by Dave Asprey
No wonder, then, that a significant number of women have reported that frequent, ongoing intermittent fasting or repeated longer fasts cause problems including sleeplessness, anxiety, adrenal insufficiency, irregular periods, poor bone health, and even temporary infertility. These reports are backed up by scientific research on laboratory animals.3 In fact, one rat study showed that two weeks of intermittent fasting shrank ovaries, disrupted sleep, and shut down menstrual cycles in female rats.4 Intermittent fasting is unlikely to have such drastic effects on you in that amount of time, because Mother Nature knows you’re not expected to pump out a large litter of babies every couple months (phew). On the other hand, even without fasting, unending ketosis suppresses menstruation! It is not an appropriate diet for women over long periods of time unless you cycle into and out of it on a regular basis, at which point it is fantastic.
FEMALE FASTING STRATEGIES
Fortunately, women can benefit from fasting without compromising their reproductive health. You just have to make a few smart tweaks. The first is to practice intermittent fasting every other day. That way, your body gets the signal that says, “I must be in an area with adequate food for my (nonexistent) baby, but I must be strong enough to go awhile without food.” That’s the sweet spot. Daily, unending intermittent fasting is too close to a famine for your body, even if you eat enough calories in the evening. It’s also important not to work out strenuously on the days you do fast. Go to a yoga class. Do some Pilates. Take a walk. Don’t do high-intensity interval training or lift heavy weights on an intermittent fasting day.
Another hack that works for a lot of women is to do Bulletproof Intermittent Fasting with zero carbohydrates and zero protein, just Bulletproof Coffee with grass-fed butter and MCT oil. The many women I’ve spoken to about this have found that they can fast more frequently this way, without experiencing negative effects. Plain intermittent fasting—skipping breakfast altogether and fasting for a large portion of the day—can also work great, but it is more biologically stressful and harder to manage, especially if you have a demanding career and family. Bulletproof Intermittent Fasting helps manage these stresses for men and women alike, but based on anecdotal data, it is especially useful in addressing the interaction between fasting and sex hormones in women.
Instead of sending a stress signal reverberating through your body that you’re starving, Bulletproof Intermittent Fasting basically tells your body to stay calm and designate resources for autophagy (cellular cleanup) and rapid fat burning (ketosis), but that it’s not a famine, either. You aren’t taking in any starches or sugars, and there’s no “famine stress” signal, so this style of intermittent fasting is unlikely to bring on adrenal fatigue. Your body uses the hormone epinephrine (adrenaline) to burn fat, and epinephrine is made in your adrenal gland; reducing strain on the gland is especially important for women due to their sensitivity to adrenal burnout.
So what do you do on the days when you’re not intermittent fasting? Have protein and fat in the morning, but not carbohydrates. Make a Bulletproof Coffee, and add some grass-fed collagen protein, 20 or 30 grams. Now breakfast is taken care of. It is not a fasting day because you had protein, so you are good to go do HIIT or lift weights (or just have a normal day!). Some women do well by eating normally all week and once a week doing a full twenty-four-hour fast. Take advantage of scheduling flexibility. Pick a low-stress day, skip breakfast, skip lunch, eat dinner. There, you did it!
In addition to lacing your fast with some MCT oil, I also recommend that you experiment with less aggressive fasting schedules. You might fast for fourteen or twelve hours instead of the full sixteen, for instance, or space your fasting days farther apart. If those fasts prove comfortable, you always have the option of adding hours and frequency. The key thing is to keep your hormones from going into panic mode. There is a reason that stressed women crave fatty and salty foods: they are experiencing a symptom of adrenal exhaustion. It’s important to pay attention to these potentially serious symptoms and not treat them as another problem to overcome through sheer willpower. Part of exerting self-control through fasting is learning to distinguish superficial cravings from genuine warning signs.
The adrenals produce aldosterone, the hormone that balances sodium and potassium levels in the bloodstream. That balance is critical for proper cell function, so if you’re feeling stressed, eating a little extra salt can help ease the burden on your overtaxed adrenals. Your body craves salty foods for a reason—listen to it! Add some mineral-rich Himalayan or sea salt to your diet. (Pro tip: stir a pinch of Himalayan salt into a glass of water and drink it first thing in the morning.) This is an easy way to boost energy and help reduce adrenal stress, and your body needs more salt (2 to 8 grams a day) when you are in ketosis anyway. If you crave fat, add some fat to your diet. Just skip the potato chips and make it the good kind, like the fat in grass-fed butter, avocado, and olive oil.
Later in the day, if your body is still telling you that you need more salty foods, there’s nothing like vegetables soaked in butter and sprinkled with high-quality sea salt. Or grass-fed steak prepared the same way! Flexible fasting isn’t just a good idea, it’s absolutely vital for your health. It helps you tap into the advantages of going without while protecting your adrenals and your fertility.
If you’re a woman over forty and/or have significant weight to lose, here’s a hack for you: before you start intermittent fasting, change your breakfast routine for about a month. Soon after you wake up, eat a morning meal with some fat (including MCT oil) and at least 40 grams of protein. It will reset your leptin sensitivity, making it easier to lose weight. You can have tea and a few eggs, a piece of meat, salmon and avocado, or whatever protein smoothie you like, as long as there are no carbs. After thirty days, do the every-other-day intermittent fasting schedule described above.
