Fasting for 18 hours a day has been touted for weight loss, better focus, and improved health.
Far from a fad, intermittent fasting (IF) was popularized about a decade ago and continues to be many health-seekers’ go-to eating plan, thanks to research suggesting its potential to melt away excess body fat (1), reset digestion, boost brain power, quell inflammation (2), crush cravings (3) and help better protect us against a variety of conditions and diseases (4). One of the most popular types of fasting is a form of IF called 18:6.
Why would you choose 18:6 over the more common 16:8 fasting timing? The longer fast time may yield greater results, especially as it relates to weight loss.
Here’s everything you need to know about the 18:6 fast, its many possible benefits and how to do it safely.
Jonny Bowden Ph.D., C.N.S. a weight-loss expert and certified nutrition specialist who has his Ph.D. in holistic nutrition.
Katie Breazeale, M.S., R.D., a registered dietitian at the Princeton Longevity Center. She specializes in a range of different areas, including sports nutrition, weight management, and gastrointestinal health.
Jason Fung, M.D., a nephrologist and leading expert on intermittent fasting and low-carb diets. He’s also the author of “The Obesity Code.”
The 18:6 method describes time-restricted eating where you fast for 18 hours and then limit all of your calories to the remaining 6 hours of the day. If your first meal of the day is at 11 a.m., you’d limit all your daily calories to the 6-hour window between 11 a.m. and 5 p.m., with the exception of water and fast-approved beverages like tea and black coffee. While it’s best to stick to calorie free beverages, many experts believe that keeping your drink of choice to under 50 calories will most likely not break your fast.
Not eating for 18 hours may sound difficult. But consider that you’re asleep for approximately eight of those hours. You may find it surprisingly easy to go without food for this length of time, says Jonny Bowden Ph.D., C.N.S., especially if you ease your body into longer fasts.
Before diving into the 18:6 plan, you’ll want to build up to that timing in increments (we’ll talk about that shortly) but first, let’s go over some of the basics of intermittent fasting.
IF has had a cult following in health and wellness circles for a decade and there are more than a half dozen ways to do it from alternate-day fasting, 5:2, and the One Meal a Day (OMAD) diet.
Where most diets focus on what to eat, IF is mostly about when to eat, giving your body a prolonged break from the intensive task of breaking down and digesting food. Studies suggest that when your body gets a break from the consuming job of digestion, all kinds of reparative functions may take place throughout the body: inflammation may cool (5), brain fog may clear, and mental focus may sharpen (6, 7). Some studies suggest that your risk for metabolic diseases, obesity, and cancer may drop, and weight loss may become a heck of a lot easier.
Over time, the benefits of intermittent fasting—whether you’re doing 18:6, 16:8, or another plan—may be far-reaching and varied, including, potentially to:
Additionally, 18:6 fasting can help rid the body of toxins that cause inflammation, improve sleep quality, and increase energy levels. Here’s how.
Intermittent fasting in general may help enhance the body’s natural process to produce certain enzymes involved in the detoxification process, all while promoting liver health—which is one of the main organs involved in this process—says registered dietitian Katie Breazeale, R.D.
“While the body has two phases of the detoxification process, phase two is most important because this is the one that eliminates harmful toxins from the body,” she explains. “And fasting creates a restriction that leads to the enhancement of phase two (8).”
As a result, this process can help reduce and prevent inflammation in the body, which research indicates is a major factor in numerous chronic conditions, such as autoimmune disorders, cardiovascular disease, neurological disorders, cancer, and diabetes (9). One review of 18 studies found that intermittent fasting was shown to reduce levels of C-reactive protein—a protein produced by the liver that rises when inflammation is present (10, 11).
In addition, a recent study found that people who dry fasted (fasting without food or liquid intake) between dusk and dawn over a four-week period reportedly lost a significant amount of weight and reduced their blood pressure levels (12).
Bowden concurs and adds that 18:6 intermittent fasting can help prevent, treat or even reverse insulin resistance. “In my opinion, insulin resistance is the biggest metabolic pandemic of our time,” he continues. “[About] 88 percent of Americans have some degree of it and it underlies every major chronic disease.”
Setting mealtimes can help reinforce the body’s natural 24-hour internal clock known as the circadian rhythm, Breazeale notes.
“Also, those who fast have higher levels of human growth hormone, a hormone produced during sleep that helps burn fat, maintain muscle, and repair the body at a cellular level while creating a more well-rested state upon waking,” she says.
Breazeale adds that fasting may also create more orexin-A, a neurotransmitter, that increases alertness. “It has been shown that those who fast have lower levels of orexin-A at night and higher levels during the day,” she says (13).
While the research is limited and mixed, one three-month-long study that involved overweight and obese women recorded that sleep duration was found to increase on fasting days (14).
