Did you know that purposefully skipping breakfast can actually help you lose fat?
Contrary to popular belief, intermittent fasting shows that breakfast isn’t always the most important meal of the day.
Today, we are going to go over everything you need to know about intermittent fasting, and how to use it to achieve great results.
Welcome to The WCT Series on Diets Explained, where we examine all of the popular diets of the 21st century so that you can determine if any of these are right for you.
Today’s post is going to cover:
- What is Intermittent Fasting?
- How Does it Work?
- What Are The Benefits of Fasting?
- What Are Downsides to Fasting?
- Who Should and Shouldn’t Be Fasting?
All your questions will get answered and more.
Alright, let’s get started.
Although we are doctors and personal trainers, we are not your doctors. The content on this site is for informational purposes only and should not substitute the advice from your healthcare professional. All kinds of exercise and dietary activities are potentially dangerous, and those who do not seek counsel from the appropriate health care authority assume the liability of any damage or injury which may occur. Please read our full Disclaimer for more information. Also, this post may contain affiliate links: meaning we may receive a commission if you use them.
Okay, let’s get started.
What Is Intermittent Fasting?
Intermittent fasting is a relatively new method of eating that takes advantage of the scientific principles of fasting.
The important thing to understand is that intermittent fasting is not a diet. It is simply a pattern of eating. In other words, you change when you eat rather than what you’re eating.
So, you could simply sum up Intermittent fasting as the practice of purposefully skipping meals, and only eating during a designated time period.
How Intermittent Fasting Works
Most people who use this pattern of eating are doing so to lose weight and burn fat.
Most people assume that intermittent fasting works because of calorie restriction. If you skip a meal or two, you will be eating fewer calories.
That’s not the whole story.
It is important to try and keep your caloric intake as close to your baseline as possible.
Dropping your calorie intake by a large margin is never a good idea, as we have extensively written about in The Importance of A Balanced Diet [3 Key Principles You Need To Know]
As a quick recap, dropping your caloric intake significantly will lead to a decrease of lean muscle mass, and slow down your metabolism.
Intermittent fasting works through other mechanisms.
So if it’s not about the calories, how does it cause you to burn fat?
It all starts with metabolism physiology.
Normally, your body will use glucose in the bloodstream to feed your brain and other organs throughout the day.
Every time you eat, your body will convert some of those calories into glucose for immediate use, and it will store any extra as glycogen. Any additional calories beyond that will be stored as fat for later use.
While you are fasting, there isn’t any glucose readily available, so it will dip into its glycogen stores for energy. Once your glycogen becomes depleted, your body will then turn to one final source of energy, fat. This is how intermittent fasting works.
When your body breaks down fat for energy, it doesn’t produce glucose, it produces ketones.
Ketones are an energy source that can be used by your brain and other vital organs.
Have you ever heard of the Keto Diet? This is how it works.
The Benefits of Intermittent Fasting
In addition to using fat as a primary energy source, there are many other potential benefits of fasting.
1. Intermittent fasting simplifies your eating schedule
If you are only eating 2 times a day, and within a specified time frame, then its hard to argue that your life isn’t a little simpler.
Having to consume 4-6 meals per day can often be time-consuming and stressful.
Since you only eat for a designated time period, there is less planning that has to go into selecting and preparing your meals.
2. Intermittent Fasting theoretically resembles how our ancestors ate
Before the agricultural revolution, our ancestors had to produce or hunt their own food. As you could imagine, there were probably long stretches of time where food wasn’t readily available to them, and they had to go through periods of fasting by default.
Today we live in a world where supermarkets are abundant and we have continuous access to food all the time.
Suffice it to say, going through periods of hunger can help you appreciate how fortunate we are to have high-quality food readily available to us.
3. Intermittent Fasting Improves Insulin Sensitivity
Insulin is the hormone that drives the glucose in your bloodstream into your cells. As we mentioned above, there is no glucose readily available to feed your cells in a fasting state.
In order to compensate, your body will then shift to ketone production for energy.
As far as we understand, insulin levels will remain low during fasting states and will rev back up during feasting.
This lack of exposure to insulin during the fast will make your cells more sensitive to it when it is present again.
