Written and medically reviewed by Rich LaFountain, PhD
As interviewed by Rich LaFountain, PhD
Dr. Mindy is a woman on a mission: She wants you to discover how powerful your body was built to be.
A renowned holistic health expert, Dr. Mindy Pelz (who goes by Dr. Mindy) educates and empowers people around the world to use intermittent fasting to overcome chronic disease and live life at their healthiest. We recently spoke with her about her best-selling book, Fast Like a Girl, and explored the rationale and benefits of fasting with your hormones in mind. Here is some of the wisdom she had to share.
Q&A with Dr. Mindy: The Healing Power of Fasting, the Fasting Cycle, and Balancing Stress
Q: What originally sparked your passion for helping others take control of their health by incorporating fasting into their lifestyle?
A: I was inspired primarily by what I saw clinically in my practice, and secondarily by what I experienced personally, in my own health. Clinically, patients were no longer coming in with one condition or complaint. For example, instead of “I have a thyroid problem” or “I can’t lose weight,” they were coming in with “I can’t lose weight, I’ve got a pain issue that won’t go away, I’m depressed, and I can’t focus.”
I started off with changing people’s diet, but then that stopped working, probably due to the rampant declines in diet quality we’ve seen in the last few decades. Plus, making food changes alone requires intensive effort; it just wasn’t enough to combat the growing symptom lists that were stacking on top of each other. This is, ultimately, how I came to fasting.
Fasting was and still is a powerful tool to help people gain and rebuild health. Back when I was first looking into it, there were only a few people exploring fasting, so I made it a point to learn from folks like Jason Fung and Valter Longo. But the science has caught up; now there are great studies published in journals like The Journal of Nutrition, Health & Aging and Cell Metabolism. They demonstrate how condensing your eating window and allowing your body to shift into fasting metabolism, even when your diet isn’t perfect, improves metabolic health and disease.
Fasting works by stimulating processes like autophagy, which unlock natural healing throughout the body. The healing benefits in my patients and in my own life, as I was going through perimenopause, were miraculous. And they didn’t require rigid changes to diet or strenuous exercise — which is great because not all patients with a long list of symptoms are interested or able to invest heavily in diet and exercise from the get-go. They could just fast.
As I began to dive deeper into the research, I found that pairing fasting with hormones was magic for women. Now I am on a mission to help women learn how to cycle their fasts in accordance with their hormones.
Q: Many people find fasting is a powerful tool for weight loss. If healthy weight loss (i.e., fat loss) is the goal, should women and men approach their respective fasting habits differently?
A: There are three hormones that influence womens’ bodies and metabolic function. Those hormones are estrogen, progesterone, and testosterone. There are coordinated changes in each of these hormones that are directly related to each woman’s cycle. Estrogen is a hormone that responds well to higher fat burning and longer fasts. Progesterone is the opposite; progesterone loves glucose levels that are slightly higher, so fasting can actually hinder healthy progesterone levels.
From a fasting perspective, to optimize fasting to a woman’s menstrual cycle, I generally recommend the following, which I’ve termed the Fasting Cycle:
- Power Phases 1 & 2: Days 1–10 and 16–19 | Fast duration = 13–72 hours
- There are two Power Phases in a woman’s cycle. During these times, your hormone levels are naturally lower, so this is the time to lean into fasts, even some longer multi-day fasts, so that you can really benefit from the healing effects of fasting. During your Power Phases, you have more energy and less hunger, which also makes fasting easier.
- Manifestation Phase: Days 11–15 | Fast duration = 13–15 hours
- The days that include ovulation I call the Manifestation Phase. At this time, you have an estrogen and testosterone peak with a slight bump in progesterone. Hormonally, this is the part of your cycle when you probably feel and even look your best. You want to limit longer autophagy fasts during this phase because your body will be expending energy to metabolize hormones after they peak. If you continue longer fasts during this phase, autophagy might pull resources away from your metabolism and estrogen excretion which may be linked to cancer risk, weight gain, and other things you don’t want to happen.
- Nurture Phase: Days 20 until Menstruation | No Fasting
- During this phase, it’s important to focus on reducing stress and cortisol levels. Since fasting is a stressor, this means not fasting, and the same thing goes for intense exercise. Focus on light exercise and leisure activities like yoga or meditation, and prioritize rest and recovery, especially sleep.