Women’s bodies are more highly attuned to stress signals (again, for fertility reasons), which is why they benefit from their morning fat and often protein. Women also are more carbohydrate sensitive than men, on average. For this reason, I suggest establishing times between fasts when you replenish your body with carbs by eating more of them than you might normally. Many men thrive on having such a “carbohydrate refeed” day only once a week. Some men perform at their peak when they eat carbs even less frequently. Most women do exceptionally well eating low to medium amounts of carbs at every dinner instead of trying to stay in ketosis all the time. This carb-laced diet works because intermittent fasting, and the power of MCT to turn on mild ketones, is enough to get the benefits; meanwhile, the carbs are great for sleep and for sending a signal to your body that it can relax—there is no impending famine.
To be clear: when I’m talking about allowing some carbs, I’m not suggesting you go crazy with the bread and pizza. Stick to high-quality carbs such as sweet potatoes, carrots, squash, and white rice. Do not eat gluten, corn syrup, and processed carbs. They may cause inflammatory responses and will very likely make you feel tired the next day. They will definitely make you feel a bit heavier the next day, because your body will store extra glycogen, along with the water that comes with it. Don’t worry, it’s just water weight! You can’t put on a pound of fat in one day no matter what you do. But even if you occasionally indulge in low-quality foods, it’s not the end of the world. Eating junk food on refuel day will cause several days of cravings and lower performance, but you can bounce back. It’s a long journey.
If you eat moderate amounts of red meat and organ meat, you’re probably getting enough iron in your diet. Women generally need more iron than men, partly due to blood loss during menstruation. Some women need supplementary iron. Low blood levels of ferritin (an iron-transporting protein) disrupt the menstrual cycle, lead to fatigue, and contribute to an overall feeling of poor health. Many women of childbearing age are anemic because they don’t get enough red meat in their diets, and this can cause complications during pregnancy.
Women need to pay special attention to iron. Too
little is bad; too much can also cause trouble. Unlike vitamin D or K2, iron isn’t one of the supplements that you want to take randomly, no matter what. It’s terrible for your performance to be anemic (low in iron), but taking enough iron to raise your blood ferritin level above about 75 micrograms per liter will age you really quickly. The best bet is to get your iron level tested to see if you need an iron supplement. You will have to ask your doctor to test specifically for ferritin, as most normal blood panels don’t run this test. A lot of standard medical testing is still not tailored to women’s physiology, unfortunately.
A woman’s body begins seeking resources for the fetus practically from the moment of fertilization. I remember an incident from many years ago, when my wife and I were trying to start a family. The first time I was sure she was pregnant was when we ordered the last bowl of an amazing lamb stew at a restaurant in Lake Tahoe. There was one big piece of lamb in it, and we were sharing the bowl. I went to scoop it up, but she took her spoon and pushed mine out of the way. As I watched her savor every bite, I thought, “Oh, my God, she’s pregnant!”
No matter what, if you eat too few calories over time, your body will get stressed in response to the famine signal and you may start having fertility problems until quality food supplies or caloric intake return to levels that support reproduction. That’s an issue whether or not you are actually trying to start a family, because fertility is a proxy for good health status overall.
The starvation-stress response is one reason why women who are suffering from eating disorders often stop menstruating. Their bodies are in panic mode and are attempting to protect them from the additional stress of pregnancy by cutting off fertility. Controlled animal studies have documented just how extreme the response can be: when female rats were given an extremely low-calorie diet, they stopped their reproductive cycle and also developed a significantly heightened response to stress.5 This is just one more reason why CICO diets built around calorie restriction are not a generally healthy practice.
I do not advocate intense daily exercise for men or women who are fasting unless they’re pro athletes practicing intense recovery, too. Many female athletes—including “weekend warriors”—stop menstruating and are no longer fertile. It’s very stressful to the body to combine extreme amounts of exercise with a low-fat, low-calorie diet. This sends a signal to your cellular epigenome that says, “You run all the time, so a tiger must be chasing you every single day. And there’s obviously no food since you’re not eating. Your life must be under threat by famine and tigers. Yikes! Don’t get pregnant!!”
Both male and female bodies respond to these messages with exhaustion, adrenal fatigue, and hormone imbalances, but women are more sensitive to these problems and feel the effects first. A diet consisting of high healthy fats, moderate protein intake, and cyclical low carb intake is extremely healthy and beneficial. I have met many women (and men like me, too, of course) who have struggled with weight and “dieting” their entire adult lives, only to finally find a sustainable way of eating when they discovered intermittent fasting, cut out inflammatory foods, and started their morning with Bulletproof Coffee. Your personal carb threshold will vary, and only you have the power to figure it out using these guidelines.
Overall, if you’re a woman, you need to exercise more caution than a man would in balancing your biology with the benefits of intermittent fasting. This is hugely important: NEVER FAST WHEN YOU ARE PREGNANT! I strongly suggest that you see a doctor before fasting if you fall into any of these categories:
You are breastfeeding or planning to get pregnant.
