What is Intermittent Fasting?
It’s making a conscious decision to skip certain meals on purpose.
By fasting and then feasting on purpose, intermittent fasting generally means that you consume your calories during a specific window of the day, and choose not to eat food for a larger window of time.
There are a few different ways to take advantage of intermittent fasting, which I learned about back in the day from Martin over at LeanGains, a resource specifically built around fasted strength training:
What it is: Fasting for 16 hours and then only eating within a specific 8-hour window. For example, only eating from noon-8 PM, essentially skipping breakfast.
Some people only eat in a 6-hour window, or even a 4-hour window. This is “feasting” and “fasting” parts of your days and the most common form of Intermittent Fasting. It’s also my preferred method (3 years running).
Two examples: The top means you are skipping breakfast, the bottom means you are skipping dinner each day:
Intermittent Fasting Schedule
You can adjust this window to make it work for your life:
If you start eating at: 7AM, stop eating and start fasting at 3pm
If you start eating at: 11AM, stop eating and start fasting at 7pm
If you start eating at: 2PM, stop eating and start fasting at 10pm
If you start eating at: 6PM, stop eating and start fasting at 2AM.
24 HOUR PROTOCOL
Skipping two meals one day, where you are taking 24 hours off from eating. For example, eating on a normal schedule (finishing dinner at 8PM) and then not eating again until 8PM the following day.
So you would eat your normal 3 meals per day, and then occasionally pick a day to skip breakfast and lunch the next day.
If you can only do an 18 hour fast, or a 20 hour fast, or a 22 hour fast – that’s okay! Adjust with different time frames and see how your body responds.
Two examples: skipping breakfast and lunch one day of the week, and then another where you skip lunch and dinner one day, two days in a week.
How to Schedule Intermittent Fasting
Note: You can do this once a week, twice a week, or whatever works best for your life and situation.
By the way, both those weekly charts above come from our free Intermittent Fasting Starter Guide (with printable worksheets).
Most people struggle with knowing exactly when to eat and when to stop eating, and actually sticking with it. We address all of that in the Nerd Fitness Intermittent Fasting Guide you get free when you sign up for our email list in the box below:
Those are the two most popular intermittent fasting protocols, and the two we’ll be focusing on, though there are many variations of both that you can modify for yourself.
Some people eat in a 4 hour window, others do 6 or 8. Some people do 20 hour fasts or 24 hour fasts. You’ll need to experiment with them, adjust them to work for your lifestyle and goals, and see how your body responds.
Let’s first get into the science here behind Intermittent Fasting and why you should consider it!
How does intermittent fasting work?
Now, you might be thinking: “okay, so by skipping a meal, I will eat less than I normally eat on average (2 meals instead of 3), and thus I will lose weight, right?”
Yes, by cutting out an entire meal each day, you are consuming fewer calories per week – even if your two meals per day are slightly bigger than before. Overall, you’re still consuming fewer calories per day. This is highlighted in a recent JAMA study[b] in which both calorie restricted dieters and intermittent fasters lost similar amounts of weight over a year period.
That doesn’t tell the FULL story, as we already know that not all calories are created equal, and that the timing of meals can also influence how your body reacts.
Intermittent Fasting can also help because your body operates differently when “feasting” compared to when “fasting”:
When you eat a meal, your body spends a few hours processing that food, burning what it can from what you just consumed. Because it has all of this readily-available, easy to burn energy (thanks to the food you ate), your body will choose to use that as energy rather than the fat you have stored. This is especially true if you just consumed carbohydrates/sugar, as your body prefers to burn sugar as energy before any other source.
During the “fasted state” (the hours in which your body is not consuming or digesting any food) your body doesn’t have a recently consumed meal to use as energy, so it is more likely to pull from the fat stored in your body as it’s the only energy source readily available.
Burning fat = win.
The same goes for working out in a “fasted” state. Without a ready supply of glucose and glycogen to pull from (which has been depleted over the course of your fasted state, and hasn’t yet been replenished with a pre-workout meal), your body is forced to adapt and pull from the only source of energy available to it: the fat stored in your cells.
Why does this work? Our bodies react to energy consumption (eating food) with insulin production. The more sensitive your body is to insulin, the more likely you’ll be to use the food you consume efficiently, and your body is most sensitive to insulin following a period of fasting .
These changes to insulin production and and sensitivity can help lead to weight loss  and muscle creation .
Next: Your glycogen (a starch stored in your muscles and liver that your body can burn as fuel when necessary) is depleted during sleep (aka during fasting), and will be depleted even further during training, which can lead to increased insulin sensitivity.
This means that a meal following your workout will be stored most efficiently.
During that period, the food you consumed will be used in a few ways: converted to glycogen and stored up in your muscles or burned as energy immediately to help with the recovery process, with minimal amounts stored as fat.
