This is an updated version of a 2012 Dear Mark column. You can find the original version stored here. The following has been completely updated for 2018.
The whiteboard hypothesis has diminished. Everyone comes into this world full of attributes, characteristics and predilections that are uniquely their own. We are all human, but we are a heterogeneous group and this makes it interesting. And even if it makes it impossible to give health advice to cookies, I consider it only an opportunity to stand out from the crowd and provide feasible advice that really helps real people.
A perfect example is biological sex. Anyone who has lived with the opposite sex, has been married or has had children of different sex knows that males and females are different, on average.
There's a ton of overlaps, do not get me wrong.
We all need fats, proteins and carbohydrates. We all have the same requirements for sustenance and well-being. We all breathe oxygen, we get stronger and fitter when we work, we use the same neurotransmitters and we produce the same hormones. The biological bases are identical.
It's the details that differ. It matters
Take the fast
Fasting as an ethical stress and the influence of biological sex
Both men and women must enter a "fasting" state to burn body fat. This should be obvious, but regularly undergoing periods when you do not put calories in your mouth is an absolute requirement for weight loss and basic health, regardless of gender.
These periods are called "fasting states" and start as soon as you stop processing the energy from your meal. An "intermittent" fast is a long period of non-use made for explicit weight loss and other health benefits.
By definition, a fast is a factor of hormonal stress – a stressful input (without food) that in the right dose triggers an adaptive response that makes us stronger and healthier. Fasting triggers Nrf2, the "hormonal pathway" triggered also by other factors of hormonal stress such as exercise, polyphenols and radiation. Nrf2 initiates a series of defensive and adaptive mechanisms that help you respond to stress and strengthen your body against future stressors. But with too large a dose, a hormonal stress factor can become a simple old stressful that overwhelms our defenses and harms us.
Making things more complicated, the size of a hormone dose is relative. What for me is hormonal could be stressful for you. Many different variables influence the amount of hormonal stressors that a person can tolerate.
With fasting, perhaps the most important variable to consider is your biological sex.
This really makes an intuitive sense.
Biology cares more about your fertility. Can you play? Can you produce a healthy offspring that survives to do the same? These things come first.
And from that perspective, the situation of a woman is more precarious than that of a man.
You have a finite number of eggs, or "chance". Men have an almost endless supply of semen.
When you are getting ready to get pregnant, your body needs extra nutrients to build a reserve and "trigger the pump".
When you're pregnant, the growing baby needs a reliable and constant flow of nutrients for almost a year. After a man has put a person pregnant, his biological involvement with the growing child is over. What or when it eats has no impact on the survival of the growing child.
After giving birth, the growing baby needs breast milk. Making that milk requires additional calories and extra doses of specific nutrients. Modern technology allows us to skip lactation and go directly to the bottle, but your body does not "know" it.
Everything indicates that women are more in tune with caloric deficits. For example, ghrelin levels of women, the hunger hormone, increase more rapidly after meals.
This is not relevant only to parents or future parents. Even if you are not interested in getting pregnant and having children, or you have children and do not expect more, the ability to do so is strongly linked to your health. Reproductive health is health. As for your body, having children is the main goal and you have to be ready to do so as long as you can.
Where does fasting come from?
Fasting is a simulated hunger. Among the most critical moments of the reproductive process, even a single skipped meal can register as a problem. The problem with intermittent fasting is that it is not just a single thing. It's a normal event. Depending on the program you follow, you can fast every day, every other day or once or twice a week. For the mostly unconscious body whose main concern is your fertility, it can be alarming.
What does this mean for women interested in intermittent fasting Unfortunately, there are not many studies examining this question in women. There are some, and I will get to those. First of all, let's move on to animal research.
What animal studies tell us
In male rats:
No matter the duration or degree of nutritional stress, the brain chemistry of a male mouse responds with similar changes. Nighttime activity and cognition remain fairly stable, regardless of the intensity of the fast. If you push the fast long enough, the males will become a little nervous and frantic, but on the whole they maintain quite well. It is as if they were endowed with the ability to manage nutritional stressors.
