Intermittent fasting is a dietary philosophy that either involves long periods of fasting followed by short windows of feasting or 24 hours of fasting followed by 24 hours of feasting (this is known as alternate day fasting).
There are several variations of intermittent fasting with the most popular fasting protocol being a 16 hour fast followed by an 8 hour feasting window.
The basis of intermittent fasting hinges on a few key ideas:
- Maximizing the time your body spends oxidizing fat
- Minimizing overall insulin load to the system
- Improved energy levels
- Increased longevity.
Recently several key studies have been carried out to examine how these claims stack up to the research and the results have been quite interesting.
History Behind Intermittent Fasting
Intermittent fasting as it is currently understood and practice is often believed to have begun with Martin Berkhan as he is largely responsible for the widespread adoption of the diet amongst body building and figure competition circles. However, the idea of fasting as a dietary principle dates back much further than that.
The ancient Greek physician Hippocrates wrote, “To eat when you are sick, is to feed your illness”. Another ancient Greek writer and historian Plutarch is also credited with penning “Instead of using medicine, better fast today”. In more recent times one of our founding fathers, Benjamin Franklin, stated, “The best of all medicines is resting and fasting”.
Thus, while the recent popularization of intermittent fasting has brought this approach to main stream health and fitness culture, the idea of fasting is as ancient as the dawn of civilized man.
General Overview of Components & Main Principles of Intermittent Fasting
Intermittent fasting is a dietary philosophy that utilizes fasting and feasting periods. There are several variations of intermittent fasting with the most popular fasting protocol being a 16 hour fast followed by an 8 hour feasting window.
Intermittent fasting does not by design prescribe specific calorie allotments, macronutrient ratios, or provide a list of good or bad foods to eat and is generally not restrictive of any foods.
Unlike many other dietary frameworks or plans, intermittent fasting relies almost solely on meal timing and meal frequency. As typically thought of, intermittent fasting usually adopts a 16 hour fasting window, followed by an 8 hour feasting window.
Most people will consume 1-2 very large meals during the feasting window, although one can consume several small meals throughout this time. Other fasting approaches, such as the alternative day fast employs a 24 hour fast, followed by a full 24 hours of feasting.
Aside from the timing restrictions and limitations, there are no hard and fast food restrictions of limitations. This is often interpreted as an “anything goes” during the feasting window.
However, in practice, the people who achieve the best results using intermittent fasting typically apply another dietary framework (such as IIFYM or flexible dieting) to give them some structure to their food intake during the feasting window.
Does it Include Phases?
Intermitting fasting does not include any phases in its dietary protocol, although some people will go through fasting cycles where they go long periods of adhering to the fasting protocols and then periods of normal eating.
Who is it Best Suited For?
Intermittent fasting is best suited for people who have busy schedules and would prefer to lump their eating into 1-2 meals a day rather than spreading them throughout the day. Fasting can also be excellent for people learning to manage hunger cues and retraining their eating habits.
Intermittent fasting is also an excellent way to help people control calories as often times shortening the amount of time one eats during the day can reduce overall calories.
How Easy is it to Follow?
Intermittent fasting is easy to follow in that it does not limit or restrict food, allows one to eat without tightly tracking calories, and will not place a burden on your social life (i.e. not being able to go out to dinner and order something on the menu). It also can make life much easier as there is less time spent cooking, eating, and cleaning up.
It can be difficult for some people who enjoy the process of cooking and eating; people who struggle learning to manage hunger during the early phases of adopting the diet may also find it difficult to follow.
Mainstream Belief Behind Diet
The mainstream belief behind intermittent fasting is that it unlocks aspects of our evolution as human beings and conveys some health and weight loss benefits when compared to our traditional 3 meals per day approach.
Several of the beliefs underlying intermittent fasting are:
- Maximizing the time your body spends oxidizing fat
- Minimizing overall insulin load to the system
- Improved energy levels,
- Increased longevity.
