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. Pamela

    I’ve just heard about a different intermittent fasting diet that will be out soon where you don’t have to count calories. It’s called The 2-Day Diet. Has anyone else heard about it? Is anyone thinking of trying it?

  2. Kimberley

    I recently started the 5:2 IF diet but wondered if I need to adjust my caloric intake to account for exercise. I cycle-commute for work and this accounts for 300 calories a day. I am supposed to eat 500 calories on fast days – should I aim for 500 intake total, or 500 overall taking exercise into account?

    • Ted

      Fasting days they would recommend no exercise, but if you do, add those calories for a total of 800 calories for that day.

  3. Melinda

    I forgot to add that with my husband and I both IF we save $200 a month on groceries!

  4. Melinda

    I started the fast-5 (like the 20/4) June 30th and have lost 22lbs. I have loads of energy and I crave healthy foods! People around me think the whole thing is crazy. Maybe everyone is different but my metabolism thrives on IF. When I ate 3 squares a day I was bloaty sluggish and pre diabetic(not to mention 22lbs heavier). I won’t say I’m never hungry. When I come down with a cold or the week before my period I do get some cravings but nothing that cant be shrugged off. Today’s dietitians are anti IF because it is a free, effective, healthy way to live and industries like Jenny Craig lose out big time! Those places are a huge industry in the states. If you are struggling with every diet out there, are not diabetic, hate, HATE counting points calories, and want to still eat the foods you love, IF is for you! Get through the first 3 weeks of it and you will swear by it.

  5. Ann

    I think that IF is a very, very logical and practical approach to fuel intake. Do we REALLY need to be eating 3-6 times a day?? Do we REALLY need to be so engrossed with our intake that it dominates our thoughts and lives? It is just one part of living! I love this concept and approach and feel that when a person is “ready” to accept certain realities about what is actually needed vs. what we’re told and bombarded with, I think this is a very simple change anyone can make. I am in my mid-30’s and I am obese (in process of losing weight and getting healthier). I’ve taken the mainstream approach- the long term slow steady weight loss by eating small meals throughout the day, exercising 5 days a week – this is all well and good, there’s nothing really wrong with it. You build good habits. But I can’t help but think – there’s got to be a simpler, more realistic way than this redundant, tedious set of rules and activities. I don’t want to consume my entire day thinking about food and exercise. IF is really basic and simple. You can’t go wrong going back to the basics. I can live, eat when I NEED to and get plenty of activity just living life and taking care of my family, playing with my daughter. I still do my weights and my treadmill, but I don’t have to dwell on it and force myself to stay on track with all the scheduled nonsense. I can put my thoughts into more important areas. When I want to eat I just ask myself a couple of questions: am I really in need of intake?? and have I allowed at least 15 (or more) hours inbetween intake sessions to allow my body to rest, heal and do the other things it needs to do? IF is pretty awesome.

  6. Robin

    I was anorexic many years ago. IF with the conscious intention to care for myself can’t be compared to that experience. However, I do believe that part of the subconscious anorexic instinct was actually a good one. Something felt right when I did not eat. Of course I had emotional problems as well, and it all got confused and screwed up, but still a part of me knew that not eating for periods of time was strengthening in some way. I was reacting to a culture that said I needed to eat all the time, yet I had to be skinny and sexy too. It didn’t make sense, and it all felt like a trap. Most emotional problems have some element of wisdom and healing instinct at their core. They just get lost in the translation.

    I’m sure some people will find these comments offensive, but as someone who was severely anorexic and also bulimic for ten years and got through it on my own, I feel I have the right to speak candidly on the subject. IF does not bring back eating disorder tendencies at all in me.

  7. RobinH

    I think it makes sense that we usually didn’t eat heavily more than once a day, on average, but I also think we probably ate a few berries or leaves, maybe some insects, in between these meals. The natural world is full of tiny healthy snacks, except for in winter. That’s why i prefer the Warrior Diet over straight IF. It allows for small amount of healthy snacks (mostly raw fruit and vegetables) during the day. This style of eating is done every day, not twice a week. I’ve been doing it for 4 months and love it. It’s close to fasting but not quite. I usually have some coffee with a touch of cream in the morning, an apple in the afternoon, and if I’m really hungry another small service of fruit or veggie. Then dinner at 6 or 7. I can’t imagine eating concentrated foods during the day anymore. It just doesn’t feel right. Even though I’m ingesting only a hundred calories or so during the day, it is much easier for me than total fasting.

  8. Steve in Denver

    How has caloric restriction proven to be ineffective? Study after study continues to prove that it extends life in nearly every living crature on earth. The only way it’s ineffective is that it takes phenomenal willpower to follow such a regime.

  9. David Nyman

    Well, I’ve done it for 10 years, on a roughly 20/4 daily schedule, and it’s been very effective both for initial weight loss, and long-term maintenance. I work out pretty much daily – on rising (i.e. well before I break my fast in the evening) – and often hike, bike, or ski on more or less the same schedule. Not only does this present no problems but it almost always delivers enhanced strength, energy and alertness. I maintain low body fat (about 8%) and perfectly adequate muscle mass at 163 lbs for 5′ 10″. If a 42 resting heart rate (185 max) and low-normal BP are any evidence, this doesn’t result in any undue physiological stress. By the way, I’m nearly 60, so no spring chicken.

    As far as appetite for food is concerned, I simply don’t think about it for most of the time, and then set to with relish in my “window”. After initial adaptation and weight adjustment, this has resulted in neither anorexia nor bingeing. I think the word “adaptation” is key here, and is rarely emphasised enough either in general discussions or research. My own approach was that I eventually found my way to this state of affairs through gradually eating more lightly during the day, and breaking my fast later. I was guided only by my desire to control calories, and the inescapable fact that I was steadily becoming more alert and far more stable in my energy levels than before. At no time did I ever starve myself or suffer from anything approaching hunger pangs. Whereas this is “an experiment of one”, there are many more long-termers out there with similar stoties to tell.