timer clock on an empty plate showing how to fast
Our most basic, primal instincts teach our brains to function best when we are hungry and physically active. (Photo: nehopelon/iStock)

How to Fast: The Beginner’s Guide

A beginner's guide to the burgeoning nutrition trend

Our most basic, primal instincts teach our brains to function best when we are hungry and physically active.

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Some of today’s most cutting-edge nutrition research suggests that you should eat less often, forcing yourself to go longer periods of time without food—a practice that was common just a few centuries back. Our basic, primal instincts drive our brain to function best when we are hungry and physically active, says Mark Mattson, chief of the laboratory of neurosciences at the National Institute on Aging. “It evolved, in part, for success in seeking and acquiring food.”

The way many of us eat today—satiating hunger with snacks high in simple carbs—leaves the body craving a constant sugar fix. Without it, you crash and suffer from fatigue, lack of mental clarity, and deteriorating athletic performance, among other things. But fasting has been shown to help stabilize blood sugar levels through a process called glucose regulation, says Mattson. By putting your body through short-term stress, you teach it how to use energy more efficiently and recover quickly, he says.

Learning how to fast and getting started can be a daunting task, but we’re here to make it simpler. Read on for your guide on how to hit your body’s reset button.

How to Fast: Choose Your Preferred Style

Fasting is distinct from the likes of a juice cleanse or a two-day restrictive diet. There are two categories—traditional and intermittent—each of which appeals to different individuals depending on their goals and lifestyles.

While both can be beneficial to your brain health, intermittent fasting is better for weight loss and maintenance. Pick the one that works best for what you want to accomplish.

Traditional Fasting

Traditional fasts typically last anywhere from 24 hours to seven days or longer. They emphasize developing willpower and honing self-discipline as opposed to weight loss, making them a favorite among those looking for a mental or spiritual refresh. While you’ll certainly see some physical effects, the changes of a single fast won’t be permanent. That said, it’s a useful tool to help you understand hunger and your reaction to it.

If you’re a beginner learning how to fast, start with a 24-hour goal: Eat dinner, and then refrain from eating until the next night. Be sure to drink plenty of water to prevent dehydration, and plan your fast for a non-training day. Going for a walk can help you get into nutritional ketosis—a state where your body starts to burn fat rather than glycogen—but don’t do anything more strenuous until you get accustomed to existing with lower energy levels.

If you’re going to try for multiday fast, consider timing it so that it ends on Sunday night. That way, you’re at work only during the first part of your fast, before it gets especially challenging.

Since this program is temporary and short-term, traditional fasting caters to those who, in addition to wanting a radical system reboot, don’t want commit to the thought and preparation required to fast every day or every week.

Intermittent Fasting

Intermittent fasting usually involves a long-term routine of short-duration fasts that last for part of every day, and its physical impact tends to be greater than that of traditional fasting. Specifically, it’s highly effective in its ability to regulate blood sugar, which prevents a host of symptoms like fatigue, mood swings, and metabolic health, Mattson says. In addition, it can protect the brain from stroke, neurotoxins, epileptic seizures, and oxidative stress, he says. It’s also an effective way to simply lose weight, depending on the fasting routine you choose.

If you’re hoping to lose weight, try either the the 5:2 diet or alternate-day fasting. In the former, you’ll eat regularly five days a week, then eat 600 calories a day for two days. In the latter, you’ll rotate between regular and 600-calorie days. You will eat fewer calories than normal, even if you follow your regular diet on the nonrestricted days. Although highly effective for those looking to shed a few pounds, these two styles of eating should be avoided by most athletes, because you won’t be eating enough calories to train properly.

LeanGains: Time-Restricted Eating

Time-restricted eating, also called leangains, is the better choice for high performers. Eat the same amount of food you normally would, but eat it during a shorter window, ideally eight hours. You’ll reap many of the benefits of fasting without restricting calories, so you can keep training hard. It’s easy to maintain your weight or gain lean mass.

With time-restricted eating, your goal is to fast for at least 12 hours a day, which is the point at which the benefits of fasting begin, Mattson says. Pick the window that best suits your life. Most people choose to eat from midday through dinnertime, because it’s easier to incorporate into a regular family and social life. It is possible to train during the part of the day when you’re not eating, though many people will choose to time their training after they have eaten some food—often after work. While 12 hours seems like a reasonable window to avoid food even when you aren’t fasting, that means no late dinner reservations, no snacks at the Friday night movie, and no crack-of-dawn coffee when you wake up for your morning workout. And if it really does feel that easy to eat only in a 12-hour window, try ratcheting it up so that you’re able to nosh for only, say, eight hours a day.

Ease Into It

Don’t start with a seven-day fast if you’ve never fasted before or are new at teaching your body how to fast. With a traditional fast, start with 24 hours, and then bump it up to three days if the first one goes well. With the time-restricted approach, don’t immediately limit yourself to eight hours a day of eating if you’re used to eating every hour that you’re awake; start with 12 hours on, 12 hours off, and go from there. Have realistic expectations, and make gradual changes to your current routine.

How to Fast: Plan Ahead and Be Flexible

Once you’re used to fasting, you may find that you can incorporate a short fast on little notice. But when you’re just starting out, make sure to plan your fast at least a few days in advance. You’ll want to ensure that your fast isn’t going to interfere with work, family, or training, all of which can counteract the positive effects of the test run.

Put some thought into where and how you will be fasting. Fast at home before trying it in the wilderness or on vacation. Have plenty of water on hand. Tell your friends and family you’re fasting so they know what’s going on if you start feeling irritable, and so you won’t have to answer the same questions 25 times at the next group dinner.

Lastly, don’t be too rigid. If you typically eat from 11 a.m. to 7 a.m., it’s perfectly fine to eat before a morning race or a big training day, breaking that fasting window. Consistency is good; inflexibility is not.

Prepare for Your Body to Feel Different

Many people feel tired, get a headache, and generally feel “out of sorts” on days two and three of any fast. That’s normal. The negative side effects of fasting typically go away by the end of day three or four. If you’re going shorter than two days, you’ll likely start to feel better just as the fast comes to a close. Once you turn the corner on day three, most people feel great after the negative symptoms have passed, and a sense of calm, well-being, and heightened concentration takes over. But if you feel like something is wrong during a fast—more than just feeling a bit tired—definitely eat. You can always try again another time.

Lead Photo: nehopelon/iStock