There is increasing evidence from recent human and animal studies that Intermittent Fasting — refraining from food or caloric beverages for at least 12 hours a day, several days a week — reduces the risks of cardiovascular disease, dementia and cancer.  Those benefits are well-documented in the hyperlinked articles, so I won’t repeat them here.  Yet many nutritionists hold that skipping Breakfast or other meals and snacks can lead to weight gain and metabolic imbalance.  Several recent articles have suggested that IF and breakfast skipping is a particularly bad idea for women. Much to my chagrin, this view been even embraced recently by a number of ‘Paleo’ advocates whom I respect, such as Chris Kresser and Mark Sisson.

In this post I’d like to address three main objections that have been raised against skipping breakfast and other forms of Intermittent fasting:

1. It spurs hunger cravings, leading to compensatory overeating and obesity
2. It causes cardiovascular disease and metabolic dysregulation of blood glucose and hormone levels
3. It’s bad for women, leading to hormone imbalance, disrupted menstrual cycle, and heightened stress response

I believe these concerns with breakfast skipping are overblown, based on an incorrect interpretation of a few animal and human studies, and flawed personal implementation.  To the contrary, adaptation to meal skipping can actually help boost stress tolerance and improve blood sugar control. If practiced correctly, intermittent fasting (IF) can actually be a powerful tool to overcome hypoglycemic symptoms, and regain control over a harried lifestyle.   And it can be particularly useful for women who are struggling with cravings, weight management and stress management.

Opposition to intermittent fasting arises from both published research and anecdotal reports.  I’d like to address both in this post.  I’ll first point out some significant flaws in the interpretation of several recent studies purporting to show negative effects of reduced meal frequency on women and other groups.  And I’ll end by pointing out how to avoid common mistakes made by many who try intermittent fasting find it to be unpleasant and unsustainable.

Approached correctly, IF can provide major health benefits for most us.

Let’s dig in to the arguments that have been made in support of these three myths about breakfast skipping and intermittent fasting:

Myth 1: It spurs hunger cravings, leading to compensatory overeating and obesity.  A number of observational studies report a correlation between breakfast skipping and obesity.  For example, a 2010 Study of 9659 teenagers found that self-reporting breakfast skippers had higher BMI, and waist size than those who ate breakfast.

Some have attempted to explain this association in terms of overcompensation for hunger.  The idea is that  skipping the first meal of the day is counterproductive because it backfires, stoking hunger and leading to a high net intake of calories later in the day.  This view seems to find support in a 2014 CDC study of eating behavior among overweight young adult women.  The participants were screened to include only those who already habitually skipped breakfast and were overweight (BMI 25-35 kg/m2).  The study measured dopamine levels (using homovanillan, a dopamine metabolite) and subjective cravings in response to different breakfasts, or skipping breakfast.   It was found that, compared to eating breakfast, skipping breakfast resulted in a gradual increase in cravings and lower dopamine levels over a 4-hour morning sampling period.

According to Heather Leidy, the lead author,

Our research showed that people experience a dramatic decline in cravings for sweet foods when they eat breakfast. However, breakfasts that are high in protein also reduced cravings for savory – or high-fat – foods. On the other hand, if breakfast is skipped, these cravings continue to rise throughout the day….It used to be that nearly 100 percent of American adults, kids and teens were eating breakfast, but over the last 50 years, we have seen a decrease in eating frequency and an increase in obesity.

It’s not really surprising that eating breakfast would reduce hunger and increase dopamine  levels relative to not eating breakfast, is it?  The more important question is whether skipping breakfast and the increased mid-day appetite leads to obesity or long term weight gain via compensatory eating later in the day.  The CDC study didn’t specifically address that question.  It could not answer the question of progression to obesity, because it started out with a pre-selected group of already overweight teenagers who were already breakfast skippers.

So who knows what led to their initial weight gain prior to the study. We don’t know whether their breakfast skipping was the cause of their high BMI.  It is entirely possible that their breakfast skipping was a consequence of their BMI or something related to it.   In fact, the authors of the study end by acknowledging these uncertainties:

Specifically, reduced breakfast frequency (i.e., breakfast skipping) is inversely associated with increased BMI, weight gain, and obesity in young people.  However, due to the lack of long-term randomized controlled trials, a causal link between breakfast skipping and obesity has not been substantially identified.

