- Fasting: A New, Old Practice
- Intermittent Fasting and Time Based Eating 101
- Are There Benefits to IMF or TBE?
- TBE & Circadian Rhythm
- Is IMF or TBE Different for Women?
- Do I Need to Worry about Thyroid or Adrenal Health?
- Beware of Under-Eating—Especially if You’re Super Active
- Are IMF and TBE Healthy Long-Term?
- My Personal Approach: Emphasize TBE
- Is There Anyone Who Shouldn’t Practice TBE or IMF?
- What About Coffee?
- Bringing it All Home
“Dr. Romm, Help! I’m so frustrated!” Liv, 54, was at an impasse. Newly menopausal, she’d been elated because after several years of being unable to lose a pound – and too often gaining weight when she tried to lose it – she’d lost 8 pounds in 3 weeks during my 28-Day Gut Reset. On top of that, her brain fog and joint pain had cleared up and she felt more energetic than she had in years. But then, post reset, the weight loss stalled and she was short of her goal – 5 more pounds to fit back into her favorite clothes, while still keeping her in a healthy weight. She joined my medical practice for some 1:1 support and asked, “What can I do? Should I try intermittent fasting?” Here’s what I told her…
Hi Everyone and welcome to Intermittent Fasting and Time-Based Eating: Is There Evidence for Women’s Health and Weight Loss?
In this article and podcast I discuss:
- The differences between and the science behind Intermittent Fasting and Time-Based Eating
- What we know – and don’t know- about the benefits – and risks – for women, specifically
- Why I don’t recommend Intermittent Fasting as robustly as I do Time-Based Eating
- How to avoid having a negative impact on your reproductive hormones while doing Time-Based Eating, especially if you’re very physically active
- My guidance for a moderate Time-Based Eating approach that’s safe and beneficial for pretty much everyone
- Who should not practice Time-Based Eating – or at least take a conservative approach
- And my personal approach to Time-Based Eating
Let's’ dive in…
Fasting: A New, Old Practice
Food trends come and go as quickly as fashion trends. The 1980s brought big hair, neon-colored clothes, and the cabbage soup diet. The 90s brought grunge and low-fat foods of every stripe. But Americans gained weight and our cholesterol went up – not down. Point being – not all trends are in our best interest (though I must admit to still having a fondness for torn T-shirts, skinny jeans, and combat boots).
Then there are the classics – those choices that are perennially smart, even if we forget about them until they make a comeback. Take high-waisted jeans – IMHO, so much better on most of us than the super low-riders of the early 2000s.
So what about fasting? Fasting is definitely having its day in the sun as a hot trend. But back to trends versus classics. Which is fasting? And is it good for us?
Fasting has been an important part of cultural, spiritual and religious traditions around the world for thousands of years. Our pre-electricity, pre-refrigeration, and pre-home delivery ancestors couldn’t just open the fridge at 7 am or 11 pm, grab some fixings and pop them in the microwave or on the stove and have a meal in 5, 15, or even 30 minutes. Fires had to be built to cook food. That meant wood had to be gathered. Water had to be procured. And the food had to be prepared. From scratch. This took time, and leftovers weren’t the norm. So breakfast wasn’t a get-up-and-go kind of thing. The chores that allowed food to be eaten had to be done first.
In the same vein, the sun set and our ancestors went to bed long before late night TV even gets ramped up in our modern world of 24/7 viewing options. Wild carnivors might have been on the prowl at just around the time you’re first tuning into your favorite late night show. So yeah – no late night snacks or midnight meals. Too much work – and you risk making your village bait for the wild things No thanks. I think I’ll wait until morning…
Whereas modern life (at least in western countries) allows us to eat from the moment we wake up until the moment we go to bed, which is often well past the time our ancestors would have remained awake, and food is always on the ready to grab, our ancestors likely enjoyed a natural period of fasting that extended roughly from about 7 pm or so until mid-morning. This gave their digestive system a rest for designated time periods, a practice which is consistent with human circadian rhythms, and is protective against inflammation and the chronic diseases that are now becoming ubiquitous, like diabetes, heart disease, and dementia. They also tended to be leaner and more muscular than most of us are today.
