By Emily Shiffer
The world is changing, and today, even when we’re not self-isolating, many of us are working from home. That creates challenges, sure. But it also creates opportunities—especially when it comes to how you structure your day. Whereas the office routine might force you into coffee-and-doughnut meetings and scheduled lunch breaks, at home, you can eat, or not, whenever you want.
That makes now the perfect time to try intermittent fasting, or IF. In recent years, the fittest guys in Hollywood, including Hugh Jackman and Terry Crews, have been singing praises for skipping meals. Chris Pratt used IF as part of a strategy to transform himself from the goober on Parks and Recreation to the action hero in Guardians of the Galaxy, and recently, Kumail Nanjiani did the same. He used intermittent fasting to get ripped for his upcoming role in Marvel’s The Eternals.
So what exactly is IF? “In general, intermittent fasting is just patterns of fasting and non-fasting throughout the day,” says Jonathan Valdez, owner of Genki Nutrition and spokesperson for the New York State Academy of Nutrition and Dietetics.
That leaves a lot of flexibility in how you structure your fast to fit it into your routine. In Nanjiani’s case, he followed an 18/6 protocol, according to an interview with Men’s Health. That means that for each 24-hour period, he fasted for 18 hours and consumed all his day’s calories in the remaining six. But that’s just one of many strategies, says Valdez.
Other common IF protocols are 16/8 and 14/10. Then there’s the 5:2 method, where you eat normally for five days of the week and limit your calories to 500 for the other two. There’s also alternate-day fasting, where you max out at 500 calories every other day, and the big 24-hour fast, where you go a full lunar cycle without food.
To varying degrees, all fasting strategies aim to mimic the periods of hunger that humans experienced naturally throughout history, before each meal was just a Seamless order away. But if you’re considering deploying IF on yourself, it’s worth knowing exactly what you’re in for. So here’s what to expect, both in terms of health benefits and potential pitfalls.
Benefit #1: IF will help you lose weight
This is one of the most well-established benefits of caloric restriction. In a February 2020 review of 27 studies on intermittent fasting among overweight and obese people, every single study found some level of weight loss.
On the low end, the weight loss was 0.8 percent of body weight. But for longer and more substantial studies, it reached 13 percent. For IF interventions lasting more than two weeks, the average participant trimmed 4.3 percent off his or her body mass index.
Benefit #2: IF can help you control your blood sugar
You might not spend a lot of time thinking about the amount of glucose in your blood, but you should. In addition to the 34 million Americans who have diabetes, another 88 million have pre-diabetes, according to the Centers for Disease Control and Prevention. And 80 percent of them don’t even know it. If you’re in the pre-diabetic group, you’re more likely to carry extra bodyweight and develop heart disease. It’s bad news.
Thankfully, fasting offers some degree of protection by keeping your blood-sugar relatively stable. In a 2018 study published in the journal Cell Metabolism, pre-diabetic men who committed to fasting for 18 hours a day experience substantial improvements in insulin sensitivity. And the effect was the greatest among guys who need it the most. That helps explain why, according to a study published in the journal Sports Medicine, Muslims who observe the fasting tradition of Ramadan are more resilient against heart disease, stroke, and dementia.
Speaking of which….
Benefit #3: IF could boost your brainpower.
By lowering LDL cholesterol and triglycerides, intermittent fasting might offer some protection against neurological diseases, such as Alzheimer’s, says Valdez. And while we don’t have the long-term studies to prove it on humans, a 2018 study on mice found the effect to bear out.
“Preliminary animal studies have associated IF with preventing or slowing cognitive impairments associated with age,” says Valdez.
Equally impressive, IF could make you feel sharper and more focused right now—just like our brain-boosting Superhuman Supplements.
As your body runs out of glucose, it starts burning body fat. This is the hallmark of fasting, and as a byproduct of converting fat into energy, your brain washes itself with cognition-boosting compounds.
One is brain-derived neurotrophic factor (BDnF), which stimulates neuron growth. Another is gamma-aminobutyric acid (GABA), which helps keep you calm under stress. Research from the journal Neurology International shows that IF also increases your serotonin levels, which can make you feel happier.
So it’s no wonder that people who practice IF are so enthusiastic about it. Now, what’s the downside?
Negative #1: IF sucks!
Okay, this one is a matter of perspective. But at some point, almost everyone who fasts ends up watching the clock for their final hour of hunger, or cracking a beer at night only to realize they’re just outside their calorie-consuming window. (Although, to be fair, more men are giving up alcohol anyway.)
In those situations, will you stick to the plan, or make an exception?
As proof that IF is challenging, a study published last year found that the dropout rates in alternate-day fasting studies—where caloric intake is severely limited every other day—is as high as 40 percent. That’s partly why 18/6, 16/8, and 14/10 fasting protocols have all become so popular. They provide flexibility. Consider starting at 14/10, and then working your way up to 18/6.
To increase your odds of success, check out our five-step strategy for building habits that stick.
Negative #2: IF can be risky for certain groups
If you have a history of eating disorders, the risk of fasting probably outweighs the benefits. It can swing dangerously close to anorexia, and if it turns into an addiction, it could result in “malnutrition, moderate damage to organs, or susceptibility to infectious diseases,” says Valdez.
Furthermore, if you have diabetes, and you’re already taking medication to lower your blood sugar, you should proceed cautiously. A 2019 study found that people in the diabetic-medicine group were at risk for hypoglycemia, or dangerously low blood sugar, when they deployed an intermediate fasting routine. “Certain medications are just not suited for changes in meal timing,” says Valdez. That doesn’t mean you can’t fast, but if you’re taking medication that affects your insulin or glucose levels, consult your doctor first.
Negative #3: IF can be hard on your body
“Fasting causes starvation,” says Valdez. As a result, it could have some weird side effects: People who fast have reported bad breath, constipation, headaches, dizziness, weakness, and sleep disturbances. A 2018 review found that intermittent fasting caused a decrease in rapid-eye movement (REM) sleep, which is the slumber phase linked to memory and cognition.
Valdez recommends you avoid fasting if you’re underweight or you have an eating disorder or compromised immune system. It’s also not smart if you’re recovering from a surgery or severe illness. But otherwise, there’s no reason to assume it’s too dangerous. Just listen to your body, and eat something if things get too weird.
And if you’re trying to lose weight but IF seem like too much misery, we’ve compiled six science-backed health strategies that are a lot more fun.