The health and fitness industry is abuzz with another diet newcomer: intermittent fasting (IF).

Studies done in the 1930’s and 1940’s give good indications that IF has positive effects on life expectancy and these studies seem to have been confirmed in more recent studies. However, it should be noted that many of the favourable results come from animal trials. To-date there have only been a handful of human studies done, and the ones that have been done have had very small sample sizes.

More recent studies using Alternate Day Fasting (ADF) – a protocol of intermittent fasting – has resulted in 3% – 4% fat loss. In addition to this, there many anecdotal reports on blogs and in the media that IF is successful for both weight and fat loss.

In addition to ADF, there are a number of other IF protocols which mainly vary the duration of the fasting and eating window.

For years we’ve been told by fitness gurus and nutritionists that the best path to fat loss is to eat small meals every few hours. This, they claimed, would keep your metabolism running like a well oiled machine while at the same time, would prevent your body from going into a dreaded fat-storing “starvation mode”.

There’s a lot of anecdotal evidence that this eating strategy works for some people, but according to a number of scientific studies, the frequency of meals has absolutely no effect on fat loss [1, 2], but does have beneficial metabolic effects on dietary thermogenesis and insulin sensitivity[3] (in other words, it helps regulate your blood sugar levels, which in turn can help keep your appetite under control).

And we think that those health benefits alone are pretty good.

But what about fat loss?

It all just boils down to: burn more calories than you consume, right?

Well… maybe not. Enter: intermittent fasting.

The health and fitness community has been buzzing about intermittent fasting as THE go-to-diet for fat loss… so FitBodyHQ decided to investigate!

What Is Intermittent Fasting?

Intermittent fasting is a short period of controlled fasting which, according to emerging scientific evidence, could lead to health benefits and fat loss.

And you may be surprised to find that it’s not actually that new.

We already know from experiments done in the 1930’s that the best way to extend life expectancy (in mice at least) was to put them on a nutrient-dense, low-calorie diet. The stunning results were that they lived up to 40% longer than their counterparts[4]. Recent findings are showing the same life extension benefits in rhesus monkeys[5].

How Does It Work?

Intermittent fasting works for weight loss because you are reducing your total caloric intake, and this combined with your usual level of activity will naturally lead to fat loss. As long as you are using more calories than you are consuming, you will lose weight. If you increase activity levels (i.e. burn more calories) and/or decrease caloric intake, over time you will lose weight.

Studies have further shown that despite the expectation that following fasting days, there would be a strong desire to consume much more than the normal caloric intake, researchers were surprised to discover there was only about a 10% increase in calories consumed.

Intermittent fasting also reduces the production of insulin-like growth factor (IGF-1). IGF-1 is like the green-light telling your body to “Go! Go! Go!” – in other words, to engage in growth processes – which is good when you’re young. By reducing IGF-1, the body goes into a rest-and-repair mode and engages in a healing-response known as autophagy (kind of like a clean-up process for your cells).

Did You Know?

During the darkest years of Great Depression (1929-33), when food was scarce due to drought, rather than decreasing, life expectancy actually increased by a remarkable six years. This prompted keen scientific interest on the effects of caloric restriction on lifespan.

What Are The Benefits?

We were surprised to discover that a similar experiment (to the 1930’s one above) had been done with intermittent fasting in the 1940’s, which also demonstrated beneficial effects on lifespan [6]. More recently, a study done in 2007 found that intermittent fasting may possibly lead to a number of health benefits[7] (although further study will need to be done):

  • Improved insulin sensitivity
  • Lower blood pressure
  • Reduced cardiovascular disease risk *
  • Reduced cancer risk *
  • Reduced risk of Alzheimers *

*(in animals, longer study needed for humans)

Further studies are showing that intermittent fasting is also a viable option for weight loss [8, 9].

There’s also mounting anecdotal and photographic evidence that IF works well when combined with vigorous exercise, for e.g.: here, here and here.

How Do You Do It?

Getting started with intermittent fasting can seem a bit tricky because there are so many different “protocols”.

Do you do the ‘alternate day fasting’, the ‘one or twice a week fast’ or even the ‘5:2 diet’? Too many options! Relax, the basic idea behind them all is the same – alternating periods of fasting with shorter windows of eating. Here are some of the common intermittent fasting protocols people are using:

Intermittent Fasting Protocols

Eat Stop Eat

How it’s done:

  • Once or twice per week you fast for 24 hours.
  • Part of the appeal of this protocol is that it’s very simple and very flexible.
  • Essentially all you need to do is skip meals from breakfast to breakfast on your chosen days.
  • On your eating days, you eat normal-sized, low-carb, nutrient-dense diet (i.e. lots of vegetables).

