Intermittent Fasting: How to Know if It's Right for You
Fans say it promotes weight loss and better health. Explore the pros and cons in our beginner's guide — and learn what to eat when you’re not fasting.
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Intermittent fasting might be the most popular weight-loss program on the planet right now. Thanks to a flurry of books and documentaries over the past few years, intermittent fasting, or IF as it’s sometimes known, is hot. Whether you’re fighting obesity or trying to lose 5 pounds, and whether it’s the 16/8 method, the 5:2 diet, or the so-called warrior diet, every form of intermittent fasting is based on one thing: fasting. Every flavor of IF involves designated blocks of time when you eat ... nothing.
But can this simple eating pattern turn you into a fat-burning machine or add years to your lifespan? Here’s everything you need to know about the diet, its possible benefits, the various methods, plus who it might work for and who should avoid it. Of course, we’ve also included what to eat when you’re not fasting.
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What is intermittent fasting?
The name says it all: You fast during specific time intervals. What can you drink during intermittent fasting? Typically, only water and black coffee, tea, or other zero-calorie beverages are allowed. On the most basic level, this diet has nothing to do with food. You can technically eat whatever you want during your non-fasting hours. IF is all about when you eat, not what you eat. Though it's usually referred to as a diet, it would be more accurate to call intermittent fasting an eating pattern.
How does intermittent fasting work?
The principle behind IF comes down to how eating and not eating trigger the release of hormones. Every time you eat, your pancreas makes insulin. This hormone lets blood sugar (or glucose) into your fat cells, where it's stored as fat. When you fast, your insulin level drops, and the fat cells release their stored energy to power your body. The theory of intermittent fasting is if you keep your insulin and glucose levels low enough for a long enough time, you'll burn body fat as you improve your insulin resistance.
Intermittent fasting schedules
There are different ways to go about intermittent fasting. Some people split the 24 hours of the day into a 12-hour fast (including overnight) and a 12-hour eating window. For some, that doesn't feel like dieting at all. Others go a more extreme route, eating normally one day and fasting the next day. This is known as alternate-day fasting. Beginners might occasionally try spontaneous meal-skipping.
Here are the most widely practiced forms of intermittent fasting:
The 16/8 method
The most popular variation on the intermittent fasting diet is the 16/8 method. Those numbers refer to hours. You have a 16-hour fast, and then you're free to eat for eight hours — plenty of time for the usual three meals a day. Most people fast from after dinner, say 8 p.m., until noon the following day. Plus, after 16 hours of fasting, your body has likely gone into a state of ketosis. At that point, your body produces ketones and starts burning fat instead of carbs, which could potentially help you lose weight. This is the foundation of the keto diet, but most people find intermittent fasting easier to follow.
The 16/8 approach makes it as easy as skipping breakfast — something many people do anyway.
The 5:2 diet
This version of the intermittent fasting diet is also popular, though most people find it more challenging. With the 5:2 diet, you eat normally five days of the week. The other two are your fasting days where you limit your intake to 500 calories (for women) or 600 calories (for men). That’s roughly one meal’s worth of food for the entire day. This kind of extreme calorie restriction is tough for most people to maintain even two days a week.
The warrior diet
This form of intermittent fasting involves eating one super-sized meal per day. It requires a 20-hour fasting window.
What are the health benefits of intermittent fasting?
Champions of the diet claim you’ll get the following health benefits from it:
• Weight loss
This is usually the primary goal of the diet, and many people report weight loss. However, this may be simply the result of reducing your overall calorie intake rather than changing the way you burn fat.
• Reduced inflammation
Inflammation is behind many chronic ailments, including heart disease, and some research suggests that fasting brings down markers of inflammation in the blood. Lowering inflammation can improve your cardiovascular health.
• Brain health
Other research shows that fasting periods prompt your brain to make more of the hormones that promote cell growth, and might even help prevent Alzheimer's.
• Reduced cholesterol and blood pressure
Some studies indicate that you can bring down your levels of LDL, "bad" cholesterol, by regularly spending time in a fasted state. Fasting might also help bring down blood pressure.
What else does scientific evidence say about weight loss and IF?
During the past 10 years, scientists have researched intermittent fasting diets and different periods of time for eating and fasting. As is the case with most nutrition research, the studies don’t all come to the same conclusion. Many of them suggest intermittent fasting can lead to weight and fat loss, with one important caveat: You still need to eat a healthy diet when you’re not fasting. A 2020 article published in the New England Journal of Medicine discusses the health benefits of intermittent fasting.
