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Editor’s Note: This post was updated on August 14, 2018for accuracy and comprehensiveness. It was originally published on August 24, 2016.

Do you ever feel like you’re exercising and hopping from one diet regimen to another for nothing?

For some folks, accomplishing desired health and fitness outcomes is incredibly frustrating. Whether it’s losing weight or improving body composition, what worked for co-worker Caroline may not necessarily work for you.

Take, for instance, intermittent fasting.

It’s easy to find stories of people who wax poetic and swear by intermittent fasting (IF), including entrepreneur-author James Clear, Coldplay’s Chris Martin, and Hugh Jackman who had to gain lean muscle for The Wolverine. Meanwhile, there are also individuals who are quick to point out that skipping meals for longer periods didn’t work for them and even led to another host of health issues.

But you’re skeptical.

Why would it work if it’s the total opposite of what the majority of us has known for a while now? We’re supposed to eat small, frequent meals throughout the day to keep our metabolism in a constant state of stoking the proverbial furnace, right?

In this blog post, we’ll get into the meat (and marrow if you want to dig deeper!) of established facts and the newest findings on IF to help you decide.

How Intermittent Fasting Works

Put it simply, anyone who goes through Intermittent fasting follows a certain cycle of fasting and eating.

While most diets will recommend specific types of healthy food to eat or recommending a calorie intake IF helps you accomplish health and fitness goals by recommending how often you should eat. The period time you consume calories will be time restricted, following by periods of fasting.

Currently, there are numerous  IF protocols out there, but the most well-known include:

Lean Gains (16/8 Method)

Leangains intermittent fasting

Martin Berkhan of (hence it’s often referred to as the Lean Gains method) popularized the sixteen–hour fast and eight–hour eating period in a day. In this method, you eat your first meal right after the 16-hour fast.

This IF style works for some folks because they don’t have to worry about being hungry for the entire 16 hours. Often, they’ll sleep (and automatically fast) for 8 hours more or less, and extend that fasted state for another 8 hours.  Let’s say you had your last meal at 7 pm, slept at 9 pm, and woke up at 5 am. You’ll eat your first meal at 11 am if you follow this Intermittent Fasting regimen.

Aside from the eating schedule,  Lean Gains also recommends a high protein diet, carb cycling, a structured exercise regimen complemented with fasted training, and consuming more calories during workout days.

Eat Stop Eat (2×24/week Method)

weekly intermittent fasting chart

In this IF regimen, you will have two fasting days, each a 24 hour period, per week. For example, you will have brunch at 10 am today and will start fasting until the same time again tomorrow. If you think you can manage better if you do it with dinner, you can also opt for that pattern.

Alternate Day Fastingalternate day intermittent fasting chart

In essence, alternate day fasting recommends that you have a fasting day every other day. In the sample alternate day schedule below by James Clear, you’d fast overnight on Monday and all day on Tuesday. You’d eat again on Tuesday at 8 pm, do your usual eating pattern all day on Wednesday, and repeat the same 24 hour-fast by Wednesday at 8 pm.

Random Meal-Skipping

Individuals who randomly skip meals believe that not giving in to your hunger pangs on certain times of the day, breakfast, for instance, may have the same benefits (discussed below) as the aforementioned IF protocols.

This less methodical approach of Intermittent Fasting is also a nod to what our ancestors supposedly experienced when hunting or foraging for food —not adhering to certain eating schedules and eating only when they were truly hungry and/or when they had enough food around.

What’s In It For Me and My Body Composition Goals?

Now that you have an idea of the different intermittent fasting protocols that you can possibly explore, let’s move on to its health benefits – what’s in it for you?

Intermittent Fasting and Insulin Sensitivity

For a start, 20-hour fasting periods has been shown to increase insulin sensitivity.

Here’s a quick lesson on what insulin does. This hormone helps clear glucose (otherwise known as blood sugar) from the bloodstream after a meal. It will primarily deliver this glucose to the liver and skeletal muscle and served as stored energy in the form of glycogen. It will either deliver this glucose (sugar from the food you eat) to your liver for storage and later use or to the skeletal muscles for energy.

However, eating way too often, too much, or too poorly can make your body less sensitive (insulin resistance) to insulin’s effects. As a result, your liver and skeletal muscles will stop receiving more glucose.

So what happens next? In response to insulin resistance, the liver produces triglycerides that are stored into existing body fat for later, just in case you’ll need them for energy in the future. This could have been useful for our ancestors ages ago when there was a shortage of food, but not so much anymore when you can just eat wherever and whenever you want.

As IF increases your insulin level and increases sensitivity, you get a one-two punch of benefits:

  • First, your body becomes less resistant to insulin, which in turn helps prevent storage of excess glucose as fat. This is good news if you’re currently working to lose fat mass (and gain lean body mass later on) as part of your plans to change your body composition.
  • Second, low triglyceride levels (resulting from increased insulin sensitivity) is associated with reduced risk of coronary disease. Research cardiologists at the Intermountain Medical Center Heart Institute have already confirmed this benefit in relation to fasting.

