Fasting For Women Is Not As Effective For Weight-Loss. Here’s Why

Image of a measuring tape to illustrate whyFasting For Women Is Not As Effective For Weight-Loss

Here’s a little secret about me: I don’t fast. Not intentionally at least. 

In 2017 I overloaded my adrenal system and came down with chronic fatigue syndrome. I tried every health trend I could think of, including fasting. Despite all the touted benefits, fasting only ever made me worse. I’ve since learned much more about why. 

Fasting is a hormetic stressor. It taxes the body and results in positive changes if you are hormonally healthy. The problem is when your hormones are already depleted or stressed, fasting just adds fuel to that fire. 

For me, a depleted hormone state and an overburdened stress response rendered fasting more harm than good. Most fit guys like me would do just fine, but women can face similar problems every month. 

Unlike men, women have a hormone cycle. Many men can react poorly to fasting if they are in a diseased state or obese, but women have a part of every month when their hormones shift massively. 

It doesn’t help that almost all the research on fasting is on animals and men.

And though fasting can work well for some women, many many more react poorly to it. Promised with weight-loss, they experience weight gain or trigger thyroid problems. Where men get massive energy, many women instead are hit with fatigue. It’s not that fasting just “doesn’t work” for women, but it is a fair bit more complex. 

So in this article, I’m going to discuss how fasting is different for women. We’ll address the limited research available, address how tools like feasting, stress reduction, and low-carb diets can be essential for making fasting work, and what fasting should be used for in women as opposed to men. 

The Current (Limited) Research On Fasting In Women

Almost all the current human research on fasting is on men, but there are more animal studies on females and a few here-and-there on human women. 

There’s too little to say anything conclusive, but it is very clear that there is a difference. 

Rat studies typically show decreases in reproductive function alongside fasting. Though decreases in fertility and sexual activity also occurred in the male rats, female rats showed decreases in ovarian size. In one study, caloric restriction and intermittent fasting in female rats caused emaciation, endocrine masculinization, increased the stress response, and caused a cease to cycling. 

Another key component is brain chemistry. Male rats keep relatively stable brain chemistry throughout a fast unless it gets excessively long. Female rats, on the other hand, respond to the caloric deficit with immediate changes. Wakefulness increases as does the stress response, not to mention blunting of the menstrual cycle. 

When it comes to human studies, some of the animal results have been reflected. Most people use fasting for weight loss. However, in women, fasting has been shown to increase insulin resistance rather than lower it as it does in men. Furthermore, though fasting has been shown to work for weight loss in obese women when compared to simple calorie restriction, fasting caused greater losses in lean body mass (muscle.) 

Most of the fasting benefits for women are medical in nature rather than metabolic. For example, research does show the same benefits for cancer prevention and treatment for women as men, and fasting is also one of the body’s most powerful ways to detox (this study showed massive reductions in heavy metals from multi-day fasting in both men and women.)

Used occasionally for these purposes, fasting can be a great tool for women. Toxins in our body promote obesity and weight issues, and using fasting to address this could help with weight loss in the long run.

However, as a direct strategy, there seem to be more important tools than fasting when it comes to female weight loss. 

How’s The Water

Before we move on, I want to make one important point. Just because the current research shows these negative effects in women, does not mean this is what happens in a metabolically healthy woman. 

In the modern era, less than 20% of the population is thought to have optimal metabolic health. Basically, 80% of us have some level of insulin resistance (which is what causes diabetes.)

And all of these studies we just referenced are on people who are from an 80% metabolically compromised population. 

It’s like the old story: 

Two fish are swimming. An old wise fish swims by and chimes “How’s the water boys?” before swimming off. One fish looks at the other and says “What the heck is water?” 

Current research can’t account for the “water” that is metabolic dysfunction. One study may show terrible reactions to fasting by women, yet if we did the same study on metabolically optimal tribeswomen would we see the same result? These women experience fasting regularly, as do all who live like our ancestors. Could it be true that it still makes them insulin resistant? Who knows. 

For this article, we’re going to keep the current research in mind and focus on some other tools. Just remember that we know very little about how our bodies act when they are actually healthy since our research is on people who are almost all a little unhealthy. 

First, Get Fat-Adapted

One of the most overlooked components of fasting is the importance of getting fat-adapted. Fat-adaptation means getting your body good at using fat (dietary or otherwise) as fuel. 

Fasting works (when it works) for weight loss because it shoves your body into ketosis: a state where fats are your primary fuel source. However, just because you’re fasting doesn’t mean your body will transition easily. Someone with a poor metabolism will deal with much more stress on their hormones. Someone who has already been doing low-carb or ketogenic diets will have a much easier time of it. 

Whether you are a man or a woman, get fat-adapted with your diet first, and use this as your primary weight-loss tool. 

