Humans have been dealing with periods of feast and famine since, well, forever. Your arrow misses the antelope and a squirrel steals your berry stash one day. The next, your fish net is full and you’re eating like a king. And for centuries, people have purposely fasted for reasons such as better health and religious traditions.
So why has the practice of intermittent fasting (IF) exploded in popularity in recent years? It took off around 2013 with the release of Michael Mosley’s book The Fast Diet.
Since then, studies have found that intermittent fasting (cycling between periods of serious calorie restriction and more normal eating days) may aid in fat loss, improve insulin resistance, boost heart health, lower blood pressure and even improve mood. (If you’re taking medication for any of these conditions, use the Optum Perks app to get coupons that can help you save up to 80%.)
“Five years ago, I would be talking about IF with patients, and people thought I was nuts,” explains Cynthia Thurlow, a nurse practitioner and an expert on intermittent fasting. “Now lots of health care providers are talking about it because lots of people are getting fantastic results.”
That sounds promising. But we’re about to hit you with a truth bomb: There’s no panacea when it comes to health and weight loss.
The research on IF is still so new. Researchers don’t know exactly how IF may affect health. And there’s no definitive evidence that it’s any more effective than tried-and-true healthy habits. That includes eating a wholesome diet, curbing stress and being active during the day.
Still, IF is on fire these days. Here are some of the reasons that people practice it — and really enjoy it.
Reason #1: There are many ways to do it
Some diets are so rigid about what’s allowed and what’s not. And that can get old (or unsustainable) really fast. With IF, there’s no single system. People like that they can try whatever option best suits their lifestyle. Plus, they can take the time they need to ease into a new routine.
Here are 3 of the most popular regimens:
With this approach, you fast for 16 hours and eat during an 8-hour window. The idea is that you choose to spend more hours of the day not eating than you do eating. An example: Unrestricted eating from noon to 8 p.m., then no eating from 8 p.m. to noon the next day.
This is a modified fasting method that has you eat normally for 5 days of the week. For the other 2 days, you restrict your calories to 20% to 25% of your caloric needs. So someone who eats 2,000 calories a day would take in just 400 to 500 calories on fasting days.
This is like the 5:2 method. But instead, people alternate a day of unrestricted eating with a day of no or very few calories.
Reason #2: It’s cheap
Many diets and weight loss programs ask you to pay subscriptions, purchase premade meals or buy and prepare specific ingredients.
Not IF. In fact, it doesn’t cost any extra money. And it can even save you a chunk of change over time if you’re eating less overall.
But that’s true only as long as you’re not chucking food you’ve bought or already prepared because of your new eating schedule. “It can make it difficult to plan for grocery shopping and meals,” says Megan Ramos. She’s a clinical educator and co-founder of The Fasting Method, which is based in San Francisco and Toronto.
That’s why it’s still important to thoughtfully plan your meals. And aim to fill your pantry with nourishing foods. (“Unrestricted” eating doesn’t mean a doughnut frenzy.)
Related reading: What to eat (and avoid) if you’re taking antidepressants
Reason #3: It may help with weight loss
Research is mixed on just how effective IF alone is compared to other ways of eating. For example, a 2020 trial in JAMA Internal Medicine divided 116 participants into a 16:8 IF group and a 3-meals-a-day group. After 12 weeks, the researchers found no major differences in weight loss between the groups.
That said, many people do find IF helpful with staying accountable to their goals. “Plus, lots of people like that you don’t have to track your calories and you can still see weight loss,” says Leslie Bonci. Bonci is a sports dietitian and founder of Active Eating Advice based in Pittsburgh. She’s also the sports dietitian for the Kansas City Chiefs.
Reason #4: It may boost longevity and lower the risk of disease
A review of research published in The New England Journal of Medicine looked at studies in both animals and humans. The researchers concluded that IF shows promise in increasing lifespan and lowering the risk of cancer, heart disease and obesity.
It’s important to take any animal research with a grain of salt. (After all, you’re not a mouse.) But the theory is that enduring longer periods of fasting flips a metabolic switch in our bodies. And this switch triggers a cascade of changes that can make our cells more resistant to stress and inflammation. The changes can also protect against chronic diseases such as diabetes and heart disease.
“Research suggests that IF can decrease stress to the cells and preserve cells for longer periods of time, which could reduce the risk of disease, even possibly cancer,” says Bonci.
Reason #5: It may improve mood and mental clarity
Like most things in life, there’s an adjustment period with intermittent fasting.
“Initially, it’s not going to be easy,” says Bonci. “Some people report a serious lack of concentration, feeling overly hungry and having less energy than normal when they first begin.”
That’s why many people ease themselves into it. But if you’re willing to tough it out, some of that uncomfortableness goes away after the first month, says Bonci.
“Almost everyone comes to IF for weight loss,” says Thurlow. “But they end up sticking with it for other benefits they experience, like mental clarity, being able to connect to true intrinsic hunger, hormone regulation and overall mood improvement.”
Many people claim anecdotal success from IF. But at the end of the day, it’s important to do what’s right for you. Always check with your doctor before starting an IF regimen, especially if you have diabetes, are pregnant or breastfeeding, or have a history of eating disorders.
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Overview on intermittent fasting: Johns Hopkins Medicine
Trial comparing eating 3 meals a day to the 16:8 method: JAMA Internal Medicine (2020). “Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity”
Review on health benefits of intermittent fasting from animal and human studies: New England Journal of Medicine (2019). “Effects of Intermittent Fasting on Health, Aging, and Disease”