Intermittent Fasting and Growth Hormone Production

The cardiologists at the Intermountain Medical Center also uncovered something else: human growth hormone (HGH) levels were elevated amongst their subjects during the 24-hour fasting period — an average of 1,300 percent in women, and nearly 2,000 percent in men.

What’s the connection with body composition?

Here’s a quick look on HGH.  One of its main function in stimulating cellular growth is to signal the liver and other tissues to secrete IGF-I (Insulin-Like Growth Factor 1). IGF-I plays a significant role in muscle growth and increasing Lean Body Mass. This is positive body composition change.

There appears to be a positive link between increases in HGH and Lean Body Mass. In an article published in The New England Journal of Medicine,  healthy men between 61 to 81 years old with low IGF1 levels were given HGH for six months. A second, control group didn’t receive HGH.

After six months, there was no significant body weight changes among the two groups. However, the HGH group increased their Lean Body Mass by an average of 8.8% and decreased body fat mass by an average of 14.4% vs. the control group. Skin thickness in the HGH group also showed marked improvements.

While men ages 61-81 is a pretty specific population with some pretty impressive results (increased LBM and decreased body fat), other more general populations have also experienced benefits linked with intermittent fasting. Recent research (2016) on the effects of Ramadan, an Islamic holy month in which practitioners fast throughout the day, may offer some additional insight.

The data revealed that while body fat loss occurred after the fasting period, there was little to no muscle mass loss. This may be due to the fact that although the participants fasted, their overall daily calorie intake remained unchanged. Keep in mind, however, that the subjects regained the body fat and overall weight they lost 4 to 5 months after Ramadan.

The Role of Exercise in Intermittent Fasting

In fitness and nutrition, it’s common advice to eat a healthy snack or meal before a workout. However, proponents of IF also recommend a regular exercise regimen with IF if you want to experience positive results with body composition and weight loss.

In a 2014 abstract presented at the Journal of the International Society of Sports Nutrition annual conference, an intermittent fasting protocol (closely similar to the Lean Gains protocol) resulted in a decrease in fat mass as well as weight loss when paired with resistance/strength training. The researchers concluded that IF may have maximum benefits to changing your body composition when it’s paired with resistance training.

Endurance athletes seem to benefit from IF too. Fasted training has been shown to boost glycogen resynthesis – which means glycogen gets replenished in the muscles faster, allowing for more activity and exertion. Cyclists who fast have also been shown to have increased power-to-weight ratios (a measurement they use to fine-tune their body compositions in search of the perfect balance of most power and least body weight).

On Intermittent Fasting and Its Role in Metabolism

Remember how you were told before that eating six meals a day will boost your metabolism? It turns out that increased meal frequency has no direct impact to body composition, particularly if you don’t exercise regularly.

Does that mean that fasting, the opposite of eating frequently, can boost metabolism? Not necessarily. In fact, metabolism may be slowed down during fasting as a means of conserving energy.

A good summary of the metabolic benefits/lack of benefits recently appeared in a blog post discussing Alan Aragon’s 2015 article Intermittent fasting: After over a decade of research, where are we today?

In his analysis, Berkhan concludes the following:

  • IF is effective for reducing markers associated with low body fat and has demonstrated superiority to other diet regimens
  • There is no metabolic advantage involved in IF’s effectiveness
  • Muscle gain may be possible in IF, but any gains may not be optimal
  • There is no significant difference in the results among popular IF protocols (LeanGains, Eat Stop Eat, Alternate Day Fasting) and all three have demonstrated effectiveness

Is Intermittent Fasting For Everyone?

While the practice of IF has been widely accepted and lauded for its benefits, there are some that report that IF may be detrimental in some cases, particularly in women’s health.

Several women who tried intermittent fasting reported irregular menstrual cycles and symptoms associated with hormonal imbalance. These reports are not to be dismissed, as fasting can also increase cortisol levels and consequently offset the hormonal balance. Hormones play a huge role in women’s reproductive cycles.

Currently, this issue is still up for debate as there are also women who report that they too have reaped the benefits of IF. If you’re a woman and planning to explore IF for your health and fitness goals, this IF for Women article by the Precision Nutrition team is worth checking out.

The Real Test: See For Yourself

To truly figure out if Intermittent Fasting really works for you, try it for yourself.

If you have existing health issues,  it’s best to consult with your physician or healthcare professional first before doing Intermittent Fasting.  In addition, it may not be a good idea to try IF if you have adrenal fatigue, hormonal imbalances, and if you’re nursing or planning to get pregnant.

Once you start IF, track your diet, calories, and body composition. Make sure that you are consuming a diet that provides you with enough calories and essential nutrients. Keep a food journal and record what you eat and how you feel during and after the fast. And test your body composition before and after IF to track any changes. By learning more about what works for you, you are already a step closer to accomplishing your long-term body composition goals.


Kyjean Tomboc is a nurse turned freelance healthcare copywriter and UX researcher.  After experimenting with going paleo and vegetarian, she realized that it all boils down to eating real food. 

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