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Disclaimer: Always consult your health care provider before trying any new regime or making big changes to your diet and lifestyle.
Chances are good you’ve heard of intermittent fasting (IF), a trend in wellness circles that doesn't look likely to disappear any time soon. Many people swear by intermittent fasting for its ability to improve energy, lift brain fog, and to help with weight (and fat) loss.
So, you might be wondering, "should I try it?"
This is something I get asked often by my clients. And my answer is usually not what they’re expecting. But before I jump into that, let me first explain what intermittent fasting is.
What does (Intermittent) Fasting involve?
Intermittent fasting (IF) involves going for extended periods of time (usually 12-16 hours) without eating. There are many ways to practice IF - many people restrict their eating to an 8-hour window each day (so from 10am-6pm, for example, meaning they fast for 16 hours, from 6pm to 10am the next day). Or some people choose to fast for one whole day a week, so not eating from sunset on Friday until sunset on Saturday, for example. There are many ways to fast, not to mention water fasts and juice fasts (which I won’t go into in this article).
The history of fasting
Fasting itself is not a new phenomenon. In fact, fasting has been a part of most cultures and religions for centuries (think of Ramadan, Lent, etc.). Whether or not ancient societies promoted fasting because of its health benefits, or for other reasons, we can’t be sure.
What we do know, through research, is that fasting has been shown to lengthen our telomeres (the little ‘caps’ at the end of our DNA; the longer our telomeres, the better!), which is the only proven way to actually slow down the ageing process. That may be why eating less has been associated with living longer (demonstrated both through animal studies, and through research on the Blue Zones).
In terms of weight loss, fasting may help because there’s only so much food one can eat in 8 hours! And by stopping eating earlier, we sleep better (since our bodies are not having to digest, and can instead focus on repair and all the other wonderful things that are supposed to happen when we sleep), which has been shown to help with weight loss.
So, do I recommend fasting?
You might think: “all this sounds wonderful; I think I should try it!”
Well, hold on a second.
If you are a woman who still has her period, or someone who is experiencing high levels of stress, then I would caution against intermittent fasting. Here’s why.
Problem #1: Fasting can increase cortisol
The (totally normal) rise and fall of our female hormones throughout the month brings with it a change in many other bodily systems, such as our metabolism. During follicular and ovulatory phases (the first half of our cycle), our metabolism naturally slows down a little, making this a good time to eat a little less (if you choose to) or to try fasting. However, during the second half of the cycle, in luteal and menstrual phases, our metabolism speeds up, cortisol is naturally higher, and we actually need an extra 200kcal per day (approx.). Since cortisol is naturally higher during this time, we don’t want to do anything that further increases our cortisol, such as super intense exercise or fasting.
Problem #2: We want to stabilise our blood sugar levels
This brings me to the second point... skipping meals causes our blood sugar levels to drop, at which point adrenaline is released into the bloodstream, and cortisol rises. This is our body’s natural way of getting us to eat something! But these adrenaline surges can have detrimental effects on the body if they are happening constantly, not to mention the rollercoaster of blood sugar levels, which can leave us feeling cranky, lethargic, and can contribute to insulin resistance and other health issues.
Problem #3: Fasting research was mostly done on men
This is where we have a paradox in nutrition: research shows that fasting can help with weight and fat loss, and yet research also shows that one of the best ways to lose weight is to stabilise blood sugar levels by eating little and often (every 3 hours)… How can that be?! Unfortunately, nutrition is one of those areas where you can have two totally conflicting, yet both evidence-based, conclusions.
That’s when it becomes important to look at that evidence and examine its validity... which is when we discover that most of the research on intermittent fasting was done on men and post-menopausal women (because the complexity of our hormones makes women of child-bearing age too ‘complicated’ to include in clinical trials). It’s not just intermittent fasting research that this applies to, but that’s a post for another day!
If you are experiencing a lot of stress in your life at the moment, high cortisol levels, or approaching/reached burnout, then doing something that raises cortisol even higher is probably not going to be good for you right now.
While cortisol is not inherently ‘bad’ (without it we wouldn’t be able to get out of bed in the morning) and some really healthy and important things raise cortisol levels (like intense exercise), if you're struggling with your cortisol anyway, you really don’t want to be doing anything to aggravate the situation. It doesn’t mean you can never exercise or fast again, it just means that now is perhaps not the best time, and you want to work on healing your body and reducing excess stress before you bring those things back into your life.
Key takeaway
In short, if you have a period, I would definitely not recommend fasting in the second half of your cycle (if you don’t know when that is, or if you have a hormonal imbalance, I would say: 'just don’t fast, period' (no pun intended)). I also wouldn’t recommend fasting to anyone struggling with their cortisol levels/with high stress, or anyone with blood sugar issues.
If you have a period but would really like to do IF (maybe you tried it before and it really worked for you) AND you track your cycle (and have a regular cycle!), then I would only recommend fasting during follicular and ovulatory phases (i.e. the first half of your cycle), not the second half of your cycle. But please note that some experts, such as Alissa Vitti, don’t recommend that any woman with a period fasts for more than 12 hours, no matter which phase of the cycle she’s in. It’s up to you to decide what works for you and feels good for your own body.
If you no longer have a period (i.e. are post-menopausal), then by all means try intermittent fasting (under the guidance of a qualified coach or health professional) to see if it helps you lose weight, clear brain fog, and generally feel good. Limiting your eating to a 10-hour window (such as 9am to 7pm) may be enough to see benefits. But I’d also recommend trying the opposite for a while too – eating little and often (every 3 hours) – to see if that helps you lose weight and prevent mood swings (etc.) by stabilising blood sugar levels. You could try 3 months of IF, then 3 months of the opposite (or vice versa) and note the results. It’s about getting to know your own body and what works for you.
Some further caveats: fasting is definitely not suitable or recommended if you are pregnant or breastfeeding. It’s probably also not going to be helpful to someone with a history of restrictive or disordered eating (unless they have worked through these issues with a professional and are under guidance the whole time whilst trying it).
A reminder that, as women, we can’t make blanket statements about what’s healthy or not for us. Things will change throughout your life (and even throughout the month!). So, tune in to yourself and your own body. Ask her what feels good. That’s the greatest source of knowledge you can find.
If you're looking for more personalised advice and tips for weight loss or healthy living, book in for a free consultation with me today.
Have you tried fasting? Did it work for you? Share your experiences in the comments below!