COVID-19 Updates: Learn how to schedule COVID-19 vaccine appointments, find information on testing, visitor policy and more.
Wellness & CareDiet & Nutrition › Intermittent Fasting: The Next Fad Diet? Maybe Not! by Julianne Dunne, MD
February 8, 2018

Intermittent Fasting: The Next Fad Diet? Maybe Not! by Julianne Dunne, MD

Intermittent Fasting:  The Next Fad Diet? Maybe Not!   by Julianne Dunne, MD

If you keep up with the next big thing in diet and health, then perhaps you have heard about intermittent fasting. And perhaps you quickly dismissed it as crazy, unhealthy, or something you would or could never do. Fasting is nothing new. It has been around for centuries. It is part of many religions and cultures. Many of us are advised to fast before a surgery or medical procedure. And no one has been worse for the wear by skipping a meal or two.


Fasting is different from starvation. Therapeutic fasting involves control. It is something you do with purpose. Fasting for health is not a dry fast. In fact, it is imperative to drink water during the waking hours of fasting. Black coffee and tea, even bone broth, can be incorporated, as well.


Jason Fung, MD, who wrote “The Complete Guide to Fasting”, compares fasting to the show “Seinfeld”. All of you familiar with the 1990’s comedy series recall it was a “show about nothing”. Fasting is the diet of nothing. There’s nothing to do. You don’t have to shop. You don’t have to food prep. It doesn’t matter if you have food allergies or sensitivities. It doesn’t take any time. AND it doesn’t cost anything!


It makes sense that eating nothing could lead to weight loss, but you might be thinking “how can eating nothing be healthy”? Well, it’s all about insulin. Insulin is a hormone secreted by our bodies when we eat, especially when we eat carbohydrates and even protein in excess amounts. Insulin is associated with hunger and cravings, plus it works like a growth factor. People who cannot make their own insulin are referred to as Type I diabetics. And those who eat excessive amounts of sugar over time may develop insulin resistance. Insulin resistance occurs when the body simply stops responding to the persistent requests to produce more insulin, and this may lead to Type 2 diabetes. Women with diabetes during pregnancy are known to have large babies due to the growth factor effect of insulin.


Insulin’s job is to take the glucose out of our bloodstream and store the unused amounts. The short-term storage form is glycogen which is stored in our liver, but it is limited to about 24 hours’ worth of energy. Any additional glucose is then stored as fat that is long-term and essentially limitless storage. Basically, when we eat, our insulin levels are elevated and we are storing fat. When we don’t eat (or fast), our insulin levels are low, and we can then burn our stored fat for energy.


When we eat, our insulin levels are elevated. Over the years, we have extended that “eating window” for more hours of the day. This leads to hunger, cravings and makes us bigger. Back in the 1950’s, people ate three meals between 7 a.m. and 7 p.m. (a 12-hour eating window and 12-hour fast) plus there was no snacking. Now we eat three meals and three snacks from when we wake until we go to bed. We have extended our eating window each day to 16 hours or more, leaving only the seven-to-eight hours we sleep for fasting.


What are the benefits of fasting?  

In addition to weight loss, fasting has numerous health benefits. Fasting is the most efficient way to lower insulin levels which will STOP insulin resistance. In turn, this will reverse or prevent diabetes as well as heart disease, stroke, dementia and even cancer. With fasting, blood sugar and insulin levels decrease as the body switches from sugar burning to fat burning. This increases metabolism, decreases hunger and provides an almost unlimited source of energy. Fasting has been shown to decrease inflammation, improve the immune system and prolong life. Furthermore, studies of prolonged fasting have found NO evidence of electrolyte imbalances.


  • Fasting is not for everyone. Fasting is NOT recommended for pregnant or nursing women, children under the age of 18, and anyone who is malnourished or underweight. And if you are taking medications, particularly for diabetes, you should check with your doctor first.


What are the different regimens for fasting?


If you decide to undertake a fasting regimen, pick one that fits your lifestyle. Keep in mind the food that you choose during your eating window will affect how hungry you may be during your fasting hours, at least initially. Choose healthy fats and protein and fewer carbohydrates as this will keep your insulin levels lower and control your hunger. Also remember that eating is often “routine”. We eat because it is time to eat and not necessarily because we are hungry. Therapeutic fasting is about incorporating a new routine. There are three basic protocols for intermittent fasting: time-restricted feeding, alternate-day fasting and extended fasting.


  • Time-Restricted Feeding refers to short daily fasts. Fasting was a hot topic at Obesity Week this past year in Washington, D.C. Data presented on time-restricted feeding revealed that participants restricted to an eight-hour eating window (10 a.m. – 6 p.m.) lost 2.6 percent of their body weight over three months. They were NOT advised on what foods to eat just when to eat. They naturally ate 350 calories less per day by limiting their eating window. Another study compared resistance-trained men (athletes who regularly lift weights) eating the same total calories consumed in an eight-hour versus 12-hour eating window over eight weeks. Those assigned to the eight-hour eating window had a decrease in their total fat mass while maintaining muscle mass. Their LDL (bad) cholesterol and triglyceride levels decreased as well.


Longer intermittent fasting regimens include a 24-hour fast (eating one meal each day 24 hours apart) or a 36-hour fast (eating dinner on Day One then skip all meals on Day Two, and not eat again until breakfast on Day 3). These are more powerful as you have used up all your glycogen (short-term energy storage) and then your body converts to burning your stored fat. These longer fasting regimens have also shown to improve all cholesterol levels and improve blood sugar and insulin values.


  • Alternate-Day Fasting alternates a day of fasting (either a 0-calorie water fast or a 500-calorie meal plan) with a regular day of eating. You might be concerned you will overeat the day after your fast, and you are correct. However, studies have shown that most people only overeat by about 500 calories. If your normal regimen is 2,000 calories per day, the post-fasting day typically averages at about 2,500 calories. Thus, the total calories consumed over the two-day period is much less. Some people follow a regimen of fasting two days out of the seven-day week. This is referred to as a 5:2 diet.


  • Extended Fasting. This is the big leagues and definitely not a place to start. This refers to fasts longer than 42 hours. Extended fasting has been used in many cultures for centuries and has been studied in medical literature over the past century. During extended fasting, the brain stops using glucose for energy and switches to the use of ketones from fat burning.




An easy way to get started is to pick a 12-hour window, such as 7 a.m. to 7 p.m. to consume all your meals. Then simply don’t eat between 7 p.m. and 7 a.m.  Please drink water, black coffee or tea during your waking fasting hours. When you master that, shorten your eating window to 10 or even eight hours each day, and watch the magic happen.


IMPORTANT: Those interested in the alternate day and extended-fasting regimens (versus the time-restricted feeding regimen) should check with their providers before starting.


–By Julianne Dunne, MD