The fitness crowd tends to throw shade at the idea of skipping meals and snacks to slim down, believing this will eat away at your hard-earned muscle, grind your metabolism to a halt and spur diet-derailing hunger pangs. These days, however, the idea of occasionally shuttering your kitchen is the guiding principle of an increasingly popular — and increasingly researched — dieting approach with a lot of weight-loss buzz: intermittent fasting.
Believe it or not, fasting wasn’t invented by Instagram hashtags — in fact, people have been fasting for thousands of years: Our ancestors did it (usually because they didn’t have a constant supply of food stashed in the fridge), and a number of religious events such as Ramadan revolve around some form of dietary fast.
As the name implies, intermittent fasting (IF) is a system during which you alternate between periods of restricted calorie intake and periods of normal eating. To be clear, IF does not restrict the kinds of foods you can eat — as do diets like Paleo or keto — just how much you can eat on certain days of the week. Many swear by IF because it’s easy to implement, requires nothing draconian like a horrible juice cleanse, and it has been proved to be one of the speediest and sustainable ways to torch fat stores and promote a lean physique.
Research says fasting has been a favorite research topic as of late, and a number of studies have found intermittent energy restriction — in which people ate fewer than 800 calories at least once per week — to be a valid weight-loss strategy, at least in the short term. In one study, weight loss was similar among participants following either a heart-healthy diet or a high-protein, reduced-calorie IF regimen for three months. However, the IF diet won out for minimizing weight regain after one year. Another investigation showed that IF was just as good at stripping body fat as simple calorie cutting. However, IF did a better job at preserving lean body mass.
As to how exactly IF helps sculpt your physique, theories abound: Some propose that IF flips a metabolic switch that encourages your body to burn more fat. Others state that since IF restricts your window of eating, you’re likely to eat fewer calories during the course of a week, helping trim the waistline with less risk of losing muscle. Even more studies propose that IF might help people get in touch with their true feelings of satiety and fullness on food-restricted days, which can put the brakes on overeating during times of normal food intake.
On another front, IF may have other positive effects on your body, such as reducing memory loss, improving cholesterol and blood pressure, and helping prevent diabetes by improving insulin sensitivity. And contrary to logic, IF could actually help — not hurt — your physical performance at the gym: A 2018 study in the Journal of the International Society of Sports Nutrition found that athletes who participated in an every-other-day fasting protocol (eating 33 percent of their normal calorie intake on fasting days) for six weeks became more energy-efficient during exercise, reported less fatigue and experienced reduced body-fat levels. Researchers theorize that occasional energy restriction might spur changes in hormones and mitochondrial function, helping you get more out of your workouts.
Fit Girl Fasting
Want to give intermittent fasting a whirl? Try this 5:2 eating plan: You eat normally for five days and reduce your calorie intake to about 25 percent of normal for two days. Drink all the calorie-free liquids you want on both days to stay hydrated and healthy, and focus on whole, nutrient-rich foods for all seven days.
5 Days a Week
½ cup rolled oats (cooked) + 1/3 cup low-fat milk + 1 scoop protein powder (Top with 2 tbsp chopped nuts + ½ cup blueberries.)
2/3 cup plain low-fat Greek yogurt + ½ cup berries
4 oz cooked salmon + 1 cup cooked quinoa + 2 cups mixed greens + drizzle of olive oil vinaigrette
1/3 cup hummus + ½ cup sliced red bell peppers
1 cup milk + 1 scoop protein powder + ½ frozen chopped banana
4 oz pan-seared boneless pork loin chop + 2 cups roasted baby potatoes + 1 cup steamed asparagus + 1 tsp olive oil
Nutrition Facts (per day): 1,953 calories, fat 93 g, protein 146 g, carbs 201 g
2 Days a Week
½ cup cottage cheese + ½ cup chopped pineapple + 2 tbsp unsalted roasted sunflower seeds
½ cup baby carrots + 1 string cheese + 1 oz almonds
1 oz jerky
Nutrition Facts (per day): 586 calories, fat 36 g, protein 39 g, carbs 34 g
Fasting Cheat Sheet
Want to try intermittent fasting? Here are a few things to note before diving in.
