Does Intermittent Fasting Help You Lose Weight?


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Intermittent fastingWe’ve been told again and again that “grazing” (consuming 6-8 small meals per day) is the best way to eat. But is it really?

Intermittent fasting is a way of eating, or rather a lifestyle, which is the antithesis of grazing, and is currently being touted by nutritionistas far and wide as the optimal method of eating.

It’s hard to decide how and when to eat if the nutrition world is spouting a million different ideologies. This article lays out exactly just what intermittent fasting is, how you can do it, and what you can expect to gain.

Which Type of Intermittent Fasting Is Best?

Although there are an infinite number of variations, a few major intermittent fasting protocols rise to the top of internet-based searches.

The biggies are:

  1. Every other day (EOD) fasting
  2. The Warrior diet (1 large meal per day)
  3. Variations (different combinations of EOD and the Warrior diet)

Intermittent Fasting: Every Other Day

EOD is relatively self-explanatory: you don’t eat anything every other day; on the days you do eat, you eat as much as you want.

On an EOD fasting protocol, even when instructed to eat twice as much on fasting days, people can rarely do it. So, this leads to a weight loss profile that somewhat humorously looks like this:

Intermittent fasting

In the study from which that figure was taken 1, they allowed participants to drink diet soda, coffee, tea, and to chew all the sugar-free gum they wanted on fasting days. With this, they fared pretty well: of the 3 pounds they lost over the course of 3 weeks, 57% of it was body fat (not bad, but not great).

Under a more controlled setting, where people were forced to eat enough to maintain their body weight, the results are less promising. In one study like this, EOD fasting led to no changes in body weight or body fat 2.

So, should you try the EOD fasting?

In the real world, where you are not forced to eat enough to maintain body weight, you might lose fat on EOD… but this isn’t due to anything magical – you simply aren’t hungry enough to eat double every other day.

Intermittent Fasting: The Warrior Diet

On the Warrior Diet, you don’t eat all day until late afternoon, then eat until contentment over the course of about 4 hours.

The major difference between this and the EOD method is the amount of time between meals. On EOD, you stop eating after dinner on day 1 until breakfast on day 3; roughly 36 hours. On the Warrior diet, you stop eating after dinner on day 1 until the start of dinner on day 2; roughly 20 hours. Leangains cuts this down to 16 hours of fasting with an 8 hour eating window. And just for reference, on a standard 3 square meals per day plan, the longest amount of time you go without food is overnight; about 10-12 hours.

The 1 meal per day plan (Warrior Diet) is somewhat more practical and the results are much better 3: people who went from 3 meals per day down to 1 lost over 4 pounds of fat but gained almost 2 pounds of muscle over the course of 3 weeks, meaning that their body fat percentage declined by over 10%. And that was without exercise!

So, should you try the Warrior Diet?

Without restricting overall food intake, people on the Warrior diet lost fat and gained muscle, a considerable improvement over EOD.

Intermittent Fasting: Variations

One variation on these protocols is “Eat Stop Eat,” and a similar version known as “Alternate day fasting (ADF)” that has actually been clinically tested. On Eat Stop Eat, you do the Warrior diet twice per week, while on ADF, you do it every other day.

In one study, people were told to eat one small meal on day 1 (75% less than usual), and 3 large meals on day 2 (25% more than usual) for 8 weeks. It was designed to be a weight loss diet, and it worked regardless of whether people ate low fat or high fat (low carb) diets 4:

Intermittent fasting

But the most interesting finding is these people lost about 15 pounds, and over 75% of it was body fat. They also gained about a pound of muscle.

So, should you try Alternate Day Fasting?

As somewhat of a compromise between EOD fasting and the Warrior diet, ADF will probably give you the best results with regard to body composition.

Which Intermittent Fasting Protocol Will You Try?

From these few studies, we can learn a few things:

  1. going a full day without food doesn’t do any favors for muscle mass (eg, EOD)
  2. in a non-weight loss setting: the Warrior diet is superior to EOD fasting
  3. in a weight loss setting: ADF is superior to the Warrior diet

While they represent the furthest possible deviation from “grazing,” intermittent fasting protocols are safe and effective at least up to 8 weeks. However, there simply aren’t enough data from clinical trials to draw more firm conclusions. Intermittent fasting can be a helpful method to get lean, but it’s not the only option, and it is definitely not for everyone.5

If you decide to give one of these diets a try, let us know how it goes! We’d love to see you post your protocol, results, and anything else you learned from it!

