Recently, I have had several of my clients and patients ask me about "Intermittent Fasting". It seems to be popular in many dieting circles. Hopefully, this blog post can answer some of you questions as well.
Intermittent fasting is one of the hottest topics among avid dieters at the "moment". Intermittent fasting has been around for centuries, primarily practiced in various religions. It wasn't until the early 1900's that some health benefits were observed among diabetic, obese, and epileptic patients (see previous post on Ketogenic Diets). Basically, intermittent fasting is a large term that encompasses an eating behavior where an individual eats very little on some days followed by "cheat" or "feast" days or very liberalized eating. The question that I get the most is "Does this work?", meaning will I lose weight with this type of eating pattern.
As with all such questions, I like to examine the scientific literature on the subject. A study published this May in the Journal of the American Medical Association: Internal Medicine examined if intermittent fasting was actually more effective in achieving weight loss than the traditional method of daily calorie restriction.
Here is the recap:
100 study participants (86 women and 14 men) that were classified as obese (but without metabolic complications like Type 2 Diabetes or metabolic syndrome) were separated into 3 groups: those that were put on an "alternate day fast", (meaning that the participants rotated a day on and off of the fast and the feast days), those that followed a daily calorie restricted diet, and those that received no intervention (the followed their 'normal' diet). The study lasted for a year and was divided into two 6 month phases. The first phase emphasized weight loss while the second 6 months emphasized weight maintenance. It is worth noting that the lead author of the study write a book advocating intermittent fasting.
Both the alternate fasting and the calorie restricted groups lost similar amounts of weight (6 % and 5.3% weight loss respectively). There was slightly more dropouts in the alternate day fasting group than the calorie restricted group (13 versus 10 dropouts respectively). The dropout rate is an important factor to consider, as it may be indicative that a plan was difficult to follow or simple produced poor adherence.
In the study, intermittent dieting was defined as consuming 25% of caloric needs on fasting days and 125% of calories on "feast" days. The calorie restriction meant that the participants were allowed to consume 75% of estimated energy/calorie needs. Mathematically, both groups consumed on average of 75% of estimated energy needs (meaning they ate 25% less calories than needed daily).
Although the weight loss percentages were very similar, the alternate day diet group had a increase in LDL cholesterol (the bad cholesterol) that the daily caloric restricted die group did not. This may be indicative that it may not be the best choice for individuals at elevated risk for cardiovascular disease (increased LDL is a risk factor for the development of heart disease). Remember, heart disease is the number one killer in America. On in three Americans will die as a result of cardiovascular related conditions.
Other reasons that are concerning to me about the intermittent fasting group is the lack of behavioral change it requires. In my practice, I have found that many of my clients have unhealthy relationships with food including general overeating with periods of starvation and binge eating. I think that the intermittent day fasting may actually enhance these negative interactions with food and does nothing to help change those behaviors. Although the data suggests both groups had similar weight outcomes, having a healthy relationship with food psychologically is just as important.
Principles of moderation, including portion control, are important in developing healthy eating habits. I think this can be best supported with consistent behavior as opposed to being on a varying daily calorie levels.
In addition, the sample size of 100 people is also small and more research should be conducted before coming to any "scientific" conclusion. However, as a registered dietitian with over 20 years of experience, I would strongly caution in applying any one study with limited participants into one's own lifestyle.
The bottom line: Don't look for an easy fix-it is simply not there. Weight management is a highly complex problem that must be addressed in a multifaceted manner by trained professionals in obesity management and nutrition. Enjoy food in moderation and practice calorie control, while enjoying a healthy dose of exercise. Stay healthy and EAT RIGHT!
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