Intermittent Fasting: Hype or Effective for Weight Loss?

By Mike Howard

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Intermittent fasting (IF), a dietary strategy that involves repeated intervals of feeding and fasting has gained popularity in the past couple of years, with proponents claiming a wide range of health benefits from insulin control to fat loss to defense against a host of diseases. The question is; is it a fad or is there sound research to back up the hype. Let’s explore!

IF, the Anecdotal

There are various permutations of intermittent fasting, with the most popular being alternate-day fasting (ADF). Promoters of this lifestyle claim that IF will increase longevity, burn fat, improve heart/lung function, improve insulin control, decrease inflammation and decrease cancer risk. One of the hallmarks of IF is it’s ability to to prevent aging symptoms of the brain and nervous system.

Many who have undertaken IF have reported feeling more “freedom” from not having to eat so often and also a sense of accomplishment and control from being able to sustain such a regimen.

There appears to be some ancient justification for intermittent fasting as some claim it is similar to how our Paleolithic ancestors ate and our systems are thus designed for such eating patterns.

IF, the research

The actual human data on IF is scarce, and no study to date (to my knowledge) has had a control group – which leaves only speculation as we don’t know if there is an advantage to daily caloric intake. The few studies that have looked at IF have shown;

  • Weight loss
  • Improved insulin sensitivity
  • Improved fat burning (oxidation)

On the downside, studies have also shown increased hunger throughout the duration of the fast.

IF, is it for you?

According to nutrition researcher Alan Aragon, IF may benefit the following people:

  • Those who have steady glucose control (not prone to hypoglycemia)
  • People who are not prone to binge eating
  • Those who don’t have the time/inclination to prepare and pack food
  • Those who drive and/or travel a lot.
  • Those who are not as concerned with gaining muscle

I would personally include those who exercise fairly vigorously more than 2-3 times per week.

Summary Points

  • IF has the potential to impart health benefits such as improved insulin sensitivity, fat loss and prevention of mental decline.
  • We don’t know if IF works better than calorie restriction, with research showing parallel benefits of calorie restriction.
  • Exercise can probably replace the benefits derived from IF/calorie restriction
  • IF may not be a sensible approach long-term.
  • There doesn’t appear to be any physiological advantage to IF
  • IF may be helpful for people trying to break a weight loss plateau.
  • You still need to eat healthfully! Fasting does not negate the need for nutritious diet.


  • Heilbronn, et al. Alternate day fasting in non-obese subjects: Effects on body weight, body composition and energy metabolism. Am. J. Clin. Nutr.2005 Jan;81(1):69-73.
  • Varady KA, Hellerstein MK. Alternate-day fasting and chronic disease prevention: a review of human and animal trials. Am J Clin Nutr. 2007 Jul;86(1):7-13
  • Heilbronn LK, Civitarese AE, Bogacka I, Smith SR, Hulver M, Ravussin E. Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Obes Res. 2005 Mar;13(3):574-81.


  1. Leah

    I think it would be best if everyone just did what was best for them. Apparently, fasting has worked for quite a few people.

    I think you guys read into things entirely too much. In all honesty EVERYTHING, every diet, every food chart of what you are “suppose to eat” is wrong. Whether you go low-carb, low-fat, paleo, long cardio, HIIT cardio, detox, or even vegan, there will be some Nay-sayer and some scientific evidence that says that “you can’t” or “it’s not healthy to because . . . ” I’ve even been told from a few doctors eating strictly fruit and vegetables is unhealthy because you won’t get all the minerals and nutrition your body needs. You know what I say?


    I’ve lost 10 pounds doing this type of fasting (I did not know it at the time) and I say, if it works for you, go do it. If you are so controlled by food that you can not stop putting a loaf of bread to your mouth for 19 hours, then by all means, keep eating whatever it is you eat. But don’t TELL others what works for them or what’s healthy for them.

  2. Dave

    I have been using Intermittent Fasting for the last six weeks ( since Jan 1st 2009 ) My own personal findings are this is the easiest way for me to lose fat I have ever done, I only wish I had used it before. I decided to blog about my progress with it, which anyone can follow at . I think to lose body fat you have to do what is best for you, no diet plan works for everyone. I just find the fact on the days I fast, I don’t need to think about what I should or should not eat. I also am Asthmatic and I have experiences a huge improvement in this area of my health.