4. Intermittent Fasting Teaches Discipline
Purposefully skipping meals requires discipline and dedication. You can build a lot of mental fortitude if you are able to ignore your hunger and your desire for food.
You are also forced to be productive in other areas of your life so that you could take your mind off of the hunger.
The Downsides of Intermittent Fasting
Alright, all of this sounds great, but there has to be a catch right?
Here are a few reasons why you might not want to do intermittent fasting:
1. Intermittent Fasting Is Very Difficult
Forcing yourself to be hungry is no easy feat. As you go through periods of intense hunger, you can develop headaches, feel faint, and experience mood swings.
Just the side effects of hunger might be enough to make you grab a Snickers.
In addition, you will face significant peer pressure to break your fasts whenever you see your colleagues stuffing their faces.
Some individuals reported feelings of intense cravings and daydreaming about what they were going to be eating when they break their fast.
Intermittent fasting is not for the weak-hearted.
2. It Can Lead to Nutrient Deficiencies
Intermittent fasting is not a free pass to just starve yourself and then eat very little when it’s feast time.
If you just eat pop tarts and french fries, then you will never get the nutrients your body desperately needs, and you will become nutrient deficient.
If your diet sucks, intermittent fasting won’t help you. It will probably make you worse off than when you started.
3. You Might Lose Muscle Mass
Unfortunately, you cannot ensure that your body will break down fat, and fat only for energy.
Any lean tissue is fair game. Your body might break down some of your muscle mass when it is desperate for energy.
Results vary depending on your activity level, your lean muscle mass percentage, and protein consumption.
4. Fasting Can Add Another Stress Load To An Already Stressed/Sleep Deprived Person
If you live a very stressful life, then using this type of eating pattern is probably a bad idea. While fasting, your body revs up energy production to keep you alert and moving. This is a stressful process.
Working a long busy shift is stressful. Being sleep deprived is stressful. Exercise is stressful.
Your body cannot differentiate between all of the different types of stress and they will all have similar effects on your body.
Chronic stress is bad for you. Really bad.
In addition, some individuals have reported trouble sleeping while using intermittent fasting, as they often wake up in the middle of the night ravenous.
If you feel that you don’t have a great handle on life stressors, then consciously skipping meals is not in your best interest.
Absolute Contraindications To Intermittent Fasting
With that said, there are some people who should never use intermittent fasting.
Absolute contraindications to intermittent fasting are:
– Anyone with a history of eating disorders should not use intermittent fasting.
– Anyone who easily becomes hypoglycemic should not use intermittent fasting.
– Pregnant women should not use intermittent fasting.
– Underweight females should not use intermittent fasting.
The Different Types of Intermittent Fasting For Fat Loss
Ok, now let’s go over the different types of intermittent fasting protocols.
We will go over the three most common approaches used.
Intermittent Fasting 16 8
This is probably the most common form of intermittent fasting. You fast for 16 hours, and you eat for 8 hours.
Most people choose to skip breakfast and wind up consuming 2 meals a day.
For example, you eat from 12pm-8 pm, and then you don’t eat again until 12 pm the next day.
Or you eat from 6am- 2 pm, and then you stop eating until 6 am the next day.
It doesn’t matter when you start and stop, just as long as it is a 16 hour fast followed by 8 hours of eating.
This approach is to be used on a daily basis.
24 Hour Fast or Alternating Days
Another common pattern is the 24 hour fast. It is exactly as it sounds.
You eat regularly on Monday and have your last meal at 8 pm. You then fast until 8 pm on Tuesday.
You resume a normal eating schedule until 8 pm Wednesday and so on and so forth.
This approach is much more difficult than 16/8.
Going 24 hours without food is extremely difficult and should not be attempted (in my opinion) by busy professionals.
The Weekly Intermittent Fasting Approach
This is by far the easiest approach. Instead of fasting every single day, or every other day, you choose to fast only once a week.
For example, you eat regularly on Monday and Tuesday, and then you stop eating after lunch on Wednesday. You continue the fast for 24 hours and then continue eating again at lunchtime on Thursday.
For obvious reasons, this approach won’t be as beneficial as the 16/8 or 24 hour fast. This protocol is useful for those individuals looking to try the diet slowly before committing to it.
