Intermittent fasting (IF) has everyone buzzing. In fact, it ranked as the #1 diet trend in Google’s 2019 Year in Search, and the latest research published in the New England Journal of Medicine reports that a six-hour eating window followed by an 18-hour fast might lower risk for cancer and obesity and increase longevity.
But what is IF, really?
“Intermittent fasting is incorporating extended periods of limited or no food intake into your eating schedule,” says Ashley Reaver, a registered dietitian at Ashley Reaver Nutrition LLC. “There’s no intentional change or focus on the types or amounts of food you eat within the ‘feeding window.’”
Proponents claim that the fast-then-feast strategy works magic on your metabolism and promotes weight loss. IF comes in many forms, including the trendy reality TV star-created Dubrow Diet (involving 12 to 16 hours of fasting per day), alternate-day fasting, 16:8 (fasting for 16 hours, then eating during the following 8-hour window), 5:2 (eat normally for five days, then limit yourself to around 500 calories per day for the next two), and the Warrior Diet (fast during the day, then eat one large feast during a four-hour span at night).
“The most popular kind at the moment is time-restricted eating, where you limit your intake to a specified period of time each day. This usually ranges from six to 12 hours,” Reaver says.
While the most recent science stands behind the disease-prevention benefits of IF—that is, if you can stick with it for the long-term—like with all diets, there are certain people who should steer clear of intermittent fasting…
Anyone with a history of eating disorders.
Whether it’s anorexia, bulimia, binge eating, or otherwise, “people with a history of eating disorders or disordered eating should absolutely not begin intermittent fasting,” Reaver says. “Likewise, those recovering from eating disorders should not focus on an arbitrary timeline for eating.” Strict food rules like these can be triggering or lead to a binge.
People who love breakfast.
If you can’t start your day without a bowl of oats or a plate of eggs, you’ll likely want to pass on the fasts. Since the eating window can be as small as six hours, if you want to dine with your family at dinner, your first bite of the day will likely come after noon.
“Breakfast can help set up your healthy routine for the day,” says Keri Glassman, RD, the founder of Nutritious Life, so if you are hungry enough to eat in the a.m.—and enjoy doing so—avoid IF.
Anyone with diabetes or blood sugar-related conditions.
“Those with diabetes also should not begin intermittent fasting, particularly if eating in the morning will be pushed back,” Reaver says, as blood sugar control is vital. Eating at regular intervals throughout the day helps the body avoid the sharp blood sugar highs and lows that can come with the feast-then-fast cycle.
To crush that next personal best, you need enough gas in the tank. Think of your body like a car. If you don’t refuel often enough, it’ll stall out. “If performance is your main goal, limiting caloric intake and impeding nutrient timing around workouts will negatively impact muscle growth and recovery,” Reaver says.
The Bottom Line
Like nearly everything in the wellness world, there is no one-size-fits-all solution. Including IF.
“Some people should certainly avoid it,” Reaver says. “But I do believe that eating on a consistent schedule when possible is beneficial for health. Our bodies like routine, and eating around the same times each day is a good pattern.” If fasting helps you stay on that schedule, and you don’t fall into any of the categories above, then IF might work for you. But again, if you like breakfast, feel free to skip this one.