In recent years, more and more people have turned to fasting as a weight loss regimen. At first glance, the idea of going without food, even for a short period of time, can seem to fly in the face of everything we were raised to believe about nutrition. And while it’s true that fasting finds its origins in religion, there’s now compelling evidence that the practice of abstaining from food and drink every other day can actually lead to many health benefits, from a longer life to an improved mood.
Fasting as a spiritual practice has been around for thousands of years. According to the Old Testament, people often abstained from food and drink for long periods of time in order to focus their attention and hear from God. In the Islamic faith, Ramadan is an entire month of fasting commemorating the first revelation of the Qur’an to the prophet Muhammad. Some Buddhists live an ascetic lifestyle, often choosing to skip meals in order to improve meditation and overall health.
Yet recently, fasting has become more widely practiced not just as a spiritual exercise but as a means of pursuing physical health. There’s even a chance that fasting can lower the risk for major illnesses like heart disease and cancer, suggesting that the men and women who’ve made fasting part of their lifestyles for millenia were onto something.
Intermittent fasting is not a diet
The practice of intermittent fasting—that is eating every other day, which is also known as alternate-day fasting—is becoming one of the hottest health and weight-loss trends. There’s a ton of research and writing online surrounding the topic, and it can be hard to know where to start. Is intermittent fasting just another fad, or does it have staying power? Even more importantly, is intermittent fasting something you should consider for yourself?
To understand what intermittent fasting is, it’s first important to understand what it’s not. Intermittent fasting is not just another diet or weight-loss regimen. It’s a pattern of eating, a conscious lifestyle choice. But why would you choose to deprive yourself of food? While eating every other day can contribute to weight loss, studies have shown that the practice actually has many other compelling benefits, such as lowering the risk for major diseases, improving mood and focus, and positively impacting insulin levels.
The Science Behind Intermittent Fasting
So how exactly does intermittent fasting work? While there is a large body of research on the health benefits of intermittent fasting, it’s important to point out that so far, much of it has been conducted on animals, not humans. Nevertheless, the results look promising. In a 2013 article published in the Canadian Medical Association Journal, Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging, says there are significant biological parallels between fasting and exercise:
“There are several theories about why fasting provides physiological benefits, says Mattson. ‘The one that we’ve studied a lot, and designed experiments to test, is the hypothesis that during the fasting period, cells are under a mild stress,’ he says. ‘And they respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease.’”
Mattson goes on to compare the stress put on cells during calorie restriction to the stress put on muscles and the heart when we exercise. Not all stress is negative and regular taxation on these systems—provided there is adequate recovery time—can increase their strength. This is similar to how cells respond during periods of intermittent fasting.
The implication is that, while a certain amount of calories can be good for you, Americans are eating too much. Earlier this year, it was reported that Americans on average consume more than 3,600 calories daily, which is way over the recommended amount, no matter who or how old you are.
But there’s also the fact that we might be eating too often. According to the abstract of another study that Mattson co-authored on the link between meal timing and health and disease, most members of modern societies consume an unusual number of meals a day. Mattson says that three meals a day, plus snacks in between, is abnormal when looking at eating from an evolutionary perspective. What’s more, studies on both animal and human subjects show that restricting energy for as little as 16 hours can counteract disease and improve several health indicators.
Stephen Mount, PhD, an associate professor at the Department of Cell Biology and Molecular Genetics at the University of Maryland, corroborates this fact. “Research in molecular genetics has long supported the idea that caloric restriction leads to longevity, and that these effects are mediated through the insulin signaling pathway,” he says. Mount has been fasting every other day since 2004 after coming across a paper touting the benefits of intermittent calorie restriction.
“Although my own research does not directly involve aging, metabolism, or nutrition, I read widely on related topics, and have followed the work of researchers who do work directly on these topics,” he says. “I’ve followed research on autophagy and stem cell maintenance that has implications for the potential benefits of intermittent fasting.”
Even with this intriguing research, most people will be drawn to intermittent fasting because of the basic weight loss benefits it provides. “For many people, intermittent fasting results in significant weight loss, and it certainly allows people to maintain a weight below their ‘set point,’ so that’s a good reason to recommend it,” Mount says.
Getting Started With Intermittent Fasting
If you’re interested in getting started with intermittent fasting, you should know that there are many different types or methods of fasting that have emerged in recent years. You may have heard of the 5:2 diet, which involves eating “normally” five days a week and then eating only 500 calories for the other two. There’s also the 16:8 diet, according to which you fast for 16 hours a day and eat only within a select eight-hour window.
Of course, it’s important to realize that not every fasting strategy will work the same for every person. On his blog detailing his fasting experiences, Mount explains in an early post the unique schedule that he follows, which is entirely different than the 5:2 or 16:8. “I haven’t changed my practice much, except that I no longer drink a latte on fast days,” he tells HealthyWay. “I still take a bit of cod liver oil in the morning and a glass of wine at night, but otherwise nothing with calories between dinner one day and dinner the next, three days each week, usually Tuesday, Thursday and Saturday, but sometimes a different three days.”