It’s certainly far from proven that breakfast skippers overcompensate due to hunger cravings and eat more as a result of skipping the first meal of the day. A 2013 study by Levitsky and Pacanowski found that while skipping breakfast does lead to increased hunger by lunch time and eating of larger lunches, by the end of the day the breakfast skippers had spontaneously consumed 400 less calories per day than the non-breakfast skippers.  Overcompensatory eating did not occur.

If skipping breakfast doesn’t lead directly to overeating and obesity, what explains the observed association? Perhaps eating late in the day “causes” breakfast skipping the next morning.  That may not be as strange as it sounds.  It could be that a large number of those who are obese skip breakfast because they overeat late into the night and wake up still feeling full from the previous night, delaying their eating until later in the day.

Myth 2:  It causes cardiovascular disease and metabolic dysregulation of blood glucose and hormone levels.  There is indeed some evidence that those who skip breakfast and also consume most of their calories after 6 pm put on more weight and are less healthy.  But is it the breakfast skipping or the late night eating that drives this?  Let’s take a look at a few studies that examined breakfast skipping and late night eating.

A 2014 study of 1245 adults by Bo et al. found that consuming more of the daily energy intake at dinner is associated with an increased risk of obesity , metabolic syndrome and non-alcoholic fatty liver disease.

A 2013 study by Jakubowicz et al. found that when daily intake was fixed at 1400 calories, eating the larger 700 calorie meal for breakfast resulting in more weight loss and better metabolic markers than consuming the 700 calorie meal between 6 and 9 pm at night.

A 2013 study by Cahill et al. at Harvard followed the eating patterns and cardiovascular health of over 26,000 men for 16 years. The men all started out free of Coronary Heart Disease.  But the men who skipped breakfast were found to have a 27% higher “risk” of CHD.  This alarming conclusion got a lot of press!

But such a bold headline deserves closer scrutiny.  Buried within the Cahill study are a number of surprises.  It turns out that the “risk” analysis was based on complex modeling that attempts to correct for numerous differences between the subgroups in order to tease out the “true” risks.  In fact, the actual incidence of CHD “events” over the course of the 16 year study was….drumroll:

• 5% among the breakfast skippers
• 6% among the breakfast eaters.

So CHD events were actually 20% more frequent (6% vs.5%)  among the breakfast eaters than the breakfast skippers!  

Then why did Cahill et al calculate  a higher “risk” for the breakfast skippers? Answer: they “corrected” the results using a statistical model. They did in an attempt to account for the fact that in their particular sample of study participants,  breakfast skippers were different from the breakfast eaters in a number of key respects. For example:

• Breakfast skippers were 5 years younger on average than breakfast eaters
• 15% of the breakfast skippers smoked vs. only 5% of the breakfast eaters
• Breakfast skippers consumed 37% more alcohol than breakfast eaters
• Cholesterol levels and other biomarkers differed between the two gropus

Through the magic of statistics and multivariate modeling, Cahill et al. “adjusted” for a large number of other health and demographic factors, converting the absolutely lower CHD incidence of the breakfast skippers into a 27% higher risk!  Magic!  Yet the adjustment is paradoxical because — other than being younger — the breakfast skippers had a number of strikes against them, such as higher smoking and drinking rates.  So you would think the fact that their actual incidence of CHD was lower, would mean that the breakfast skipping behavior was protective, not risk-enhancing.

The “corrections” made by Cahill’s team of modelers led to another head-scratcher:

In stratified analyses, among men ≤60 years of age, those who skipped breakfast had a 50% higher risk of CHD compared with men who ate breakfast (multivariate RR, 1.55; 95% CI, 1.09–2.22), whereas this association was not significant in the older half of participants (RR, 1.06; 95% CI, 0.84–1.33; P for interaction=0.01;

Huh?  If you believe the Cahill analysis, skipping breakfast increases your risk of CHD if you are younger than 60, but that risk suddenly disappears entirely after you reach age 60!  It seems to me that the Cahill analysis is an example of placing undue faith in a model, rather than taking the unvarnished incidence data at face value.  Data massaging for risk analysis is often warranted, but it can sometimes lead to perverse and nonsensical results, especially when the risk relationships are complex and non-linear, and when the absolute risks are relatively small and similar in magnitude.

