Intermittent Fasting (IF) has added greatly to my quality of life in so many ways: energy, athletic ability, extra time, weight management, and many more.
Since it is one of my favorite tools for maintaining a healthy weight and for improving my performance at the gym, I’d like to share more about it here. I’ll do a series of posts over the next few weeks about my experience with and what science has shown about IF’s effect on health and athletic activity.
To start, with this post I’ll discuss what IF is and how to do it.
Next week, I’ll get into IF’s effect on many physical health, weight management, and mental health markers.
Then the third week, I’ll show very cool data on how IF impacts athletic ability and weight training in particular.
Note: Scores of research studies have been done on what is popularly known as “Intermittent Fasting” or what researchers like to call “Time-Restricted Feeding.” These terms, as well as their abbreviations (IF and TRF), I will use interchangeably to cover all forms of limiting eating to only a specific time window.
How IF Works in Your Body
The two main types of energy your body and brain use to function are glucose/carbs and ketones.
Your body uses glucose when you are in a “fed state” or several hours after eating. Your body uses some glucose that is absorbed immediately after eating but then stores the rest in your liver and muscles for use over the next several hours.
Your body uses ketones when you are in a “fasting state” or after your body has used up all its glucose stores. Ketones come from broken-down fat stores. Basically all of the fat you eat and even some excess carbs are stored as fat to be used if needed in this fasting state.
Your body uses up all of its glucose stores and switches into a fasting state approximately 12 hours after your last meal, sooner if your last meal is smaller.
The many different versions of IF all put your body into a fasting state for some period of time regularly every day or every week.
As it turns out, this period of time that you are in a fasting state offers your body many great health benefits that I’ll get into next week. For now, I’ll talk about the different ways that are commonly used to get your body into that fasting state regularly using IF or TRF. Basically, they can be broken up into either daily or weekly fasting methods.
Daily: 16:8 (or 18:6 or 14:10 or 20:4) Method
This is an everyday method and the numbers describe the number of hours you fast & eat every day.
This is my preferred method because it’s just easier for me personally to get into and keep up daily routines rather than weekly routines.
The 16:8 method means you fast for 16 hours of your day and eat all of your daily calories during an 8 hour period. For example, you only eat between 8am and 4pm every day, or only eat between noon and 8pm every day.
As your body typically enters a fasting state 12 hours after your last meal, this gives you 4 hours per day, every single day, of beneficial fasting time.
Many people contract this eating time to 6 hours per day and fast for 18 hours or even eating 4 hours per day and fasting for 20 hours. You can also relax this substantially and eat for 10 hours per day and fast 14.
If you’re used to the typical American eating pattern of eating and snacking all waking hours, it can be helpful to start by shortening your eating time to 12 hours per day then gradually shortening more over time from there.
Daily: OMAD (One meal a day)
This is similar to above in that it is a daily practice but to the extreme of eating only one (very large) meal per day.
Not for me, but some people can do it and love it.
Weekly: 5:2 Method or Alternate Day
This method refers to days of the week where some days you fast substantially and the rest of the days you eat normally.
The 5:2 is a popular method where you fast for 2 (non-sequential) days of the the week and then eat normally for the other 5 days per week.
Importantly, the 2 days per week are NOT sequential but separated by days of eating in between.
On the fasting days you can either eat nothing at all or only eat a small amount of calories.
When eating a small amount of calories on fasting days, an often chosen limit is 400-600 calories but the number is arbitrary.
I’d recommend picking a number of calories around 1/4 or less of your daily energy needs/total daily energy expenditure (TDEE calculator here). However, it may be helpful to start out eating a higher amount, like 1/2 of TDEE calories or more, on fasting days and slowly taper it down week by week.
Alternate Day Method
The alternate day method is where you eat as much as you want one day, then the next day eat only 1/3-1/2 of your daily energy needs/total daily energy expenditure (TDEE calculator here). Continue to alternate days indefinitely.
Again, if you want to choose this method, it may be helpful to start out eating a higher amount, like 1/2 of TDEE calories or more, on fasting days and slowly taper it down week by week.
The important part about this way of eating is that the majority of your months/years are spent intermittently fasting. But there’s really no need to be afraid of exceptions.
If once a week or a couple times per month you have holidays, dates, family get-togethers, etc, and want to eat outside of your given hours, it’s not going to ruin anything and you can and should be merry and eat as you desire.
If you go on a few week-long vacations every year, feel free to forget the schedule and again eat as you desire during those weeks. It’s not going to ruin anything. (Though I love the way it makes me feel so I don’t want to anyway!)
