Intermittent Fasting 101: A Beginner's Guide

An alarm resting on a plate next to a fork and knife representing intermittent fasting

Fasting is one of the oldest practices in human history.

Cultures across the globe have used fasting as part of religious practices as well as a form of treatment in traditional medicine to promote healing and prevent future illness. Even the “father of medicine,” Hippocrates believed that fasting was a powerful tool to help the body heal itself.

In recent years, fasting has become one of the most popular means to diet for fat loss. And it’s easy to understand why as some of the latest research suggests that fasting, in its various forms, may help you lose weight, improve overall health, and perhaps even live a bit longer.

Here we discuss all things intermittent fasting -- what it is, how to do it, and what (if any) additional benefits it provides.

What is Intermittent Fasting?

Intermittent fasting is a pattern of eating that alternates between periods of feasting (eating) and fasting.

It’s all the rage right now in the dieting world, and a lot of hoopla is made surrounding the “mystique” of it all, but essentially intermittent fasting is the purposeful and targeting intake of food during a small window of your day.

All other times, you avoid food and consume only non-calorie containing beverages (plain water, sparkling water, mineral water, black coffee, unsweetened tea).

Can I Drink BCAA While Fasting?

This is an incredibly common question regarding fasting in all of its forms, and it’s easy to understand why as quite frequently it is recommended that if you are performing fasted training or fasted cardio, you should consume a BCAA supplement (such as Steel Fuel®) to protect against muscle breakdown as well as enhance resistance to fatigue.

However, what many people do not realize is that if you drink BCAA while performing “fasted” cardio, you are no longer fasted. The reason for this is two-fold:

First, BCAAs contain calories, around 4 calories per gram.

What this means is that if you are consuming 5-10 grams of BCAA around your workout (before, during, or after), you’re ingesting somewhere between 20-40 calories. Now, this isn’t a lot of calories, but it still is something.

Second, BCAA cause a small release of insulin in the body, since the branched-chain amino acids, Leucine, in particular, are insulinogenic amino acids. <1,2,3> When insulin levels are elevated, the body is no longer in a fasted state, and fat burning is reduced.

Therefore, if you want to practice intermittent fasting, BCAA supplements do not qualify as a zero-calorie drink option and should not be consumed during your fasting window. If you do want to consume a serving or two of BCAA, drink them immediately pre-workout, which is when your fasting period will end.

What are the Different Methods of Intermittent Fasting?

While the term "intermittent fasting" in fitness circles typically refers to eating only during a small window each day, there are several different approaches to intermittent fasting used in research.

16:8 Protocol (LeanGains)

Far and away, the most prevalent form of intermittent fasting these days is the 16:8 protocol that was first popularized by Martin Berkhan, creator of the popular LeanGains protocol.

For this style of intermittent fasting, you fast for 16 hours of the day and consume all of your daily calories during an 8-hour window. Now, it's worth mentioning that women tend to do better with slightly shorter fasts. Ones that last ~14 hours, thereby giving them 10 hours to eat.

While this might sound a bit extreme, it's not all that odd.

All you're skipping is breakfast.

Here’s an example of a commonly used 16:8 intermittent fasting protocol:

  • 12:00 PM: Meal 1 -- pre-workout meal
  • 1:30 PM: 1 serving of pre-workout supplement (such as Steel Pump®)
  • 2:00 PM: Training
  • 4:00 PM: Meal 2 -- post-workout meal
  • 8:00 PM: Meal 3 -- dinner

That’s all there is to it!

You've confined you're eating to a tidy 8-hour window, and outside of this, you will be avoiding any calorie-containing foods.

And, as an added benefit, you'll also avoid the potential increased muscle breakdown that accompanies fasted training because your 2 PM training session takes place in your feeding window.

Now, the 16:8 protocol doesn't always have to be 12-8PM. If that doesn't work for your schedule, your window could be 10 AM - 6 PM or 2 PM -10 PM.

Choose whichever schedule works best for you and stick to it.

Generally speaking, most people do best when deciding to skip breakfast and fast in the morning. The reason for this is that most people typically aren't as hungry in the morning, and it's easier to stick to socially as the afternoon and evenings are when happy hour, and dinner outings are more likely to occur.


Eat-stop-eat is a form of intermittent fasting that requires a bit more discipline as you fast for an entire 24-hour period one or two non-consecutive days per week.

This method was popularized by Brad Pilon, a Canadian author with a graduate degree in Human Biology and Nutritional Sciences from the University of Guelph in Guelph, Ontario, Canada.

The easiest way to incorporate the eat-stop-eat protocol is to fast from one day’s dinner to the next, giving you a complete 24-hour fast. You can also fast from lunch-to-lunch or breakfast-to breakfast. The choice is yours, but they all accomplish the same thing -- not eating for an entire 24-hour period.

If you are doing eat-stop-eat to lose weight, then you must consume your usual amount of calories during your eating days.

As we mentioned above, eat-stop-eat is a bit more challenging than the 16:8 protocol as you're going for an entire day without eating. If you're new to fasting, you may want to first experiment with 14-16-hour fasts and see how you respond before proceeding to the full 24-hour fasts.

5:2 Diet

The 5:2 diet involves eating normally for 5 days of the week while limiting calorie intake to 500-600 on two non-consecutive days of the week. This style of intermittent fasting was popularized by British doctor and journalist, Dr. Michael Mosley, who also referred to the 5:2 diet as the "Fast Diet." <5>

This style of eating is also similar to a fasting-mimicking diet, a nutritional approach popularized by Italian-American bio gerontologist and cell biologist Dr. Valter Longo, who has become well-known in the biohacker and keto circles for his work on the role of fasting and nutrient response genes on cellular protection aging and longevity.

For the “fasting” days of the 5:2 diet, it’s generally advised that women consume 500 calories, and men consume 600 calories.

For example, if you're interested in trying the 5:2 diet, you might generally eat on every day of the week except Tuesday or Friday.

To date, only one study has specifically investigated the effects of the 5:2 diet on markers of weight loss and metabolic health. <6>

For the year-long clinical trial, researchers took 137 people with type 2 diabetes and placed half of them on a 5:2 diet and the others on a “continuous” energy-restricted diet, where they ate 1200-1500 calories a day.

At the end of the study, researchers observed that the individuals following the 5:2 diet experienced similar reductions in HbA1c (an important marker of diabetes progression) and weight loss as those following the standard weight loss approach. <6>

What this indicates is that from a weight loss and metabolic benefit standpoint, intermittent fasting isn't doing the "work" here, the driver of the improvements in health is the reduced energy intake and weight loss.

Keep this in mind going forward.

Alternate Day Fasting

This style of intermittent fasting is pretty self-explanatory.

Alternate day fasting alternates between days of eating normally and days of complete fasting.

Now, some “riffs” on alternate day fasting allow for an individual to consume up to 500 calories per day, which would make it more akin to a fasting-mimicking diet than a true on-off style of eating and fasting.

Several studies have investigated this dietary approach and found that it yields similar results to daily energy restriction in regard to weight loss and markers of metabolic health. <7,8,9>

However, one study found that individuals following the alternate-day fasting protocol were more likely to abandon their diet and/or consume more calories than allotted on their fasting days <8>, indicating alternate-day fasting has a bit of a more demanding “learning curve” than other forms of intermittent fasting.

Alternate-day fasting is more demanding than other styles of intermittent fasting, and as such, it is not recommended as the "gateway" approach to those looking to try their hand at intermittent fasting.

The Warrior Diet

If you want to feel like one of your paleolithic ancestors, you might want to try your hand at the Warrior Diet, an intermittent fasting approach popularized by Ori Hofmekler.

Eating like a “warrior” essentially involves eating small amounts of fruits and veggies during the day, and ending your day/night with one huge feast where you eat the vast majority of your calories within a 4-hour eating window.

The Warrior Diet also emphasizes foods that are in line with the paleo diet philosophy of eating.

How Does Intermittent Fasting Affect Cells and Hormones?

When we fast, we are depriving our bodies of food, which forces it to run on its stored energy (i.e., body fat).

During the fasting window, a few notable things happen with our hormones:


Most notably, when we fast, insulin levels remain very low <9>, which can be useful for those with type 2 diabetes and metabolic syndrome who struggle with insulin resistance and chronically high blood sugar levels.

As a result of these low insulin levels, fat oxidation (fat burning) is increased, which makes sense. Insulin levels rise in response to feeding, and when we are in a fed state, the body will use the energy from the food we just ate instead of relying on stored body fat to power it.

Now, do not confuse fat burning with weight loss, while the two terms are often used interchangeably, then do not mean the same thing. Technically, you are “burning fat” whenever your insulin levels are low.

But, if you are consuming an equivalent amount of calories to those that you expend each day, you will not lose weight.

And this is one of the biggest “secrets” a lot of keto and low-carb gurus won’t tell you. You can eat all the fat and avoid all the carbs you want, but if you are not in an energy deficit, you will not lose weight.

This is also why studies that have found similar results in weight loss between various fasting protocols and daily energy restriction. The driver of weight loss is not the fact that you are fasting; it's the fact that your body is expending more energy (calories) than it is consuming.


Part and parcel with low insulin levels is an increase in noradrenaline, a fat-burning catecholamine that stimulates the release of stored fatty acids from adipocytes (fat cells) when you are in a fasted state.

Remember, when you’re fasted, fat burning is increased. To kickstart the fat burning process, noradrenaline is released to bind to the beta receptors on your fat cells, releasing stored fatty acids into the bloodstream so that they can be picked up by carnitine and transported into the mitochondria for beta-oxidation and used to create ATP.

Growth Hormone

Similar to the hoopla that compound exercises like squats <10> receive concerning their ability to increase growth hormone secretion, intermittent fasting has received similar praise. Some research indicates that fasting may increase growth hormone as much as 5-fold. <11,12>

However, this transient increases in hormone levels will likely have little effect in the grand scheme of weight loss or muscle growth.

Cellular Repair

When you fast, your cells initiate various repair processes, such as autophagy, where cells “digest” (break down) and recycle old, dysfunctional proteins that accumulate within cells and use them to regenerate healthy cells. <29>

Metabolic Rate

One of the other alleged benefits of fasting is that it “boosts” your metabolic rate, and a pair of studies have documented that fasting for two days may boost metabolism between 3-14%. <13,14>

And, while this might sound impressive on paper, it should also be noted that fasting for longer than 48 hours has been shown to slow metabolism. <15> The reason for this is simple -- the body realizes it is being deprived of energy and naturally starts burning fewer calories to conserve its energy stores.

The takeaway here is that the effects on hormones and metabolic rates from short-term fasting are just that -- short-term. The notable and significant changes that happen to insulin, metabolic rate, BMI, body weight, etc. happen as a result of weight loss and a calorie deficit, not the fact that you are fasting.

Is Intermittent Fasting Powerful for Weight Loss?

Intermittent fasting can be a useful tool for weight loss, but several studies have shown that it is no more effective when it comes to losing weight and improving markers of metabolic health than continuous energy restriction <30>, as we discussed above in detail.

The one instance where fasting may be more “powerful” is in regard to adherence. The success of any fat loss diet ultimately boils down to your ability to stick to it for as long as needed to lose the weight you want to lose.

You could have the best fat loss diet ever created, but if you're miserable, hungry, and always feeling deprived, your chances of sticking to the diet (adherence) are slim and none.

If you find that by following intermittent fasting, you can maintain your calorie deficit more easily and feel less deprived than when you usually eat, then feel free to follow it.

Just realize that intermittent fasting doesn’t have any “magic powers” that make it more effective for weight loss than regular dieting where you eat your calories whenever you want to during the day.

Is Intermittent Fasting Good for Building Muscle?