It’s the known health benefits of this more biologically inherent way of eating that have led to two popular diet ‘fads’ that are the rage – but which, actually, aren’t simply fads.They’re classics that have been dusted off, shaken out, and given a whole new look. They’re called Intermittent Fasting (IMF) and Time Restricted Eating (TRE), however, because I don’t like using the words restricted and eating in the same sentence – not good for our mental health and food relationship, I refer to this practice as Time Based Eating (TBE) to my patients – and I will in this article and corresponding On Health podcast episode as well.
Intermittent Fasting (IMF) and Time Based Eating (TBE) 101
First, let’s get onto the same page by clarifying the nomenclature, because the terms Intermittent fasting (IMF) and time-based eating (TBE) have been erroneously used interchangeably – and they’re not the same thing.
Here’s what they are, and how they are different:
Intermittent fasting technically refers to going either entirely without food or severely restricting calories (water is allowed) for 24 hours or more consecutively, typically at regularly scheduled intervals or numbers of days per week.
The two most common types of intermittent fasting intervals are:
- The 5:2 fast which involves eating your usual diet for 5 days out of the week. The other 2 days are fasting days, when you completely abstain from eating or you severely restrict calories (to usually no more than 500–800 calories – 500 typically recommended for men, 800 for women.
- The alternate-day fast (ADF) involves fasting every other day, limiting what you eat to around 500–800 calories on the fasting days.
Time-based eating (TBE) is what most people are actually referring to when they tell their friends they’re practicing intermittent fasting. With TBE, you consume your day’s calories within a specific time frame. It’s usually an 8- to 12-hour ‘feeding window,’ as it’s sometimes called. Then you completely fast during the remaining 12 to 16 hours – which is meant to at least partly occur overnight (while you sleep). It’s not meant to be about calorie restriction whatsoever, though studies show that it does commonly lead to consuming slightly fewer calories in a day.
The most common methods for following a time-based eating plan are:
- The 16:8 method, in which you fast for 16 hours of the day and limit your eating window to the other 8 hours. For example, eating between 9 a.m. and 5 p.m. or 11 a.m. and 7 p.m. and having nothing but water during that time.
- The 14:10 method, which is more liberal, in which you fast for 14 hours of the day and only eat during the other 10 hours.
One can choose to do an IMF plan daily, or limit IMF to just 1 or 2 days per week.
Now that you know what IMF and TBE are, and the difference between them, let’s explore whether doing either is good for your health.
Are There Benefits to Intermittent Fasting or Time-Based Eating?
Both IMF and TBE are areas of robust scientific exploration as researchers seek ways to prevent and reverse the epidemics of chronic disease that are causing a devastating impact in terms of both human quality of life and costs to the healthcare system.
Weight loss is a major area of study, and has shown promising results. Research (mostly in animals but some promising small studies in humans) has suggested IMF and TBE can have a host of additional beneficial effects – from improving metabolic and cardiovascular health to protecting memory and cognitive performance to extending lifespan, all of which are particularly important for women’s long term health, particularly after menopause, and about which there remains a paucity of much needed studies.
While IMF and TBE are often lumped together in popular parlance, the science behind them is somewhat different. Interest in intermittent fasting grew out of studies that show that when animals eat less food over their lifetimes, it extends their lifespan and has beneficial effects on aging, obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative diseases. Research suggests that one key reason for these benefits is that after an extended period without food (about 12 hours in humans, which can include the time in which one is not eating overnight), metabolism switches from burning glucose (our usual energy source) to utilizing stored fat. When this metabolic switch is flipped, the liver starts converting fatty acids to ketones, which become the main source of energy during fasting. This is one of the metabolic effects of the ketogenic diet, as well.
The extended fasting of IMF also seems to trigger a potentially helpful stress response that tamps down inflammation, improves the function of our mitochondria – the parts of our cells that generate most of the chemical energy needed to power our cell's biochemical reactions – and increases stress resistance and antioxidant defenses, while promoting a process called autophagy that removes and recycles damaged cell components. This cellular clean-up process may also help remove cells that are at higher risk of becoming cancerous due to malfunction.