Intermittent fasting can lead to increased energy levels by revving up mitochondrial production—the body’s hub for energy production, says Breazeale. “It triggers the production of new neurons in the brain that use ketones as an energy source,” she adds. “And because of those ketones, it increases our mitochondria production and gives us more energy.”
Better stamina can also lead to a better mood. Research suggests fasting for 14 hours is associated with not only improved energy and mood, but also reduced hunger levels (15).
One small study found that men and women who fasted for 18 hours a day lost an average of 2.9 percent body fat in one month (16). Still, more studies on the effectiveness of the 18:6 fasting protocol for weight loss, in particular, are needed.
The 16:8 fasting method—which is similar, though less intense—is backed with more research. In one study (17), participants lost an average of 8.8 pounds after following a 16:8 fasting protocol for 12 weeks. And since one review concluded that fasting for longer than 16 hours typically yields no greater weight loss results than if you stuck to 16 hours, you might experience similar results with an 18:6 method (18).
While IF is generally considered safe for most, there are some people that should avoid fasting:
Always check with your doctor before starting any type of fasting regimen.
As with all nutritional advice, there is no one-size-fits-all answer to this, as every person’s body and lifestyle are different from one another. More to the point, what “working” looks like may be different for each new faster. Intermittent fasting may be used for weight loss, but, as we discussed, it isn’t the sole benefit of embracing a timing-based diet plan.
That said, the benefits of an 18:6 fast might be attained a little faster than some of the other types of fasting, says Fung, and the reason why is rather simple: because 18:6 fasting is a more intense fast, it may produce longer and greater results.
While 18:6 is a fantastic fasting window to progress to, “I wouldn’t start with it,” says Bowden. Instead, he suggests this approach:
Start with a 12:12 fast—12 hours fasting, 12-hour eating (e.g.: Fast from 8PM to 8AM and eat between 8AM and 8PM). During this time eat three meals (let at least 4 hours pass between meals) and no snacks.
After several days or a week, move to a “brunch fast” of 14:10, then 16:8 intermittent fasting, and then to 18:6 intermittent fasting.
“And remember what you eat during the window matters,” says Bowden. “Eat real food, always.”
To fill up on quality food and a variety of nutrients that means avoiding highly processed food, fast food, simple carbs and sugary treats and opt for nutrient-dense whole foods that include plenty of vegetables and fruits, high-quality protein, healthy fats and nuts and seeds.
Not every day has to be the same when it comes to fasting. In fact, Bowden and Fung both agree it’s best to occasionally modify your fast-to-feeding windows. Some days, you’ll be hungrier and will need a longer eating window, while other days, you’ll be able to sustain super-long fasts and may only need a single meal, OMAD-style.
Above all, listen to your body and monitor your progress. If you feel your progress slipping, dial it in for a period of time with a stricter schedule. The beauty of IF is how fluid and flexible you can be from one day to the next, while still reaping the many benefits of fasting.
In other words, consume snacks or meals that are low in fat, sugar, and fiber content since they will require less work for the digestive system. “Foods high in these items can put your system in overdrive and cause bloating, diarrhea or stomach cramps,” explains Breazeale. “I recommend either a small smoothie, a simple soup (like chicken noodle) or scrambled eggs.”
Be mindful of how much you’re putting onto your plate, emphasizes Breazeale. “It’s easy to get excited about increasing your eating window and then end up overeating,” she says. “Keep in mind your stomach is used to smaller quantities of food and overeating will lead to bloating and discomfort.”
She suggests starting with smaller foods that pack a punch nutritionally, such as two scrambled eggs (12 grams of protein), 1 cup plain Greek yogurt (20 grams of protein) or a protein smoothie pouch (12 grams of protein).
Beginning your eating window with a glass of water can help curb appetite, as well as prevent overeating, continues Breazeale. “Also, the act of drinking water will give you something to physically do,” she adds. “The goal is to slow down your thoughts and actions of getting food fast—before potentially selecting foods that may be higher in sugar and fat.”
All diets vary, which is why fasting can create nutrient deficiencies, Breazeale explains. That’s why she recommends a multivitamin supplement, especially for someone who notices they’re missing important food groups from their typical eating plan.
“Also, while the body adjusts in the beginning of fasting, a vitamin B12 supplement is often recommended to help with energy,” she adds. “It can be taken in the morning in a fasted state or even worn as a patch.”
And while some supplements contain zero carbs and won’t create an insulin response, they could contain up to 15 calories, Breazeale notes. “So depending on your goals and structure of your fasting plan, you may want to take all supplements once the fast is over.”
But regardless of your preferred eating style, she highlights the following supplements that will break anyone’s fast:
18:6 is one of the most popular forms of intermittent fasting. In this type of fasting, you abstain from eating for 18 hours, then eat during the following 6. 18:6 intermittent fasting has been associated with weight loss, gut health, cognitive benefits, lower inflammation and reduced insulin resistance. 18:6 intermittent fasting can be intense, so start with a less-intense form of IF, and work your way up.
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