Traditional bodybuilding lore is that if you want to build muscle, you need to eat 4-6 small meals per day, otherwise, without a constant influx of food, your body will go catabolic and will start breaking down muscle tissue.

This has many to believe that intermittent fasting is an inferior dietary approach for those wanting to build mass.

A recently conducted study by Tinsley et al. sought to investigate the effects of intermittent fasting (time-restricted feeding) in combination with resistance-training in females. <16>

40 females took part in the study and were randomized into one of three groups:

  • Control
  • Time-Restricted Feeding
  • Time-Restricted Feeding + HMB Supplement (3 g/d HMB)

What is HMB?

HMB is a metabolite of Leucine that was the bee's knees about 10 years ago in bodybuilding. It was promoted to help prevent muscle breakdown due to some research showing that it has anti-catabolic properties.

Based on this, several studies were launched to see if HMB could enhance muscle growth or protect against excessive muscle breakdown in resistance-trained individuals.

Unfortunately for HMB, the vast majority of research shows that it confers no benefit to resistance-trained individuals who consume an adequate amount of dietary protein each day, and these findings were echoed in the latest study by Tinsley et al. <16>

Now, there is one “infamous” study from 2014 in which HMB was touted to deliver “steroid-like” gains in size and strength <17>, but it’s come to light that some data-frauding may have occurred, which is why most other HMB studies find no benefit from its supplementation. <18,19,20,21,22>

The takeaway here is that, if you're consuming enough dietary protein each day, don't bother spending money on HMB.

Now, back to the Tinsley study and its findings.

Time-Restricted Feeding and Muscle Building

At the end of the 8-week trial, researchers observed that intermittent fasting did NOT impair resistance-training adaptations in females. In other words, intermittent fasting didn’t cause them to lose out on any gains compared to the control group who ate normally.

These findings are especially noteworthy for physique competitors who may be concerned about losing muscle when dieting for the stage and are concerned about excessive muscle loss in prep.

The takeaway here is that the timing of your meals isn’t as important as ensuring that you are getting in enough total calories and protein each day.

Now, the caveat here is that if you have very high calorie needs to gain weight, it can be difficult for those with low appetites to get in all of their calories within a 6-8 hour feeding window.

Can I Take Supplements While Fasting?

That depends on whether the supplements contain calories and/or generate a release of insulin.

Supplements like whey protein, BCAA, and some pre-workout supplements (ones that contain BCAA) will cause a small release of insulin, and technically speaking, break your fast. As such, you should not consume them during your fasting period.

Other supplements like multivitamins and fish oil generally do not cause an insulin spike and should be ok to consuming during your fasting window. Just realize that some vitamins and minerals are fat-soluble, meaning they require fat to be present in your digestive system to be absorbed.

If that is the case, then you will want to wait until your feeding window to consume those supplements.

What are the Health Benefits of Intermittent Fasting?

The main reason that individuals choose to adopt intermittent fasting is for reduced feelings of hunger (as strange as that may seem), which helps them stick to their calorie deficit and lose weight.

But those are not the only benefits attributed to intermittent fasting. Studies have found several other benefits to be had from brief periods of restricting food, including:

  • Improved Insulin Response and Regulation <23>
  • Decreased Risk of Type 2 Diabetes <23>
  • Increased Fat Oxidation <24>
  • Reduced Inflammation <25>
  • Better overall brain health, via increased brain-derived neurotrophic factor (BDNF) <26>
  • Longer Lifespan <27>
  • Greater Cardiovascular Health <28>

Now, it should be mentioned that these benefits may sound fairly impressive, but they are not exclusive to intermittent fasting. The same benefits can be had from following a reduced-calorie diet, shedding excess body fat, eating right, and exercising regularly (resistance-training in particular).

Remember the "magic" of intermittent fasting is that it helps some people stick to their diets better by taking the emphasis away from food. If you know that you can only eat during a specific window of the day, that frees you up mentally to focus on other things, like work, and not stress about when your next meal is or what that will contain.