If you still have confidence in the Cahill multivariate models, there is yet an even more alarming result:  Those who ate late at night or through the night had a 55% higher CHD risk than others, and this higher risk was mediated by body mass index, hypertension, hypercholesterolemia, and diabetes. Unlike the analysis for the breakfast skippers, a key point is that this difference persisted even independently of the statistical risk model.  In absolute terms,  over the 16-year study, fully 9% of the late night eaters had CHD, vs. 6% of the non-late night eaters — more significant than the impact of breakfast habits.

In addition, Cahill found a 25-30% increase in CHD risk among those  who ate more than 5 times a day.  Snacker and grazers take note.

A 2014 study by Kutsuma et al. examined the eating habits of 14,068 Japanese adults with a variety of eating patterns. Multivariate analysis showed that the combination of late night dinner eating and breakfast skipping was associated with obesity and metabolic syndrome, and yet this association was absent in the case of either breakfast skipping alone or late night eating alone.

Looking at all these studies, we can ask:  What’s the real problem:  breakfast skipping, or eating frequently and late into the night?

We need to be careful not to link intermittent fasting with effects that may originate from a very different pattern of eating — in which breakfast skipping is associated with a common cultural pattern of eating late at night and snacking frequently.  Many such breakfast skippers may start eating around lunchtime, and continues snacking and eating through the afternoon and evening, culminating in the midnight snack.  Maybe even “healthy” snacks. Know anyone like that?  By contrast, most who practice IF deliberately confine their eating to an interval of about 5-7 hours.  Typically, they skip breakfast, eating lunch and an early dinner, or perhaps just an early dinner, going to sleep on an empty stomach.

Going to bed on a full stomach eliminates the nighttime fasting that kicks in for those who partake of lighter or earlier dinners.  Late eating may prevent the benefits of fasting and low insulin levels during sleep brought on by autophagy — the process of nutrient recycling that reverses the accumulation of metabolic damage and underlies many of the health benefits of intermittent fasting.  If eating a big meal at night is followed by eating breakfast again early in the morning, there is not much of a “fast” to break, even if one waits until lunch for the next meal.  Autophagy kicks in only when you don’t eat for about 12 hours. (It can also be activated by severely restricting protein and/or carbohydrates).

Myth 3:  It’s bad for women, leading to hormone imbalance, disrupted menstrual cycle, and heightened stress response.   Recent articles by Stefani Ruper and the Poliquon blog cite animal and human studies to substantiate this claim.  In her blog post, “Shattering the myth of fasting for women”, Ruper cites a combination of biological research, anecdote and personal experience to buttress her main thesis:

Many women find that with intermittent fasting comes sleeplessness, anxiety, and irregular periods, among a myriad of other symptoms [and] hormone dysregulations.  I have also personally experienced metabolic distress as a result of fasting, which is evidenced by my interest in hypocretin neurons.  Hypocretin neurons have the ability to incite energetic wakefulness, and to prevent a person from falling asleep, should his body detect a “starved” state.  Hypocretin neurons are one way in which intermittent fasting may dysregulate a woman’s system…the mere fact of being more sensitive to the strains of fasting simply by being a woman is, I would assert, pretty important for a woman who is contemplating or already practicing IF.

Ruper’s reference to hyopcretin neurons draws upon a rat study by Martin et al., showing that 6 months of calorie restriction was beneficial for male rats but detrimental to female rats, causing them to “masculinize”.  The fasting female rats stopped ovulating, exhibited heightened alertness and memory, and slept less.  The authors showed that these changes came about by activating the hypocretin “arousal” system in the brain’s hippocampus.  These arousal and food-seeking behaviors are presumably beneficial as an evolutionary adaptation to starvation. Chronic activation of these arousal systems could interfere with reproductive capacity and cause other health problems.