If you’re doing 16:8 or 14:10 TBE plan, you may begin to get some of the same benefits seen in the longer fasts of IMF. The metabolic switch to burning fat, which puts you in very mild ketosis, usually begins after 12 hours of fasting, and autophagy is triggered after 16 to 48 hours into fasting, depending on the study, so the long fasting window of even a 14:10 can bring you benefits, while the 16:8 TBE method would be needed to begin to trigger autophagy.
But TBE has its own unique benefits that are different and additional to IMF. The main rationale for TBE is rooted in our growing understanding of the circadian rhythm and the way eating affects this daily 24-hour cycle.
Time Based Eating & Circadian Rhythm
Almost all tissues and cells in our bodies have a circadian clock that regulates the expression of many genes that have daily fluctuations in their activities. The master circadian clock is in the brain – specifically in a part of the hypothalamus called the suprachiasmatic nucleus (SCN) – and light is the main signal that ‘sets’ this master clock. That’s why exposure to bright light at night can profoundly disrupt our sleep.
But light isn’t the only factor that helps set our circadian rhythm. In recent years, animal studies have suggested that when it comes to the circadian clocks throughout the rest of the body, outside of the SCN, “the timing of food intake is the most powerful cue.” So the idea behind TBE is that it improves our circadian rhythm by keeping our eating cues in line with the light cues that keep the master clock ticking along properly. That’s important because we know that chronic circadian rhythm disruption is associated with a range of health problems, including glucose intolerance, weight gain, liver diseases, various forms of cancer, depression, sleep problems, disruption in thyroid hormone production, reduced immunity, and cardiovascular disease. This is something I explain in detail in my books The Adrenal Thyroid Revolution, and Hormone Intelligence because of their significance in women’s hormonal health, stress, sleep, metabolism and more.
By limiting food intake to a reasonably short daytime window of 8 or 10 hours, we eat during the time that our metabolism and gut function – including our gut microbiome – are optimized for digestion and assimilation. Your digestive system wasn't meant to be “on” all the time, and it was especially meant to be at rest at night; melatonin released before sleep inhibits insulin secretion, which is perhaps why the same meal when eaten in the evening provokes a larger glucose spike compared to when it’s eaten in the morning.
Its effect on the gut microbiome might be part of the reason TBE can be so beneficial. Just like our own cells have a circadian rhythm, there are daily fluctuations in the activity and composition of the communities of bacteria that live in our digestive tract. In a 2015 study, when mice were put on a high fat diet, it dampened these cyclical fluctuations in their microbiomes; but when they ate the same diet in a TBE window, the circadian fluctuations were partially restored. Researchers suggest TBE might promote a more diverse gut microbiome because different species of bacteria bloom during the eating period, while others thrive during the fasting period, potentially protecting us from the problems that have been linked to altered microbiomes and reduced microbiome diversity, including metabolic syndrome, depression, inflammation, and cancer.
One important difference between IMF and TBE is that when practicing IMF, on your fast days you are putting yourself in a state of caloric deficit, while TBE is not about restricting how much you eat or eliminating specific foods – it's all about food timing. While many people do naturally end up consuming fewer calories when practicing TBE, you don’t have to eat less in order to get the health benefits.
For those who do have established metabolic syndrome or obesity, a longer fasting window of up to 16 hours, so a 16:8 TBE schedule, may be even more beneficial. It’s recommended that you start with a lighter TBE plan, i.e., 12:12, then up to a 14:10, and work your way up to 16:8 over a matter of weeks. But it’s not necessary to do the 16:8, you can still get benefits with the shorter fasting periods. Further, there may be some cumulative benefits to combining IMF and TBE, for example, doing TBE daily, while having 1 to 2 days weekly of skipping food completely or capping food intake at a maximum of 800 calories for women a couple of times per week. Again, not necessarily, but possibly having some added benefits.