Compare this to a regular day (no intermittent fasting): With insulin sensitivity at normal levels, the carbs and foods consumed will see full glycogen stores and enough glucose in the bloodstream, and thus be more likely to get stored as fat.
Not only that, but growth hormone is increased during fasted states (both during sleep and after a period of fasting). Combine this increased growth hormone secretion:, the decrease in insulin production (and thus increase in insulin sensitivity ), and you’re essentially priming your body for muscle growth and fat loss with intermittent fasting.
The less science-y version: Intermittent fasting can help teach your body to use the food it consumes more efficiently, and your body can learn to burn fat as fuel when you deprive it of new calories to constantly pull from (if you eat all day long).
TL/DR: For many different physiological reasons, fasting can help promote weight loss and muscle building when done properly.
I know Intermittent Fasting can be overwhelming, so I created a free guide and worksheet to help you get started on the right foot.
Sign up for the free Intermittent Fasting Starter Guide and Worksheets when you put your email in the box below:
But why does every health book say “6 small meals?”
Small plate of sausages – eat it on YOUR schedule
There are a few main reasons why diet books recommend six small meals:
1) When you eat a meal, your body does have to burn extra calories  just to process that meal. So, the theory is that if you eat all day long with small meals, your body is constantly burning extra calories and your metabolism is firing at optimal capacity, right? Well, that’s not true.
Whether you eat 2000 calories spread out throughout the day, or 2000 calories in a small window, your body will burn the same number of calories processing the food . So, the whole “keep your metabolism firing at optimum capacity by always eating” sounds good in principle, but reality tells a different story.
2) When you eat smaller meals, you might be less likely to overeat during your regular meals. I can definitely see some truth here, especially for people who struggle with portion control or don’t know how much food they should be eating.
However, once you educate yourself and take control of your eating, some might find that eating six times a day is very prohibitive and requires a lot of effort. I know I do. Also, because you’re eating six small meals, I’d argue that you probably never feel “full,” and you might be MORE likely to eat extra calories during each snack.
Although grounded in seemingly logical principles, the “six meals a day” doesn’t work for the reason you think it would (#1), and generally only works for people who struggle with portion control (#2).
If we think back to caveman days, we’d have been in serious trouble as a species if we had to eat every three hours. Do you think Joe Caveman pulled out his pocket sundial six times a day to consume his equally portioned meals?
Hell no! He ate when he could, endured and dealt with long periods of NOT eating (no refrigeration or food storage) and his body adapted to still function optimally enough to still go out and catch new food.
A recent study (written about in the NYT, highlighted by LeanGains) has done a great job of challenging the “six-meals-a-day” technique for weight loss :
There were [no statistical] differences between the low- and high- [meal frequency] groups for adiposity indices, appetite measurements or gut peptides (peptide YY and ghrelin) either before or after the intervention. We conclude that increasing meal frequency does not promote greater body weight loss under the conditions described in the present study.
Factor in the potential physiological benefits listed in the previous section, and you got yourself some damn good science-backed evidence to consider trying Intermittent Fasting if you want to decrease body fat and build muscle.
Why intermittent fasting?
Intermittent Fasting Apple Plate
Now that we’re through a lot of the science stuff, let’s get into the reality of situation: why should you consider Intermittent Fasting?
Because it can work for your goals. Although we know that not all calories are created equal, caloric restriction plays a central role in weight loss. When you fast, you are also making it easier to restrict your total caloric intake over the course of the week, which can lead to consistent weight loss and maintenance.
Because it simplifies your day. Rather than having to prepare, pack, eat, and time your meals every 2-3 hours, you simply skip a meal or two and only worry about eating food in your eating window. It’s one less decision you have to make every day. It could allow you to enjoy bigger portioned meals (thus making your tastebuds and stomach satiated) and STILL eat fewer calories on average.
It requires less time (and potentially less money). Rather than having to prepare or purchase three to six meals a day, you only need to prepare two meals. Instead of stopping what you’re doing six times a day to eat, you simply only have to stop to eat twice. Rather than having to do the dishes six times, you only have to do them twice. Rather than having to purchase six meals a day, you only need to purchase two.
It promotes stronger insulin sensitivity and increased growth hormone secretion, two keys for weight loss and muscle gain. Intermittent fasting helps you create a double whammy for weight loss and building a solid physique.
It can level up your brain, including positively counteracting conditions like Parkinson’s, Alzheimer’s, and dementia. As explained here in this TEDx talk by Mark Mattson, Professor at Johns Hopkins University and Chief of the Laboratory of Neurosciences at the National Institute on Aging fasting is grounded in serious research and more studies are coming out showing the benefits: