Before I answer that question, I want to admit from the beginning that talking about fasting elicits a not so rational response in me (i.e. makes me wince). One of the reasons is, as have mentioned before, I grew up religious, and though fasting was not a requirement, it was often highly encouraged during times of crisis (aka "imploring God to change His mind), as a way of controlling "impure" thoughts (aka "if you fast you won't think about sex as much"), or even as a way of showing solidarity with the poor (In college we would have specified meals where we would donate the cost of that meal from our meal plan to a local cause. I don't have a problem with the concept, but most of us ate elsewhere and didn't experience hunger). The second reason is that as a female student in her late teen's/early 20's during the 1990's I was exposed to my fair share of people starving themselves to excessive thinness, a condition know as anorexia nervosa (Hat tip to those who work with people with this problem, it is not my cup of tea). The third reason is the link between poverty and obesity, a situation fueled by the availability of high caloric food that doesn't actually provide any nutrition (Link), and it reminds me of quote attributed to Eusebius Sophronius Hieronymus (aka St. Jerome, yeah I studied my church history) that states "When the stomach is full, it is easy to talk of fasting."
OK, now that's over with. Deep breath.
So you are wondering about Intermittent Fasting, are you? Possibly because of the publication of the The Fast Diet and a similar book called The 2 Day Diet? Or maybe you have heard about one of the variations where you consume 20% of your usual caloric intake on fasting days or just don't eat in between meals? Or cutting down to 2 meals per day? Is there any benefit to all of this when it comes to shedding extra pounds?
Well, maybe. I have already written two somewhat related posts, a few weeks ago I talked about how it might benefit some people to skip breakfast and how the advice about eating six smaller meals a day is more fallacy than fact. Basically the concept of intermittent fasting is another technique to get people to 1) eat less (Thank you, Captain Obvious) and 2) not have readily available sources of energy so their body will be forced to draw from the stores (sounds good). And I am putting the emphasis on technique here, because even though we all know that weight loss comes from reducing your intake of calories, and for those with insulin resistant related problems you need to make sure that you reduce your level of carbohydrate, all the while making sure you get enough protein, fat, etc; how you actually get there is easier said than done. (Remember the quote from St. Jerome?) A weight loss plan and weight-gain prevention plan are only as good as they are sustainable, and for some people the thought of cutting out certain things for the foreseeable future seems impossible, so the idea of varying "moderate" eating with "restrictive" eating sounds more doable.
As far as the research is concerned, the human studies are small but positive looking when it comes to helping people lose weight and reduce lipids, improve insulin resistance, etc (One here and another here). Now, intermittent fasting has also been touted as a way to live longer (particularly if you are a lab rat), but when it comes to studies done in primates, it looks like diet quality and your genetics have the upper hand there.
So should you practice intermittent fasting to lose weight? I am going to point you back to this post and this post where I basically discuss the caveats. I will add that apparently people who have trouble with blood glucose regulation do not do well with this, and men and post-menopausal women tend to fare better than women in their reproductive years. And this will still require some pre-planning and discipline. If you know that your co-workers always bring the doughnuts on Tuesday mornings, then maybe that is not the best day to do this. If your co-workers bring in snacks every single day, then you might have to avoid certain areas of the workplace. If you live with another person/other people, you will have to have a frank discussion about the support you can expect from them. This might be an "easier than" technique for you to reduce your intake/help your body use up reserves, but it still requires effort.
1) Yes, I know, some people do have to cut out certain foods for the foreseeable future when they have allergies or huge increases in blood glucose after eating them.
2) Some people have adopted a particular diet that severely limits certain foods groups and still find it sustainable (congratulations, you have worked hard to do so). That doesn't mean everyone can or will.
3) Make sure that your fasting days are based on healthy protein/fat and vegetables. Getting all your calories from junk food will be more likely to keep you feeling miserable and hungrier sooner.
Take home message--Intermittent fasting could be a useful technique for loosing weight but it still requires planning.