Scientific Studies and Interpretation of Data
There are quite a few studies that delve into the benefits of intermittent fasting as a tool to promote fat loss.
As mentioned prior, the ideal of fasting to promote health benefits has been around since ancient civilization.
Today, many of the general speculations regarding the general health benefits of fasting still ring true, however whether or not this has more to do with caloric restriction is still up for debate.
Below we will outline some of the studies that have been conducted that lay out these benefits in an unbiased platform.
Fat Loss Benefits
One of the major claims of intermittent fasting is that it is an excellent tool for fat loss. There have been several studies that have examined the role of meal frequency in fat loss, including things like alternate day fasting and even the intermittent fasting protocol.
For a long while these studies were brushed off by social media and fitness forums as they were not truly studies of the specific intermittent fasting protocol; however, recently one study was done that followed the traditional 16/8 fasting/feasting protocol as prescribed by traditional intermittent fasting protocols1.
In this study, the group following the intermittent fasting protocol did lose about 3.5 pounds more fat than the normal dieting group; however, this also occurred concurrently with lower calorie intake than the normal diet group so it is likely the greater fat loss was due to lower calorie intake.
One of the more interesting notes about this study, as mentioned by Greg Nuckols is that, “Testosterone and IGF-1 levels decreased, levels of several pro-inflammatory cytokines decreased, cortisol levels increased, insulin and blood glucose levels decreased, triglyceride levels decreased, T3 levels decreased and RER decreased slightly.
Those are all things you’d expect to see in a calorie deficit. And while it’s true that the IF group was in a calorie deficit, it was a very small one (less than 10% below maintenance) – probably not a large enough deficit to explain those effects.
On the whole, this study makes it seem that IF “tricks” your body into thinking you’re dieting, even if you’re at (or at least close to) caloric maintenance, in a manner that’s generally consistent with improved health and longevity”2.
Muscle Building Benefits
When you look closely at the fasting literature it appears that intermittent fasting does not appear to convey any additional benefits to muscle building when calories are held equal.
That being said, periods of fasting may improve the quality of muscle tissue by increasing its cellular cleaning processes (e.g. autophagy and heat shock protein response)3,4,5. However, this research is currently preliminary and is mostly speculation at this point.
Overall Health Benefits
Of all the areas of research on fasting, the effects of fasting on overall health and longevity perhaps the most interesting. Several studies in animal models have shown that periods of fasting increase lifespan and improve several metabolic parameters as these animals age6,7.
Perhaps the best known phenomena of fasting is increases in autophagy, a cellular “cleaning process”. There is some good animal evidence to also suggest that fasting may increase longevity; however, the data in humans is short term and long term data is not available, so much of this is still speculation8.
Intermittent fasting offers a food-flexible approach to dieting and may have some unique metabolic benefits for health and longevity. From a fat loss perspective, intermittent fasting can be an excellent tool, mainly due to controlling calorie intakes.
Intermittent fasting can be used in its widely known format of a 16 hour fast followed by an 8 hour feasting window; the alternate day fasting approach with a 24 hour fast followed by a 24 hour feast. Intermittent fasting is easy to follow in that it does not limit or restrict food, allows one to eat without tightly tracking calories.
- Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males
- The “Leangains” Intermittent Fasting Study Is Finally Here
- AMPK Activation of Muscle Autophagy Prevents Fasting-Induced Hypoglycemia and Myopathy during Aging
- Autophagy is required to maintain muscle mass.
- Long-Term Calorie Restriction Enhances Cellular Quality-Control Processes in Human Skeletal Muscle
- Apparent Prolongation of the Life Span of Rats by Intermittent Fasting
- Fasting: Molecular Mechanisms and Clinical Applications
- Effect of 6-Month Calorie Restriction on Biomarkers of Longevity, Metabolic Adaptation, and Oxidative Stress in Overweight Individuals A Randomized Controlled Trial
Also, can the fasting window change? If I have a late dinner do I just push back the next day or is it best to keep the same window each day?