In female rats:
Any degree of nutritional stress (fasting or mere calorie restriction) causes an increase in waking (during the day, when they normally sleep), a better cognition (to find food), hyper vigilance and more energy. In short, female rats become better at finding and acquiring food when they fast, as if their bodies were not so well equipped to cope with the stress of going without food. They also become less fertile, while males actually become more hornier and more fertile (probably to explain the decline in fertility of females). The size of the ovary decreases (bad for fertility), the size of the adrenal glands increases (which in the rats indicates exposure to chronic stress) and the menstrual cycles begin to disregulate in proportion to the degree of caloric restriction.
A recent study found that the introduction of young rats of both sexes on an intermittent fasting program had negative effects on fertility. While male rats had lower testosterone levels, female rats stopped ovulating, had trouble sleeping, and underwent a reduction in their ovaries.
What humanistic studies tell us
One study found that while the IF improves insulin sensitivity in male subjects, women did not see any improvement. In fact, the glucose tolerance of fasting women has actually worsened. Another study examined the effect of fasting alternative day on blood lipids. Women's HDL improved and their triglycerides remained stable; the male HDL remained stable and their triglycerides decreased.
Subsequently, both men and obese women lost body fat, body weight, blood pressure, total cholesterol, LDL cholesterol and triglycerides on a fasting regime. These people were obese, however, and perimenopausal women were excluded from the study, so the results may not be applicable to thinner people or women in the perimenopausal window.
One study compared continuous caloric restriction (fewer calories a little bit each day) to intermittent caloric restriction (fewer calories from time to time, similar to fasting) in overweight and obese women. Both groups lost a similar amount of weight, but the intermittent restriction group lost significantly more lean mass. As I've always said, the type of weight loss we want is not "weight loss". It is the loss of fat and the retention of lean mass (or gain).
In the only ongoing human study on fasting and chemotherapy, seven women (including a 44-year-old woman who was probably premenopausal, given when menopause usually compensates, although not explicitly stated) and three males have discovered that IF has improved their tolerance and recovery from chemotherapy.
Takeaway: males and females (mostly middle aged, although this is the population that generally gets cancer and undergoing chemotherapy), chemotherapy patients seem to equally benefit from IF.
What about the effects of training during fasting?
One study examined healthy men and women who practice a moderate-intensity morning, fasting (at night) or eating (at breakfast). Although both men and women showed higher increases in VO2 max muscle glycogen concentration and rest in response to fasting cycling training, only men showed greater adaptations of skeletal muscles during fasting. Women had better muscle adaptations when they were fed.
Another study has fasted and fed overweight women on an interval training protocol for six weeks. Both groups improved body composition and oxidative capacity in equal measure. Being fasted or fed has had no effect.
It's sad to say, but it's all for fasting education studies on women. The great majority deals with men.
What do you think of the psychological effects of fasting?
In women, two days quickly moved the nervous system to the sympathetic domain. Although their cognitive function was unaffected, they were stressed. In men, a nervous system shifted two days in the opposite direction, towards the parasympathetic predominance. They were well rested and relaxed. Their blood pressure has dropped. Their cognitive performance has improved.
How about autophagy?
One of the main advantages of intermittent fasting is an increase in autophagy, the process by which our body eliminates cellular debris and repairs damaged cell structures such as mitochondria. A decrease in autophagy is usually linked to an increase in aging; an increase in autophagy tends to avoid the ravages of aging. Fast-induced autophagy is usually a good thing.
One of the most commonly cited documents in the intermittent fasting literature is this, which shows how short-term fasting induces "deep" neuronal autophagy. Only this could not be true for both sexes; another study shows how, while "male neurons" respond to hunger as we would expect – undergoing autophagy – "female neurons" respond by resisting autophagy.
Less autophagy is not necessarily a bad thing. Some diseases benefit from the process of autophagy, turning it against us by eliminating and killing healthy cells and women tend to be less vulnerable to these diseases. But if you are a woman aiming for autophagy, fasting may not be a reliable method of induction.