References

  1. Heilbronn LK, Smith SR, Martin CK, Anton SD, Ravussin E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Am J Clin Nutr. Jan 2005;81(1):69-73.
  2. Soeters MR, Lammers NM, Dubbelhuis PF, et al. Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. Am J Clin Nutr. Nov 2009;90(5):1244-1251.
  3. Stote KS, Baer DJ, Spears K, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. Apr 2007;85(4):981-988.
  4. Klempel MC, Kroeger CM, Varady KA. Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism. Aug 10 2012.
  5. Due to a generally biased nature of diet studies, BuiltLean supports eating moderate and healthy meals rather than fasting as the healthiest course.
Medically reviewed by Richard Yoon, M.D.
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Does Intermittent Fasting Help You Lose Weight?, 4.2 out of 5 based on 25 ratings

24 Comments on “Does Intermittent Fasting Help You Lose Weight?

  1. David
    January 7, 2013 #

    Interesting post but I’m a bit confused by this statement:

    “But the most interesting finding is these people lost about 15 pounds, and over 75% of it was body fat. They also gained about a pound of muscle.”

    If only 75% was fat then the other 25% must have been lean mass so how did they GAIN a pound of muscle?

    1. Simon
      January 8, 2013 #

      maybe some of that weight was water retention? just a thought i could be wrong

    2. January 8, 2013 #

      Hi David, thanks for the comment and great catch! They lost ~ 16 pounds of total body weight, and fat mass declined by 12 pounds. Fat free mass increased by about a pound, so there are 5 missing pounds. Since this type of change in body composition is so rare, it’s hard to know exactly what happened (and the authors didn’t address it). study design? eg, baseline values on body weight included all 35 subjects, but body composition data were limited to the 32 completers?… it’s hard to say for sure, but even if the data are off by a few pounds, it’s still a very robust effect.
      Thanks again,
      Bill
      http://www.builtlean.com/author/william-lagakos/

  2. Eric
    January 7, 2013 #

    I am 36 years old have kept myself in really great shape and health for over ten years now but could never get really “cut” before. About four months ago I stumbled on an article about IF and decided to do the “Warrior Diet.” I have found that for me this has been the best way of eating for my body and mind. I lost fat in areas I could never target with workouts. For the first time I actually had a six pack! After two weeks of eating really nutritiously charged wholefoods such as yams, fish, and veggies along with vitamins supplements etc– I had boundless energy- no crashes and I never had bouts of low sugar crashes etc. I am gonna try ADF next and see if there is any real difference but I have found IF to be a key for myself in getting fit and healthy inside and out.

    1. January 8, 2013 #

      @ Eric,
      Awesome! I look forward to hearing how it compares.

  3. Anthony
    January 7, 2013 #

    @David, your body is transforming so the more body fat you lose then the more lean mass you gain.

    I would like to do this but I feel like I would die if I go 20+ hours without eating.

  4. Miguel
    January 8, 2013 #

    I’m trying the Eat Stop Eat (I’m 200lbs and need to get to 188-190 for aprox 10% body fat). Yesterday I had a normal grazing day with 3 healthy meals and a couple of snacks, High Protein Mid Carb. Today I’ve only had coffee and water, I plan on eating a big meal aroud 4-5pm and a couple of snacks through 8pm.

    Is this the right way to do this? I play soccer, and I’ve programmed it so that on soccer days I have grazing days. Do you think this is beneficial for me? Or does it make no difference how I eat on soccer days?

    1. January 8, 2013 #

      Hi Miguel,
      The short answer is yes, nothing but coffee and water until dinner is approximately the Warrior Diet; and a few grazing days per week bumps it up to Eat Stop Eat. However, while it’s reasonable to assume that an increase in lean mass won’t impair your soccer performance, these studies only addressed body composition. Keep experimenting and let us know how it works out!