You should do your best to keep it in the same window, but if you must make an adjustment, push back.
Based on your research and work, is IF successful for women in their 50's? I attempted to try fasting but I experienced some hair loss and freaked out so I stopped. Any suggestions on how to prevent it? Thanks
Hi, Kim. Leaving this up for Brad to answer if he sees it. I haven't worked directly with IF for women over 50, but according to the research I have seen, it can help and make positive differences. However, there can be side effects such as hair loss in some cases. Seek medical attention for the hair loss.
I would like to know if i divided the fasting & feasting as per the below order
6 AM-12 PM FASTING
12 PM-8 PM FEASTING
8 PM-6 AM FASTING
As I'm also willing to work out from 8 PM for fat burn & muscle gain type of workout
Please advise if anything is incorrect in what was listed above, Thank you...
One last thing, for how long, shall I be on intermittent fasting?
That’s not combining anything. You’re fasting from 8pm til 12pm and feasting 12-8. That’s the traditional 8/16 feasting fasting plan.
I would like to do this, I’m planning my meals at 12, 16 and last meal at 20 o clock. But I have a big doubt after my workout, do I need to wait until 12 to drink my protein right? I’m planning to workout before 11. Thanks
Should you fast a certain amount of day in a week or any specific day or just pick and choose how many days you want to fast. Any specific guideline?
During the 16 hours fasting and 8 hours feasting diet plan, when would be the best time to workout?
Just before you start feasting? Four hours into feasting? Doesn't really matter?
While feasting. You don't want to train in a fasted state.
Hope this helps!
Hi, thanks for wonderful information. I would like to ask about my 2 days fasting Monday & Thursday, these days I am fasting from dawn to sunset and not even drinking water. I am trying to transform my body. Please suggest which diet plan should I follow ?
Mashallah that’s a great idea. Best 2 days to fast. You can do some light cardio or even train abs right before an hour of breaking your fast
I think without actual information about your weight, height, BMI, fat, etc... it is difficult to just suggest a dietary plan. Have a look online comparing to where you are now, and where you want to go.
However, one extremely foolish idea is to not drink water. The way your wrote ("not even drinking water") might imply that you think it's a good idea, it's not. Drink plenty of water, any day. It also helps keep your appetite in check while fasting.
Suggest you reduce the cardio and replace with interval training AND start intermittent fasting if you want to lose weight.
its because of religion fasting.
Would not recommend not drinking water. I had collapsed one day and my left side would flare in pain whenever I did anything related to it. Doctor said I didn't drink enough water while working out, I was prescribed medication and I had to drink at least 3 liters a day to counter-act the balance.
It's insane to not drink water.
Brad I am fairly new to endurance racing and Triathlons over the last three years I lost 40 lbs but after each season of racing I am gaining weight and then instead of losing the weight I start to bulk up into muscle.
My calorie intake is super low as I started to lose 10 lbs by dropping food and maintaining routines but I am exhausted all the time and I get 7-8 hrs of sleep with a pretty low stress lifestyle.
My calorie count is around 800-1000 as I am petite 5’2 and am trying to get back down to 110 but at 135 currently with lean body fat on arms and legs and back and chest but a pokey tummy -
How do you lose the muscle with out just turning the inches into fat? So need some hints
My work outs are
Mon wed Friday swims at noon for an hour & runs 6 days a week
Tuesday thursday yoga & Pilates in the morning with cycling for an hour and weights
And Saturday’s are 2 hours of spin with a 6-10 mile run
Meals are 30/30/30 carb/protein/fat
Chia pudding with fruit or protein green spinach smoothie
Lunch is salad with or meat & cheese roll ups
Snack power bar protein bar vanilla
Dinner is soup or portabello large mushroom cap made into pizza or veggie wrap with meatless crumbles tacos.
Avoiding breads and sweets other than fruit and the protein bar
Coffee with almond milk 30cal or green tea
Way too much cardio