High, low and start slow
There are different ways to put IF into practice, and since the jury is out as to which style yields the biggest benefits, choose the one that best fits your lifestyle.
The most common method of IF is 16:8. Here, you eat during an eight-hour window, say between 10 a.m. and 6 p.m., and fast the remaining 16 hours in that day. There is also the eat-stop-eat method during which you do a 24-hour fast twice a week and eat normally five days a week, and the 5:2 method during which you eat normally for five days, then reduce your food intake to about 25 percent of normal (which usually totals about 500 to 700 calories) on two nonconsecutive days per week.
If you’re new to IF and aren’t sure you can hang, ease into it so you have a better chance of sticking with it long term: A JAMA Internal Medicine study found that while people on an alternate-day fasting regimen (25 percent of energy needs on fasting days) experienced weight-loss benefits, about a third of the participants failed to make it to the end. To increase your chances of follow-through, consider the 12:12 method: Here, you fast for 12 hours per day and eat within a 12-hour window — which probably isn’t that far off from how you’re eating now. This method also could increase your chances for fat loss: A 2018 British investigation found that people who simply delayed their breakfast by 90 minutes and ate their dinner 90 minutes earlier than normal — with no imposed restrictions on what they could eat — lost twice as much body fat over a 10-week period than those who ate their meals at their normal times. Experts theorize this is owed to a decrease in both appetite and overall calorie intake.
Food for thought
If you choose a routine such as the 5:2 method during which on fasting days you simply eat less, don’t waste an entire day of calories on a couple of slices of gooey pizza. Make those calories count, and focus on nutrient-dense, satiating foods such as legumes, vegetables, fruits and fish — items that deliver plenty of nutrients relative to the number of calories they contain.
Also, beware of the feeding-day binge: Since IF doesn’t dictate the types of foods you should eat, you might be tempted to reward yourself with less-than-healthful foods during normal eating periods. But IF only works for fat loss if you focus on nutrition, not just calories, so on non-fasting days, fall back into a normal diet full of whole, clean foods, and stick to your regular eating schedule of several meals and snacks per day.
Dehydration can exacerbate hunger and leave you in a candy-worshipping hangry rage. Keep plenty of calorie-free liquids like water and tea nearby when fasting to promote satiety and replace some of the liquid you’re missing by cutting out much of your food. Not sure you’re getting enough H2O? Keep track of your urine color: The darker the color, the more water you need. As for caffeine — don’t worry about it. Recent research proved that it does not dehydrate people as much as it was once thought, especially if you’re a regular coffee drinker.
Train to gain
The days you train and the days you feed or fast should align properly. If your goal is to nail a personal-record 1-mile run or improve on your strength with heavier lifts, train during non-fasting periods when you have more available energy. If your goal is fat loss, exercise on a fasting day to create a metabolic environment that favors fat burning as your carbohydrate stores become depleted. That being said, however, if you feel exhausted and lightheaded when exercising on a fasting day, either call it quits or eat some food. Your workout will be half-assed, and you’ll increase your risk of injury.
Pop a pill
On fasting days, consider taking a multivitamin to ensure you’re getting all the nutrients your body needs to stay healthy: A study published in the British Journal of Nutrition also found that women following a weight-loss diet reported less hunger when supplementing with a multivitamin. Make sure your multi also includes the B vitamins that help turn food into energy and control appetite. To reduce muscle breakdown, think about branched-chain amino acids or including a protein powder supplement to your regimen, if it works into your fasted calorie allotment.
It may not work
Like many diets, the success of IF will vary from person to person. Some may rave about their success with fat loss and their clearer mind, while others may experience nothing but prolonged fatigue and irresistible cravings.
It often takes a couple of weeks for your body to adjust to IF, and side effects of fasting like raging hunger, brain fog, grumpiness or low energy will likely subside with time. If you’re still miserable after three weeks, IF is probably not right for you.
WARNING: Certain medical conditions can be worsened by fasting. Consult with your doctor if you’re diabetic, have low blood pressure, take medications, are underweight, are pregnant or are trying to become pregnant, or are breast-feeding before beginning any sort of intermittent fasting.