How It WorksPricingBlogRecipesStoriesGroups

Finally, A Beginner’s Guide to Intermittent Fasting That Will Make You A Pro In 5 Minutes Or Less (That’s Based On REAL Science)

Avatar Nutrition Staff

September 20, 2017


How many times have you heard…

“Kick start metabolism with a big healthy breakfast.”

“Eat regular small meals every two to three hours.”

“Never skip a meal or metabolism will slow to a crawl!”

These weight loss tips have been repeated so often that many accept them as fact. Except…they’re not!

What if I told you there is no metabolic advantage created by eating breakfast? Or splitting calories over 6 meals rather than 3? Your body will not go into “starvation mode” if you skip a meal. In fact, some weight loss science actually supports a pattern of eating that promotes skipping meals.

We’re talking about intermittent fasting. Will it help you reach your goals?

Breaking Down Intermittent Fasting

Intermittent fasting sounds complicated, but it really isn’t. It’s simply going an extended period of time without eating—usually between 14 and 48 hours. This means that when you sleep you practice intermittent fasting!

Think of it this way—your life consists of periods of eating (feeding) and periods of not eating (fasting).

Let’s take a look at your day.

Say you eat dinner at 6pm, go to sleep at 10pm, and wake up and eat breakfast at 8am, you’ve just fasted 14 hours. You have eaten all of your meals between 8am and 6pm, which means you’re “feeding” time is 10 hours. In this way, you’ve practiced intermittent fasting since you spent more time fasting than you did feeding!

There are several versions of intermittent fasting, with the length of the feeding window differing between each. For example, some people will strategically eat over an 8-hour window (16/8 fast) or a 4-hour window (20/4 fast), whereas others may skip an entire day or two of eating altogether. Still, others choose to alternate days of eating and not eating (Alternate Day Diet).

Why Fast?

Although it may sound miserable to some, most people start intermittent fasting with the intent to lose weight.

Going long periods without eating is a pretty good way to eat fewer calories overall, and by cutting out an entire meal, you can consume more food at other meals and still be in a caloric deficit. This means that rather than continuously battling hunger, you can limit that feeling to a fixed period and eat comfortably the rest of the day!

In addition to making calorie restriction and fighting cravings more manageable, research shows that there may be other benefits to intermittent fasting, including [1-4]:

  • Better immune function
  • Lower inflammation
  • Reduced oxidative stress
  • Enhanced cognitive function
  • Increased autophagy (recycling of damaged cellular components)
  • Improved insulin sensitivity
  • Improved blood lipid profile

Now, to be fair, many of these benefits occur simply because of calorie restriction and losing weight in general, so it’s not possible to attribute them specifically to intermittent fasting. But, it is possible that the process of fasting itself initiates physiological changes that boost these benefits to a greater degree than what might be achieved through conventional calorie restriction alone. Let’s talk about why.

What Happens To Your Body During a Fast?

People are evolutionarily hardwired to intermittent fast [5]. Our ancestors needed to be able to thrive in conditions with a limited food supply, so there was a survival advantage for those who could tolerate and adapt to long periods without food. One of these major adaptations is the switch from glycogen as a fuel source to fatty acids and ketones [1]. It works like this:

When you stop eating, your body is forced to turn to its reserves for energy. First, it burns through sugar in your blood, and then it turns to the stored sugar around your liver and muscle (glycogen). Without sugar to pull into cells and burn for energy, the hormone insulin drops and the body becomes increasingly reliant on its fat stores. After about 24-hours of fasting (give or take a few hours), glycogen stores are depleted. At this point, being primarily reliant on fat for energy, the liver begins to ramp up its production of an alternative fuel source called ketone bodies.

Ketone bodies are always present in your blood at a minuscule level, but are progressively increased within 24 to 48 hours of fasting (depending on activity and prior nutrition status). Unlike fat, ketones can cross the blood-brain barrier and fuel central nervous system cells. In this way, they act as a substitute for sugar. But serving as an energy source isn’t the only thing ketone bodies do—they also:

  • Stimulate pathways that reduce oxidative stress and inflammation
  • Enhance brain function
  • Induce autophagy to remove cellular garbage (such as damaged cell components) [2,6].
  • If that weren’t enough, along with lower levels of insulin, ketone bodies work to suppress appetite!

There’s Just One Catch…

All of this sounds great, but before you decide if intermittent fasting is right for you, there are some practical implications to consider. Mainly, the length of the fast will determine the degree of benefit you get from intermittent fasting, as well as the degree of risk.