In my studied opinion, and in my experience with my patients, TBE gives much of the best of both worlds of TBE and IMF – without the restrictiveness of skipping food for 24 hours once or twice weekly required with IMF. As I’ll discuss, with TBE, you don’t experience the potential risks of caloric restriction that can accompany IMF, and be particularly problematic for women’s nutritional status, hormone production, bone health, and more. And, importantly, TBE is much more sustainable than the longer, regular fasts of IMF, making you more likely to maintain a commitment to TBE and feeling successful at it, without feeling chronically restricted or deprived.
Is Intermittent Fasting or Time-Based Eating Different for Women?
While IMF and TBE have become popular, it should be noted that most of the evidence of benefits comes from animal studies – and, as with so many studies influenced by medical bias, even in the selection for male gender in animal studies, most of those were on male rodents! The human studies that have been done thus far have been small, usually short-term (lasting just a few months), and mostly conducted in overweight/obese individuals. We need more research to fully understand the benefits and potential risks of these eating practices over the long term, and particularly in women.
As researchers have begun to conduct IMF/TBE studies in both male and female rodents in recent years, they have uncovered some significant sex differences. For example, in a 2021 study, young male and female mice were fed a high-sugar, high-fat diet which is the mouse equivalent of our standard Western diet during a 9 hour TBE eating window. They found that the males, but not the females, were protected from weight gain, had lower fat mass, and more muscle mass. Likewise, TBE only seemed to protect the males, not the females, from adipose inflammation and elevated cholesterol levels. On the other hand, both sexes showed less-fatty liver and better-controlled blood sugar.
Meanwhile, in humans, there have certainly been some studies conducted only in women that demonstrated impressive benefits. For example, in a 2017 study of more than 2,000 people with breast cancer, those who fasted for 13 or more hours had significantly reduced breast cancer recurrence risk. In a 2020 study, women over the age of 60 saw an average body fat loss of about 4.5 pounds after 6 weeks of following a daily 16:8 TBE plan.
But since most human studies thus far have been small, they usually haven’t been large enough to detect if there are any differences between men and women. And the few that have specifically looked for potential differences have often found them.
For example, a 2005 study put several men and women on an alternate day fasting schedule for 3 weeks. At the end, glucose response to a meal was slightly impaired in the women but not the men. In a 2023 study, overweight, older adults ate in an 8 hour TBE eating window for 6 weeks. While both the men and the women lost a similar amount of weight, only the men saw a significant decrease in visceral fat mass and waist circumference.
Now, this is significant for two reasons. One, it's the visceral fat mass and waist circumference that are actually the high risk for cardiovascular disease. So being overweight is not necessarily a health risk for most people. Being obese is a medical condition and that's a medical risk, but being overweight, you can be in a bigger body and be very healthy, but when you have that increased visceral fat mass, that increased weight circumference, that's the inflammatory producing fat tissue and that puts you at risk.
And two, for women particularly in our menopausal and postmenopausal years, that increased fat on our buttocks and our thighs is actually beneficial for producing small amounts of what is called estrone. That's the estrogen that we produce after menopause, and that estrone continues to have some heart and bone and brain protective effects. So when losing weight on our butt and our hips we may find that we like how we fit into our pants better, but it may actually not be beneficial for our hormones in those years of our life, and if we're not losing the visceral fat, we're not getting that increased inflammatory protection.
So it's kind of an interesting spin and a nuance, right?
When we look at it just sort of straight on, we're like, oh, you lose weight, that's great, but it's not the right kind of weight for the protective effects.
On the other hand, in a small 2020 study, researchers concluded that premenopausal women, postmenopausal women, and men who did alternate-day fasting for a few months lost a similar amount of weight and saw similar improvements in metabolic measures like insulin resistance and blood pressure. And if you're trying one of these plans for a more extended period of time, i.e., 3months, 6 months, 12 months, consider getting follow-up on your blood work to make sure that things are moving in the right direction for you. If you're doing this as this one particular study showed, and at the end of the day you're not actually getting improvement in your insulin resistance or your blood sugar measures or it's possibly even getting worse, that's not a good result.