However, other recent research indicates the opposite. A 2020 study published in JAMA Internal Medicine found in a randomized clinical trial (the gold standard) that intermittent fasting may not help reduce body weight. In fact, it likely leads to lean muscle loss.
Who is intermittent fasting for?
In general, this diet works best for people whose daily habits create easy opportunities for fasting. This might include those who eat dinner early and don’t snack at night or people who don’t like eating breakfast.
For hormone-related reasons, intermittent fasting may be better for men than it is for women, so guys may be more inclined to give it a try.
Who should not do intermittent fasting?
Missed menstrual periods can be a potential side effect of intermittent fasting and of spending too much time in a fasted state. If women do want to try it out, they should opt for a shorter fasting window, at least at first, and watch how they feel in terms of side effects. Women who are breastfeeding or trying to conceive should probably steer clear of the practice of fasting altogether.
Another group who should never attempt an intermittent fasting diet are those who have or are in recovery from an eating disorder. The experience of ignoring hunger pangs — a staple of the diet — can be triggering, and the diet itself can cause a relapse.
What should you eat for intermittent fasting?
Many dieters are drawn to this diet by the promise that as long as you’re not fasting you can eat whatever you want during intermittent fasting. And it’s true that no specific foods are encouraged or outlawed on the program. However, the safest and most effective way to follow an intermittent fasting diet is by eating the same kind of nutrient-dense, balanced meals you would on most other diets. In other words, follow the USDA dietary guidelines.
• Eat healthy foods
That means plenty of vegetables and lean proteins, not so many refined carbs. Carbohydrates like whole grains and beans are healthy staples, but if you’re living on carbs like french fries and brownie sundaes whenever you’re not fasting, you’re unlikely to lose weight or reap any health benefits. That said, there's definitely a place for treats on an intermittent fasting plan.
• Eat nutrient-dense foods
The freedom to eat what you want on an intermittent fasting diet shouldn’t overshadow the need to eat well. In some ways, fasting makes this even more important. You’ll be better able to manage the hunger that comes along with fasting if you fill up on satisfying whole grains and fiber-rich foods like legumes that deliver the sustained energy you’ll need.
Intermittent fasting recipes
Here are some recipes to keep in mind if you decide to try an intermittent fasting diet.
If you're wondering how to break a fast, this nutrient-dense breakfast is a filling, great-tasting option.
You could technically eat any cookies for breakfast on an intermittent fasting diet, but these are packed with fiber and potassium.
This cheesy, protein-filled omelet will hit the spot, whether you break your fast in the morning or at lunchtime.
Hummus and vegetables layered between slices of whole-grain bread will give you sustained energy on intermittent fasting diets.
Lentils are among the world’s healthiest foods, and this savory soup makes for a filling dinner. Pair it with a salad and fresh bread.
This flavorful entree contains all your favorite taco ingredients — beef, beans, salsa, and corn — in salad form.
Dried spices add complex layers of flavor to this speedy shrimp dish, which also happens to deliver the lean protein intermittent fasters need.
Asian-inspired noodle salads can really bust a cooking rut. This one brims with bright, fresh flavors and with healthy ingredients like tofu. Packing plenty of vegetables into your meals helps you meet your nutritional needs on an intermittent fasting diet.
This marriage of tender chicken thighs, briny olives, and sweet red peppers will bring everyone to the table. Getting ample protein can help you preserve muscle mass as you lose weight. Serve this dish with a side of roasted vegetables.
Pork tenderloin is a great weeknight option because it’s a quick-cooking lean protein. A citrusy, spiced marinade takes it to another level.
This mildly spicy creamy curry dish is the perfect choice for Meatless Monday or any night you want a vegetarian supper. And the generous amount of fiber from the chickpeas and cauliflower will help you feel full.
Carbs are not your enemy on an intermittent fasting diet. Enjoy pasta night with this Italian-inspired fettuccine and sausage feast. One of the major perks of intermittent fasting is the freedom to splurge on carbs and cream once in a while.
Ground turkey lightens up this classic comfort food by replacing saturated fat-rich beef. Freeze leftover slices for easy meals later on.
Quinoa is a superfood that acts like a grain but is really a seed. It’s full of protein and fiber and makes an ideal base for these zesty Mexican flavors.
A top perk of the intermittent fasting diet: Dessert can be part of the program. This satisfying hot cocoa delivers plenty of antioxidants, too.
Let’s get healthy, together
If you’re interested in exploring more healthy eating ideas, including how intermittent fasting compares to other popular diets, Yummly has plenty of helpful resources. Check out these next articles to get started.