Making Intermittent Fasting Less Difficult

So, after reading all of this, you’ve decided to give intermittent fasting a shot, but you are slightly intimidated by the thought of going for long stretches without eating.

Well, here are some of our best tips for making the transition:

Stay Hydrated

Consuming enough fluids and electrolytes is essential to staying hydrated, which helps avoid fatigue and supports optimal cognitive function. This becomes all the more important during fasting periods when you’re not consuming any food.

Plan & Prepare

Knowing what you're going to eat and when you're going to eat (e.g., meal prep) will help you avoid obsessing over food during your fast, which helps keep stress at bay and lowers the chance you'll break your fast early and engage in a food binge.

Additionally, if you are planning to undertake any of the 24-hour fasting protocols, such as alternate-day fasting, make sure you’re not performing your most intense workouts. The reason for this is that performing a hard workout with no food in your system is the perfect recipe for poor performance and increased muscle protein breakdown.

If you do want to exercise on your fasting days, keep the intensity low, and the duration relatively short. Fasting days are ideal for active recovery (walking), yoga, or stretching. Save the HIIT and heavy lifting workouts for your feeding window. Being in a fed state will help you train harder and avoid any unwanted muscle protein breakdown.

Eat High-Quality Foods

This is a no-brainer, but just because you are practicing intermittent fasting doesn’t mean you can eat like garbage.

As with any other fat loss diet (or any diet), you should focus on eating foods that are high in fiber and rich in vitamins, minerals, and other micronutrients to help energy levels and blood sugar stable.

Eating nutrient-dense foods also help keep you feeling fuller longer, which can help avoid hunger pangs and potential binges when dieting.

If you’re using intermittent fasting as a tool for fat loss, make sure you prioritize protein. Remember, when you diet, your body is in an energy-deprived state, which increases the likelihood of muscle loss. Consuming adequate protein helps protect against muscle wasting and excessive protein breakdown when dieting.

Get Enough Sleep

No matter what your goal in life is -- productivity, muscle gain, fat loss, etc... sleep is vital. When we are deprived of sleep, a whole lot of metabolic mayhem takes place, including disruptions to hormones that affect your appetite, satiety, and hunger signals like cortisol, leptin, and ghrelin.

Insulin sensitivity also gets thrown for a loop, which makes your body utilize and dispose of glucose in skeletal muscle less efficiently.

Essentially, when we don't get enough sleep, we tend to be hungrier the following day and crave the foods that aren't in line with a healthy diet.

Start Slow

For most people, undertaking intermittent fasting requires a bit of a transition. Very few people, if any, go straight from a normal pattern of eating to 24 to 48-hour fasts.

The easiest way to enter into the world of intermittent fasting is by simply starting to experiment with skipping a meal. For most people, the meal to skip is breakfast.

Instead of having your normal breakfast, skip it and have water or black coffee when you wake up. Then break your fast at lunch as we outlined earlier when discussing the 16:8 fasting protocol.

Give It Time

The first couple of days, you may experience increased lethargy, sluggishness, and feelings of hunger when experimenting with intermittent fasting. Realize that these feelings are temporary (for most people) and will subside as your body acclimates to the new eating schedule.

If after a week or two, you're still struggling to adapt, then intermittent fasting might not be the right diet for you. Return to your normal pattern of eating and be on your way!

The Bottom Line on Intermittent Fasting

Like most fad diets, intermittent fasting can be a bit overblown in regard to its benefits. It can be a useful tool for weight loss, in so far as that it helps you eat fewer calories.

Just realize that a lot of the benefits attributed to intermittent fasting are on account of an individual losing weight, not the fact that they only ate food during a specific window of the day.

If intermittent fasting reduces the stress of dieting and helps you stick to your fat loss diet, then feel free to use it as a tool to help you lose weight. However, you do not “need” to follow intermittent fasting to lose weight or be healthy.

If it works for you great, if it doesn’t, then don’t sweat it. The only way to know if intermittent fasting is for you (as with most things in life) is to try it and see how you respond.


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