However, a closer look at the Martin et al. study makes it clear that none of the diets examined was a reasonable model of breakfast skipping or intermittent fasting.  The five diets studied were:

1. ad libitum (control diet)
2. 20% CR (calorie restriction)
3. 40% CR (calorie restriction)
4. IF (intermittent fasting)
5. HFG (high fat / high glucose)

Restricting calories by 20-40% is really quite severe, and it is not surprising that it could lead to loss of ovulation. But what about the so-called “IF” diet?  The article makes it quite clear that the IF diet was also a forced calorie restriction diet.  Unfortunately, few details are provided regarding the precise degree of calorie restriction or the feeding schedule. However, the authors do give us this clue:

Whereas males on the HFG diet showed a greater increase in weight than those on the control diet, females on HFG and control diets gained similar amounts of weight. Males and females exhibited similar body weight responses to 20% CR and IF diets (i.e. a small increase in body weight). Both male and female rats responded to 40% CR by losing a significant amount of body weight during the study.

From this, together with the fact that the researchers explicitly state that the IF diet was calorie restricted, it is reasonable to infer that the IF diet was probably in the range of 20% calorie restriction.

Here’s the problem: Nothing about intermittent fasting mandates or even recommends net calorie restriction! With IF, you eat all you want — you just eat it within a restricted time window. True IF is more like an “ad libitum” diet than a calorie-restricted diet, in that it allows your appetite to be fully sated.  The neat thing about IF is that it has been shown to provide many of the health benefits of calorie restriction without any actual net reduction in calories!  Quite a few IF practitioners do spontaneously reduce calorie intake over time, as their appetite adjusts.  But many IFers do not significantly cut back on calories — they just alter the temporal pattern of intake.  In either case, IF has been shown to provide health benefits.

In short, the Martin et al. rat study cited by Ruper fails to say anything about intermittent fasting the way most people practice it: without forced calorie restriction.  It’s certainly not the way I practice or advocate it.

Ruper does seem to acknowledge the difference between calorie restriction and IF, but she appears to confute IF with longer term fasting:

It is well-known in both the research and the nutritional communities that caloric restriction is horrible for female reproductive health.  This is not news.  But what of fasting regimes?  Should women go long periods without eating, even if maintaining normal caloric input?

Long periods without eating?  Intermittent fasting involves short term breaks from eating of 12-24 hours, and the the degree of net calorie restriction can be modest to none.  We are not talking about “long periods” of going without food or any significant amount of calorie restriction.

On that note, Ruper cites a 2005 study by Heilbronn et al. showing that alternate day fasting improved insulin sensitivity men, but slightly impaired glucose tolerance in women.  The study had a very small sample size (eight men and eight women) and the effects were slight, but even granting its validity, the protocol involved so-called Alternate Day Fasting (ADF).  This involves continuously alternating between 12-hour eating windows and 36-hour fasts for two weeks.   In my view, this is starting to push the fast a bit long. I certainly wouldn’t recommend ADF to anyone as an “introductory” version of IF.  Longer fasts require a period of adaptation.  I occasionally do longer fasts myself.  But my recommendation to newbies is always to start out gradually, by skipping snacks and then a few meals, rather than taking a heady plunge into longer fasts.

One of the most common misunderstandings of hormesis that I encounter on this blog is a failure to appreciate the dramatic difference between modest, intermittent stress and intense, chronic stress.  Hormesis is all about the benefits of low dose, intermittent stress.  This applies to exercise, diet, immune response, vision therapy and even psychology.  People think that if a little is good, a lot is better.  Moderation and gradualism are essential to reaping the benefits of hormesis.

Hormones out of whack? The posts by Ruper and the Poliquon Group also both cite a 2007 study of meal frequency by Stote et al, comparing consumption of three meals a day with consumption of the same amount of food once daily for dinner.  The results were a mixed bag:  Those eating a single daily meal lost body fat, and saw their cortisol levels decline.  However, they apparently also experienced greater hunger, less satiety, and modest elevations in blood pressure and LDL and HDL cholesterol levels.  Ruper’s verdict:

In sum: patients on the one meal/day regiment were unhappy, hungry, lost a little bit of weight, increased cholesterol.  This was a small sample, included ~menopausal women, and all people of normal body weight.