There have also been concerns raised about whether IMF/TBE could have a detrimental effect on women’s hormones, menstrual cycle, and fertility. That’s because IMF/TBE often involves some degree of caloric restriction (though in TBE it doesn’t have to – more on that later) to which women are biologically sensitive, the most obvious consequence being something called hyopthalamic amenorrhea, which may occur on its own due to calorie restriction, or as part of the ‘athletic triad’ associated with calorie restriction, over-exercise, or high levels of stress. Hypothalamic amenorrhea leads to anovulation (meaning you’re not ovulating), thereby impacting fertility, and also progesterone production which when reduced can lead to a host of hormonal symptoms.
Some animal studies have certainly been concerning. In a 2013 study of young rats, an alternate day fasting regimen disrupted the estrous cycle in female rats, as well as altering serum concentration of estradiol, testosterone, and luteinizing hormone (LH). The researchers concluded that IMF “negatively influences reproduction in young animals due to its adverse effects on complete hypothalamus-hypophysial-gonadal axis.” On the other hand, the mice in that study were quite young – comparable to prepubescents in human terms – so it’s not clear that the impact on fully grown female mice would be that detrimental.
When it comes to human studies, we don’t have much to go on. A 2022 review noted that “very few studies have examined how intermittent fasting impacts sex hormones.” The handful of studies they could find – which were small, short term, and only in premenopausal women with obesity – suggest that 5:2 IMF and TBE may decrease androgens, while increasing sex hormone-binding globulin (SHBG) levels. The authors suggest that IMF and TBE could therefore be beneficial for women with elevated androgen levels from polycystic ovarian syndrome (PCOS), which physiologically could improve ovulation and reduce the common and troubling symptoms of excess androgens that women with this condition experience: cystic acne, hirsutism, and female pattern hair loss. Combined with a high protein diet and increased high intensity exercise, this approach could potentially provide an effective and non-pharmacologic approach to PCOS for many women. On the other hand, decreasing androgens and increasing SHBG could potentially lead to symptoms of lower androgen – lower energy, drive, and more. So still a lot to be determined with further research.
A small 2022 study was the first to look at how TBE affects hormones in postmenopausal women as well. It concluded that with an eating window of 4-6 hours women, estrogens, progesterone, androgens, and SHBG did not change. But in both groups DHEA was reduced – the significance of which is unclear, but overall suggests a limited negative impact on sex hormones.
The bottom line is that there appear to be clear physiologic benefits to eating both intermittent fasting and time-based eating, but we need much more research specifically on how these practices impact women across our life cycles and how they impact women with various medical risks and conditions.
Do I Need to Worry about Thyroid or Adrenal Health?
I’m frequently asked whether IMF or TBE are safe and appropriate for women with hypothyroidism or Hashimoto’s, or whether they might negatively impact cortisol levels due to a possible impact on the adrenal-stress response system. Concerns have also been raised as to whether IMF might have a detrimental effect on hormonal circadian rhythms.
A recent review of the literature reported that in rodent experiments, complete fasting for 24 hours lowered serum T3 ( triiodothyronine), and likewise, in humans, the (T3) level started to decline quickly with fasting. One (dated) study reported that serum T3 decreased up to 55% after 24 hours of fasting, while TSH levels remained unchanged. A 2019 study on IMF using the alternate day fasting (ADF) method found lowered levels of T3 without impaired thyroid gland function, suggesting a possible thyroid hormone conversion issue.
The clinical significance of these changes is still unclear, and more research is needed. Also, 2020 study compared the IMF pattern of alternate day fasting (ADF) to daily calorie restriction in adults with subclinical hypothyroidism: They found that both are equally effective in producing clinically significant weight loss (7-8%) over 6 months in adults with subclinical hypothyroidism, with no clinically significant impact T4 or TSH levels. They concluded that ADF does not appear to negatively affect thyroid hormone levels in subclinical hypothyroid individuals, but they did not study the impact on euthyroid, or hypothyroid individuals.
However, due to the impact of calorie restriction on thyroid physiology, I tend to recommend against IMF and extreme TBE (less than an 8 hour eating window) for women with subclinical and clinical hypothyroidism, pregnant women (maintaining normal T3 levels is essential for fetal growth and brain development) and in women trying to conceive, because the impact of normal T3 levels is also important in this setting.
When it comes to stress and cortisol levels, as mentioned earlier, IMF may, counterintuitively, have a positive impact on stress, resilience, and cortisol levels. But we do know that for women in particular, highly restrictive diets, particularly when low blood sugar occurs chronically or often, can trigger the stress response and has been associated with the same problems associated with circadian rhythm disruption, and mentioned previously.
Overall, however, there is a lack of adequate rearch exploring the impact of TBE on either cortisol or melatonin levels, and more research is also needed on whether the strategy of skewing the eating window to earlier in the day, or later in the day makes a difference, i..e, skipping breakfast and eating slightly later in the evening, or eating breakfast earlier, and having the last food of the day very early in the evening. A 2021 review which explored the impact of TBE during the Islamic annual month-long fast of Ramadan found a blunting in circadian cortisol rhythm and a reduction in melatonin which, according to the researchers, could theoretically lead to reduced sleep duration and quality.
The bottom line here for me is that while it can be helpful at reducing inflammation and improving brain fog and aches and pains, I recommend avoiding IMF and treading carefully with TBE, sticking with a 14:10 window which is highly unlikely to have a negative impact thyroid, stress levels, or cortisol in most women if you struggle with these. Similarly a 16:8 plan is also likely to be well-tolerated, but it’s important to err on the side of caution if you do struggle with fatigue, and above all, pay attention to how you feel on either plan.
You can also modify it to just a couple of days of TBE per week if you want to achieve some of the potential benefits without skipping meals on a daily basis. If it’s not working for you, don’t keep doing it. Eating healthy foods as close to their natural form as possible, not too late at night, and not too much, is still phenomenally healthy, without doing any IMF or TBE!
Beware of Under-Eating—Especially if You’re Super Active
In contrast to IMF methods where you consume minimal (or no) calories on your fasting days, in TBE, you aren’t intentionally eating less than you normally would in a 24 hour period – you’re just compressing your eating into a shorter window.
However, especially when doing TBE with the shortest eating windows, many people automatically reduce their calorie intake slightly. According to one recent review, in trials on TBE, participants have tended to reduce overall calories by 7% to 22%. If someone is very physically active and practicing TBE, they might therefore inadvertently not consume enough calories to support the energy they’re burning through exercise, causing a syndrome called Relative Energy Deficiency in Sports (RED-S) (the athletic triad I mentioned earlier is a subset of this syndrome).
Over time, RED-S can lead to amenorrhea (loss of the menstrual cycle), loss of bone density and increased risk of fractures, and disruption of the hypothalamic-pituitary-gonad axis (HPG axis) – the brain-ovary connection, and the hypothalamic-pituitary-adrenal axis (HPA axis). Symptoms include fatigue, depression, frequent illness, and declining athletic performance, as well as interference with menstrual cycle regularity and ovulation.
While RED-S can affect men and women, it is especially common in women (the condition was previously known as the Female Athlete Triad). According to a recent review, 20% of exercising women have menstrual irregularities, as do over half of women endurance runners.
Dr. Satchin Panda, a prominent researcher on circadian biology and TBE, has developed an app, MyCircadianClock, where users can track their meals and activity and share the data with researchers. He has noted that they have gotten reports from women who developed RED-S symptoms after starting TBE, while also exercising frequently – which would only be more likely to occur with IMF, because it’s inherently calorie restrictive.
That’s not to say it’s not possible to do TBE while being an athlete – it just may require being more careful to ensure you’re getting enough food to support your activity level. While there haven’t been that many IMF/TBE trials in physically active people, a 2019 study found that young women who did resistance training while following an 8-hour TBE eating window saw similar gains in muscle and strength compared to women who ate within a 13-hour period. Importantly, the two groups consumed the same amount of energy and protein – that’s the critical piece.
Are Intermittent Fasting and Time Based Eating Healthy Long-Term?
Besides RED-S, there may be unknown side effects from IMF/TBE when used long-term that we don’t know about yet. For example, a 1991 epidemiological study found that a long overnight fasting period (of greater than 14 hours) was associated with nearly double the risk of gallstones in women compared to those who fasted just 8 hours per day.
According to Dr. Valter Longo, another prominent fasting researcher, until further studies give us a better understanding of the risks and benefits, IMF and more extreme versions of TBE should be limited to short-term use and not adopted by the general population.
In contrast, TBE periods of approximately 12 hours, according to Dr Panda, “appear to be associated with benefits without known negative effects.” Dr. Panda agrees that, for those who aren’t trying to lose weight, are eating a healthy diet, and are physically active, sticking to a 12 hour fast may reduce the risks – and offer plenty of benefits. And this is good news – it’s sustainable and still beneficial!
In rodent studies, most of the benefits of TBE are seen with a fast of only 12 hours, although the shorter the eating window, the greater the benefits. While there haven’t been very many human studies of 12 hour TBE, one recent Swiss randomized trial showed that people who reduced their eating window to 12 hours (while not changing their diet at all) lost as much weight as those who switched to a healthier diet with fewer processed foods. On the other hand, a 2021 study found that those who followed the 14:10 diet while incorporating nutritious foods and consistent exercise lost more weight – showed a more significant improvement in blood glucose levels – than those who did the 12:12 diet.
But, given that according to the data collected by the MyCircadianClock app, more than a half of adults eat during a window of 15 hours or longer everyday. So compressing it to 12 hours would be a significant change for many people.
My Personal Approach: Emphasize Time Based Eating (TBE)
Personally, as I've gotten older (I'm 56 now), I’ve found that TBE with an eating window of 10-12 hours and fast of 12-14 hours is a more natural daily eating pattern for me. And in my clinical experience, a 12:12 or 14:10, TBE window is highly achievable, sustainable, and not psychologically challenging for many women. It also reduces sleep disturbances, as well as reflux at night, which independently causes or exacerbate sleep problems, both of which are often even more problematic in perimenopause and early menopause, when inflammation and weight gain may also start to creep up.
How you time the hours of your eating window is up to you, though I highly recommend having your last food of the day no later than 7 pm if at all possible – it’s important to not go to sleep within 3-4 hours of eating your last meal of the day. And it’s ideal to wait about an hour after waking up before eating your first meal of the day. There’s some evidence that an eating window earlier in the day is somewhat more beneficial than later in the day.
But that might be more difficult to maintain socially. After all, most dinners out with friends aren’t over by 6 pm! As much as possible, stick to the same window every day – just like having a consistent sleep schedule is helpful for maintaining healthy circadian rhythms, so is having consistent meal times. Further, while studies on this continue to be contradictory, there is some evidence that skipping breakfast may increase all-cause mortality in women, so there may be benefit to starting your eating window on the earlier side, for example 9 am, and then completing your food intake for the day 8 to 10 hours later, depending on the ratio of eating times to fasting you’ve selected.
It may take some experimentation to figure out the window that best fits your body, schedule, and lifestyle. TBE definitely doesn't work for me on especially demanding work days – for example, if I have to give a morning presentation. I know to eat before any major work or physically strenuous events. It also might not be best for you if you do heavy workouts early in the morning – in that case you can theoretically fast for the last meal of the day – but I find that this leads people to be hungry at night and not sleep as well, or even binge late at night, so I don't recommend it.
How you break the fast is important. Psychologically, you might be tempted to reward yourself with an all-you-can-eat meal. But this is counterproductive. If you eat a giant feast your primitive brain will tell your body to store that extra energy in the form of fat for later use. Instead, I recommend breaking your fast with a simple, filling healthful meal containing protein, greens, a healthy carb, and a good quality fat, and eat only until just satisfied, not full. Then, if you get hungry before your next meal, choose snacks that are high in healthy fat or protein, like nuts, bone broth, a hard boiled egg, or if you need something a little more, 8 oz. of a protein shake. If you want a sweet treat, have 1/2 cup organic fresh berries or 2 squares dark chocolate.