You have fertility problems or irregular periods.
You are underweight or malnourished.
You have a history of eating disorders.
Remember, fasting is a process, not a single act. Respect the process, approach it with care and dedication, and you will soon find yourself in a much better place.
THE OLDER GENERATION
There’s a whole other aspect of fasting for women that I haven’t talked about yet: the way it plays out for women who are past menopause. There are about 50 million women in the United States who fall into this category,6 but you sure wouldn’t know it by looking at the articles and studies about fasting. Older women are nearly invisible when it comes to fasting, which is not okay.
I have an up-close perspective on this topic, because my wife is at the end of perimenopause and she practices intermittent fasting with me. What we see—personally, anecdotally, and in the limited scientific literature—is that there’s a tremendous range in the way women’s bodies respond at and after menopause. I think the most important thing to point out is that everything shifts when you enter menopause, so inevitably your response to fasting is going to change as well. It may very well shift every month.
Everyone is susceptible to becoming addicted to fasting (what I call the “fasting trap”—more on that shortly), but women seem to be especially vulnerable, perhaps because there is so much social pressure to be thin. Compulsive fasting, like any other kind of addictive or craving-driven behavior, is not good for you. I hear stories from women all the time: The fasting made me feel really good. Then my sleep quality went away. Then my hair started to fall out. Then my menstrual cycle went bonkers. Often women don’t recognize these as symptoms of the fasting trap, because the effects can resemble those of perimenopause.
When you reach perimenopause, your hair really is likely to get thinner, and some of it may fall out. You may experience hot flashes, anxiety, and changes in your sleeping behavior. Those changes may distract you from the ways you could be overdoing fasting. But even if you had developed a smart, balanced, flexible dieting plan for yourself before perimenopause, you are going to need to make some adjustments. Your body has a lot of new things going on. You want to be kind to yourself: face down your anxiety, yes, but through transcendence, not through suffering.
After menopause, after you’ve stabilized, you will probably do very well on intermittent fasting, possibly even better than before. My mother loves it, for instance. She does intermittent fasting and one meal a day (OMAD) almost all the time. It took her a while to get used to it, but now she says she feels much better when she fasts. For my wife, who is still in perimenopause, the effects of OMAD are more erratic. Some days she feels amazing, others not. The way you feel on any given day during a fast is also very much tied to where you are in your menstrual cycle, if you still have a cycle.
For women who are in menopause, you need to make a whole new self-assessment. Take a good look at how metabolically fit you currently are. If you are average, the answer is probably “not very fit at all.” You can actually start out gently by just skipping breakfast and having a Bulletproof Coffee. No proteins or carbs for breakfast—a little bit of going without. Maybe the first day you will have a whole stick of grass-fed butter with your coffee. Just live it up. Does that sound odd? Once you try it, you’ll be a believer. It’s like a hot milkshake. If that feels like too much fat at the beginning of the day, you can back off.
Tell yourself, “I’m just going to go until lunch.” Okay. All you did was skip breakfast. You can do this. Then you increase the size of your fasting window. You get it up to a sixteen-hour fast. Now you have dinner maybe around 6:00 p.m. Then you go without eating till 6:00 a.m. That’s twelve hours. Now go another six. That’s lunchtime. You’ll be okay. Moving around also helps a lot. It’s very doable.
Once you’ve got that solid foundation, start eating gently. Once you’ve got that going, you want to move into a longer rhythm, like an ongoing 16:8 fast. The basic rules of fasting are the same for everyone, men and women, premenopausal and postmenopausal. It’s really in the fine-tuning that women in perimenopause and beyond need to make special allowances. Things that worked for you a few years ago might not work so well anymore. If you’re feeling worse than you did before, the fast might not be the cause—but it might. Adjusting the way you fast might also be part of your solution to boosting your e
nergy and focus and reducing your stress and anxiety.
In general, if you are entering perimenopause, try shorter intermittent fasts, and don’t do them back to back until you are sure they are working for you. This is to minimize the chances of accidentally making any symptoms you have worse! Drinking alcohol, even a glass of wine, may make fasting harder. I recommend seeing a doctor and getting a hormone and thyroid panel done to assess your health and get a clearer picture of what you are working with. Changes in body composition and weight are a normal part of menopause and are not just the results of your diet. Even if you do the world’s most perfect intermittent fasting plan and eat all the best-quality foods, an underfunctioning thyroid will still make you put on weight. The changes in your estrogen-to-progesterone ratio can also make weight loss challenging.
I don’t need to tell you that it’s okay and normal for the appearance of your body to change as it ages; there is nothing to apologize for there. But even if weight loss isn’t your goal or losing weight has become challenging, I still recommend intermittent fasting. It will help you maintain muscle tone and fight the loss of bone density that can lead to osteoporosis. Recent research has also revealed that intermittent fasting helps increase a molecule called kisspeptin and stimulates your ovaries and adrenals to make estrogen and progesterone7—which can help ease the symptoms of menopause.