Overall, I think the 16/8 approach is by far the best method out of the three.
Does Intermittent Fasting Affect Women Differently From Men?
There are a few studies that have looked at the differences between men and women with respect to fasting.
Preliminary data shows that women may not experience the same positive effects as men.
Women tend to be extremely sensitive to starvation responses which can alter hormonal balance (more on this later).
Some experts have recommended that women might benefit from decreasing the fasting time frame and increasing the eating window.
So instead of 16/8, women may try a 14/10 eating schedule. As with all things in fitness, give it a try and see how your body responds to it.
Others state that women might benefit from crescendo fasting, in which you fast on 2-3 non consecutive days of the week.
Always give yourself at least 2-4 weeks to see if you notice any changes in your body.
Can I Drink During The Fast?
You can drink any beverage that does not contain calories. This includes water, black coffee, and unsweetened tea. It’s probably best to avoid the zero calorie crap like Gatorade and diet soda.
Don’t mess this up. You will defeat the whole purpose of intermittent fasting if you don’t abide by these rules.
What Should I Eat During The Feast?’
It should go without saying that you should eat a healthy diet while on this eating protocol.
Since you only have a short window to eat, it is important that you obtain all of the necessary macro and micronutrients as efficiently as possible.
Make sure to eat plenty of leafy green vegetables, high quality protein, complex carbohydrates, and a lot of mono and polyunsaturated fats. We go over the best foods in each category in How To Start Eating Clean Even With An 80 Hour Work Week.
Fasting for 16 hours and then only eating 800 calories of low quality food is a recipe for disaster. Sure, you will lose weight, but at the expense of your health and your metabolism.
This is not a free pass to just starve yourself at all times. Do your best to consume a sufficient amount of calories during your feast time.
Most people find it easier to just consume 2-3 large meals in the eating window.
On the contrary, you should eat responsibly.
Don’t go ham and binge. This is how you develop eating disorders.
Can I Workout While Fasting?
This is a common question. I don’t have any strong feelings either way.
Some people swear by fasting cardio or fasting workouts, while others think it is a bad idea. The only way to know is to give it a try.
Everyone is different and everyone’s body will handle the stress of a workout differently.
Keep in mind that your body could potentially begin to use up muscle mass to feed itself if you workout too hard and too often.
If you do want to work out, make sure you do it correctly.
Download our free workout template to get started on the right foot.
How Should I Start? Intermittent Fasting For Beginners
If you are interested in trying intermittent fasting, it is always best to start off slow.
Work your way up. It doesn’t make sense to go from eating 4 times a day, to a 16 hour fast the next.
Perhaps you should start with a 10 hour fast and see how you respond. Chances are, you’ve probably done a 10 hour fast in the past without realizing it.
You will experience side effects of fasting, there is no way around it. Give your body a little bit of time to acclimate itself to the fasting state.
Your body likes it when you give it a routine. Treat the fast just like everything else in life that you are starting for the first time.
As you get used to it, you can increase your fasts to 12, 14 and then 16 hours.
In addition, you may benefit from fasting every other day, or a couple of times a week as an introductory phase.
After 1 week, begin increasing your fasting frequency.
To Recap: Intermittent Fasting Pros and Cons
We just went over a lot of information. To sum it all up:
- Intermittent Fasting is a pattern of eating where you schedule periods of fasts followed by periods of eating
- There are 3 approaches: 16 hour fasts, 24 hour fasts and once a week fasting
- Fasting can boost your body’s ability to burn fat for energy in the absence of glucose
- Fasting can improve your insulin sensitivity
- To get the full benefits of fasting, it is important to consume high quality foods during the feasting period
- Fasting is difficult and should not be practiced by individuals with high stress loads
Frequently Asked Questions
Will Intermittent Fasting Work Without Exercise?
Yes, intermittent fasting can work even in the absence of exercise. Diet contributes to approximately 80% of all of your fitness attributes.
With that said, everyone should exercise. Find something that you enjoy. Get up and move. Be active. Stop sitting so many hours a day.
If you would like to lift weights, check out How To Create A Workout Plan To Fit Your Busy Schedule.
Is Intermittent Fasting Safe/ Healthy?
If done correctly, intermittent fasting is safe and healthy. The problem is, it is very easy to do it in a very unhealthy manner.
Always ensure that you are adequately hydrating yourself while you are fasting and always ensure that you are eating enough calories during your feast.
If you drop your caloric intake by a large margin, or if you do not consume high quality, nutrient dense foods, then you can easily alter your hormone balance, ultimately damaging your metabolism and your health.
If you are going to try intermittent fasting, start slow, and do it right!
Will Intermittent Fasting Affect My Periods?
As we mentioned above, intermittent fasting does seem to have different effects on women as compared to men.
One possible side effect of fasting is hormonal disruption. Your hypothalamus secretes a hormone called GnRH which tells your pituitary gland to secrete Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
These two hormones act on your ovaries and uterus to grow your endometrial lining and prepare for pregnancy. If a pregnancy does not occur, your endometrial lining will shed and you will have a period.
GnRH tends to be very sensitive to signals from other hormones, and fasting can disrupt the natural GnRH pulse. As a result, some women have experienced irregular periods when fasting.
If you are underweight you should not fast.
If you work out regularly, you should not use an aggressive fasting protocol. Try fasting 2-3 times a week, and/or shortening the fasting window.
Don’t forget, there are also plenty of other dieting strategies you could use to achieve great results.
How Quickly Can I get Results From Intermittent Fasting?
Results always vary, but typically you should begin to see results in as little as 2-4 weeks. I recommend that you start off slow and acclimate to the fasting state before going all in.
Can I Use Intermittent Fasting With a Low Carb Diet?
Yes. Intermittent fasting is not a diet. It is just a pattern of eating. You can use intermittent fasting with a low carb, high carb, low fat, or high fat diet.
Just make sure to consume real, high quality, nutrient dense foods often. I cannot stress this enough.
Can I Use Intermittent Fasting To Gain Weight?
Yes. In order to gain weight, you will need to increase your caloric intake. Consume large meals during your feasting periods. Train hard and use compound movements when you exercise.
Slowly but surely, you should be able to gain 1 +/- 0.5 lbs a week. Check out The Best Workout Template For Busy Individuals for a simple workout regimen you could use.
Does the WCT Recommend Intermittent Fasting?
Intermittent Fasting is great, but it is not necessary.
As with all diets and eating patterns, none of them are perfect.
The biggest problem with intermittent fasting is the rigid schedule.
If you work weird hours and have an inconsistent/unpredictable schedule, then I wouldn’t recommend intermittent fasting.
When your schedule is all over the place, you cannot ensure that you will have 8 peaceful hours to consume a sufficient amount of calories and still maintain a healthy diet.
Don’t forget, you aren’t necessarily changing the quantity of food you consume drastically, rather you are changing when you eat.
In addition, you may work a job that requires very fine attention and concentration. The last thing that I want to feel while performing a long surgery is hunger and fatigue.
The WCT Diet
That is why we prepared a comprehensive diet for busy professionals. It outlines a step-by-step process on how to incorporate healthy eating habits into your life.
These are the same strategies that we use to lose over 10 lbs of fat, and stick to our diet for 4+ years of medical school and residency training.
We don’t like the idea of having a very short window to eat. We tend to eat more frequently.
Generally, we have approximately 4-6 meals per day, which we have written about here.
With that said, intermittent fasting has worked great for many individuals.
If you have a regular predictable schedule, and you can ensure that you’ll get all of your food in the 8 hour window, then it’s worth a shot.
Next, you should read:
- The Mediterranean Diet 101: Sample Food List
- How To Lose Weight Without Dieting
- How We Meal Prep Working 80 Hours A Week
Now we turn it over to you.
Have you ever done intermittent fasting? Did it work for you?
What are your thoughts on this diet?
Post your comments and questions below.
Know anyone who might benefit from this information? Share it with them!
Alex Robles, MD, CPT / Brittany Robles, MD, MPH, CPT
Alex & Brittany Robles are physicians, NASM Certified Personal Trainers, and founders of The White Coat Trainer: a resource dedicated to improving the health and fitness of busy professionals using time-efficient strategies. Their advice has been featured in My Fitness Pal, Prevention, Livestrong, Reader’s Digest, Bustle, The Active Times, and more. Learn more about them here.