Scientific studies, researchers and client success stories consistently show that Intermittent Fasting (IF) is an extremely effective strategy for weight loss, weight maintenance, getting lean, and boosting health.

Intermittent fasting is both powerful and flexible. It is one of the fastest ways to lose weight, yet it can also be used as an effective way to simply maintain your weight. It's a technique that takes the focus off the food, maximizes your will-power, and puts you in control. Instead of counting every little calorie and cutting out whole categories of foods, you can build this technique into your daily routine and enjoy the benefits of a healthier body weight.

This tactic will allow you to lose half a pound, one pound, or two pounds a week—or simply help you maintain your weight if that's what you want. Besides turning your body into a fat-burning furnace, it will lower bad cholesterol, improve insulin and blood sugar control, increase alertness, and boost energy.

It's something you can do long-term, a true lifestyle strategy.

And yes, you can do it on ANY diet.

What Exactly Is It?

This is a strategy where you go entirely without food ("fasting") for a relatively short period of time followed by a normal eating period where you can basically eat freely. This pattern is called "intermittent fasting" because you're not fasting continually -- just on a strategic basis

During the fasting period, water or zero-calorie beverages like coffee or tea are allowed. Fasts can range from 16 hours to 24 hours, or even days..

If you're new to this concept, don't freak out. It's easier and more powerful than you think and you can do it without feeling like you are starving. It's something your body is designed to do (humans have evolved to handle fasting).

The ability your body has to regulate energy during times of no food ("famine") is a feat of "evolutionary engineering". Only in modern times have humans had food always available. Going without food for a day or most of the day or longer was likely a common occurrence in early man.

For thousands upon thousands of years (millions, even), "intermittent fasting" is the way humans lived and ate. Sometimes there was plenty of food to eat, and occasionally there was none until people could gather, hunt, or grow some more. The human body has adapted itself over uncounted years to deal very efficiently with an occasional lack of food. We're actually very starvation-resistant.

Over the vast sweep of human existence, when food was hard to come by and going without was a frequent occurrence, people who quickly stored fat had a real survival advantage in starvation situations. But now that high-calorie food is always available, those of us whose bodies are extra effective at fat storage have too much of a good thing. Our metabolism is designed to cope with frequent temporary food shortages, not a constant supply and frequent excess like we have today.

Surprise! ... You Already Do Intermittent Fasting

Most people don't realize this or think about it, but you already do intermittent fasting every day when you sleep during the night. Breakfast is called "break-fast" that for that very reason. When you eat in the morning you are breaking your fast from the day before. This nightly fast is often around 12 hours. Intermittent fasting simply extends that period longer.

The fact is, there is no scientific evidence that proves you must eat immediately upon waking, or that you must eat a certain number of meals a day. The "rule" that says you have to eat breakfast hasn't ever been proven. On the other hand, if you ate breakfast, there's no rule that says you have to eat lunch or dinner. You could eat once a day, twice a day, or not at all and there's no harm done.

Of course, how fasting affects you and whether or not you choose to add it to your personal weight loss strategy is something you can only know by trying it out.

Practical Weight Loss Benefits

The beauty of IF is that it automatically reduces your calories over time, without daily calorie counting. It simplifies eating. You're either eating or you're not. No obsessing all day about whether you're eating too much or whether you're eating the "right" kind of food. Just eat the food that works for you, and the fasting periods will reduce overall calorie intake. Simple.

Basically, IF is not about what you eat, it's about when you eat (how long between feeding periods).

During the eating windows, you can basically "eat what you want". Many, many people have done just that ... and still lost weight. That said, some people may need to be more careful during eating periods. Your results will give you that answer.

Intermittent Fasting...

Can be used for weight loss on a long-term basis. There's no health problem with fasting intermittently as a lifetime practice.
Is perfect for weight maintenance. Simply sprinkle in as many IF days as needed to keep your weight under control. It really can be that simple. How long and how often is entirely up to you.
helps remove the "deprivation" problem. You don't have to permanently banish your favorite foods. (See below for some caveats.)
Can be empowering. Going without food even when it is available helps you put your mind in control of your behavior. Taking even this little bit of control over your life gives you a feeling of empowerment, improved self-image, and confidence.

