We need to talk about intermittent fasting.
I’ve been hearing about something along the lines of this practice for years, but apparently there’s a new fad around it in recent weeks because I’ve now heard about it over the course of three days from two very different sources. The first was my in-laws, who mentioned it over dinner, apparently very swayed by recent reporting on it in reputable sources like the Wall Street Journal. The second was morning radio, with the two DJs arguing over whether it was healthy and the one in favor saying “if we knew what to do with our bodies we wouldn’t have all these programs – I’m just trying this out to see how I feel”. My immediate inclination is to say that intermittent fasting is not good for your body, but as someone who has never felt personal, medical, or societal pressure to diet, I recognize that I am coming at this issue from an ill-informed perspective. So I wanted to approach the issue of intermittent fasting in terms of the historical precedent that tells us this is a simpler way to treat our bodies, from the medical research, and from the modern wellness movement that has capitalized on both.
Intermittent fasting is a broad category of dieting that encompasses any diet restricted by time rather than calories or specific food – i.e. hours, days, or months during which the dieter is not allowed to eat at all or must follow a specific regimen, paired with other times during which the diet is unrestricted. Those of us raised in an Abrahamic faith context – Christian, Jewish, or Muslim – will immediately recognize this kind of dietary restriction because some form of it is common to all of these practices. Asceticism in its various forms also heavily leans on intermittent fasting as an expression of simplicity and self-denial. And of course there are many wellness trends in recent years that employ some form of intermittent fasting, such as the ketogenic diet, dry January, and detoxing. What seems to have reinvigorated the most recent spate of intermitted fasting in the public consciousness is a few health studies that showed potential benefits to the practice, so I’ll start there.
In August, the Wall Street Journal published an essay by Dr. Andreas Michalsen that exuberantly extolled the benefits of intermittent fasting, based primarily on studies of mice. After observing that mice could eat a high-fat diet limited to a particular window of the day and still lose weight, as well as be less likely to develop Alzheimer’s, Michalsen determined that humans should stop eating breakfast to achieve similar results. He says:
If you sleep from 11 p.m. to 7 a.m., you’ve already fasted for eight hours. Now you only need another six. It’s healthy to avoid eating late in the evening to let your body burn energy from food rather than store it, so if you eat dinner by 7 p.m., that’s another four hours. For breakfast, you can limit yourself to coffee or tea (maybe with a small piece of fruit) and make lunch your first proper meal. By that time, you’re clearly beyond the 14 hours and don’t need to restrain yourself: You can eat until you are full.
There are two glaringly obvious problems with Michalsen’s argument. The first is that his main evidence, the only information he actually presents with any specifics, is based on rodent studies. Not only are rodents not humans, but the studies are much more extreme than any diet people would actually engage in. The other main issue is that the behavior he describes is what plenty of people who have difficulty losing weight already do: they don’t eat after they finish dinner and then they skip breakfast, supplementing with caffeine to keep them from gnawing off their own hands until lunch. So what is supposed to be different about intermittent fasting?
To get a little more insight, I followed up on Dr. Michalsen’s background to take a look at the book he was promoting when he wrote the WSJ piece. His book is called The Nature Cure: A Doctor’s Guide to the Science of Natural Medicine and it’s now available on Amazon. The book was pretty much written to be criticized by this blog.
Sunlight. Forest bathing. Fasting. Cold-water baths. Bloodletting. Leeches. Cupping. These ways of healing have been practiced in different cultures around the world for centuries. But as a cardiologist working with the most high-tech medical tools, Dr. Andreas Michalsen was taught that these practices were medieval and outdated, even dangerous. As he saw surprising results in his patients, however, Dr. Michalsen explored more deeply those seemingly “outdated” methods of healing. The more he researched, the more he was convinced by the power of natural medicine–naturopathy–to heal the human body.
Like other current wellness trends, Michalsen’s book hinges on both your reliance and distrust of modern science – science is cold, rational, and fact-based, but the medicine that comes out of it doesn’t care about you. So Michalsen and other experts in the wellness movement use scientific methods to justify older medical practices that have an air of hominess about them. Which is why even though his love of intermittent fasting is presented as part of new medical research, it is absolutely the same thing as historical fasting practices.
I wanted to see what the larger medical community had to say on the matter. The major health concern that struck me as a potential problem with intermittent fasting is the massive swings in blood sugar, and this is indeed a focus of medical research. But because of our societal obsession with curing disease rather than preventing it, studies looking at the link between fasting and blood sugar swings have only focused on whether the practice can be used to treat diabetes, not whether it could actually cause insulin resistance. Some poorly-designed studies have shown that intermittent fasting can replace insulin as a treatment for Type II diabetes, based on long-standing knowledge that in some cases diabetes can be cured with weight loss. Meanwhile, other meta-studies have advised caution in drawing too many conclusions from these, arguing that these studies only show that more research is warranted, and that there are real health concerns to intermittent fasting, such as chronic dehydration, insulin swings, and protein malnutrition. While some studies have shown that intermittent fasting can lead to weight loss, they have not shown improvements in actual indicators of health, since weight is not a reliable indicator of overall bodily health.
So what about the historical precedent for fasting? Is religious fasting just a way of signaling commitment to a way of life, or is it based in some sort of communal wisdom about health? When we talk about religious fasting in the West, we are mostly referring to specific events in the Abrahamic faiths such as Lent, Yom Kippur, and Ramadan. Of those, Ramadan is most obviously a proper intermittent fast, since it requires a total restriction on eating and drinking for a full month, as opposed to Yom Kippur, which is only one day, and Lent, which traditionally only limits particular kinds of foods. Moreover, Ramadan is an excellent comparison for the exact modern trend of intermittent fasting, because it limits eating to specific hours of the day.
To that last point, my mother-in-law argued that it’s not a true comparison because observers of the Ramadan fast cannot eat during daylight hours, which is nearly the opposite restriction to the intermittent fast currently being preached. As Dr. Michalsen argued in his WSJ piece, it’s better to stop eating further from bedtime to increase the number of awake hours during which you are digesting, to use up the calories you’ve just ingested and prevent your body from storing them as fat. But studies have shown that this thinking is outdated. Sleep studies during which participants were given glucose infusions found that the metabolism only slows by 15% during sleep, because 80% of the metabolic process is dedicated to keeping your body functioning. Nutrition studies focused on late-night eating found that eating a snack before bed did not contribute to weight gain or hinder weight loss, and that it could actually help create muscle proteins. So the time of day that you eat has no particular bearing on how you process the calories you eat over a 24 hour period, even though your metabolism does change over the course of a day.
Studies of the health effects of fasting during Ramadan are mixed. While popular news outlets tout the health effects of the Ramadan fast, it seems that these reports are largely based on the same desire for a cure-all diet that fuels any popular reporting on intermittent fasting. Large surveys of health outcomes from the Ramadan fast are entirely inconclusive (although the same study found that the Greek Orthodox Lenten fast and the Daniel Fast, both of which are similar to intermittent periods of macrobiotic veganism, had positive outcomes both in terms of weight loss and health markers such as cholesterol). Moreover, observant Muslims often report weight gain after Ramadan, due to the fact that the fasting prompts them to eat a richer diet and exercise less out of fatigue. In cases where fasters lost weight over the month, it was quickly regained. So, in the example of a well-regulated intermittent fast that has been in practice for 1300 years, there is no indication of an overall improvement in health or greater ease of weight loss.
It strikes me that proponents of intermittent fasting have hardly given serious thought to what established fasting practices do for health, even though they rely on the public’s familiarity with these traditions to advertise their own fasting regimens. There is, as yet, no “Ramadan diet”, nor has the Greek Orthodox church marketed proper observance of Lent as a cure-all. And yet these traditions inform the way we think about dieting over the course of the year. For Christians and those living in largely Christian societies, the calendar year follows a wax and wane in eating, as people eat more and richer foods toward “the holidays” and then begin a prolonged process of dieting heading into “swimsuit season”; although these periods are now shaped around social events like family gatherings and summer outdoor play, it’s easy to see how this way of thinking could have been formed by the religious calendar, with the Christmas season being a time of indulgence, followed by the Lenten fast in the spring. But in a modern world driven by science and the eschewal of religion except as a personal moral code, intermittent fasting can’t sound too much like religious observance, no matter how similar they are. This is especially true if the religious observance in question has an air of being not European (dun dun dun Orientalism). And of course we should largely ignore Jewish and non-Abrahamic fasting traditions, which seem to us to be based entirely in faith or entirely in scarce resource management, and thus not appropriate for modern middle-class Western life.
The crux of modern wellness, and especially diet culture, is also a mainstay of that middle-class Western life: individualism. You need to find the right diet for you. What people have done in the past only works if you distill it and tailor it to your individual needs. It’s an odd push-pull, because the evidence that something will work is that it has worked for other people, but the evidence that something doesn’t work is that it has worked for everyone else but you. This is not to say that people shouldn’t feel their problems are unique or that they don’t require tailored solutions. Rather, I’m suspicious of medical advice that repackages knowledge that’s already freely available as something unique and personally customizable. It both puts too much onus on the individual and relieves them of too much responsibility. It’s simply inconsistent to say that the problem isn’t your fault but the solution is, that our issues are systemic and cultural but our fixes need to be individualized. This logic strikes me as predatory and disingenuous.
I won’t say you shouldn’t try intermittent fasting. If you feel that it helps you curb your caloric intake and that’s the most important issue for your health, then by all means follow your own wishes. I think there’s a lot to be gained by a brief but intensive practice – being vegan for a month could certainly help you to change your tastes and your overuse of animal products, just as waking up at 6am every day for a year can teach you to get moving more energetically. But don’t be fooled by the spin – intermittent fasting is a long-standing tradition with complex roots that may or may not have real health benefits, and health studies haven’t shown it to be anything other than something that people decide to do. If you are looking for an individualized regimen that is different from what you’ve been told to try in the past, intermittent fasting certainly is not it, and the people telling you it is are just playing on cultural biases.