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This question originally appeared on Quora. Answer by Darren Beattie.

Is intermittent fasting (IF) a good idea for weight loss? It can help with dietary adherence in some folks and probably help them manage or at least learn about hunger sensations.

It’s not for everybody though, you should probably experiment with different variations of it and consider it after making some key basic nutritional adjustments. It doesn’t suit everyone’s lifestyle but it might suit yours.

It can only create fat loss the same way any other eating strategy does, via an energy deficit.

I think it's first necessary to recognize that the majority of us naturally fast 12-14 hours per day already during our sleep.

Then we need to establish some ground rules about Intermittent Fasting as there are numerous methods.

  1. 24 Hour Fasts (Once or Twice per Week)
  2. Alternate Day Method (Eat Every Other Day)
  3. 16 Hour Fast Method (popularized by Martin Berkhan at Lean Gains )
  4. 20 Hour Fast Method (popularized by the Ori Hofmekler's Warrior Diet)
  5. Religious Fasting (period fasting as related to religious practices)

Probably others…

IF has become all the rage recently because it has some good evidence pointing in the direction of fat loss in particular. However, it’s important to keep in mind that there is actually very little research in this field (no one wants to fund not eating).

It has never really been shown to be any more effective for fat loss (AKA weight loss) than simple caloric restriction when calories are accounted for directly (i.e. not personal recall, which is always inaccurate). Which makes perfect sense from a physiological stand point because you can’t defy the laws of physics just by eating only at a certain time.

When IF does seem more effective for fat loss it’s probably just because it creates a calorie restriction in certain people and frankly people who don’t have success with a strategy just don’t rave about it as much as people who do.

A colleague, Dr. John Berardi, wrote a great (and free) book on the subject a few years back. Based on his experience and did an little experiment on himself utilizing blood work. You can read it here: PN-IF

What you may note is looking at the health markers of this case study, not a lot actually changed for him (though he did get leaner), presumably because before he started fasting he already had a solid foundation of eating healthfully. Now this isn’t a formal study, so a lot of variables haven’t be accounted for.

In a great deal of nutrition research I’ve plowed through over the years inducing a change from a test subjects ‘normal’ (in this case taking someone out of their usual diet routine) diet in pretty much any way yields significant changes in various health markers. Though not necessarily weight (again an energy deficit needs to be present for weight loss or more specifically fat loss to occur).

What this case study suggests to me is that giving yourself a feeding window or a fasting window doesn’t really create much of a change outside of the existing diet. When people do get dramatic changes, it’s probably more related to the fact that doing IF caused a more dramatic shift in their eating and potentially training habits.

For instance, training is a significant part of the lean gains protocol.

Sound eating habits and a generally sound diet, utilizing foundational eating skills like these (disclaimer, my blog - Eating for Fat Loss - Skill Based Fitness ) will probably yield better health marker changes by comparison assuming that in doing IF you do not change any of your current habits of eating, you simply cut out food for an extended period of time. Of course the fat loss that occurs with a skill based approach is still the result of creating an energy deficit.

In my opinion developing these habits (and there are potentially others) is the first step or foundational step in eating as a generalized consideration (more veggies, better/more lean protein, enough healthy fats and carbs to match training/exercise requirements).

Meaning, if you plan to try IF (as I've read of many people doing unfortunately) with your current diet of simple carbohydrates, sweets, and other nutrient-free calories, you will probably not get the results you are looking for. Or you may get the results you are looking for but with a disregard for the possible health outcomes down the road.

I would warn that IF is not an excuse to eat whatever you want at re-feed times and that assuming it to be a miraculous cure for low body fat would be a mistake. Many people appear to treat it as such.

The real benefits of IF appear to be:

  • Individual adherence (i.e. an eating strategy that works for the individual)
  • Probably helps suppress/manage hunger and/or recognize hunger cues better

Meaning that if fasting helps you achieve an energy deficit and your goal is weight loss, then great, dietary adherence is probably the most crucial thing to consider in any eating strategy.

