Intermittent fasting, sometimes abbreviated IF and also called “time restricted eating” has been gaining in popularity in recent years. Used both as a method of dieting and to improve health and longevity, there are several ways to implement it in your life if you believe it is the right choice for you.

What is Intermittent Fasting?

Intermittent fasting is the conscious decision to eat at certain times and not eat at others. Basically, it is patterned eating, the opposite of “grazing.”

Drinking water is a MUST! I will explain the details of different styles of intermittent fasting below. But it is important to realized that fasting does not give you the freedom to eat whatever you want with abandon when you do eat. Nutrition and food quality are still the bigwigs of human health and longevity.

The History of Intermittent Fasting

Fasting has been part of the human condition since the beginning of time. Mostly because food just wasn’t always available.

Humans, like other animals, ate when they could find food and didn’t when they couldn’t.

In recent centuries fasting became part of many religions, but other than that it has fallen by the wayside as food has become available on every street corner in the western world.

However, the constant access to ever cheaper but less nourishing calories has come at a health price. We are fatter and sicker than ever.

And the more we diet, the fatter we end up and rates of metabolic diseases like diabetes, heart disease, high blood pressure and high cholesterol are skyrocketing. Our bodies could really use a break from the nearly non-stop processing of food.   

Why Intermittent Fasting is Good for You

When our bodies are processing food the pancreas releases insulin to move glucose (blood sugar) from the blood and into the cells where it can be used as energy. When there is insulin in the system your body is not burning fat because there is plenty of fuel in the form of glucose.

When you fast, all of your glucose gets used up and your body shifts to using glycogen (stored in the liver and muscle cells) for fuel and your insulin levels begin to drop.

After six to eight hours you run out of glycogen and your body must start burning fat (Don’t worry. That’s how it’s designed to work).

Not having insulin in the system and burning fat helps with insulin sensitivity. It also gives you body a chance to clean up cells that aren’t functioning at their peak level.

You can think of them as zombie cells. They are there, but they aren’t really doing their job. When your body isn’t focused on processing food, it gets a chance to notice, “Hmm this cell is not in good shape” or “This one didn’t replicate right” and it can dispose of them.

Just like your computer can only run a defrag to clean up the memory when you’re not working on it.

Plus, the calorie restriction that happens naturally with intermittent fasting and the resulting ideal body weight have been shown to increase longevity.

Will Intermittent Fasting Help with Weight Loss?

Yes. Intermittent Fasting has been shown to be as useful in creating weight loss as calorie restriction diets and many people find it to be much easier.

We have had clients report that it takes less willpower to say, “not yet” for a scheduled period of time than it does to say, “just a little” all of the time.

We have a client who has lost 60+ pounds using a version of 16/8 intermittent fasting (explained below).

The upside of intermittent fasting as compared to calorie restriction is that the fat to muscle ratio being lost is better. Typically, 25% of weight lost is muscle. However, with intermittent fasting that drops to 10%.

Will Intermittent Fasting Make Me Too Thin?

For those who struggle to eat enough to maintain a healthy weight, either due to an eating disorder or just not being “big eaters,” intermittent fasting is likely not an ideal choice. However, for the rest of us, using intermittent fasting does not seem to cause our bodies to get “too thin.”

It took us about six months of intermittent fasting while moving towards a whole-food plant-based lifestyle for us to reach our ideal weight. Since then, our weight has been stable within a few pounds.

With our active lifestyle, it could be assumed that if intermittent fasting was going to make someone too thin, it would be us. But that has not been the case at all.

Will I Binge Eat After My Fast?

It is unlikely that you will binge eat when you break your fast, assuming that you choose good quality, nutritious foods to break your fast.

If you eat highly processed foods loaded with fat, it’s going to be REALLY easy to eat to the point that you are miserable and take in way more calories that you need.

However, studies indicate that most people ingest about 10% more calories after a fast than they normally would. Which means that you’re 90% down from what your normal intake would have been had you not fasted.

Will Intermittent Fasting Ruin my Metabolism?

No. Your metabolism does not respond to fasting the same way it does to calorie restriction.

In calorie restriction there is a reduced amount of fuel available over a long period of time. During that time your body learns, “There is consistently only this amount of fuel available. We had better conserve our energy” and turns down your metabolism.

This can lead to the frustrating experience of a weight loss plateau, followed by gaining weight even though calorie intake is still low.

By contrast, intermittent fasting teaches your body that there are always plenty of calories available on average. They just aren’t available ALL the time.

So, your metabolism keeps humming right along, doing what your body is designed to do; burn fat when fasting (That’s how you stay alive through the night). In fact, your metabolism may go up a bit while fasting because your body thinks, “Hey! Get off your backside and go find some food!”

Will Intermittent Fasting Lead to an Eating Disorder?

No. An eating disorder is an emotional or psychological condition that manifests in the way a person engages with food.

Intermittent fasting will not CAUSE someone who does not have an eating disorder to suddenly have one. However, if someone has an eating disorder, intermittent fasting could be used as an excuse to engage in disordered eating.

I (Dr Robyn) have a history of disordered eating, having had anorexic tendencies in my early to mid-twenties.

When I decided to add intermittent fasting to my life, I was careful to pay attention to my thoughts about food, eating and my body. Fortunately, my emotional anxiety due to lack of control and having no say in my life have been resolved.

I have not experienced any desire, thoughts or internal pressure to engage in disordered eating in almost two decades. Intermittent fasting has not changed that (it has however helped bring back the body I remember and love).

If you engage or have engaged in disordered eating, please work with a professional to address the underlying factors prior to adding intermittent fasting to your lifestyle.

How Intermittent Fasting Helps Diabetes

Because intermittent fasting gives your body a break from insulin and reduces fat in the system it helps with insulin sensitivity. It also helps with diabetes as a mechanism of weight loss.

Dr McDougall talks about patients on the verge of amputation showing up at his program in wheel chairs and walking out after using a ten to thirty-day water fast and then following a whole-food plant-based diet.

Clearly fasting of this nature should only be done under the strict supervision of a doctor knowledgeable in both fasting and diabetes.

If you are taking diabetic medications, work closely with your doctor to monitor your medication needs. Adding fasting and/or moving toward a whole-food plant-based lifestyle can rapidly reduce your medication needs.

Can I Work Out While Intermittent Fasting?

Absolutely. When you first start fasting you might find that your body is a little “cranky” about working out, particularly if you typically eat before you work out. That is just your body being in the habit of not having to burn fat.

Start out by doing one of your less strenuous work outs on a fasting day. We workout five days a week, regardless of it being a fasting day or not. It took a few weeks for our bodies to adapt, but now we don’t even think about it.

I (Dr Robyn) have done hard cardio on fasting days and Russ has done legs (his most strenuous work out – not that all his workouts aren’t strenuous ????) without a problem. Of course, make sure you stay hydrated while working out. That’s good advice whether you’re fasting or not.

What Breaks an Intermittent Fast?

Anything that causes metabolic activity in your body breaks your fast. That means, anything with calories or anything your body thinks SHOULD have calories.

Chemicals that make your brain think it’s getting calories (ie artificial sweeteners) have been shown to turn the system on. You’re going to want to avoid both fake and real calories.

Most experts agree that plain tea, water and unflavored sparkling water are fine. There is some disagreement about black coffee, generally most seem to think it is fine to drink while fasting. However, be aware that the acid on an empty stomach might not be the best option.

Can I Chew Gum While Intermittent Fasting?

Because of the artificial sweeteners in gum, we do not recommend chewing gum while fasting (see the above paragraph).

When Should I Eat After Intermittent Fasting?

When you eat depends on what style of fasting you choose and what works best for your lifestyle. There really is no wrong way to add intermittent fasting to your life.

What Should I Eat After Intermittent Fasting?

The best choice for breaking a fast is something rich in nutrients. If you are whole-food plant-based, that isn’t going to be a problem.

If you are still moving towards being plant-based, you’re going to want to stay away from animal products to break your fast. They are going to sit heavy in your gut and, because you are hungry, it will be SUPER easy to eat way too much.

We laugh at ourselves because when we break our fast, we want to eat all the things! Everything in the house looks and tastes amazing (a side benefit of fasting is your taste buds go on high alert and everything is yummier)!

Inevitably, I (Dr Robyn) end up having to put some of what I made back in the fridge because my eyes are bigger than my stomach.

Which Intermittent Fast Works Best?

The short answer is, whichever style you can make work with your life on a consistent basis. There are benefits to fasting for as little as 12 hours and they go up as you hit 18 hours, 24 hours and 36 hours (for the record, we have NEVER fasted 36 hours straight).

Fat burning tends to be at its peak between 16 and 24 hours into a fast and there have been some studies that suggest that 24-hour long fasts are “best” for weight loss. But that certainly does not mean that shorter fasts aren’t beneficial.

Is a Juice Fast the Same as Intermittent Fasting?

No. A juice “fast” is no different for your body at a metabolic level than eating because there are calories to process. In fact, it’s not as good for you as eating whole-food. We don't juice and recommend that our clients don't as well for a couple of reasons:

Juicing removes all of the nutrients attached to the fiber, which are SUPER important for healthy gut bacteria (they need to eat too).

It also makes the calories more quickly available to your system (Just blending food makes it 15% faster for your body to process), and at the same time, you lose the full feeling from chewing and the bulk that lets your brain know you've taken in enough energy.

We suggest just eating the whole veggie or fruit. Your body will thank you.

Intermittent Fasting – Where to Start

You are already fasting. Every night when you go to sleep your body burns through your glucose stores and into your glycogen.

Depending on how long you go between eating at night and eating in the morning, you might even start burning fat.

