Nutritionist: Is intermittent fasting the magic diet pill?

Popular bloggers, podcast nutritional stars, and fitness gurus have recently all endorsed their support of intermittent fasting. Intermittent fasting (IF) is an age-old practice of restricting food for specific periods of time. New age supporters urge that IF increases lifespan, reduces risk of disease, improves immune system, and cuts cancer potential. Popular health gurus have been known to get caught on fad concepts before the evidence based methods have been developed. Is this the case for IF?

The majority of scientific evidence supporting IF have come from animal (mostly mice) studies. These report positive impacts on insulin control, weight management, nervous system, and lifespan. Human studies, conducted on very small scales and with shady methodology, have shown potential benefits for asthma, blood pressure, Alzheimer’s, Parkinson’s, diabetes, and inflammatory markers.

A meta-analysis, published by Horne et al. (2015), found only 3 randomized controlled trials reviewing IF in humans. All 3 models found individuals who practiced regular IF showed reduction in body fat, triglycerides, LDL cholesterol, and C-reactive protein (inflammatory marker). Only 2 models showed the further ability to reduce risk for diabetes and increased human growth hormone.

Let’s take a step back for a second

To analyze how IF works, one must look at a theory for different states of the human body: fed versus fasted. In a typical fed state, the body has consumed enough macronutrients to begin the digestion process. During the four to five hours after eating, insulin is increased to signal absorption and/or storage of nutrients. It is very difficult to burn fat during a fed state. A fasting state generally occurs eight to 12 hours after eating. The body’s insulin level is low enough to transfer energy production from carbohydrates to fat stores. Thus, in the fasting mode the body will, in theory, be burning fat.

With this theory explained, is IF just another way of reaching a caloric deficit? Or, in other words, is it the same as starving yourself skinny? The answer is yes. Not eating for 16 hours out of the 24-hour day, or not eating for 24 hours of a 48-hour period is a strategical way to reduce input. Reducing input will hopefully reduce the waist line. Benefits from losing weight have been well documents for decades. Thus, most of the benefits from IF could actually come from fat loss.

Nonetheless, losing weight is a good thing in a person who has a few pounds to shed. If you do not have time to prep and eat 3 to 6 small, square meals in a day, IF could be your answer. The cautionary tone is coming here: There are no large scale, well-designed studies for long term effects of IF. Thus, until better evidence is out there, the ability as healthcare professional to recommend IF is limited. But, definitely worth experimenting more!


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