It also appears effective at teaching/managing/mitigating hunger sensations (at least in certain people). And well hunger usually accompanies energy restriction, so anything a person can do to manage hunger effectively can really help a person lose fat. If you’re better at recognizing when you’re really hungry, then you can probably manage a real energy restriction better.

Note that there are many other ways to manage hunger too, like increasing protein, so it’s really about finding something that works for you.

It might not be a great strategy if you:

  • Want to gain weight/muscle (though the lean gains approach certainly has some history here, so if you can create an energy surplus with a restricted feeding window by all means - some people use it to some success to gain muscle slower and reduce the amount of fat that generally comes with weight gain)
  • Have a history of disordered eating you might want to consider something else (along with getting the necessary help)

Fasting for weight loss fundamentally works like any other form of caloric restriction. For any evidence I've read showing positive changes in health markers we do not know for sure if these are not more directly related to the caloric restriction than anything else.

Caloric restriction has been shown to increase longevity and improve many health markers.

There is some other evidence I've read revealing that there are also possible downsides to certain health markers to go with the good changes. It’s a mixed bag and hard to determine.

As a coach who's played with a few types of IF it personally did not appeal to me as it may to you. I have used various types successfully with certain clients though. I often go through a 1–2 week experiment with clients to give them an appreciation for what real hunger is. I do not like the sensation of purposefully putting off eating as it didn't jive with my social life, my sports performance or when I genuinely do feel hungry (sometimes I would cut my planned fast short because of this...). For other people it works with their schedule, their training schedule, their lifestyle, etc…

I also have some general concerns about it's use with certain individuals in that it can create an odd relationship with food and may for instance encourage or lead to eating disorders but the research on that is also a bit of a mixed bag.

Too much caloric restriction can mean just as much malnutrition as it can longevity, and in my opinion could hinder your quality of life (even if it becomes longer).

Based on this, I generally consider Intermittent Fasting (IF), as more of an intermediate to advanced nutritional strategy for weight loss for most folks. I prefer to start more simply (with strategies listed above) and build up to something like this. It won't be any better than any diet solution for many, particularly without good nutrition already in place. It would still have to create an energy deficit for fat loss.

I would also say that IF is more appropriately used as a short-term strategy that helps already lean people, get more lean. What some people in the bodybuilding community refer to as ‘cutting.’ You know, you've been hovering just above 10% body fat, and you want to get below that so you can do a photo-shoot with your abs pulsating, that kind of thing. It just clicks with certain people too.

Ultimately, if you are doing the majority of those things especially well already, but still not getting where you’d like to then IF may be something worthwhile to experiment with. It has some merits, most of which I believe are more hunger/lifestyle related as opposed to weight-loss specific, but a lot of the time that’s all a person needs to get over the plateau.

I would encourage you to think of IF as just a tool (like in my opinion Calorie Counting, Nutrient Timing, or Carb Cycling is) you can use from time to time, once you've developed some quality eating habits. Simply doing IF on it's own with no consideration as to what you are ingesting would be a waste of time in my opinion.

The timing doesn’t matter as much as what that restricted feeding window ultimately does. If you overeat in 8 hours, it has the same effect as over eating in a 12 hour window = weight gain. The same goes for under eating = weight loss.

I would start with the Lean Gains approach (pretty much skipping breakfast) as it's the least daunting of those listed and then work towards adding hours.

The Warrior Diet is a 20 hour fasting method, whereby you can consume small amounts of veggie shakes to reduce hunger during your fast (among many other dietary suggestions).

For info on the Warrior Diet or Method of IF, check out Ori Hofmekler's website at The Warrior Diet.

For the longer 24 hour fasting method(s) you can also check out the book, "Eat, Stop, Eat" by Brad Pilon.

Each has their own merit, but usually based around the adherence/hunger factors for people. I found going an entire day without food challenging, let alone doing it weekly, which would help me stick with it right? The more moderate methods worked more effectively for me personally, but I’m not you. So don’t do anything that you can’t/won’t stick with, it won’t help you in the long run.

Whatever you choose to do, I encourage you to experiment with it and gauge how it makes you feel and operate.

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