My conclusion … For now
I would be inclined to agree that pre-menopausal women (and perhaps the peri-menopause) are more likely to have little or at least different experiences with intermittent fasting (at least as a weight loss tool). That said, it seems to be a potentially gender-neutral therapeutic tool for chemotherapy, cancer and patients with age-related neurodegeneration.
So who should and should not consider fasting?
Have my tips changed?
If you have not met the usual "pre-requisites pre-IF", how to be fat, get a good and sufficient sleep, minimize or reduce stress and exercise well (not too much and not too little), you should not fast.
These pre-requisites are absolutely crucial and non-negotiable, in my opinion, especially the adaptation of fat. In fact, I suspect that if an IF study was conducted on women who burned sugar compared to women who were fat-friendly, you would see that fat-burning beasts could perform better and suffer less (if any) from mismatching.
I would also like to warn the already thin, already hypocaloric woman who throws herself head to head in IF. I mean, fasting is finally sending a message of scarcity to your body. This is a powerful message that can get a powerful response from our bodies. If you are already thin (which, depending on the degree of thinness, probably sends a message of scarcity) and limiting calories (which certainly sends a message of scarcity), the response to fasting can be a little too powerful.
I would also say that daily fasts, at 16/8 or even at 14/10, run the risk of becoming chronic stressors and should be approached with caution by women. The same applies to ultra-long fasts, such as a 36 (or even 24 hours) marathon.
Above all, however, I would simply suggest that women interested in fasting be prudent, that they are self-conscious and do so only if it comes naturally. It should not be a fight (for anyone, really). You should not interrupt the cycle or make it more difficult for you to get pregnant. It should improve your life, do not make it worse. If you find that the fast has those negative effects, stop doing it. It should happen WHEN (when hunger breaks out naturally), if it happens completely.
Some warning signs to keep an eye on
Weight Gain (especially in the middle section)
Muscle loss or reduced gym performance-It's perfectly reasonable to suffer in the gym on fast days, but watch out for persistent loss of strength. If your fitness and strength levels tend to consistently downward, fasting may not work for you.
Loss of your period: skip meals, not menstrual cycles.
Excessive hungry for hunger-hunger is good for everyone and makes food taste better; constant satiety is a trap of modernity. But you should not be hungry. Food thoughts should not consume you.
The good news is that most of the negative effects of fasting are evident and conspicuous. They do not hide. They do not hide in the background. They are really hard to ignore, so do not do it!
Some thoughts for women who want to fast
Instead of aiming for the longest fast you can tolerate, aim for the shorter fast that gives results. Do not try to feed through a 24-hour headache, headache and foggy thinking and oppressive hunger. Try to have dinner before, so you will have 12 hours of "fasting" simply by going to bed and having breakfast at a normal time.
Do not fast unless you have a good reason. Good reasons include:
Have significant amounts of fat to lose.
Your oncologist gives you the go-ahead to try using it to improve the effects of chemotherapy.
Your neurologist gives you the green light to try to use it to improve brain function in the face of cognitive decline or dementia.
Bad reasons include:
Keep the weight of pregnancy at bay.
Going from 15% body fat to 12%.
To upgrade 5x weekly CrossFit sessions.
Men and women have metabolic and hormonal differences, and it is evident that these differences partly determine the way we respond to a stress factor such as intermittent fasting. I have never prescribed intermittent fasting as an essential part of the Primal lifestyle, but rather as an elective addition, a personal choice, only as a potentially therapeutic strategy that each individual must test for himself.
Generally fast when it makes sense – if I'm traveling and good food is not available, if I'm not hungry, stuff like that. I do periodically on 16/8 or 14/10 (ie eating in a window of 8 or 10 hours) and I find that it works great for me because I am completely adapted to fat. But even I do not keep myself strictly rigid. It is not for everyone. And this has not changed.
This is all for me today. And you? If you are a woman who has tried to fast, or know someone who fits the description, let us know your experiences. I am intensely curious to know as many of you as I can. Thanks for reading.
By the way … because this is an updated version of a previous article (as I noted at the beginning), the previous comments will continue to be viewed. Keep in mind that they can refer to the context of that version of the previous article.
The post Intermittent Fasting for Women: What We Know Now appeared for the first time on Mark's Daily Apple.