When someone first proposes you go an extended period of time without food, it's normal to panic. But when you hear all of the potential benefits of intermittent fasting, curiosity will likely start to override your initial fears. Easing into a fasting schedule will allow your body to adjust without feeling constantly famished, and in turn weight loss, boosted immunity, and better sleep could also become regular parts of your routine. If you're looking to lose fat and possibly even lengthen your life span, you may want to consider this dietary regime. Before giving it a shot, make sure you don't fall into the category of people who should refrain from fasting, such as serious athletes or those with diabetes.
Since we know fasting isn't a simple practice (trust us, we love food just as much as the next person), we asked nutrition experts to advise on how to navigate this lifestyle change.
What Is Intermittent Fasting?
Unlike going Paleo or getting your body to ketosis, intermittent fasting isn't a diet, says Carrie Burrows, PhD, certified nutritionist and personal trainer. Rather, it's an "eating pattern that helps get your blood sugar in line," she explains.
Insulin is a hormone your body secretes in response to glucose in the bloodstream, or after a meal, says Adam Splaver, MD, board-certified internal medicine and cardiovascular specialist. Insulin helps the body repackage sugar into fat, Splaver explains. "The more and more sugar you have in your body, or the more and more carbohydrates you have in your diet, the more and more insulin it takes to do the same job it did yesterday," he says.
If your body is desensitized to insulin, it won't metabolize food as efficiently, Splaver adds. By fasting, you're creating periods of time when your body isn't exposed to as much insulin, he told POPSUGAR, which increases your sensitivity to the hormone and boosts your metabolism.
What Are the Rules?
The best part of intermittent fasting is there aren't any restrictions on what you can or can't eat. Yes, you heard that right, but don't get carried away. "You have to make sure that when you eat food after the fast, it's mostly healthy," says Mike Israetel, PhD, former United States Olympic sports nutrition consultant and head science consultant for Renaissance Periodization. Though there aren't hard and fast rules for what you should be consuming, you'll see the best results if you stick to fresh and whole foods, Israetel adds.
Now for the tricky part: how long do you have to go without food? Burrows says the key is easing into it. Start by fasting for 12 hours, meaning you might finish your last meal at 7 p.m. and wait until 7 a.m. to eat again, Burrows recommends. "I want [my clients] to work up to a 16-hour fast, and I think it's easier for most people to increase every day or every other day by an hour and another hour," she says.
Sixteen hours of fasting and eight hours of eating per day is what you should strive for, Burrows told POPSUGAR. Splaver practices intermittent fasting himself and says he only eats between the hours of 12 and 8 p.m.
Hydration is another key to being successful fasting, Splaver says. Drinking water not only helps with bowel movements but with all metabolic processes, he adds.
What Are the Benefits?
Improving your metabolism is just the beginning of intermittent fasting's upsides, and fat loss is one of its most enticing benefits. "It's highly likely that you'll end up in a caloric deficit, which means you don't eat as many calories as your body needs to maintain its bodyweight," Israetel says. "You end up losing weight, which usually means you lose body fat."
Israetel also explained a smaller body mass means the organs don't have to exert as much stress to survive, "which means they repair themselves better and they last longer." Though it may be counterintuitive, scientists have found eating less correlates with a longer life span and a more active immune system, Splaver says.
Burrows has found intermittent fasting can help people sleep better at night. "They're not eating and then going to bed and digesting their food all night while their body is trying to repair and heal from a full day," Burrows told POPSUGAR.
Though it may be challenging in the beginning, Burrows says once fasting becomes routine, an array of benefits follow. "Intermittent fasting shows you we kind of eat out of habit, not out of actual hunger," she says. "It helps practice discipline."
What Are Possible Side Effects?
As with many lifestyle changes, it's important to consult your doctor before trying intermittent fasting, especially if you're taking prescription medication. "If you're an insulin-using diabetic, fasting is absolutely out for you," Israetel says. Injecting insulin while the body is in a fasting state will cause the blood sugar to drop to a dangerously low level, he explained.
Israetel also cautions that intermittent fasting may not be a sustainable eating habit. "If you go to work and you haven't been eating, by about 1 p.m. your brain is doing nonsense," he says. Most people do experience some cognitive decline from fasting, Israetel adds, and athletic performance is another area that can suffer.
Bodybuilders or athletes in intense training programs shouldn't try intermittent fasting because their bodies are in need of constant fuel for repair and recovery, Splaver explains. "In terms of diets in general, if there was a one-size-fits-all, we'd be done," he says.