  3. JLL

    ^ Nothing like anecdotal evidence to dispute science, eh?

    On that note, I have to say intermittent fasting has worked pretty well for me. I’m not so into gaining muscle mass, but reading other people’s blogs I get the sense that you CAN combine heavy exercise with IF. After all, you don’t have to eat less calories; just eat double the calories in a shorter period.

    I’ve documented my experiences here:

  4. Marcel

    fasting is dangerous! I tried that and started passing out when I stand up! I also had a lot of head aches.

    I was one of the luck ones that found a diet that worked wonders for me.

    I put a link you guys here so you can have a look

  5. Judith

    A controlled study on IF

    The study population are LDS member, some of whom practice IF. Those that practiced IF had a lower risk of Coronary Artery disease (atherosclerosis, heart attack, stroke). Other confounding lifestyle factors, booze, coffee etc., did not account for the differences between the IF and control group.

    IF is thought to increase insulin sensitivity. A hallmark of diabetes (and prediabetes) is insulin resistance. Insulin resistance means that the cells in the body become less sensitive to normal levels of insulin. This leads to high levels of circulating glucose, which in the long run is very damaging and increases the risk of CAD. A brief fast seems to help reset the system.

  6. Spectra

    Our bodies are designed to be able to run on intermittent fueling. That’s why we have stomachs, livers, and pancreases. If we were designed to eat constantly, we’d have tiny stomachs and we’d only be able to keep a little glycogen on hand to use for energy.

  7. Mike H.

    Thanks for the wealth of education on this, Mike. I’m glad you chimed in here and shared your observations.

  8. blah

    How does it make sense? Our ancestors ate regular meals whenever the food sources allowed them to.

  9. Leslie

    Amen, Sister!!

    Nothin’ like good ol’ paleo-diet!

  10. Spectra

    If you really think about it, IF makes sense in the whole scheme of things. Do you think our ancestors ate 3 meals a day and 3 small snacks or whatever? I’m pretty sure it was more like one larger meal every day or so, when they’d hunt or forage or whatever. I think the whole eating 3 times a day thing happened as we became a more agricultural society and had a more predictable food source.

  11. Ed

    I actually did an interview with a nutrition expert who wrote a book about intermittent fasting called Eat Stop Eat. He’s a friend of mine and poured over research studies while getting his Master’s Degree.

    Check the interview out on my blog at:

    I’ve personally been practicing intermittent fasting since May (once a week) and feel awesome. I’m not someone who needs to lose weight (I’m a fitness expert and personal trainer), I just do it because Brad has sold me on its benefits.

  12. resveratrol wine

    I am beginning to settle on the thought that I should be following all those life extension discoveries with a grain of salt. First it was resveratrol, its supplements and SRT501. September’s studies said it was only extending life in overweight people. We were left with caloric restriction, which has in turn proven to be ineffective. Let’s see what the next breakthrough will be. I personally would never go as far as living a life of deprivation, even if it is intermittent.

  13. SCal

    Marc David Rocks!

  14. Leslie


    Cari is a Fat Acceptance blogger/activist!!!

    If not, you sure sound like one..whatever, more power to ya.

    IF has worked for me, I have lost 120 pounds after half a thyroid (sans meds) and 2 kids 2 years apart and my quality of life is soo much better.

    Not to mention they don’t make cute plus sized clothes, I can fit and squeeze by almost anywhere and I’m sorry if I sound effed up to you but there are like a million other ppl that agree with me, rock on IF!!!

  15. Mike OD - IF Life

    Just to clarify too, most people think a 24 hr fast means no eating every other day, I would NOT recommend that. Plus that is really a 36hr fast…the 24 hr fast is when you say stop at 6pm one day and fast till 6pm the next day. I would never recommend going a day without food (as I need my calories! ;)). I’d recommend anyone wanting to give it a try to start slow, most people go into it “all or nothing” and will just end up crashing. Starting with a 16-18hr fast (like just not eating till noon-1pm the next day) a couple times a week will not kill anyone (unless there is some medication condition present). Start slow, see how your body reacts and remember that you still want to eat and eat healthy. It’s not a pass to just eat whatever you want. Like anything….always check with your Dr before attempting just in case there are any medical conditions to be considered. A lifestyle of no more shakes/bars and plastic tupperware with chicken and rice is a more relaxing way to live in my book.

  16. Mike OD - IF Life

    Actually no it isn’t by my definition as you can eat high carb, low carb, 3 meals a day, 2 meals a day, low calories, fast 1x a week, fast 3x a week, fast 16hours, 18hours or 24 (I wouldn’t recommend more for people not used to it and I personally just do 16-18 almost daily). No hard and fast rules like a “diet” would have you follow. All it is simply is a compressed eating window plain and simple. While I agree many will market their program and way of doing it to sell a diet book, technically you fast everytime you go to sleep….so nothing new for the body to experience. Also nothing today shows greater potential for anti-ageing, increasing cellular resistance to stressors, improving brain/heart/lung action, reducing inflammation, preventing cancers and alzeimers, increasing FFA (free fatty acid) oxidation aka burning fat, increased GH pulses (saves muscle) and so on. Also many people suffer from too many mental attachments to their foods and need the break to learn they don’t need to eat all the time. It’s the mainstream mentality of needing food all day long for a faster metabolism that is not getting any results….just look around. It’s still about the calorie intake and insulin control, master those 2 things and any weight loss is possible.

    I do agree it may not work for everyone, as many may already be suffering from more severe issues of hypoglycemia/insulin resistance/pre-diabetic state and may need more blood sugar management throughout the day. Although short fasts will of course help to improve insulin sensitivity along with exercise. Also because it does heighten the SNS response system, people already prone to anxiety or mood swings may need to be careful (as SNS will just amplify emotions as well).

    It’s a great tool to use, once one really understands how to control their eating and emotional responses. Diets don’t give anyone control, as they just tell you how to eat and never let you get back in tune with what your body is trying to tell you in the first place.

    Plenty of research out there on it as well…well none that will show up in Men’s Health, but still lots of positive findings to learn about.

  17. Scott Kustes - Modern Forager

    IF works for me. I maintain a body weight of 185lbs at about 10% body weight, eating some 3000 calories per day, but most days in a 4-6 hour window. After experimenting for about 3 years with various IF protocols, I’ve found one that works for me. Here are the keys I’ve found:

    – Eat enough for your activity level. You can only withstand real hunger for so long. The nice thing about IF is you learn to distinguish real hunger from psychological hunger.
    – A diet of real foods works best, which typically ends up being low-carb. I find that when I eat much in the way of grains or other high-carb foods, my body is aching for something good by lunch the next day.
    – Eat when you’re hungry. Sometimes, it’s good to push through hunger, as our bodies are primed for feast-and-famine conditions. But if food is all you can think about…eat. Some days I eat lunch cause I feel I need it. Other days I don’t. Sometimes I eat breakfast just because I love breakfast. Other days I don’t.

    You just have to play around with it and see how it works for your body. That said, I think getting quality under control is more important. I’d make sure I am eating a diet of grass-fed and pastured meats, wild seafood, seasonal vegetables, fruits, and roots, with possibly some nuts and such before worrying about when or how much I’m eating.

    Scott Kustes
    Modern Forager

  18. Dr Lomar

    Actually it is a diet. I’m not sure why people steer so clear of that word.

    I think trying to make certain diets work for everyone is a very bad idea. Use what works for you. I’m not saying I would approve of eating nothing every other day..but if that works for you then go for it. Your body is alot tougher than you think and unless you have some kind of medical condition..IF wont hurt much.

    I would note however that if your doing something like this and you start to feel side effects that prevent you from doing normal every day tasks..please save your local ER some time and stop fasting.

  19. Katie Nemargut

    I was going to say the same thing! Martin Berkhan is fantastic. Leigh Peele also did an interview with him on her website about his IF programs It goes into detail more about his program and how it all came about.

  20. nancy

    call me a skeptic but i think the ‘skipping meals will slow your metabolism’ train of thought is only pushed because it helps fuel the capitalist machine. i don’t think you’ll ever find a mainstream health / fitness magazine explore IF fully because it might kill their advertising revenue.

  21. Mike OD - IF Life

    Intermittent fasting is not a diet….it’s just an eating style. You still have to get enough calories, get the right macronutrient ratios, and do it “intermittently”…hence why it is called IF. Many ways to do it…and many can be wrong ways too. If you use it as a pass to eat whatever you want mostly carbs and sugar, then you lose the benefits. If you eat smart for your lifestyle and goals, you can get results.