The Basics Of Low-Carb & Ketogenic Diets

Alright, I’m about to try to condense a topic worthy of (many) books into a short piece of this article. Bear with me. 

As we said, the purpose of these diets is to get your metabolism better at using fat for fuel. Because of high carbohydrate diets, even the fittest among us are often bad at using fat for fuel. 

This means we store body fat that our body never needs to burn, and is slowly forgetting how to. 

What’s the solution? Lower your carb intake. After a few weeks, try a ketogenic diet where you get over 70% of your calories from fat and less than 5% from carbs. The ketogenic diet imitates fasting in that your body enters ketosis, but doesn’t require you to go without eating. 

The ketogenic diet appears both in research and anecdotally to be much more successful for women than fasting. Perhaps this is because humans have evolved for millions of years eating high amounts of fat and protein. Where fasting sends signals of starvation, the ketogenic diet lets you get the benefits of burning fat without the survival signals of fasting. 

Anyway. I’m a fan. 

In observing hunter-gatherer societies, humans eat far fewer carbohydrates than we do. The highest recorded carb consumption is 36% of daily calories, and most tribes sit closer to 15% for their yearly calories. 

So I suggest aiming for 20% of daily calories from carbs. Your preference may relate to your genetic heritage. Those with equatorial bloodlines typically do better with higher carbs and those with northerly bloodlines (English, Scandinavian, etc.) typically do better with lower carbs. 

As far as protein and fat? I always recommend ample protein of 25% of your daily calories. This might look like 20% carbs, 50% fats, and 30% protein. I do not think it is common or easy to eat “too much protein.” People who do this are usually body-builders who are constantly redlining on protein powder. Despite what you may have heard, protein does not appear to really be an issue in most people unless you have kidney disease. 

This will be your “base” diet.

After 6 weeks or so of this, it’s time to try keto. 

The Ketogenic Diet Quick Guide

The ketogenic diet involves lowering your carb intake to less than 5% of daily calories and increasing dietary fat intake to 70% or more. This should cause you to enter “ketosis:” a state where your body uses fats as its primary fuel source and creates “ketones” that replace glucose in many bodily functions. 

That’s all well and good, but the real point is ketogenic diets are massively helpful for making you fat-adapted. They have been used to put diabetes in remissions (can’t officially say cured) in many users, and weight-loss success stories are commonplace. 

Keto can get technical though. For example, keto does not monitor food quality or restrict rancid vegetable oils. 

These oils are fats, but they are so easily oxidized that they end up causing damage to our bodies. Heck, they may even be the lead driver of insulin resistance rather than sugar. 

So within the ketogenic diet, I suggest a few more guidelines:

  1. Eat whole foods and avoid ultra-processed junk
  2. Avoid high PUFA vegetable oils
  3. Supplement electrolytes to face “keto-flu”

Eat whole foods is pretty self-explanatory. As Robb Wolf said so famously, “If it didn’t have a face, don’t eat it.” 

If your food doesn’t look like it wandered the pasture or grew from the earth, don’t put it in your gob. There is literally no way to make corn oil using simple tools. Yellow #7 dye doesn’t grow on trees. 

Eat plants. Eat animals. Avoid grains (they need to be processed to be edible and are also high carb) and avoid ultra-processed food. 

Now, beyond that is the problem of high PUFA vegetable oils. These oils were not in our diets before the 1800s when companies repurposed junk oils from cottonseed production as alternatives to lard and butter. 

The problem is these oils are 1. never a part of any animal diet in history and 2. are easily damaged by light and heat. 

By the time they end up in your mouth, they are made up of free radicals that steal electrons from your cells and drive insulin resistance via inflammation. 

The other big problem? These oils are in almost everything. 

While U.S. dietary guidelines have demonized red meat and saturated fat, the biggest increase in consumption of any food has been these vegetable oils. Correlation doesn’t causation make, but diabetes, obesity, and heart disease have all erupted alongside this trend. 

I could spend a day describing which oils are high in PUFAs, but it’s easier to describe which ones are not. 

Olive oil, Avocado oil, and saturated fats (solid at room temperature) like ghee, butter, animal fat/tallow, and coconut oil are all lower in PUFAs. 

WARNING: Most commercial olive oils and avocado oils are cut with high PUFA junk that is not on the label. This is why I recommend using Mark Sisson’s Primal Kitchen brand for Avocado oil (and all condiments) and using Bragg’s extra virgin olive oil

Avoid Dairy

Lastly, I suggest avoiding dairy and egg whites (yolks are ok.) Many people are reactive to dairy and egg whites from a food-allergy perspective. Though you may do fine with them, if you are having trouble with health or weight-loss, try going without. 