It’s about the everyday/everyweek. It’s a small amount of time daily/weekly but adds up to big results yearly.
Obviously, the more exceptions you make, the less beneficial effect it will have. A few exceptions won’t be noticeable at all. But truly, even many exceptions will still benefit you because you still have some fasting time when you haven’t made exceptions.
What Time of Day
Of note, if you choose to do daily IF, such as the hourly method or OMAD as above, there are some minor benefits to choosing to eat earlier in the day rather than later.
Multiple studies have shown many benefits when the majority of food is eaten earlier in the day.
When attempting to lose weight, people consistently lose more weight when they eat the same number of calories earlier in the day compared to later in the day (Garaulet, 2013; Jakubowicz, 2013). This is likely because melatonin naturally increases later in the day. Melatonin prevents your body from making insulin (the hormone that lets you use/burn carbs) so your body can’t make as much insulin to use the calories you are eating as effectively in the evening and so they end up getting stored (Tuomi, 2016).
This also plays a role in Type 2 Diabetes. As above, eating later in the day means that the melatonin in your blood is preventing your body from sending insulin into the blood (Tuomi, 2016) and therefore your blood sugar remains higher for a longer period of time which is harmful in Type 2 Diabetes because your blood sugar is already too high.
When people ate enough calories to maintain their weight, eating early in the day, from 8am to 2pm, improved their insulin sensitivity, blood pressure, and oxidative stress levels even though they didn’t lose weight! (Sutton, 2018) Another study showed that women who ate early in the day had significantly greater reductions in insulin and fasting glucose levels compared to women that ate later in the day, even when both groups ate the same number of calories each day (Jakubowicz, 2013).
Large vs Small Meals
It doesn’t matter if you choose to eat fewer large meals or many small meals as long as you are only eating during the designated time each day. Choose whichever you enjoy more or whichever fits better into your lifestyle.
As I noted above, your body uses up all of its glucose stores and switches into a fasting state approximately 12 hours after your last meal, but sooner if your last meal is smaller.
If you would like to increase the time you are in a fasting state, eat a smaller meal as your last meal. Eat more of your calories earlier on in your eating-time window. Additionally, since the fed state relies on the amount of carbs eaten, eating fewer carbs in your last meal of the day will decrease the fed-state time and increase your fasting-state time.
Tips for Starting Out
You may have a hard time going through with the fast the first couple days because of hunger. Rest-assured, your body really does get used to it surprisingly quickly. You really only need a couple days.
Again, as above, eating a larger meal as your last meal will keep you in a fed state longer and can make it easier when first starting out.
It also helps to track calories when you’re first starting for two reasons.
Firstly, since you’ll be eating fewer times per day, you want to make sure you are consuming enough calories to be safe.
Secondly, you will likely feel emotional, habitual hunger during your fasting period when you are first starting. Tracking calories reassures your brain that you have indeed eaten enough calories for the day and the hunger it is feeling is emotional and not physical.
So here we have all of the ways Intermittent Fasting can be done and how to get started. Stay tuned for the next coming weeks where we’ll discuss the amazing scientific benefits of these time-restricted diets – even how it improves your athletic ability!
Garaulet, M., Gómez-Abellán, P., Alburquerque-Béjar, J. J., Lee, Y. C., Ordovás, J. M., & Scheer, F. A. (2013). Timing of food intake predicts weight loss effectiveness. International journal of obesity (2005), 37(4), 604–611. https://doi.org/10.1038/ijo.2012.229
Jakubowicz, D., Barnea, M., Wainstein, J., & Froy, O. (2013). High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity (Silver Spring, Md.), 21(12), 2504–2512. https://doi.org/10.1002/oby.20460
Sutton, E. F., Beyl, R., Early, K. S., Cefalu, W. T., Ravussin, E., & Peterson, C. M. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell metabolism, 27(6), 1212–1221.e3. https://doi.org/10.1016/j.cmet.2018.04.010
Tuomi, T., Nagorny, C., Singh, P., Bennet, H., Yu, Q., Alenkvist, I., Isomaa, B., Östman, B., Söderström, J., Pesonen, A. K., Martikainen, S., Räikkönen, K., Forsén, T., Hakaste, L., Almgren, P., Storm, P., Asplund, O., Shcherbina, L., Fex, M., Fadista, J., … Mulder, H. (2016). Increased Melatonin Signaling Is a Risk Factor for Type 2 Diabetes. Cell metabolism, 23(6), 1067–1077. https://doi.org/10.1016/j.cmet.2016.04.009