What is Intermittent Fasting?
Intermittent fasting (IF) is a style of eating that alternates between periods of fasting (i.e. not eating) and periods of feasting (eating).
No foods are off limits on the diet, unlike other popular dietary approaches. The only thing that is restricted is the hours each day that you are allowed to consume food.
The reasons an individual may choose to adopt intermittent fasting vary, but generally speaking, it is for the purpose of weight loss. Other reasons an individual may fast may be for religious, ethical, or health reasons (such as trying to improve insulin sensitivity).
As a practice, fasting is as old as the human race.
You see, centuries ago, food was scarce, meaning there wasn’t a drive-thru restaurant or food truck on every street corner.
If an individual didn’t hunt or forage for their own food, they went without it (i.e. they fasted) until the found some.
In fact some IF proponents hold that regular fasting is actually more akin to the way humans are supposed to eat than the current three or four main meals each day.
What are the Benefits of Intermittent Fasting?
Supports Weight Loss
As mentioned above, the primary reason most people try intermittent fasting (IF) these days is for its potential weight loss benefits.
By restricting how many hours per day you are allowed to eat (your feeding window), individuals may be less likely to overeat.
Furthermore, since you know that you are only allowed to eat during a certain window each day, you (hopefully) will spend less time during your fasting window thinking about when your next meal is and focus instead on more important things, like work.
May Help Combat Type 2 Diabetes
Fasting has been shown to improve various biomarkers of metabolic health related to the development and progression of Type 2 diabetes, including:
- Reducing blood sugar
- Decreasing fasting insulin levels
- Promoting greater insulin sensitivity
Promotes Cardiovascular Health
A form of intermittent fasting called alternate-day fasting (which we’ll discuss more below) has been shown to help reduce “bad” LDL cholesterol and blood triglycerides as well as certain inflammatory biomarkers -- all of which are factors associated with an increased risk for heart disease.
Several studies have found that various forms of fasting lead to significant reductions in inflammatory markers, including CRP and IL-6.[3,4]
In case you weren’t aware, chronic systemic inflammation has been implicated as a driver of many chronic diseases.
Preliminary animal studies also indicate that intermittent fasting may help prevent certain forms of cancer, and it may even increase lifespan.[5,6]
However, these benefits have yet to be conclusively shown in human trials.
Drawbacks of Intermittent Fasting
No Better than Conventional Dieting
A recent study involving 100 overweight individuals investigated the weight loss results of three different eating plans:
- Alternate day fasting
- Continuous calorie restriction (how individuals typically diet)
- Control (individuals at as they normally did)
At the end of the year-long study, both dieting groups lost weight compared to the group not following a diet (big shock there.)
However, the fasting group did not have any greater weight loss than the group following the traditional way of dieting
May Not Be Sustainable for Everyone
One other point to mention about the study above is that the group assigned to the fasting protocol had a relatively high dropout rate (38%).
This suggests that intermittent fasting may not be an effective tool for everyone all the time. It may work for some individuals, but for others, fasting just leads to low energy levels and never ending thoughts about food, which would lead them to abandon their diet and overeat.
Lastly, it should be mentioned that nearly all of the IF-related studies to date are short term. What this means is that we have no concept of what the long term ramifications (be they good or bad) of what intermittent fasting is.
How Do I Start Intermittent Fasting?
If you feel like intermittent fasting may be something you’d like to try, you should know that there are several different ways in which you can incorporate the dietary approach.
Leangains 16:8 Method
Popularized by Martin Berhkan, the creator of Leangains, the 16:8 IF protocol entails fasting for 16 hours of the day and eating all of your day’s calories within an 8-hour window.
While a 16-hour fast might seem outrageous to those of you not accustomed to fasting, it really just involves you skipping breakfast.
Here’s an example of a frequently used 16:8 intermittent fasting protocol:
- 12:00 PM: Meal 1 -- Pre-workout meal
- 1:30 PM: 1 serving of your favorite pre workout supplement (such as 1UP for Women or 1UP for Men)
- 2:00 PM: Work out
- 4:00 PM: Meal 2 -- Post-workout Protein shake & Tri-Carb
- 5:00 PM Meal 3 Post workout meal
- 8:00 PM: Meal 4 -- Dinner
Note that you don’t have to eat between 12 and 8PM each day. You just need to fast for 16 hours and feed for 8 hours.
So, if you prefer starting your feasting at 10AM and having your last meal at 6PM that could work too.
We’d caution against starting your feeding window too early, especially if you’re the night owl-type as you may be more inclined to overeat.
Alternate Day Fasting
As the name implies, alternate day fasting involves alternating between days of fasting and eating.
On the eating days, you would consume your normal amount of calories (i.e. maintenance calories).