Health Benefits

The weight loss benefits are great -- but fasting is also fantastic for your health and hormones.

This gets little technical, so if your eyes start to glaze over a bit, just skip ahead.

IF has very strong scientific support and many health and nutritional benefits. It engages multiple chemical and hormonal processes that put you into an extreme fat-burning mode.

Here's a list:

Increased levels of "good" HDL cholesterol, lower levels of "bad" LDL. HDL is a cholesterol compound that helps keep arteries healthy and protects against heart disease. LDL is the "bad" cholesterol; if levels are too high, it clogs arteries.
Decreased blood glucose levels. Ideally, blood glucose levels should be between 80 and 100 mg/dl. If you have a healthy insulin response, blood glucose will generally rise to 110 or 120 after a meal--then insulin tells the body to clear glucose out of the bloodstream and blood glucose slowly drops back to a level in the 80s or 90s. When fasting, these up-swings in blood glucose don't occur.
Decreased insulin levels. Fasting for 24 hours dramatically decreases insulin levels which creates excellent conditions for the body to release fat and burn it for fuel.
Increased insulin sensitivity. Fasting increases your body's sensitivity to insulin. Insulin sensitivity is important; research shows that poor sensitivity to insulin (possibly due to the body having constantly high insulin levels) is a contributing factor leading to type 2 diabetes.
Increased norepinephrine and epinephrine levels. These stimulant compounds, which are naturally produced by the body, give a feeling of alertness and also help release fatty acids from storage to rebuild muscle protein and provide energy (fat burning).
Increased glucagon levels. During fasting, the liver releases glucagon, which helps keep blood glucose levels from getting too low. It's also a signal that there's an energy shortage and it's time to start metabolizing stored fat.

Protocol Examples

"Protocol" actually makes it sound too fancy. This is a very flexible tool, and very simple.

Although certain patterns have been popularized, there is really nothing sacred or superior about any of them; they all follow the same principles.

With IF, whether you extend or shorten a fast by an hour or several hours, or skip a meal, add a meal, or how often you fast, or in what pattern — all of that is entirely up to you. That said, there are certain benefits to various ideas that may fit your personality, lifestyle, schedule and biology better than others.

Popular Methods
Note: All the examples here allow water (or zero-calorie beverages like coffee or tea).

16:8
Fast for 16 hours, followed by an 8 hour eating window. Most people prefer to skip breakfast, and eat during lunch and dinner hours (Noon to 8pm for example). But if you prefer, you could eat in the morning and afternoon and stop eating 16 hours before breakfast the next day. People generally eat 2-3 meals within the 8 hours but it's up to you. This was popularized by Martin Berkhan of LeanGains.com.

20:4
Fast for 20 hours, followed by a 4-hour eating window. For example, only eat between 2pm and 6pm. Due to the limited timeframe, most people only eat one large meal or two smaller meals. This was made popular by Ori Hofmekler's "Warrior Diet".

24 Hours
Fast for a full 24 hours. This means for example, eating dinner on Day 1 and not eating until dinner the next day. Typically, there isn't a limited eating window, meaning you can eat anytime after the 24 hours is up.

OMAD (One Meal a Day)
This is simply a 24-hour fast but repeated for multiple days in a row. You might also call it 23:1 because you have just one meal rather than a longer eating window as with 20:4. You could do OMAD for as long as you're comfortable.

5:2 Diet
Here, you break up each week so that you fast for 2 days, and eat regular meals the other 5 days. The fast days are not consecutive (they are usually separated by a regular eating day). This was popularized by "The Fast Diet'" book by Michael Mosley. In Mosley's plan, on the fast days, men eat 600 calories and women eat 500 calories. You can spread the calories throughout the day but typically it means two small meals, or a snack plus a larger meals, etc.

Alternate Day Fasting (ADF)
Every other day is a fast day. The days between are normal eating days. That means half the time you are on some kind of fasting schedule or low-calorie plan, the other half you basically don't worry about anything.

ADF happens to be the most studied form of intermittent fasting, so it has a lot of evidence behind it (but that doesn't mean the other ideas aren't valid). It was studied and developed by Krista Varaday in the "Every Other Day Diet" book. Her protocol was to limit the "fast" day to 500 calories. So, every other day you are eating 500 calories. On the non-fasting days, people usually eat more than usual but it doesn't offset the reduced calories the day before.

