Intermittent Fasting: how to do it, the science, and more

You’ve likely heard of the term “Intermittent Fasting” or “IF”. You might be thinking, “Where did this fasting talk come from?” “Is it another fad?” Well, here’s the short answer. It’s no fad. You’ll continue to hear about fasting and after learning the science, you’ll likely want to try it yourself.

Fasting has been around for a long time . Let’s visually time travel back to the 1970’s. There was breakfast, lunch and dinner. No snacks. Kids didn’t need a snack before being active and after dinner was served, food was done for the day. Now, let’s look at what’s happening today. We eat breakfast, get a mid-morning snack, eat lunch, get an afternoon snack, eat dinner and finish with an evening snack. We are eating all day long.

The NHANES survey results confirm this trend (1-2). We went from eating 3 meals/day to 6 meals/day. We’ve doubled the number of times we eat and simultaneously, increased the rate of obesity and chronic disease development. Yes, the types of foods we eat factor in as well,  but timing of eating cannot be overlooked. (Let’s be honest, most people are not snacking on broccoli or wild-caught salmon!) Snacks tend to be quick, processed and high in sugar.


So what is Intermittent Fasting (IF)?

Intermittent fasting is a way of eating. There are a variety of ways to practice IF and you can see examples below. Simply put, it’s a method of eating in which food is only consumed during certain hours of the day. The rest of the day, meaning a 24-hour period, there is no calorie consumption. The fasting period starts after the last calorie intake in the evening and ends upon calorie consumption the next day.


Some examples of intermittent fasting

For a 16-hour fast and 8-hour eating window or what’s often referred to as the 16:8 protocol (the most common form of IF), the day could look like this: First meal at 10 am and last meal at 6 pm. That eating window equal 8 hours which means the rest of the day is 16 hours of fasting. That same window could start at 8 am and end at 4 pm or start at noon and end at 8pm. The exact hours are flexible though it’s encouraged not to eat too late in the evening as it can disrupt the circadian rhythm or the sleep and wake cycle.

For a 14 hour fast and 10 hour eating window, the day could look like this: First meal at 8 am and last meal at 6 pm or first meal at 9 am and last meal at 7 pm. The times can be shifted.

For a 12 hour fast and 12 hour eating window, the day could look like this: First meal at 7 am and last meal at 7 pm. Again, the hours could shift per the individual’s preferences

Another form of IF is a 24 hour fast though most people practice the other versions of fasting before embarking on the longer hour fas


The science behind IF

The word “fasting” can seem scary to many people because we’ve been taught that if we don’t eat for hours, we enter “starvation mode.” This is an unfortunate myth. During a “fed” state, the body is using and storing the energy from food. That food could be carbs, protein or fat—doesn’t matter, it’s using it or storing it. During a fasted state (like sleep) the body will use some of that stored energy. Nobody is “starving” overnight because the body has mechanisms to use glucose, stored glycogen or fatty acids as fuel. Starving is when an individual has no access to food. Fasting is different due to the fact that food is available, if desired. A fast can be broken at any time.

If the body has available glucose or stored glucose (known as glycogen), it will not starve. Once it has used up the stored glycogen, it will begin to use fatty acids from body fat.

How IF aids in Type 2 Diabetes (T2DM)

Most therapies for T2DM include targeted drugs or diets to reduce glucose levels, they don’t focus on insulin or the hyperinsulinemia that often coincides with T2DM. Nor do they focus on the inflammation component of the disease. Unfortunately, most dietary recommendations for T2DM include 6 meals per day with 30-75 grams of carbohydrates per meal. That’s a lot of carb and that recommendation is keeping insulin elevated all day long. It’s doing the opposite of what we want. According to experts like Dr. Jason Fung, treatments that lead to decreasing insulin like fasting and low carb diets should be implemented for reversing obesity and T2DM (3). Additionally, inflammation should be targeted as it plays a role in underlying causes for T2DM and research has shown that fasting can reduce inflammation markers (3-6). Fasting protocols address both of things. It reduces insulin levels and inflammation (5-7).

The process of fasting can seem intimidating at first. But, after reviewing the science behind it and understanding that you can ease into it with different eating and fasting window, it many people become excited to delve in. If you decide to try intermittent fasting yourself, some initial tips are to ease with a large eating window (perhaps the 12 or 10-hour example), reduce your carbohydrate intake at other meals to reduce the glucose spikes and hunger hormone triggers and think of this as an experiment! There’s really no way to mess up a trial of intermittent fasting!

Fung, Jason. The Obesity Code: Unlocking the Secrets of of Weight Loss. Greystone Books. 2016.


Additional fasting research:

Fung, Jason; Moore, Jimmy. The Complete Guide to Fasting: Heal your body through intermittend, alternate day and extended fasting. Victory Belt Publishing, Inc. Oct. 2016