A closer read, however, pinpoints some telling details. First, how was hunger measured?  “Subjective satiety and hunger were assessed daily before consumption of the evening meal“.  Well duh!  Obviously this is going to be precisely the  high point of hunger for those eating one meal per day, and hunger will obviously be much more attenuated for those who ate lunch just a few hours earlier!  Seems to me that it would have been fairer to do the hunger assessment after the dinner, or perhaps upon waking in the morning, for both treatments.   Personally, some increased hunger is a good thing, particularly if it makes food tastier and the meal leaves you satisfied.

The Poliquon article interprets the Stote article as evidence that intermittent fasting causes hormone dysregulation:

The effect of intermittent fasting on hormones and circadian rhythms is devastating. First, the entire hormonal cascade (metabolic hormones like insulin, anabolic hormones like testosterone and growth hormone, and energizing hormones of the adrenal glands) is interrelated. When one hormone-producing gland gets out of whack, you can bet that others will be negatively affected. This can produce any of the following: Poor metabolism and body composition, inability to build muscle, infertility, chronic fatigue, sleep disorders, a pro-inflammatory state, and increased risk of disease.

A glimpse of this with intermittent fasting comes from an 8-week study [Stote et al.] in which middle-aged people went on a 1-meal-a-day diet or a regular 3 meal-a-day diet—calories were not restricted. Results showed that the 1-meal-a-day group diet lost 2 kg of fat compared to the 3-meals-a-day group, however they also had a significant increase in blood pressure. Elevated blood pressure is indicative of altered circadian rhythms.

In addition, cortisol, which was measured in the late afternoon before eating the 1 meal, was 48 percent lower than at baseline. This is further evidence of diurnal dysregulation. Yes, you want to minimize cortisol for health and body composition, but that doesn’t mean you want irregular cortisol, which is a symptom of adrenal fatigue.

Quite an indictment!  But this is taking a few tidbits out of context and wildly speculating about them.

First of all,  the slight blood pressure elevation that Stote saw in the once-a day eaters was most likely an artifact of the time  of day at which blood pressure measurements were made, as Stote et al themselves suggest:

In animal models, intermittent fasting without caloric restriction has been shown to decrease blood pressure and heart rate (15). The observed increase in blood pressure in our subject population consuming 1 meal/d may be due to a circadian rhythm in blood pressure (23). Diurnal changes may have occurred, because blood pressure measurements were obtained in the late afternoon in the 1 meal/d diet versus early morning in the 3 meals/d.

Second, the concern about the 48% drop in cortisol over the day is misplaced.  This is not dysregulation or a sign of “adrenal fatigue”.  To the contrary, it is perfectly healthy! According to Chinnock et al. a normal cortisol pattern starts with a rise in the morning, followed by a gradual decline throughout the day, precisely as was found in the once-a-day eaters.  Later in this article, I’ll reference another study by Taylor et al., confirming normal levels of cortisol and other hormones in intermittent fasters, and no impact on the menstrual cycle.

The Poliquon article’s charges of adverse hormonal effects of intermittent fasting are unfounded.

Another anomaly of the Stote study is that subjects eating once daily were required to eat the same amount of food as the three-meal-per-day group in a single setting.  All 2400 calories, whether they wanted to or not.  In other words, appetite was not allowed to control eating. Yet they still lost weight.  Imagine if it had been an ad libitum study.  Yet I think this is a big defect of the study and may be responsible for some of the negative effects on blood lipids and blood pressure. It is not a natural way to eat.  And it may have been responsible for the high dropout rate of the study.  As the authors note,

Our study withdrawal rate was 28.6%. Typical rates of withdrawal from human feeding studies at our facility are ≈4–7% (18–20). We can hypothesize that subject withdrawals increased because the subjects were asked to consume all food for the day in 1 meal; however, only 1 subject specifically stated this reason for withdrawing.

So far from stoking hunger, the authors worry that their once-a-day feeding protocol made subjects feel too full!

Stote concludes with the view that IF might be OK for overweight women, but not for women of normal weight, light sleepers, those with irregular menstrual periods or conditions like acne.

The solution, then, in moving forward, is to look at options, to be honest about priorities, and to listen to one’s body with awareness and love.  Is fasting worth trying if a woman is overweight and trying to improve her metabolic markers, and so far hasn’t had much success?  Perhaps.  Should it be undertaken if a woman is of normal weight?   What if she is a light sleeper?  What if her periods begin to dysregulate?  Or stop?   What if she starts getting acne, getting a stronger appetite, or losing her appetite altogether?    These things happen, and I see them in women who fast and contact me time and time again.