36 Hours
As surprising as it sounds, many people have found they can gradually work up to 36-hour fasts without too much trouble. Example: Eat dinner on Day 1, fast all of next day, go to sleep, and eat breakfast on Day 3. In fact, this can sometimes work out better because it avoids the temptation to really overeat dinner on Day 2 as with a 24-hour fast.

Extended
As explained by Dr. Fung, author of the Obesity Code, you can actually fast indefinitely without any issues. The world record is 382 days! That said, to avoid certain rare-but-still-possible problems, it's best to limit fasts to 5 - 10 days. And, for fasting greater than 48 hours, a multivitamin is recommended to make sure there is no vitamin deficiency.

Your Options

Intermittent Fasting gives you a lot of options to to consider.

What works for you with fasting is very personal. Insulin sensitivity and other factors that affect the fasting response differ from person to person. You can start with a smaller, easier fast like 16 hours before working up to a longer fast. Generally, the more you fast, the easier it becomes.

So, the length of time you fast AND how often you do it is a personal decision.

Generally, those two factors: fasting length, and fasting frequency determine effectiveness. More fasting days per week are more effective for weight loss than less. Lower-calorie, monitored fast days are more effective than higher calorie fast days.

For example:

Some may fast more frequently such as Alternate Day fasting or 24 hour fasts 3 times a week over a few months (maybe 2 - 3 months) to help reach a certain weight; then they do it more occasionally (like 1 - 2 times a month) to maintain, or strategically (like after a weekend of gorging)
Some people do a moderate fasting schedule like 16:8 every day as a lifestyle
The variations are infinite

Whatever you choose, how you feel on a long-term basis is important. Your pattern of eating/not-eating needs to feel sustainable and doable for you.

For less frequent protocols, like ADF or 5:2, you'll need to tightly control what you eat on fast days to ensure you have a real calorie deficit. That's why they generally aim for 500 calories or so. But you don't have to: if 1000 calories on a fast day or 1200 or whatever gives you a significant drop in calories compared to your normal calorie intake, that could work. It depends on your goals. Maybe all you want to do is maintain, and an occasional less dramatic fast day will work.

One reason why alternate day fasting is attractive is because you're only really monitoring calories every other day (the fast day). ADF studies show people do in fact eat more than normal on alternate days, but not so much that they don't lose weight. People doing ADF routinely report they no longer feel hunger on fast days after about 2 weeks. That may be true for other protocols as well -- though it is likely that by fasting every other day is often enough to really force your body to get used to it.

Generally, for maximum weight loss you should undergo longer fasting periods. That's because the longer you fast the more fat you are burning. The most actual fat burning tends to occur after 16 or 18 hours -- in other words 24-hour (and longer) fasts are ideal for fat loss -- but that doesn't mean an "easier" schedule won't work. Because even the 16:8 schedules start tapping into fat stores AND on average, help you reduce overall weekly intake.

Keep in mind there is a transition period where your body needs to adjust. Your physical body "learns", and you (your mind, emotions, etc) will learn how to handle hunger better. The first time you try it may or may not feel fantastic. But over time you'll adapt.

The only way to know is to just decide one day to give it a try. See how long you can go before feeling overly hungry. Maybe you'll end up fasting 24 hours, maybe you won't. Just give it a shot.

If you just can't handle 24 hours, then try for something less. Many people can do a 16:8 daily schedule without any issue. But if even that's too hard, then do 16:8 every other day.

Drink Lots of Water

Start a fasting day with a large glass of water. Carry a water bottle with you, if possible, and sip from it as often as you can. Whenever you get a surge of hunger, drink a large glass of water. It's more effective than you might think. If you dislike plain water or have a hard time drinking a lot, you can drink zero-calorie flavored water.

Water doesn't count as food--it's free. In fact, water is even more important than usual when you're fasting. Water is necessary for metabolism and all sorts of other basic life processes, so if you're dehydrated, your entire body--including the fat loss you're trying for--functions less effectively. You want to make sure you give your body its best chance to do the fat metabolizing that it'll be working on while you fast. While some types of religious fasting that occur less regularly (once a month or once a year) include going without water, it's not a good idea to go without water like that on a regular basis. Being hungry while fasting is hard enough; extreme thirst is an extra problem you don't need.

What about other liquids?
Chicken broth or beef broth are highly recommended. Broth helps replace electrolytes and is very healthy. You can drink it anytime you feel hungry.

Coffee and tea are okay to drink on fasting days, as long as you don't add extra calories to them. You can drink them without sabotaging your fasting day. Just be careful what you put into coffee and tea. Don't add sugar, and stay away from chais and lattes (even sugar-free versions still contain lots of cream, milk, etc., and can pack a significant amount of calories). If you need to sweeten your coffee or tea, try a natural, zero-calorie sweetener like stevia.

Zero-calorie diet drinks like diet soda and Crystal Lite are okay to have, too. And remember that water is the ultimate zero-calorie drink; anything else you drink is in addition to water, not instead of water. Coffee, tea, and soda cannot replace water and may even require you to drink extra water, since caffeine actually dehydrates you.

For more details on drinking water, see Drink Water.

Hunger

It's helpful to know that for most people, biological hunger disappears after awhile. Initial morning hunger tends to come as a passing wave -- it's basically just "alert" from your brain that tells you your stomach is empty -- but the feeling tends to go away if ignored.

Over time, your body seems to "learn" and it accepts longer periods with no food and so sends you less (or no) hunger signals during fasting periods. For many people (but not all), hunger just seems to become a non-issue during fasting.

But if you are in fact being constantly annoyed by hunger pangs or cravings... the most helpful technique for most people is to stay busy. It's especially helpful to schedule a fast for a day when you know you can be fully immersed in a project you enjoy doing.

Have you ever gotten so involved in an activity that you lost track of time and forgot to eat? Typically it's a mental activity (versus physical) where your mind is completely immersed in one of several things: a deadline-driven challenge at work or home, an activity you thoroughly enjoy, or a day packed with people, conversation, and appointments. Activities you enjoy are important because if you are bored or not enjoying what you are doing, it's easy to start thinking about food.

(Side note: The fact that it's possible to distract yourself from feeling hungry for a few meals is additional evidence that daily eating is largely habitual and mental, rather than a physical necessity.)

Best Way to Break the Fast

If you're afraid of overeating once your fast is over -- or if you just simply want a great way to increase satisfaction with fewer calories (and thus reap even more benefit from you fast), here's the secret: you need to prepare your stomach to eat less.

The best way do do that is to employ the Pre-Fill technique. Here are the basics. Roughly 30 minutes before your fast-breaking meal, take one or more of the following:

One or two full glasses of water.
One serving of a protein drink.
A serving of any kind of fiber-based supplement like glucomannan.

You may also choose to eat a few crunchy raw vegetables. You could add the vegetables to the items mentioned above, consumed 30 minutes beforehand, or simply eat them FIRST right at the beginning of the meal.

Then, eat a good-sized portion of lean protein. Then some cooked vegetables. The protein and fiber will fill you up faster and make it much easier to keep your meal to a normal size. Also remember to Savor your food.

Then -- and only then -- eat other food types you've been wanting or craving.

As mentioned earlier, with IF it is possible (though not guaranteed) to "eat whatever you want" when you are not fasting and still lose weight or control your weight. However, you increase your chances of doing just that if you follow the break-the-fast ritual mentioned above.

Not Getting the Results You Want?

The only reason IF wouldn't work for weight loss is if you ate too much following the fast. This is typically only a problem with protocols of 24-hours or less (like 16:8, 20:4, or 24 hours) where it is possible to eat your entire day's worth of calories during the eating window following the fasting period.

To avoid overeating, follow the ideas above for your fast-breaking meal.

You may also want to restrict your eating to 500 calories on your fast day (like the Varaday ADF protocol). The next day (a normal eating day), you might discover you eat more calories than usual but if you're like most people in research studies, you won't each enough to overcome the calorie deficit from the fast day if the calories were controlled.

If fasting tends to make you extremely hungry, then you may find a 16:8 protocol more effective because the fasting period is much shorter.