    Myth: Your metabolism with plummet: Truth: Short fasts do not lower metabolism, overall calorie intake for days (if not weeks) puts you into a starvation response. Most researchers try to measure thyroid output which will normalize and increase with any feeding window. It’s not about starvation….well unless you don’t eat enough or eat the wrong foods and deprive your body of nutrients.

    IF is a freeing lifestyle once you know HOW to use it. Otherwise to put the hopes on eating 6x a day for the rest of our lives is pretty depressing.

  22. vlm


    I lost it by following a Paleo-type eating plan. I din’t realize that was what I was doing until afterward, when I started doing some reading.

    I had been diagnosed with diabetes and, with the agreement of my dr., tried to control it with diet and exercise. I religiously tested my blood sugar after every meal and began eliminating everything that pushed my it high. After about 6 months I had eliminated all prepared foods, all grains, most starches and all sugar, and the weight just fell off. I was never hungry and still am not, 2 years later. Controlling my blood sugar seems to control my appetite. Even though my husband isn’t diabetic, he agreed to eat the same way I do and he has dropped about 60 pounds. He does not IF.

    We also work out quite a bit – I gave my car to my university-bound son and I walk to and from work with a weighted backpack, and do 3 hours of ‘boot camp’ a week, including resistance training.

    The benefits have been nothing short of tremendous.

  23. blah

    How is it “pretty obvious”?

  24. Spectra

    Although I don’t fast often, I do it on occasion with no ill effects. I’ll go for 24 hours with no food sometimes, but not usually longer than that. Surprisingly, I’m never really hungry when I do that. Or rather, I get hunger pangs for a little while, but they seem to disappear pretty quickly. I work out a lot, but not usually on the days that I fast.

    I know a lot of people who do a modified fast where they eat only fruit and vegetable juices for a day to give their digestive systems a “break” from things. I don’t know if that would necessarily count as the same thing as IF, but it sounds close enough for me. I’ve heard of the “Hollywood Miracle Diet” or whatever it’s called…it’s basically a juice drink with laxatives and diuretics in it. You’re supposed to drink it and eat no food for 48 hours and you can lose up to 10 lbs (most of which is probably water and food weight). Not exactly the smartest way to lose weight, but if you’re starting a long term weight loss plan, it may give you a bit of a psychological boost that could help you stick with it.

  25. Becky

    How did you lose the 75 pounds?

  26. Becky

    Wow that sounds realy intresting.. I think I am gona check out the web sight. I can go a day without eating once a week.

  27. Marc David

    Thanks for the quick write-up. My friend now is doing more of a calorie restriction type diet although it seems more like a constant, unplanned, fasting style diet.

    As with anything, we’ll see how it pans out. At this point until a decent long term study comes out, it is nothing more than individual personal experiences and theories being batted around.

    Not sure why IF comes up so much in the bodybuilding world. Strange since you absolutely need food for fuel and recovery and fasting is already being done by thousands of skinny guys and gals all over the world today. Heck, IF worked for me when I was a teenager. That’s how I kept lean and under 150 lbs! I guess I was doing IF on weekends without even knowing it.

    Thanks again for the quick rundown of IF.

  28. Venkat

    In India, persons with religious leanings often fast for whole days together. Most religions observe fasting as a ritual. MOslems call it Ramzan. Christians, at least the more austere ones, practice this as Lent. Hindus have it in a variety of formats. Jains and Buddhist probably observe this in its most rigourous format. Jains are regularly known to fast for 10 days or so at one stretch.

    I myself underwent a Buddhist Vipasanna mediation course for 10 days and found amazingly that I could easily do with just one good lunch each day.

  29. Supplements

    again another fad that won’t be around over the long term. if there is a way to make money off a diet then people will do it.

  30. Never teh Bride

    I don’t fast personally because it’s never made me feel good or refreshed. At the same time, I can’t see there being anything particularly dangerous about IF, considering animals (spec. predators) in the wild will often go a day without food if nothing comes their way. I’m not going to say I agree that it has mega health but I don’t think it’s harmful. If it energizes you, then enjoy!

