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The Skinny About Intermittent Fasting

John Bankston John Bankston April 1, 2021
Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

Intermittent fasting is all over social media and mainstream media but that doesn’t make it a fad. In the 1980s, inspired by Urban Cowboy, people across the United States and much of the world donned big hats and danced to country music. The next decade, just as many sported plaid shirts while screaming to songs with indecipherable lyrics when grunge became the style of the moment. Yet you can still find cowboy hats, country music, and bars with mechanical bulls across the South and Southwest. Plenty of Pacific Northwest residents dress and enjoy music that seems transported intact from the 1990s. That’s because their lifestyles existed long before outsiders adopted them and endured long after the “fad” faded.


Intermittent fasting is practiced by billions. Jews, Christians, Muslims, Hindi, Buddhists and innumerable others use fasting as part of a religious observance. Fasting has long been used by nonreligious groups for health reasons, while in the U.S. Native American tribes fasted prior to vision quests. Human beings evolved with a feast-and-fast metabolism. Intermittent fasting addresses that. So what exactly is intermittent fasting, what are the best ways to get started, and most importantly––does it work?


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Intermittent Fasting - Overview

Intermittent Fasting - Overview

Going from Feast to Fast


Back when humans hunted and gathered, intermittent fasting was routine. People couldn’t count on regular meals. As they stalked their prey, their bodies consumed the stored energy of fat. They enjoyed the release of hormones which quieted hunger pangs and anxiety. Modern researchers tried to link the current obesity epidemic to the so-called thrifty gene. This suggests  that famines are selected for genes which promote efficient fat deposition. Although evidence (and logic) suggests heavier people would survive longer in famine conditions, studies show a predisposition to obesity isn’t a genetic survival method. Indeed, much of our current obesity is connected to modern eating and modern lifestyle. Our ancient ancestors actually gave us numerous genetic gifts that put most of us in control of our weight.


Although farming offered more reliable food sources, “three squares” a day is a modern invention. Warnings about the dire risks of skipping breakfast may sound scientific, but they began as a way to increase cereal sales. Romans actually ate one meal a day––usually around noon. What’s great about the 16/8 intermittent fasting method is that it doesn’t implicitly eliminate breakfast or reduce the number of meals you eat.  Also known as the Leangains Protocol, after the developer and promoter of this eating style, it is by far the simplest fast.


Just eat for eight hours, then don’t eat for 16. Water, coffee, and other non-caloric beverages should be consumed during the fast. Individuals on a traditional work schedule generally stop eating around 9 pm and don’t resume eating until early afternoon. This is one reason people who adopt the 16/8 method of intermittent fasting often report significant weight loss. These fasters quickly shift from three meals to two, with perhaps a healthy snack after the last one. Assuming the two meals aren’t twice as large as before, intermittent fasters who use the 16/8 method often cut one-third of the calories from their diet. 

Take the Fast Slowly


Studies consistently support the benefits of this type of fast. In one, males who used resistance training like weights and adopted the 16/8 method were examined after eight weeks. Compared to the control group, they had a decrease in fat while maintaining muscle mass. This is significant. Weight lost by dieters can be as much as 25% muscle. Even if you already fall within a healthy Body Mass Index, there are other reasons to consider intermittent fasting. Besides improving insulin sensitivity and reducing glucose spikes (that light headed feeling that many link to “skipping a meal”), there are studies suggesting that intermittent fasting or caloric restriction improves longevity and brain function


Although the 16/8 method is by far the most popular, it isn’t for everyone. Some prefer fasting completely for one or two days per week. Not eating from sunset to sunset is the most common way to fast for 24 hours. The 5:2 diet is when you restrict your calories to around 500 on two non-consecutive days of the week. Fasting isn’t trouble free. Women in particular have reported side effects including missed periods. In one study, men benefited while women had worse issues with blood sugar. Indeed, anyone with hypoglycemia or diabetes should only undertake this program under medical supervision. The same advice applies to anyone who has been treated for an eating disorder as fasting can be a trigger. 


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Intermittent Fasting - Science

Intermittent Fasting - Science

Many blood sugar issues are connected to consuming foods high in simple carbohydrates rather than fasting. So it is important that when you are eating, you are eating well. The same advice you’ve heard for years applies here. Eat plenty of lean protein, nuts, legumes, fruits, and vegetables. Avoid sugar, processed meals, and meats while reducing your intake of rice, pasta, and bread. Start your fast slowly. With the 16/8 plan the key is to start small. Try going 12 hours without eating and slowly increase the fasting time. It’s okay if you never hit 16––14-, 15-, even 12-hour fasts have been linked with weight loss and other health benefits. Total fasts should be approached cautiously. Make sure you are taking in plenty of fluids, and don’t start with anything longer than one day. 


The best diets aren’t diets in the “going-on-a-diet” sense. Those diets are often over in a week or a month––concluded as soon as the weight loss goal is achieved. Intermittent fasting is a lifestyle. It doesn’t work for everyone. Yet its advocates say it combines simplicity with fast results. 

Doctor Profile

John Bankston


John Bankston is a published author of over 150 nonfiction books for children and young adults including biographies of Jonas Salk, Gerhard Domak, and Frederick Banting.

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