In a more recent blog post, Mount goes into further detail on his current practice. “My fasts have evolved a little over time, but my basic practice has remained the same: three one-day fasts each week,” Mount writes. “I’m flexible (for example, if I’m meeting friends for lunch on Saturday, I’ll fast on Sunday instead). Fasting means no calories between dinner one night and dinner the next night (with minor exceptions…). The fasting period is typically about 23 hours, but I don’t pay attention to precise timing. I eat dinner at the time I would normally eat based on other considerations. There’s a lot of variation (from 19 to 28 hours).”
If you’re interested in trying intermittent fasting for the first time, it’s important to make sure you do it safely, which means you still need to maintain a healthy caloric intake daily. For specific schedules and tips on how to ease yourself into fasting, the folks at Precision Nutrition have some excellent suggestions.
However, don’t get intermittent fasting confused with simply not eating. “During the 13 years I’ve been at it, intermittent fasting has become much more popular,” Mount says, “first with the 5:2 diet, and more recently with people who seem to think that skipping breakfast counts as intermittent fasting.” Mount highlights the fact that intermittent fasting is an intentional practice, not just deciding not to eat.
He also notes that each person has to find an intermittent fasting routine that works for them. “To be honest, I’m not a proselytizer,” he says. “People have to find what works for them. What I like about fasting is that it’s simple. It is so much easier to simply not eat because it’s Thursday than [to] limit yourself to one cookie and not two.”
The Impact of Intermittent Fasting
Different for Men and Women
Most evidence suggests that intermittent fasting has different effects for women than it does for men. “While some women who try IF say it’s the best thing that’s happened to them since grapefruit, others report serious problems, including binge eating, metabolic disruption, lost menstrual periods, and early-onset menopause,” writes Helen Kollias in a Precision Nutrition post on the practice. “This has happened in women as young as their mid-20s.”
Kollias goes into further detail, explaining that intermittent fasting can drastically affect women’s hormone regulation. “It turns out that the hormones regulating key functions like ovulation are incredibly sensitive to your energy intake,” she writes. “Even short-term fasting (say, three days) alters hormonal pulses in some women…There’s even some evidence that missing a single regular meal (while of course not constituting an emergency by itself) can start to put us on alert, perking up our antennae so our bodies are ready to quickly respond to the change in energy intake if it continues.”
Mount says he’s heard a few concerns from women who try intermittent fasting. “The only reasons I can think that intermittent fasting might be different for women are: A) pregnancy—I think fasting during pregnancy might be a bad idea, B) menstrual disorders (missed periods) due to caloric restriction. I have heard this reported by women who have started intermittent fasting. I’ve also heard of this associated with heavy exercise (e.g. marathon training) or extreme weight loss,” he says.
“It’s also true that more women than men have told me that they tried intermittent fasting but could not keep it up,” Mount adds. “That could be due to a different response to fasting.”
When it comes to weight loss, intermittent fasting has shown to be an effective tactic, especially in obese women and in young overweight women. In a study on young overweight women, intermittent energy restriction (IER) was found to be an equivalent alternative to continuous energy restriction (CER) when it came to weight loss and lowering disease risk. The other study showed that intermittent fasting when combined with calorie restriction was “an effective means of reducing body weight, fat mass, and visceral fat mass in obese women.”
The takeaway here is that intermittent fasting can’t be considered the same for everyone, and that women especially should approach the practice with caution. “Considering how much [to fast] remains unclear, I would suggest a conservative approach,” Kollias writes. “If you want to try IF, begin with a gentle protocol, and pay attention to how things are going.”
Successful Intermittent Fasting
If you’re ready to try intermittent fasting and looking for strategies for success, there are a few that the experts recommend:
Do plenty of research.
The data surrounding the benefits of intermittent fasting is plentiful. Spend time doing your own research, and find a routine that you like and works for you. “I can only suppose that what works for me might work for others,” Mount says. “The key is to find something that is compatible with your lifestyle.”
Don’t binge on non-fasting days.
Intermittent fasting is not about “treat days.” The point is not to overindulge on junk food every other day just because you can. If you do, you will counteract all of the good effects of the practice.
Don’t try intermittent fasting if you’re suffering from other health issues.
Fasting can often be incompatible with other health issues, especially if your body needs to be taking in regular calories to fight an illness rather than experiencing caloric restriction.
Additionally, Mount suggests that if you try fasting and experience adverse effects, you should stop. “I think that if someone has given fasting a fair shot (three weeks) and still suffers from extreme fatigue, inability to concentrate, or irritability on fast days, then intermittent fasting is probably not for them,” he says. “My advice for everyone is to find out what works for them!”