  31. Methuselah - Pay Now Live Later

    IF is a lot easier if you are on a low carb diet already. The lightheadedness and shakyness should be much less likely then. I regularly fast for 24 hours on only water and never get any of the symptoms I would have had if I’d tried it when I was on a high carb diet…

  32. Ally

    As someone mentioned here, couldn’t this lead someone down the path to anorexia? And how is it done, REALLY? I eat very healthy and have a healthy weight, but if I go too many hours without food I get very lightheaded and shaky (I’m not anemic, hypoglycemic or diabetic.) Also, are any beverages at all included? Water can severely dilute you if you don’t take in appropriate nutrients. Are juices allowed?

  33. Mason Hamilton

    IF is just one more diet fad with little or no clinical data to support it. The field of nutrition has long been plagued with inadequate clinical information and this is why you see an almost constant revision of even the most basic nutrition guidelines. I think there is a legitimate concern that the stress created by IF may out weigh any benefits achieved by it. If one generality has become very clear and repeatedly enforced in the history of nutrition science, it’s that nutrition is more about balance and variety, than about deprivation. I work in the field of nutrition research (animal) and to date I have seen only one diet system that provides broad, consistent and predictable results – it’s called the South Beach diet. (I have no relationship of any kind with those that market the related products – nor do I recommend the products – just the process). It is far from perfect, but it does work long term (no other diet system that I know of can make that claim) and I think the principles of blood sugar control through management of simple carbohydrates along with a balanced diet high fresh vegetables, make far more nutrition sense than IF. If your diet was imbalanced before IF – what possible nutrition gain are you going to achieve with IF that betters your nutritional intake?

  34. Charles

    I have included fasting in my health routine and have found that I feel great following a fast. More energy, contorl of my appetite, better sleep, even weigh management.

    However, when I fast it’s usually for 24 hours and it’s only once maybe twice a month.

    Every other day fasting sounds a bit extreme, and impractical for 99% of people.

  35. Cari

    “feeling more “freedom” from not having to eat so often and also a sense of accomplishment and control from being able to sustain such a regimen.”

    Freedom from not having to eat???? Hey I don’t know about that. ME? Eating is a joy and a delight and a happy experience why on earth would I want to be free from something that now that I’ve stopped dieting and restricting and starving, not to mention all the sneak guilt eating I used to do brings me great pleasure?

    And you know that sense of accomplishment and control? Been there, done that…. and that sense of control was precisely what opened the door to anorexia.

  36. Barry

    That old adage is superstition, nothing more. Alan Aragon, referenced in this post, has debunked the idea that metabolism is stoked by increased meal frequency.

    He says that it’s more about eating at regular intervals rather than about how many times you eat.

  37. Katie

    Just my experience with fasting, it actually helped with cravings I have had to binge eat, because once I had decided to not eat for such a period of time, the cravings went away, and when they returned (a.k.a., when food was an option again), it was the same as before, not worse. And really, the hunger goes away very quickly.

  38. Barry

    Go check out Martin Berkhan’s website, leangains dot com.

    He has before and after photos of his clients. It’s pretty obvious that intermittent fasting has benefits regardless of what the very limited body of science may or may not say at this time.

  39. vlm

    After a year of tight blood sugar control, I started IF. 1 day a week I don’t eat anything, only drink water throughout the day, so it essentially amounts to a 36 hour fast, once a week. It’s not difficult at all and I think the tight blood sugar control going in is the key. On the day that I fast I don’t feel very hungry (there seems to be some psychological\physiological benefit to knowing in advance that you won’t be eating that day). Around 4 in the afternoon I feel some mild hunger that passes pretty quickly. It’s not even difficult to sit through dinner while my husband is eating.

    I’ve been on IF for about 4 months and don’t find it difficult to maintain, even though I exercise fairly heavily.

    IF helps me maintain my 75 pound weight loss (still eating sensibly the other 6 days of the week) without a lot of effort.

  40. Kym

    Doesn’t this sort of go against the old adage of “don’t skip meals because it’ll slow down your metabolism”?

    My mum, who once had a fairly high blood glucose level, told me about how people would “magically” cure themselves of diabetes by fasting and drinking water. Thus she tried to ignore her tummy’s gnawing desire — her low insulin levels…and she couldn’t sustain it.

    Just as I thought.