While it’s true that extending a fast from say 16 hours to 48 hours will bring about much higher ketone production and possibly a greater level of associated benefits, it also creates a greater stress on the body and increases the risk of losing muscle and maybe even slowing metabolism.

Although a gradual increase in growth hormone and ketone production (which is protein sparing) limits muscle loss while fasting [7], research has shown that there is an increase in the rate of protein breakdown in the body between 15 hours and 30 hours into a fast [8]. After a very lengthy fast—think more than a day or two—there may also be a reduction in thyroid hormone and testosterone in men [9, 10], acting to slow your metabolism down and make you more energy efficient. You definitely don’t want that when you’re trying to cut weight!

Really, the key to successfully fasting is to get in and out with your skeletal muscle and metabolism intact. This means fasting for the right length of time to reap some of the benefits of intermittent fasting while minimizing any potential downsides!

How To Implement Intermittent Fasting

Intermittent fasting is not for everyone. In fact, if you can relate to the following, you would probably do better to avoid intermittent fasting:

  • You love eating every two or three hours
  • You have trouble controlling your blood sugar levels
  • You’re extremely active and require a lot of fuel
  • You’re eating higher calories and need all the meals possible to fit them in
  • You’re unwilling to risk losing muscle (i.e. your goal is muscle gain)

However, if you are eating lower calories and want to give intermittent fasting a try, we recommend sticking to the 14-18 hour fasting window (i.e. eating only from 8am to 6pm or Noon to 6pm). This shorter fast is more manageable and less stressful on the body, carries a lower risk of muscle loss and any adverse effect on metabolism, and is more conducive to an active lifestyle.

At the same time, you will benefit from eating satisfying meals rather than “fun size” meals that leave you wanting more, and you can break any mental addiction you have to food and the need to constantly snack. You may also reap some of the other health benefits of intermittent fasting, particularly if you are restricting calories and exercising.

“No matter how small the feeding window, it’s still possible to overeat or under eat and sabotage your body composition goals”

Although intermittent fasting may make it easier to hit lower calorie targets, this doesn’t mean you should ditch tracking your intake. After all, no matter how small the feeding window, it’s still possible to overeat or under eat and sabotage your body composition goals! To ensure you progress toward your goal, continue to hit the daily macro targets Avatar Nutrition sets for you.

Remember that intermittent fasting is not magic. You’re not going to lose more weight using intermittent fasting than you would be eating an equal amount of calories distributed evenly throughout the day [11], and the increase in growth hormone that occurs over the fasting period isn’t going to make you jacked (you’re not even eating any nutrients that feed muscle during this time). But intermittent fasting can be a useful tool to make hitting lower calorie targets more manageable, and it may even have some additional health benefits.


[1] Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab. 2014 Feb 4;19(2):181-92. doi: 10.1016/j.cmet.2013.12.008. Epub 2014 Jan 16.
[2] Youm YH et al. The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease. Nat Med. 2015 Mar;21(3):263-9. doi: 10.1038/nm.3804. Epub 2015 Feb 16.
[3] Azevedo FR et al. Effects of intermittent fasting on metabolism in men. Rev Assoc Med Bras. 2013 Mar-Apr;59(2):167-73. doi: 10.1016/j.ramb.2012.09.003.
[4] Rothschild J et al. Time-restricted feeding and risk of metabolic disease: a review of human and animal studies. Nutr Rev. 2014 May;72(5):308-18. doi: 10.1111/nure.12104. Epub 2014 Apr 16.
[5] Mattson MP. Challenging oneself intermittently to improve health. Dose Response. 2014 Oct 20; 12(4):600-18.
[6] Veech RL et al. Ketone bodies, potential therapeutic uses. IUBMB Life. 2001 Apr;51(4):241-7.
[7] Moller N et al. Growth hormone and protein metabolism. Clin Nutr. 2009 Dec;28(6):597-603. doi: 10.1016/j.clnu.2009.08.015. Epub 2009 Sep 20.
[8] Tsalikian E, et al. Increased leucine flux in short-term fasted human subjects: evidence for increased proteolysis. Am J Physiol. 1984 Sep;247(3 Pt 1):E323-7.
[9] Merimee TJ, Fineberg ES. Starvation-induced alterations of circulating thyroid hormone concentrations in man. Metabolism. 1976 Jan;25(1):79-83.
[10] Nair KS et al. Leucine, glucose, and energy metabolism after 3 days of fasting in healthy human subjects. Am J Clin Nutr. 1987 Oct;46(4):557-62.
[11] Seimon RV et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418 Pt 2:153-72. doi: 10.1016/j.mce.2015.09.014. Epub 2015 Sep 16.