So, if you choose to follow this IF approach, an example week may look like:
- Monday - Fast
- Tuesday - Regular diet
- Wednesday - Fast
- Thursday - Regular diet
- Friday - Fast
- Saturday - Regular diet
- Sunday - Regular diet
Now, a common “tweak” individuals following alternate day fasting allow for is the consumption of up to 500 calories per day, similar to a protein-sparing modified fast or a “fasting-mimicking” diet (FMD) than a true eat-fast approach.
Note: if you choose to follow this approach it would be wise to save your heavy resistance-training workouts for the days you’re eating food. Fasting days should coincide with low intensity physical activity or active recovery workouts.
The 5:2 IF approach involves eating normally for 5 days of the week, while restricting calorie intake to between 500-600 on two non-consecutive days of the week.
This style of intermittent fasting was popularized by Dr. Michael Mosley, an English doctor and journalist, who also referred to the dietary approach as the “Fast Diet”.
An example week of the 5:2 diet could look like:
- Monday - Regular diet
- Tuesday - Regular diet
- Wednesday - 500 calories day
- Thursday - Regular diet
- Friday - Regular diet
- Saturday - Regular diet
- Sunday - 500 calorie day
Again, with this approach, make sure you reserve your most intense workouts for the days you’re fully fueled so that you don’t bonk in your training sessions.
It may also be useful to place your 500-600 calorie days not on the weekends as Saturday and Sunday are typically the days most people relax and go out with family, friends, or significant others and indulge.
Progressing the 5:2 diet one step further is the eat-stop-eat protocol popularized by Brad Pilon.
Eat-Stop-Eat requires fasting for an entire 24-hour period one or two non-consecutive days per week.
The simplest way to incorporate this IF protocol is to fast from one day’s dinner to the next, which yields a 24-hour fast.
You could also fast from one day’s breakfast to the next day’s or from one day’s lunch to the next.
How you set up your eat-stop-eat protocol is entirely up to you -- they all accomplish the same end result (fasting for 24 hours.)
Do I Need to Follow Intermittent Fasting to Lose Weight?
In a word, no.
You do not “need” to follow intermittent fasting (or any of its forms) in order to lose weight.
All that is required to lose weight is a calorie deficit.
Intermittent fasting is a tool that can be used to help you achieve and sustain a calorie deficit such that you lose weight. If restricting what hours of the day you can eat helps you adhere to your fat loss diet, then feel free to use IF.
The most important thing when selecting any particular dietary approach to help lose fat is one that covers all of your nutritional needs as well as one that you can stick to.
Even the most perfectly optimized fat loss diet will fail if you cannot stick to it.
As such, IF works incredibly well for some, but for others it may not. If it works for you great, follow it and succeed. If it doesn’t, don’t sweat it and follow a dietary approach that does work for your lifestyle and goals.
Intermittent fasting is a dietary approach that involves alternating between periods of eating and not eating.
There are several different methods of intermittent fasting, including 16:8, alternate day fasting, and eat-stop-eat.
One of the most popular reasons people try IF is for its potential weight loss benefits.
However, other individuals are fascinated by animal research demonstrating that incorporating regular fasts may help reduce cancer risk and slow the aging process.
Intermittent fasting can be an effective tool for weight loss (if fasting works for you); however, it does not provide superior weight loss benefits to conventional forms of dieting.
Experiment with IF you are curious and adapt your nutrition plan accordingly based on how you respond to the diet.
- Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, 164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013
- Varady, K. A., Bhutani, S., Church, E. C., & Klempel, M. C. (2009). Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. The American Journal of Clinical Nutrition , 90(5), 1138–1143. https://doi.org/10.3945/ajcn.2009.28380
- Aksungar, F. B., Topkaya, A. E., & Akyildiz, M. (2007). Interleukin-6, C-reactive protein and biochemical parameters during prolonged intermittent fasting. Annals of Nutrition & Metabolism, 51(1), 88–95. https://doi.org/10.1159/000100954
- Faris, M. A.-I. E., Kacimi, S., Al-Kurd, R. A., Fararjeh, M. A., Bustanji, Y. K., Mohammad, M. K., & Salem, M. L. (2012). Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Nutrition Research (New York, N.Y.), 32(12), 947–955. https://doi.org/10.1016/j.nutres.2012.06.021
- Rocha, N. S., Barbisan, L. F., de Oliveira, M. L. C., & de Camargo, J. L. V. (2002). Effects of fasting and intermittent fasting on rat hepatocarcinogenesis induced by diethylnitrosamine. Teratogenesis, Carcinogenesis, and Mutagenesis, 22(2), 129–138. https://doi.org/10.1002/tcm.10005
- Sogawa, H., & Kubo, C. (2000). Influence of short-term repeated fasting on the longevity of female (NZB×NZW)F1 mice. Mechanisms of Ageing and Development, 115(1), 61–71. https://doi.org/https://doi.org/10.1016/S0047-6374(00)00109-3
- Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, May 2017.
- Mosley M, Spencer M. The FastDiet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting. Atria Books. 2013