These fears about intermittent fasting seem unfounded.  Hormonal dysregulation might be associated with longer term fasting or other lifestyle or dietary conditions that raise cortisol.  But that is not the situation with IF, which was even shown to reduce cortisol levels.

By failing to distinguish intermittent fasting from extreme calorie restriction and long term fasting, I think that Ruper and others do a disservice to women in particular.  I know quite a few women who have adapted to IF quite well and swear that it has improved their health and their lives.  That fact that it works for some women quite well should be enough to refute the idea that IF is only suitable for men.  I do not  doubt that the transition to IF may be difficult for some women — but that is also true for some men.  I’ll deal with the practicality of how do adapt to IF towards the end of this article.

True intermittent fasting.  Now let’s look at a few studies that actually looked at real intermittent fasting — eating less frequently (but generally at least once a day) and within a confined time window, but without any attempt to limit or equalize net daily calorie intake.

A 2014 Salk Institute study published in Cell looked at true non-calorie-restricted intermittent fasting in mice.  Unlike the Martin et al. study, these mice were allowed to eat all they wanted, but just within a restricted eating window.  Mice that ate within a 9-12 hour window ended up weighing significantly less than control mice allowed to eat as much as they wanted around the clock — even though they ended up consuming the same net amount of daily calories! The reduced weight gain was true even for rats given diets high in fat and sugar.  Even more impressively, the IF rats maintained good lipid profiles and insulin sensitivity, unlike control rats that could feed ad libitum.  Interestingly, the strong weight control and metabolic benefits persisted even when the rats were allowed to go off the diet on weekends!  A slightly longer 15-hour eating window provided more modest benefits.

Great for rats, but how about humans, and specifically women?

A 1998 study of meal frequency in women by Taylor et al. compared the metabolic effects of eating 3 daily meals plus a snack versus a single daily dinnertime meal of equal daily caloric, macronutrient and micronutrient composition. The same seven women were studied eating these two different patterns for two separate 3-day study periods.  It should be pointed out that the investigators approached this study with the mindset that “the ingestion of fewer large meals may be metabolically worse than the ingestion of frequent small meals.”  The fact that the authors labelled the eating of one daily meal as “binge eating” rather than “intermittent fasting” tells you something about the investigators’ presumptions!   With that said, it’s worth looking at what this study actually found:

Ingestion of an entire day’s calories at dinner resulted in a significant increase in fasting glucose levels and a dramatic increase in insulin responses to the evening meal. The diurnal pattern of leptin secretion was altered, such that the gradual rise in leptin from 0800 h observed during the normal diet was abolished, and leptin did not begin to rise during the binge diet until at least 2 h after the evening meal.

This is of course not at all surprising.  The question is whether it a more concentrated peak rise in glucose and insulin, and change in the timing of the leptin peak could result in hypothesized insulin resistance or hormonal dysregulation, based on prior studies associating these problems with “binge eating”.   It turns out that those fears were not actualized:

No changes were demonstrated in insulin sensitivity, follicular growth, or ovulation between the two diets….Importantly, there was no difference in cortisol excretion between the two diets.

It is also worth pointing out that despite higher morning (“fasting”) blood glucose levels on the once-daily pattern (94 mg/dL) vs. multi-meal (86 mg/dL), the average blood glucose over the day  for the once-daily  pattern (97 mg/dL) was significantly lower than for the multi-meal pattern (107 mg/dL).  It seems to me that average blood glucose is a better indicator than a single morning reading of what your brain and peripheral tissues are seeing most of the time.  And 97 is definitely better than 107!   Eating once a day may cause bigger “spikes” in blood sugar but average blood glucose levels are lower, and remain lower for a more sustained, uninterrupted time. Adaptation to this pattern can be especially valuable for people with blood sugar issues, because elevated blood sugars can cause all sorts of problems.

Somewhat surprised that their study found no problems with one meal per day, Taylor at al. ended their paper with the suggestion that perhaps something more is involved with true binge eating than merely reduced meal frequency:

as most binge eating episodes in the population are associated with the ingestion of excess calories, it is hypothesized that binge eating behavior is associated with even greater metabolic dysfunction than that described herein.