      Bill
      http://www.builtlean.com/author/william-lagakos/

  5. Maria
    January 8, 2013 #

    Here is a link to a site that offers detailed information on IF. The author goes into detail on different approaches he’s tried and what he felt worked well for him and what didn’t. I thought this was very informative, objective, and a good read if you would like to try it or want to learn more about it:
    http://www.precisionnutrition.com/intermittent-fasting

    1. January 8, 2013 #

      Thanks Maria, John Berardi is a great nutrition writer.
      Bill
      http://www.builtlean.com/author/william-lagakos/

  6. Faisal
    January 9, 2013 #

    Hi,

    Yesterday I read an article and it talked about eating every 2 hours to keep the blood sugar levels balanced. The author also talked about eating balanced combination of carbs and protein. This alone with keep sugar level balanced will cause our body to lose weight.

    And I read this article today and am actually confused on which diet to chose. I rarely exercise but I walk about an hour a day.

    What do you think is the best option to lose weight?

  7. uncadonego
    January 9, 2013 #

    I would be very interested to hear from BUILTlean team members on this. I’d like to know if they’ve personally experimented with any of these methods and what their personal results/opinions were on them. These are quite the opposite of what I’m doing, but I’ve sometimes wondered about fasting, even one day a week.

    1. January 9, 2013 #

      Hi Faisal, thanks for the comment. Besides being inconvenient, I don’t think eating every 2 hours is very bad for you (or very good for that matter). With regard to the best diet, there really aren’t a lot of data on all these intermittent fasting diets, but I think they are supported by enough good theory to warrant a little self-experimentation. Pick one and try it! That’s the only way to really know.
      @ uncadonego, I haven’t personally tried any intermittent fasting diets, but I don’t see any red flags with any of them.
      Bill
      http://www.builtlean.com/author/william-lagakos/

    2. January 10, 2013 #

      I’ve played around with IF a little, but I’m not a huge fan. I think most people will be better off with the typical 3 meals and 1-2 snacks per day. That does not mean IF is invalid, or doesn’t work, and it may even be awesome for some people. Given you are doing the BuiltLean Program, you know I prefer relatively frequent meals and snacks. I’ve found it’s much easier to control calories this way on a fat loss program. Given what you are doing is clearly working, I would definitely not go on an IF diet. Once you reach the body fat level you are happy with, then consider IF. That’s my two cents!

  8. James
    January 13, 2013 #

    I am 41 and in good shape and health. Being a hard gainer I struggled to put on any mass till I moved to more frequent feeding ( 6 to 7 meals ). I have since found it hard to cut my body fat without compromising muscle mass.

    I am keen to try IF, but unsure how this will affect my training. Do I train as normal? At the moment I train 2 days on 1 day off. How do I ensure I can maintain adequate energy for training intensity?

  9. January 14, 2013 #

    Hi James, these are all good questions, and I don’t think the answers are known. My gut says if you want to optimize body composition, don’t train while you’re fasting. If you really want to try an IF protocol, make sure the fasting phase isn’t anywhere near exercise time.
    Hope this helps!
    Bill
    http://www.builtlean.com/author/william-lagakos/

  10. John
    January 23, 2013 #

    I’ve been intermittent fasting 2 to 3 days week pretty much every week since I saw IF in September when I was 101kg (222lbs). I’m a tiny fraction under 6′ tall and fairly active but my diet was appalling.

    I’m now to 86kg (189lbs), my bodyfat (measured with Accumeasure calipers) is around 13.8% which (if it’s true) means I’ve retained just about all of the lean body mass I had when I was over 100kg.

    The first month or so the weight just fell off, since then I’ve also been doing some body weight exercises to try and retain muscle.

    The thing is now I’m getting down to a reasonable size and I’m happier with what I see in the mirror I’m more inclined than before to make some proper effort with training and a good clean diet (which I’m sure is the best way forward) but it’s the fasting that’s got me to the point where I can be bothered to make a real effort.