Feast So You Can Fast

Honestly, you could stop reading this article here and still get the take-home message: Becoming fat adapted with your diet is more powerful for women than fasting (for weight-loss.) 

However, we also know that it’s not just men who experienced feast and famine in ancient times. 

Knowing that fasting has benefits for detoxification and cancer prevention, I do think occasional fasting is ideal for everyone once they are fat-adapted. 

What’s a great way to do it? Feast.

Once a week, regardless of your diet, have a feast day. This means increasing your carbs, protein, or calories. The purpose of this is to restore glycogen and give your body a break from calorie deficits, fasting, and keto. 

Research shows that even in men, prolonged calorie deficits will cause the metabolism to slow down. I think people underestimate the importance of occasional feasting on both sides to let your body recover, carb load, and cycle out of ketosis. 

For women, I also know that many doctors have had success by having female clients feast leading up to their cycle. For that full week, and during your cycle, increase carb intake based on cravings. 

In a healthy individual who does not eat addictive foods, cravings have a purpose and a meaning. I myself eat a high protein, low carb diet. Still, today I was craving carbs so I had a large sweet potato for lunch. I have experienced no fatigue, sugar crash, or other issues. When your metabolism works, carbs are just fuel. 

Not Planning To Fast? I Still Recommend Cyclic Feasting

Whether you plan to do any fasting or just do low carb, I still recommend a weekly feast day, and being more open to carbs in the week before your cycle. 

Many people get on low-carb diets or keto for months and even years. Then they start developing issues with electrolytes that could be solved with 1 or 2 higher-carb days. 

Remember that our ancestors didn’t discipline their diets. They ate based on what they could. In ideal circumstances, this meant lots of meat and fat from animals, and in less ideal circumstances: hardy plants that required fermentation. 

But to forgo honey, fruit, and other low-toxin carbs would have been ridiculous to a caveman. Except in a few places like the arctic, hunter-gatherers eat carbs. Far less than we do, and usually not year-round, but it’s still part of their diet. 

And, Finally, Fasting For Women

So, here we are at last. We’ve looked at the research and seen that when it comes to weight loss, fasting isn’t necessarily the best tool for women. 

Unlike men, fasting can actually make insulin resistance worse. It also tends to turn off your reproductive cycle and can exacerbate anxiety. For these reasons, I suggest avoiding intermittent fasting and instead focusing on your diet if your goal is weight loss. 

However.

Fasting does have many powerful benefits for detoxification and cancer prevention. Furthermore, in a hunter-gatherer society, both men and women experience feast and famine cycles. Men likely experienced intermittent fasting daily due to hunting and other things, but women definitely also fasted. 

This is why I think fasting does have benefits for women if it is done properly, occasionally, and after you have already become fat-adapted with your diet. 

For the purposes of long-term health, detox, anti-cancer benefits, and possibly the tertiary weight loss effects of the aforementioned benefits, I suggest 6 weeks to 3 months of low carb and keto before starting any fasting. 

Once you have been low carb comfortably for this time, I do recommend a multi-day fast once a year (4 to 7 days) and if up to one 24-hour fast a week twice a month. I don’t recommend fasting during the week before your cycle, or during your cycle. 

You see, despite the research I’ve discussed in this article, I also know of many women who see great benefits from fasting. Mikhaila Peterson uses fasting quite often to great results. The caveat? She is also very well fat-adapted due to years of a highly restricted ketogenic diet. 

Is it the first tool you should use for weight loss? Probably not. Does it have benefits and did our female ancestors regularly experience fasting? Absolutely.

There is definitely nuance to the ways these practices affect women as opposed to men, but we should be careful not to throw the baby out with the bathwater. Try low carb. Try keto. Get fat adapted. And Feast once a week as well as leading up to your cycle. At that point, fasting may be not only tolerable but feel great. 

As always, thank you so much for reading and I hope this better prepares your Ready State!

7 thoughts on “Fasting For Women Is Not As Effective For Weight-Loss. Here’s Why

  1. Avatar
    fitwithliz123 says:

    Question – you referred to studies relating to the effectiveness (or lack) of fasting. What are your references to support the efficacy of keto? What’s the evidence to support the claim that humans are evolved to eat protein and fat over carbohydrates? My understanding of evolution is that we are evolved to be able to adapt to what’s available, which served very well up until recently.

    • Avatar
      keenanerikssonfitness says:

      There are radio-isotope studies showing that humans very often ate more meat than wolves and other high-trophic carnivores: https://www.pnas.org/content/106/38/16034 . This is reflected in modern hunter-gatherer diets. Even in the most carbohydrate reliant groups, they only account for about 30% of daily calories. Most modern hunter-gatherer tribes consume closer to 20% of daily calories from carbohydrate annually, and many go as low as 5% or in some cases, less than 1%: https://pubmed.ncbi.nlm.nih.gov/21745624/ . Though there is variance, overall they consume less carbohydrate and more animal foods than the majority of humans living in modern society. I don’t think we need to be in ketosis all the time. I do believe we are very adaptive, but I also think it is perfectly fine to be in ketosis often. Since many of us are addressing metabolic dysfunction, ketosis is a tool to correct that. Overall though, I’m a fan of cyclical ketosis which is why I promote feast days and feast weeks.