Here’s a moderate approach to TBE if you’d like to try this, that’s likely to be risk-free for most people:
- Keep your eating window to 10-12 hours, with a 12-14 hour overnight fast.
- Consider TBE on 1 or 2 days per week only, instead of daily.
- As much as possible, be consistent with your eating window, or TBE days, to help set your circadian rhythms.
- Don’t eat within 3-4 hours before bed.
- Pay attention to how you feel, stay hydrated, and adjust your energy (food) intake accordingly as needed, for your energy expenditure.
Is There Anyone Who Shouldn’t Practice TBE or IMF?
Intermittent fasting and time-based eating are not for everyone. Here’s who should tread very carefully, or avoid fasting completely:
- You have a history of struggling with an eating disorder: I don’t recommend intermittent fasting as I find that the extreme restriction is an emotional trigger for many women who have previously been overly fixated on food intake; one does need to be thoughtful that TBE isn’t a way that you’re practicing an eating disorder unwittingly, but in my experience, a light TBE practice can be done safely and effectively as long as you are recovered and not actively experiencing symptoms, and as long as you stay honest with yourself about your motivations and how you’re feeling on the plan.
- You’re pregnant or breastfeeding: If you are pregnant or breastfeeding, it's not an option. You need the nutrients from more meals – and this is not a time to be cutting back. Pregnant and nursing mommas need that more around the clock nutrition.
- You’re underweight: If you’re underweight, IMF is not an option, but TBE might be acceptable because it doesn’t require a reduced food energy intake, just a compressed eating window; however, as stated, it often does lead to reduced calorie intake. If weight gain is your goal, this might not be the best option; however, working with a nutritionist to guide your energy intake might allow you to get the other benefits of TBE while still allowing you to consume adequate amounts of food and getting the calories you need.
- You need to take medication with food at certain times: If you need to take medications with food, and at certain times of day, speak with your medical provider about whether TBE is an option for you.
What About Coffee?
The jury is still out on whether having that morning cup of coffee (or caffeinated tea) ‘counts’ as eating and breaks the fast. On one hand, some studies showing benefits of TBE have allowed black coffee or tea during the fasting window. For example, that study showing that a greater than 13 hour overnight fast was associated with a reduced risk of breast cancer recurrence allowed black coffee during the fasting period. But the consensus from most researchers – sorry to say if you were hoping for a different answer – is that it probably does reset some of your body clocks and take you out of the fasting state. According to Satchin Panda, a cup of coffee in the morning is similar to an hour of bright light exposure – which does reset your circadian clock. It’s more unclear however, to what extent drinking coffee/tea kick-starts metabolism thereby taking you out of the fasting state and stopping autophagy to some degree or another.
While the data is still unclear, experts in the field of circadian biology tend to suggest a conservative approach that permits coffee and tea only during the designated window of eating. And if you choose to have coffee or tea before eating for the day, it should be black (no cream, milk, nut milk, sugar) – otherwise it definitely is considered the start of ‘eating.’
Bringing it All Home
Many of my patients have adopted TBE practices that integrate easily into their busy lives, that leave them feeling satisfied throughout the day, and improve their energy, digestion, metabolism, sleep, chronic aches and pains, sense of well-being and more. In fact, a lot of my patients start TBE on a temporary basis, but they continue it indefinitely because they feel so good and because it’s really quite easy.
While no one way of eating is for everyone, time-based eating may be a return to natural eating rhythms in a man-made world that can feel busy, chaotic, and over-stimulating – quite far from the circadian rhythms in which our nervous systems – and digestive systems were inherently programmed to thrive. If you have no contraindications to it, are curious, and would like to give it a try, pay attention to how you feel, giving yourself a couple of weeks to adjust to the new rhythms – that’s the best way to know if it’s for you – or not. If you’re eager to try but preparing food is what feels foreign or overwhelming to you – I’ve got you with dozens of recipes on my website, and hundreds of recipes and weeks’ worth of meal plans in my books, The Adrenal Thyroid Revolution, and Hormone Intelligence, along with more ideas for supporting and resetting your circadian rhythm, reducing inflammation, balancing blood sugar, and supporting your hormonal health at any age.
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