If you want to start consciously using intermittent fasting, you just have to stretch that time window out a bit. It is possible that you could just skip breakfast and you’d have a 16-or-so hour fast.

There are a few different “styles” of intermittent fasting. None is really better than another. Remember to drink plenty of water to keep yourself well hydrated while fasting.

Five Methods of Fasting:

•    16/8 or using a feeding window. This is likely the easiest way to ease into intermittent fasting because you can just skip breakfast every day. It is called 16/8 because you fast sixteen hours a day and “feed” during an eight-hour window.

Example: you would eat all of your meals between noon and 8pm. Some people push that even farther. We have a client who eats only one “meal” a day between 4pm and 8pm pretty much every day. She has been doing it for a little better than a year at this point and last I heard she was down 60-70 pounds (she is also mostly plant-based).

•    5-2. This method of fasting was made popular by the BBC Documentary, Eat, Fast and Live Longer (available on YouTube except in the UK). With this method you eat normally five days a week and fast on two non-consecutive days.

On your fasting days you are allowed 500-600 calories. Some suggest eating all of your calories at once. Others say it’s okay to split them up.

This is the style of fasting Russ and I started with and we ate all of our calories at one time. Our logic being, if the goal is to eliminate insulin, why would you eat 250 calories in the middle of your fast?

•    Alternate day fasting. Just like it sounds, you eat every other day. But that means you’re fasting three or four whole days every week. That seems like a lot to us.

•    24-hour fasts. You fast for one or two periods of 24 hours each weekly. I’m not sure when it happened, we didn’t ever talk about it, but this is the style of fast we do now. Somewhere along the way we moved from eating 500 calories on a fasting day, to fasting for 24 hours and then eating a regular meal twice a week.

•    Multi-day water fasts. Instead of fasting on a weekly basis you could do three consecutive days every month. That doesn’t sound even a little bit fun to us (I would be intolerably cranky).

For very ill patients, long (30+ days) water fasts have shown positive benefits. HOWEVER (this is really important), we DO NOT recommend fasting for more than about 36 hours without the supervision of a doctor who has specific knowledge about fasting.

What is the Downside to Intermittent Fasting?

Experts agree that there really is no health “downside” to intermittent fasting. People fast all the time before procedures and getting bloodwork done. Doing it regularly just extends the benefits.

The only real “negative” is being cranky if you are fasting more than about twelve hours. Once your body figures out how fasting works and learns to burn fat without complaining about it, that crankiness goes away. It gets better in about a week but it might take up to six weeks to be really gone.

If you’re worried that you’ll get hungry and that the hunger feeling will build until you’re ready to eat your arm (or your neighbor’s arm), don’t worry. That’s not how hunger works.

Sure, your stomach might growl at you (we have found that bubbly water helps with that) and you might think, “I’m hungry.” But drink some water, work on a project or get engaged in something you enjoy and hunger will take a break.

Eventually it will be more of, “Hey, we could eat” and you’ll think, “Yeah, I know. We’ll do that later.”

Intermittent Fasting – The RnR Way

When we started fasting, we chose the 5-2 method and decided that Wednesdays and Saturdays would be our fasting days. It only took us about two weeks to realize that fasting on a Saturday was really bad for our social life (fortunately we have a couple of biking riding friends who put up with us biking with them and then hanging out at their house to visit and drink water).

We switched our days to Mondays and Thursdays (which you know if you watch our daily lives on Facebook). That has worked well for us.

We have tried having our fasting day meal as breakfast (about 9:30am) and as an early dinner (about 4pm). We have found that 4pm works better for us. Mostly because I (Dr Robyn) don’t like going to bed hungry.

When we were doing the “real” 5-2 a 500-600 calorie meal might be a sweet potato with hummus or oatmeal with fruit (no seeds).  Now that we are doing 24 hours two days a week (still Mondays and Thursdays), we typically fast between 22 and 26 hours depending on when we stop eating the night before and what time we break our fast.

Interestingly, we noticed just recently that in addition to our regular 24-hour fasts, it is common for us to eat dinner around 6:00 at night and then not eat again until breakfast at 9:30.

Which means we are also doing a 15.5/8.5 type fast on a pretty regular basis. We have also noticed that we aren’t nearly as hungry as we used to be when we were eating a more Mediterranean style diet. I think that is because we are getting FAR more nutrients than we used to and our cells are just happy.

Of course, we are also both at our idea weight now, so we aren’t having to feed the extra pounds of chunky-monkey we were carrying around.   

Here's What to Do Next...

Option 1 - If you are a member, join the conversation with your thoughts or comments on the community page. We would love to hear your stories or experiences with intermittent fasting!

Option 2 - If you're not a member yet, join us now to get support from Dr. Robyn, Russ and other members who are also on their journey to better health. All journeys are better when you have someone to share it with.

Finally, this is a great TedTalk about intermittent fasting we believe you will enjoy!