Similar to: 5/2 diet

Further resources:

Alternate Day Fasting

This protocol was recently featured in the program Eat, Fast and Live Longer.

How it’s done:

  • Alternate fasting days with eating days.
  • On eating days, you eat as you would normally.
  • Repeat this pattern.
  • Can be rigid and hard to maintain long-term; about 36 hours of fasting every other day.
  • You will be fasting at least 1 day every weekend.

A milder form of this method is the Alternate-Day Diet, where:

  • On fasting days you eat approximately 25% of your recommended daily intake.
  • Thus it’s easier to maintain long-term.

Further resources:

Eat, Fast and Live Longer
Alternate-Day Diet on Amazon


The Leangains method is geared towards people who are involved in fitness and strength training, with a focus on getting as lean and as strong as possible. This means that the emphasis is placed on pre-workout and post-workout nutrition. It encourages hormonal entrainment, so requires a more constant schedule and while it is very comprehensive, it is also more complicated; so not newbie friendly.

How it’s done:

  • 16 hour fast each day (or optionally 14 for women).
  • 8 hour window of eating (or optionally 10 for women).
  • You never go to bed hungry (e.g. according to your schedule, you can have food in the afternoons and evenings).
  • This makes it much more attractive to maintain long-term.
  • Three days of strength training, with majority of calories consumed in the post-workout meal.
  • You train in a fasted state (other than consuming branch-chained amino acids pre-workout).

Further resources:

Leangains Guide

Warrior Diet

Also known as the 1 Meal A Day diet.

How it’s done:

  • You eat 1 meal a day; at night, in order to accommodate circadian rhythms.
  • You can eat small amounts during the fast; whey protein, berries and greens.
  • Accommodates different fitness training intensities, by recommending pre-workout and post-workout meals.

Further resources:

The Warrior Diet on Amazon

Weight Loss Results

Intermittent Fasting works for weight loss because it reduces your total calorie intake and some studies have shown that intermittent fasting does contribute to weight loss:

  • Over 22 days, non-obese patients lost an average of 4% total fat [9].
  • Obese patients, consuming 25% of daily calorie needs on fast days, lost 5.5 pounds in eight weeks and about 3% body fat [10].
  • Was found to be as effective as calorie restriction for promoting weight loss in young, overweight women [11].

In the studies above the alternate day fasting protocol was used.

There have also been favourable weigh loss reports in the media [12, 13].

Differences For Men vs. Women

In the studies that have been done, there have been definite differences in response across the genders; male rats seemed much better equipped to handle nutritional stressors.

Two excellent articles going into detail about the differences in response, are here and here.

Tips To Making It Easier

  • Start off simple; try the Eat Stop Eat method or the Alternate Day Diet.
  • Understand that intermittent fasting is less a diet and more a lifestyle change.
  • Remember: sleeping hours count as fasting hours!
  • Keep busy during fasting hours; it’s a great time to get engaged in meaningful work.

Things To Be Aware Of

Most importantly: before starting any new diet and exercise program, you need to check with your doctor and clear any exercise and/or diet changes with them before beginning.

Stay adequately hydrated regardless of which protocol you’re using.

Intermittent fasting isn’t magic; you still need to eat a healthy, nutrient-dense diet and perform adequate exercise.


According to the small number of studies done so far, intermittent fasting may have a number of health benefits, positive effects on lifespan and promote weight loss.

But, more human studies with greater sample sizes, will need to be done in order to form a meaningful conclusion [14].

Until then there are a myriad of anecdotal reports which claim weight loss and health benefits, so it is really down to the individual (under the guidance of his / her doctor) whether to try this diet.

Next Steps

Since the anecdotal results sound so promising, we’ve decided that we’re going to take this to our Fitness Lab (not an actual lab) and use ourselves as guinea pigs.

Stay tuned for our next in the series: FitBodyHQ Experiments With Intermittent Fasting.


Alternate-Day Diet on Amazon
The Warrior Diet on Amazon
Leangains Guide
Eat Stop Eat


3 Responses to “Intermittent Fasting For Fat Loss: What It Is, How You Do It & Does It Work?”

  1. Kiki

    so on fasting days (eat stop eat or the alternative days method), you just workout like you normally would right?

    • FitBodyHQ

      Yes. Of course, you could always add a pre-workout shake if you find that you can’t bring as much intensity to your workout.

  2. heartburn

    18/6 IF eliminates the heartburn for me (active female).

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