As many of you have noticed, I am periodically implementing Intermittent Fasting into my dietary regiment. This is a controversial diet method, so I expect to get lots of feedback. I thought it might be easier to post some general points about Intermittent Fasting, as well as some great links to read more, in one central place. I encourage you to read up on the subject and offer your feedback. My studies have intrigued me, and I am sure many of you will be intrigued too.
First of all, what is intermittent fasting? Intermittent fasting is basically alternating periods of eating and periods of fasting. Some of the most common forms of intermittent fasting include Alternate Day Fasting (ADF) (see description here), The Warrior Diet, LeanGains, Fast-5, Every Other Day Diet, Banta Diet or Eat Stop Eat. There is even a version called Paleo Fasting.(I am not endorsing any of these diets, just showing the options.) Most intermittent fasting programs have you do a water only fast for a certain number of hours a day, and then eat pretty much whatever you want the remaining hours. An example of this is Fast-5, which has you fast 19 hours a day and eat for 5. Other fasting programs have you fast for a certain number of days a week. This could be every other day or maybe even just a day or two.
One of the strongest arguments against intermittent fasting is that it will slow down your metabolism. For short-term fasts this is simply not the case. Alot of scientific references are given at A to Z Diet Reviews. Fitness Spotlight also covers this very well in their article Eating More Meals Does NOT Speed Up Your Metabolism. I suggest you read both of these pages, especially the second one, to better understand this. You can also read an article of someone who has changed their opinion on this in the article Eating and Metabolism Revisited.
If you are like me, you kind of understood what intermittent fasting was, but you would like to know if it is really a healthy dietary choice. Fortunately, there are several studies out there that indicate it is indeed a healthy diet. The following are some of the more intriguing bits of information about intermittent fasting:
The following quotes come from an article titled, “Running on Empty, The Pros and Cons of Fasting“. This was published in the Los Angeles Times.
According to Mark P. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging: “In normal health subjects, moderate fasting — maybe one day a week or cutting back on calories a couple of days a week — will have health benefits for most anybody.”
Dr. Marc Hellerstein, a professor of endocrinology, metabolism and nutrition at UC Berkeley, who studies fasting states, “We’re brilliant at this (referring to humans’ physical reaction to not eating). We’re not good at responding to too many calories, but we’re very good at responding to fasting. Fasting, in itself, is not an unhealthy process.”
Among 448 people surveyed, intermittent fasting was associated with more than a 40% reduction in heart disease risk. Fasting was also linked to a lower incidence of diabetes. The study was published in October in the American Journal of Cardiology.
According to a PNAS study on Intermittent Fasting, “The only environmental variable that has been shown to markedly affect the rate of aging in a wide range of species is caloric intake”.
While the study targets Asthma patients, there are some interesting results in this 2006 study on Alternate Day Calorie Restriction.
Another great study to read is at the American Journal of Clinical Nutrition. It is titled, “Alternate-day Fasting and Chronic Disease Prevention: A Review of Human and Animal Trials“. The one thing this study really points out is that the human evidence is sparse at best. Unfortunately, most of the studies have been performed on animals; however, there are some promising conclusions that have come out of some of the human studies. When you read the results of the human studies which do not seem to support the positive conclusions for humans, keep in mind the variables of the study, which are disclosed.
This study at PNAS compares the differences in Intermittent Fasting and Calorie Restriction (which has more supporting evidence).
While just an abstract, this study on The Effects of Intermittent Fasting and Calorie Restriction on Cardiovascular and Cerebrovascular Systems is interesting.
You might be interested in listening to an online NPR show on Intermittent Fasting which points out many of the benefits.
Michael R. Eades (of Protein Power) has some interesting things to say about Intermittent Fasting and Protein Power.
In November 2009, the American Journal of Clinical Nutrition did a study on alternate day fasting. What did they find? After just eight weeks, participants had lost an average of 12 pounds, their total cholesterol dropped 21%, their LDL cholesterol dropped 25%, and their blood pressure dropped five points. Pretty impressive.
This is really just barely scratching the surface. There are many, many resources about intermittent fasting out there, just head to your favorite search engine and check it out. I will also update this page as I run across other interesting studies or other information.
With all this being said, how am I implementing intermittent fasting in my dietary regiment? At this time I am choosing to follow my chosen diet, the South Beach Diet, any time I am eating. Two or three days a week I choose to fast. I either do a full day without eating, which ends up being about 36 hours, or I go from supper to supper without eating, which is about 24 hours. I think there are benefits of eating low-glycemic foods as part of a fast. Foods that are cause your blood sugar to spike (high-glycemic) tend to cause you to have feelings of hunger. As a result, I think these are best to avoid.