Intermittent Fasting: A Dietitian's Take on an Increasingly Popular Diet

A registered dietitian weighs in on the pros and cons of this unconventional eating strategy
Flickr/diekatrin CC by SA 2.0

Although it goes against a great majority of the most common dietary advice, in some circles, intermittent fasting (IF) is becoming an increasingly popular eating strategy.

How it works is essentially how it sounds: you fast intermittently throughout the day, eating a few large meals during what’s referred to as the “feeding period,” and fasting for the rest of the time.

There are several different ways to apply IF, but the most common method, which was popularized by Martin Berkhan on his website Lean Gains, follows a daily cycle that calls for 16 hours of fasting followed by an 8-hour feeding period. 

For example, this could mean fasting from 8 p.m. to 12 p.m. the following day, and then eating all of your meals during the day’s remaining eight hours.

Essentially, it’s less about reducing your calorie intake and more about optimizing the timing of your meals. The idea is to maintain a “fasted state,” which supposedly encourages the body to use stored fat as an energy source rather than the glucose from a recently consumed meal.

The research behind this method of dieting is still in its early stages, some studies have shown that it may be an effective way to improve both health and fitness. And from those who have successfully implemented IF into their daily routines, there’s a good deal of anecdotal evidence to support it as an effective fat loss tool.

But what does a dietitian think about this highly untraditionally diet strategy?

Dr. Caroline Cederquist MD, creator of bistroMD and author of “The MD Factor Diet,” doesn’t claim to be an expert on the topic, but says she’s known about it for years and has been particularly intrigued because a physician and neurologist she respects, Dr. David Perlmutter, recommends IF for its ability to increase substances that are beneficial to the brain.

Still, though, from her perspective, it may not be the best method for some.

“There are many, many variations on [IF] out there, some of which recommend restricting eating to one meal per day,” Cederquist said. “However, I recall research from almost 20 years ago when I started my practice, showing that eating one large meal a day was the best way for the body to gain weight. In addition, during the fasting state, the body is breaking down our muscle tissues to meet our daily requirements for protein. This causes us to lose muscle.”

However, there are several reported benefits associated with IF, including weight loss, reduced insulin levels and decreased cravings for sugar. In fact, there are a few studies that support its effectiveness as a method for weight loss and several others suggest that it may help reduce the risk for cardiovascular disease and cancer and improve insulin resistance.

On the other hand, as Cederquist points out, many of these effects can also be achieved with a balanced, lower calorie diet.

“Following a lower calorie diet with the regular intake of lean protein and controlled amounts of carbohydrates and fats, as I recommend in my practice, allows for the lowering of insulin levels and decreased cravings of sugars and starches, all while leaving our muscle tissue intact,” Cederquist said.

While most IF proponents recommend following a nutritious, whole foods diet during the “feeding periods,” others, as Cederquist pointed out, sometimes call for “free for all” days where no foods are off limits, essentially encouraging IF followers to indulge in more decadent, less nutritious foods while they “feed.”

“I think this pattern of restricting and then overdoing it negates any possible health benefits that may occur with intermittent fasting,” Cederquist explained. “I find this eating pattern present in many of the patients I see in my practice. They will restrict and binge and end up overweight and demoralized.”

By following a pattern of more regularly scheduled meals and snacks, Cederquist says her patients can lose weight successfully and, more importantly, sustain that weight loss in the long-term.  

Ultimately, when it comes down to choosing a strategy that can help you eat more healthfully, it’s important to consider your personal preferences, as well as advice from your doctor and/or a nutrition professional.

There’s some scientific evidence to support the benefits of IF, but for some people (especially those who might have a hard time  getting used to such a dramatic change in their eating habits or those with medical conditions that effect insulin levels) it may not be the most suitable method.   

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