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    Sonia Hennessy says:

    Great article – to a point. You’ve missed referring to the fact restrictive diets like keto are generally not sustainable for life, which then has longer term negative consequences. Plus, restrictive diets like keto are a leading cause of a person developing an eating disorder, further if a person has an diagnosed eating disorder a restrictive diet like keto will encourage a deepening of ED behaviours. AND you’ve totally forgotten to highlight that all women ARE NOT THE SAME. A woman who has a menstrual cycle responds differently to a woman who is peri or post menopause. The loss of estrogen and progesterone in the peri and post menopause periods mean that women cannot become ‘fat adapted’ due to the impact these hormonal changes have on the metabolising of fat. Consequently, fasting AND keto type diets are harmful to a woman’s health in these periods not only from the ‘weight loss’ issue, but that nutritionally women need to be mindful of the risk of osteoporosis and a tonne of other things. We need to start differentiating the various stages of womanhood and not lumping all women as the same. Women now live a third to half their life POST menopause. Just like we need to differentiate the fact women are not small men, we need to also be highlighting a 50 year old woman simply does not respond the same as a 30 year old woman. Having said that, thankyou for writing an article that highlights the point that the success of fasting is for men!

    • Avatar
      Tracy Allen says:

      Sonia, as someone approaching menopause, I would love to learn more about “… the impact these hormonal changes have on the metabolising of fat.” Can you point me to some reference materials? Thanks!

    • Avatar
      keenanerikssonfitness says:

      Hey! Good points here. However, I do recommend cyclical ketosis rather than prolonged ketosis. This is why I suggest feast days. You are right that I did not address peri and post-menopause. The truth is, I honestly just don’t have enough to say about fasting to talk about either life stage. There is not much research, but overall I’d give the same advice that women should probably avoid fasting, and favor other tools for fat loss. Currently, Dr. Stacy Sims is writing a book about the subject. She covers a bit of it in her book Roar. I’m hoping she uncovers more about this poorly researched but very necessary topic.

  3. Avatar
    Tracy Allen says:

    You reference the research, or lack there of, for fasting in those with female reproductive systems but don’t mention any research related to keto and its effects. As described above, both have metabolic impacts to the human body so I would think keto could also have the potential to mess with stress response, menstrual cycle & thyroid. I’m also wondering if the benefits or risks would be affected by stage of life, in particular after menopause. Is there any research specific to women and keto? I personally know of one woman in her forties who had great success with weight loss on keto but went on to develop severe thyroid issues. I personally believe the same cautions you apply to fasting should also be applied to something as impactful as switching to a ketogenic diet (i.e. any of us might have underlying health issues that could get exasperated by making such big changes).

    • Avatar
      keenanerikssonfitness says:

      I think that Keto is fine for women, but that it is not necessary to stay in ketosis all the time. This is why I suggest feast days weekly, and a feast week monthly before your cycle. Similarly to fasting, there is not much female-specific research with Keto, however here I think we can lean into the anthropologic data a bit more. Modern hunter gatherers consume at most 30% of their yearly calories from carbohydrate. Many tribes go as low as 1%. To me, this means that humans, male or female, should be able to rely on fats for fuel. I don’t suggest being in ketosis all the time. Carbs have uses, and benefits, especially for women, but I suggest upping carb intake once a week at least, and for a full week before your cycle. On such a diet, you would be cycling out of ketosis for 10 days a month or more. That’s hardly a prolonged ketogenic diet.

      As far as thyroid issues, there isn’t much data for or against keto, in men or women, regarding thyroid. The issue may have more to do with the types of foods used though. High dairy diets can trigger thyroid issues, and lots of oxidized vegetable oils certainly won’t help, yet both of these foods are technically ok on a ketogenic diet.

      I am happy to follow the anthropologic evidence that ketosis is a perfectly normal part of human nutrition, along with nose-to-tail consumption of animals and occasional fasting, but we have to remember that fat vs. protein vs. carbohydrate is only half the puzzle, if that.

      Rancid vegetable oils, preservatives, pesticides, dyes, and the toxins in our bodies that have accumulated over years in a modern world are the other half. No tribesman or woman in the paleolithic would be exposed to any of these.

      I’m comfortable with recommending keto and low carb, but the first step regardless of diet should be to remove as many of these toxic foods or compounds that have never been in our diet. In my opinion.

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