The Science Behind Intermittent Fasting

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Intermittent fasting (IF) has only recently gained popularity among those of us interested in getting stronger, more muscular, and less fat.

Perhaps the very first person who ever put intermittent fasting under the spotlight was Martin Berkhan back in 2007. Since then, lots of other people have followed suit and are now preaching about the efficacy of IF.

For a long time, it was common belief that we needed to eat multiple times per day to keep the metabolism running and avoid muscle loss.

But, as research piled on and as people adopted IF and managed to get great results, our mindset slowly shifted away from that myth. In the 2010-2012 period, the interest for intermittent fasting skyrocketed and it’s been high ever since.

But, is there science behind intermittent fasting? Does it deliver benefits? Let’s find out.

Related: The Leangains Method: The Art of Getting Ripped. Researched, Practiced, Perfected.

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Martin Berkhan is the creator of leangains and is known as the father of Intermittent Fasting

The Science Behind Intermittent Fasting

For a long time, the only research on IF was done on rodents. Very few human trials saw the light of day, until recently.

The first study done on experienced lifters was published back in 2016 (1). In it, the participants were mostly in their late twenties and early thirties with at least five years of lifting experience.

They were split into two groups:

Group 1 ate all their calories in an 8-hour window: at 1 pm, at 4 pm, and at 8 pm.

Group 2 ate in a normal, 12-hour window: at 8 am, at 1 pm, and at 8 pm.

Calories and macronutrients were recorded at the start of the study, and the subjects were instructed to maintain their eating patterns throughout the weeks with the goal of having them eat around maintenance calories.

There weren’t any significant differences between the groups, and their caloric intake stayed more or less consistent throughout the study. The subjects also consumed 1.8-1.9 grams of protein per kilo of body weight.

Both groups trained three times per week, and the study lasted for eight weeks. The first session consisted of bench press, incline flyes, and curls. The second workout consisted of shoulder press, leg curls, leg press, and leg extensions. The third session consisted of two lat pulldown variations and tricep press downs.

The training volume wasn’t high, but the program was well-balanced.

The results were interesting:

Group 1 saw some fat loss (about 1.6 kilos/3.5 lbs) compared to Group 2. This could be because the IF group was eating in a slight caloric deficit, but researchers also suggest that this can be attributed to a hormone called adiponectin which was higher in Group 1 compared to Group 2.

(Adiponectin may signal the brain to increase energy expenditure, among other things (2).)

Also, Group 1 saw a decrease in testosterone, IGF-1 and T3 levels. Cortisol levels increased, insulin, blood glucose, and triglycerides decreased.

Both groups maintained their muscle mass and strength.

It would appear that intermittent fasting makes your body think that it’s dieting, even when calories are just below maintenance (as they probably were for Group 1). The researchers concluded that IF could be a viable option for resistance-trained men to lose some fat, maintain their muscle mass, and improve certain health markers.

And coincidentally, a review published the year prior concluded (3):

Clinical research studies of fasting with robust designs and high levels of clinical evidence are sparse in the literature. Whereas the few randomized controlled trials and observational clinical outcomes studies support the existence of a health benefit from fasting, substantial further research in humans is needed before the use of fasting as a health intervention can be recommended.

And seeing as IF has been shown to have health-promoting effects on healthy and active guys, we can add one point to fasting.

Health benefits of IF have also been shown in numerous other studies:

  1. Fasting may enhance human growth hormone levels (4, 5).
  2. Fasting may enhance cellular repair mechanisms in the body (6, 7).
  3. Fasting may decrease blood insulin levels and enhance fat burning (8).
  4. Fasting may decrease blood sugar levels and offset insulin resistance (9).

Additionally, some research done on obese individuals following a fasting protocol has shown promising results (10, 11, 12):

  • High adherence to dieting;
  • Reduced body weight and fat mass;
  • Decreased LDL cholesterol and triacylglycerol concentrations;
  • Lower blood pressure;
  • Reductions in markers of oxidative stress;

And it doesn’t end there:

Research has also looked at IF in relation to muscle mass, and there doesn’t appear to be a ‘hampering’ effect on those sweet gains (13, 14).

In other words, total number of calories and protein in addition to a sound training program are the biggest predictors of body changes, not meal frequency (15, 16, 17).

We’ve known this for a while, but it’s a nice reminder to stop obsessing over meal frequency (18).

The Bottom Line on Intermittent Fasting

Although the science behind intermittent fasting doesn’t show superior muscle-building benefits, it has been shown to help subjects adhere to the consistent caloric intake. This, in and of itself can make bulking and cutting periods much more effective with little to no ‘slip-ups’ in the process.

If you are someone who constantly struggles with hunger while both bulking and cutting, IF may very well be the solution you are looking for. By having a dedicated eating window, you are going to have a much easier time eating just the right amount of calories and not go over that number.

You’ll be able to have fewer, bigger, and more satisfying meals while still reaching your body composition goals. Think of it this way:

If you are cutting and you’re eating 2500 calories each day, you are going to have a much easier time adhering if you skip eating in the morning, drink some coffee, break your fast around 1 pm with a big meal and eat another big meal around 8 pm.

Also, IF has been shown to improve many health-related markers in both lean and overweight/obese subjects.

Intermittent Fasting has also been shown to have beneficial effects for blood glucose and insulin and the prevention of type 2 diabetes.

On top of all that, intermittent fasting provides a great benefit:


Having fewer meals to worry about each day makes it much simpler to enjoy your diet and not stress out.

If you would like to learn more about Intermittent Fasting, please check out The Leangains Method by Martin Berkhan.


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Hey, I'm Brian, the creator of I've been weightlifting / bodybuilding for 20 years and now I'm ready to share some knowledge. Check out my About Me page to hear my story.

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