the patients at my functional medicine clinic.

But depriving the body of food for longer stretches of time raises some concerns for our hormones—like insulin, stress hormones like cortisol, and female hormones like estrogen and progesterone. If you have adrenal fatigue, irregular cycles, or a thyroid issue, should you be experimenting with fasting—or steering clear? Here are some common hormones and how IF might affect them:

1. Hunger and fat-storing hormones (insulin, ghrelin, and leptin):

When it comes to improving the hormones that directly affect your hunger, blood sugar, and metabolism, this is where intermittent fasting shines. In fact, it's one of the top tools I use for combating blood sugar problems. Intermittent fasting has been shown to decrease insulin resistance—lowering diabetes risk and enhancing metabolism. Intermittent fasting has also been shown to have a positive effect on the hunger hormone ghrelin. And surprisingly, the changes in ghrelin release during IF improved dopamine levels in the brain, improving cognitive function. (Another example of the gut-brain axis at work in your body.) If your blood sugar is not stable, I suggest leaning into intermittent fasting protocols slowly, working gently with your body as you create glucose stability, and always talking to your doctor before making any drastic lifestyle changes. Leptin resistance, another hormonal resistance pattern that can lead to stubborn weight gain, has also been shown to benefit from IF.

2. Female hormones (estrogen and progesterone):

The brain-ovary axis or hypothalamic-pituitary-gonadal (HPG) axis is the way your brain communicates with your ovaries. Your brain speaks by sending hormones, which are basically chemical emails, to the ovaries, and this prompts your ovaries to release estrogen and progesterone. A healthy HPG axis is essential for your general well-being and also for your ability to get pregnant.

Women tend to be more sensitive to intermittent fasting, and this is due, in part, to something called kisspeptin. Women tend to have more kisspeptin, and research is suggesting that kisspeptin creates a greater sensitivity to things like fasting. This can cause women who try intermittent fasting to miss their period, throw off their cycle, or just make them feel hormonally unbalanced overall. This could also, in theory, affect fertility as well as metabolism—but more studies need to be done.

It's important to remember that no two women are exactly alike. Clinically, I find that some women do great with intermittent fasting, and some don't. Does this mean that women who are sensitive to intermittent fasting shouldn't do it at all? Not entirely. For these individuals it may just require a gentler approach. Crescendo fasting is a tool I use for my patients who don't do well with other intermittent fasting protocols. Here's exactly how to do crescendo fasting:

  • Fast two nonconsecutive days a week (such as Monday and Friday).
  • On fasting days, take it easy on the exercise. Maybe light walking or gentle yoga.
  • Shoot for a fast of 12 to 16 hours.
  • After two weeks, try adding another fasting day (such as Monday, Wednesday, and Friday).
  • During this protocol I typically suggest adding around 6 grams of branched-chain amino-acid supplements (BCAAs), which come in powder and capsule form. BCAAs help take the edge off and improve the experience and positive impact of the fast.
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2. Adrenal hormones (cortisol):

Your main stress hormone cortisol is secreted by your adrenal glands, which sit on top of your kidneys like little kidney hats. Adrenal fatigue is when your brain-adrenal (HPA) balance is thrown out of whack. Cortisol will be high when it should be low, low when it should be high, or always high or low. In short, there all different types of HPA-axis dysfunction. In general, though, I find that people with circadian rhythm issues like this aren't rock stars with intermittent fasting. If you have a circadian rhythm dysfunction but still want to experiment with IF, I suggest starting with crescendo fasting or a beginner protocol.

3. Thyroid hormones (T3 and T4):

Thyroid hormones affect every single cell of your body, so if your thyroid isn't working well—nothing is. In addition, there are a ton of reasons a person might develop a thyroid hormone issue during their lifetime. For example, there are autoimmune thyroid problems like Hashimoto's, thyroid conversion issues like low T3 syndrome, thyroid resistance (which is similar to insulin resistance), and thyroid problems that are secondary to brain-thyroid (HPT) axis dysfunction. Each one of these thyroid hormone pathway disorders can respond differently to intermittent fasting, so I approach it on a case-by-case basis and would recommend working with a functional medicine expert.

If you are one of the millions of people who suspect they have a hormone problem but don't know for sure, check out my guide on the topic to get more answers. If you're all cleared to start intermittent fasting, how do you begin? Here are a few ways to get started:

Beginners:

  • The 8-6 window plan: One simple way to IF is to try eating just from 8 a.m. to 6 p.m. This window allows for a longer fasting time that stretches from the early evening to a reasonable time in the morning.
  • The 12-6 window plan: This is the one I personally do during the workweek. It’s the same as the last option, only this one extends the fasting period until lunchtime, when you’ll have your first meal of the day. I drink lots of water and herbal tea in the morning and enjoy lunch so much more!
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Intermediate IF:

  • The modified 2-day plan: Another way to intermittent fast is to eat a regular clean diet for five days a week and then pick any two days of the week to restrict your intake of food to less than 700 calories. This caloric restriction still activates many of the same benefits as a full intermittent fasting day.
  • The 5-2 plan: Another relatively simple intermittent fasting protocol is to completely fast for two whole nonconsecutive days in a week. For example, fast on Monday and Wednesday but eat regular clean foods the other five days.

IF for the pros:

  • The every-other-day plan: For this intermittent fasting protocol, you would fast fully every other day. This plan is a bit intense but can be great (and very effective) for some people.

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