    1. January 24, 2013 #

      Hi John,
      Over two stone of fat loss in ~ 5months is incredible! Are you going completely without food on fasting days, or just restricting your feeding window?
      Congrats again on your progress and thanks for telling your story.
      -Bill
      http://www.builtlean.com/author/william-lagakos/

  11. John
    January 24, 2013 #

    Bill

    Thanks, I was actually 235lbs Xmas 2011, by Sept 2012 I’d got down to 222lbs, but I’d done all the things everyone says don’t do, 3 weeks strict diet – give up for a month – 2 weeks stupidly hard cardio plan – give up for 5 weeks and so on and I’d have probably put the 13lbs I’d lost back on over Xmas if I hadn’t started the fasting plan.

    I’ve been restricting pretty heavily on the “fasting” days, the figure given on the BBC program was 600 calories on a fasting day.

    I’m not utterly convinced the weight loss is anything to do with fasting and is probably more to do with dropping 4000+ calories a week from my intake as well as stepping up the physical effort as I saw the pounds falling off.
    As I said I’d tried a few times to lose the weight but still over 220lbs I just didn’t have the motivation to cut a few hundred calories a day from my diet every single day only to have the scales move down by just a pound or two or wreak a weeks effort with a heavy night out.

    But the fasting was easy, anyone can do one day, 600 calories carefully chosen is actually quite a lot of food, enough to get through the day without starving, then the next day eat what you like.

    And as I got into better shape my motivation to get into even better shape increased.
    When I look now at what I’d eat 4 months ago on a “feeding” day I can barely believe I’d eat that rubbish or that amount! My diet now is quite good, junk and takeout’s are reserved for social events and even then ordered with some though, not just a 12″ pizza and 4 beers (and that’s 4 18oz cans, not 4 little bottles!) as I can’t be bothered to cook.
    But I needed the intermittent fasting to give me the results before I’d start to let go of my beloved pizza!

    Getting started was the hard thing, actually that’s not quite true, staying started for more than a week or 2 was the hard thing, now I’m in what I know is quite good shape for a 42y/o carrying on working out and being mindful of what I eat seems natural.

    Great website BTW!

    1. Jerry
      January 25, 2013 #

      Hi John,
      Your results are amazing. Can you give some detail on what you ate on fasting and non fasting days – I ‘ d like to try it! Thanks,
      Jerry

  12. John
    January 27, 2013 #

    On fasting days I’d tough it out as long as I could in the day, then have something like 1/2 a tin of baked beans on a couple of slices of toast, that’s barely 300 calories and surprisingly filling. Or really anything around the 3-400 calories mark.
    Then later, sort of late evening (I don’t like going to bed hungry) just something to hold back the hunger pangs. A couple of Shredded Wheat (skimmed milk and no sugar!), a yogurt with a few strawberries and grapes, anything – just keep the calories down.

    I didn’t used to concern myself with protein levels, I do now as I’m nearly getting slim and am more concerned about body composition. I’ve also discovered a protein shake is surprisingly filling.

    But the interesting thing was either as I saw results or as I got used to not eating a lot (or both) my desire to eat the bad foods and the overall amount I wanted to eat went down.

    It’s good, many many years ago I was in shape (170lbs, 10% BF) and now it feels like that person is on his way back.
    All those years eating junk, drinking alcohol every night it’s like there was a veil over my thoughts and my decision making was running on automatic. Eating badly and the resulting poor physical condition didn’t just hurt my body it numbed my mind. It’s not that I couldn’t see a out, it’s far worse than that; I didn’t know I was lost.

    1. Ngamu
      February 6, 2013 #

      John, Kindly let me know how long was each fast?

  13. January 30, 2013 #

    John, thanks for the responses.
    Yeah, it’d be difficult to tease out whether the calorie deficit per se caused the weight loss, but that doesn’t rule out the possibility that the CR protocol influenced your remarkable retention of lean mass (eg, the Warrior Diet and/or ADF). In any case: awesome.
    -Bill
    http://www.builtlean.com/author/william-lagakos/

  14. Emma
    February 4, 2013 #

    this is really interesting and I want to give it a try…. but I’m kind of confused. The best results for weight loss was stated as the ADF as opposed to the Warrior Diet….

    so for ADF, on one day you eat normally, then the next day you do the warrior diet and just have one meal in the afternoon, then the next day eat normally, and so on…. is this correct?

    any help much appreciated

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