Indeed.  Binge eating, like bulimia and anorexia, is a true eating disorder.  Eating disorders typically arise from issues associated with body image and self-control, perhaps exacerbated by a poor diet or metabolic dysfunction.  But binge eating should not be confused with intermittent fasting.  Practitioners of IF are motivated by its documented health benefits and additionally by the freedom to offers from cravings and food obsessions.

Conclusions and recommendations.  The purpose of this post was not to make the positive case for intermittent fasting. For that, you can check out the hyperlinks in the first sentence of this post, or watch my talk on Intermittent Fasting for Health and Longevity.  Rather, this post attempts to examine and respond to some recent claims that IF can cause obesity, cardiovascular disease, and disordered glucose, hormone levels, and menstrual cycles.  I believe that these criticisms hinge upon several fundamental misunderstandings of IF and misinterpretations of a number of scientific studies.  By closely examining the evidence, we can draw two main conclusions.

• Many breakfast skippers are indeed overweight or unhealthy, but this most likely reflects other associated habits such as frequent snacking and eating late at night.  IF is best practiced by confining eating to a 4-6 hour window, and preferably eating dinner early and well before bedtime.
• While dysregulation of hormones and menstrual cycles can be disrupted by severe calorie restriction and very long fasts, there is no evidence that such problems result from shorter daily fasts of about 12-24 hours.

While I believe that intermittent fasting is generally safe for most people, including women, I think there are better and worse ways to implement it.  Many have stated that IF is not suitable for people with diabetes, hypoglycemia or other metabolic issues. However, I’ve heard and read of many instances of people who used IF to reverse those conditions — to normalize blood glucose and lipids and to bring hunger and hypoglycemia under control.  For just one instance of this, read this inspiring post by Lee Shurie, who reversed his diabetes using IF:

How I defeated Type II Diabetes

Of course, I have no doubt many of you reading this have had very negative personal experiences trying intermittent fasting. But I suspect that many of the negative experiences that some individuals have had with IF stem from making a very common and understandable mistake:  moving too quickly.

If you are habituated to a pattern of eating three or more meals a day plus snacks, trying to suddenly switch to one meal a day may be a bad idea.  While some people can do that (I did), many will find it to be both psychologically and physically intolerable. Eating and appetite are under the control of a complex system of hormones and enzymes.  It can take weeks to change the timing of induction and secretion of these modulators.  Symptoms can range from hunger pangs and unbearable cravings to headaches, hypoglycemic light-headedness, sweating and fainting. Not a good idea.

I strongly advise gradualism.  Make small changes each week and allow them to set in before proceeding further.  First, eliminate between-meal snacks and avoid eating for at least an hour before bedtime.  Those changes can be hard enough and may take weeks to adjust to. But even that first step is already beneficial. Once snacking is eliminated, try delaying breakfast rather than skipping it.  Eventually you may be able to skip breakfast.  You can also try to finish eating dinner earlier and avoid eating after 8 p.m.

Interestingly, the benefits of intermittent fasting can be significant even if you can manage a 12-18 hour mini-fast once or twice a week.  You don’t have to do it every day to see health improvements.  Of course, if you can skip breakfast 5 or more days a week, more power to you.

Your appetite will adjust, as your hormone and enzyme levels gradually change to the altered eating schedule.  Just as Pavlov trained his dogs by repetition, you can train your mind and digestive apparatus to learn a new pattern. Hunger is much more susceptible to conditioning that you may think — read this New Yorker article and my page on Appetite the Deconditioning Diet.  And be patient!

I’ve summarized my recommendations on transitioning to intermittent fasting in an earlier post, Learning to Fast.  It includes a lot of useful tricks, such as the use of “training snacks”.  Learned correctly, intermittent fasting doesn’t ramp up hunger — it tames hunger. Many people have told me that post was very helpful in helping them adjust to intermittent fasting with a minimum of effort and discomfort. I’d be interested in additional feedback and comments from others regarding what has or has not worked for you in your efforts at intermittent fasting.

Happy (and gradual) intermittent fasting…just in time for the Holidays!