So we’ve talked a lot about women, but what about men? Men are governed primarily by one sex hormone, testosterone, which is released about every 15–20 minutes. Consequently, there does not appear to be a need to cycle fasts to the same extent as women do. Men might then vary fasts based upon specific goals: If you want to stimulate autophagy, you will want to fast for at least 17 hours. If you’re interested in stoking fat burning and busting weight loss plateaus, a 36-hour fast can do wonders. These goals and fasts are great for women, as well, but women will want to be more aware of what day in their cycle they are on before leaning into specific fasts, especially the longer ones.
Q: In Fast Like a Girl, you explain the importance of managing stress. Can you please tell us a bit more about how following the Fasting Cycle helps women maintain health so they can thrive and properly balance stress?
A: Just like exercise and many other healthy habits, fasting is a hormetic, or good, stress, but it needs to be coupled with adequate rest and recovery, especially at the right times. For women, sensitivity to stress is higher during specific times in their cycle when hormone levels are high. For example, from day 20 of their cycle to the start of their period, stress sensitivity is higher. This is a great time to emphasize rest and recovery in what I call the Nurture Phase, because this can boost oxytocin, which can override some of the stress effects from cortisol.
During the Nurture Phase, rather than adding stress to the system with fasting and vigorous exercise, it’s more important that your eating window be expanded and that you allow yourself more time for mindful meditation, light movement such as yoga, or more leisurely activities that you enjoy. Your body kind of tells you this, as most women have a tendency to be more inward-focused and have cravings that match the body’s need for more glucose at this time in their cycle.
Basically, the Fasting Cycle matches natural hormone shifts with appropriate fasting targets. As you vary your fasting to meet the needs of your body and, if you’re a woman, your menstrual cycle, you can build health and avoid over-stressing your body. I see this all the time especially in type-A, highly driven women and men — you can’t grind your way to health in the long term, especially when your stress and rest are out of balance. There’s no survival advantage for the body to lose weight when cortisol is chronically high. Therefore, people who have too much cumulative stress in their life often have a hard time losing weight and improving their health, even if they’re doing a lot of the “right” things. You have to balance out your stress levels, and that means using your natural hormone shifts if you’re a woman, or some other type of cue if you’re a man, to cycle your fasting habits instead of just piling on more and more stress.
Q: Thyroid hormone levels are tightly linked with sex hormone levels and metabolic health. Why do you see fasting as a necessary tool for promoting healthy thyroid function?
A: I get asked questions about thyroid health all the time. When we look at research, one of the challenges we have is a constant preference toward absolutes. For example, if one study shows that your bioactive thyroid hormone triiodothyronine, or T3, levels are reduced when you go into a fasted state, the translated absolute we hear is that fasting is bad for maintaining healthy thyroid levels and metabolism. The interpretation of that particular study might be, “Oh my gosh, don’t fast because thyroid hormone levels go down!”
If you dive into the literature more, what other studies have demonstrated is that thyroid-hormone reduction is a transient, appropriate response to fasting. Once you bring nutritious food, especially carbohydrates, back into the equation, thyroid hormone levels like thyroxine (T4) not only go back up, but they can surpass baseline. So fasting can actually help thyroid function.
That’s the first thing. The second thing I want to say is that, in order to get thyroid hormones to work right, you of course need a healthy thyroid, but you also need a healthy brain, liver, adrenals, and gut, so your cells can be receptive to the thyroid hormones. For example, fasting, and more specifically autophagy fasting of 17 hours or more, maintains and repairs neurons in your brain so you can effectively signal thyroid hormone production from the pituitary gland. All fasts also lower inflammation so that the thyroid hormone can be welcomed into cells instead of inflammation keeping it out. I put a specific fasting protocol in Fast Like a Girl just for thyroid conditions, and it helps improve the health of all the organs that contribute to proper thyroid function. Thyroid health is particularly important for women because women are ten times more likely to experience thyroid problems — in part because of the tight linkage with sex hormones, and women have more variability in their sex hormones than men.
One last thing I think is very important and that I see in people, especially women, who want to lose weight or become enthusiastic about fasting, is that they unintentionally put themselves in a calorie deficit. When I’m working one-on-one with individuals, I am always sensitive to the fact that you need sufficient calories for the thyroid to be healthy. So when you open up that eating window, you have got to get enough healthy, nutritious food in order for your thyroid health to be good.
Wrap-Up
Like every important health habit, fasting is not something you can “set and forget.” As Dr. Mindy has shared, you can get the most out of your practice by cycling through different types of fasts according to your natural hormone fluctuations, stress levels, and other lifestyle needs. For more information on the Fasting Cycle and to stay in touch with Dr. Mindy, please visit her website, follow her on Instagram, subscribe to her YouTube channel, and check out her latest book, Fast Like a Girl.
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