What Intermittent Fasting Does To Your Body


Before we can discuss intermittent fasting benefits, we must first know what intermittent fasting is.

Intermittent Fasting (IF) is the self-imposed abstaining from food for a specified period, usually about 16 hours with a window of 8 hours to consume meals. Most commonly, this is achieved by skipping breakfast and having the first meal of the day at around noon, but some people take intermittent to mean abstinence of anywhere from 12 to 18 hours.

Intermittent Fasting Explained


Often referred to as time-restricted feeding, intermittent fasting is a catch-all term for diets which focus on spending part of the day without eating, (fasting), followed by a period of time in which you do then consume food.

Just as everyone is an individual, there is no one-size-fits-all approach when it comes to intermittent fasting.

In fact there are many different styles of IF that you can choose based on your current schedule and desires:

The LeanGains Approach:

This style of IF is arguably the most popular which promotes a ratio of 16-hour fasting period followed by an 8 hour eating period.

Alternate Day Fasting:

A popular IF protocol used in most research; this style includes 1 day of fasting and consuming only ¼ of normal calorie intake followed by 1 day of normal eating. This two day cycle is typically continued indefinitely. 

Warrior Diet:

This is an extension of the lean gains approach, with a 20-hour fasting period followed by a 4 hour eating period.

Eat Stop Eat:

This style includes 2 days a week of complete fasting with 5 days of normal eating.

Nick’s Metabolic Fast:

This is a unique approach to intermittent fasting with a health, metabolic, and hormonal focused approach. It is similar to the basic 8:16 lean gains approach; however I recommend a specific macronutrient ratio. 

Learn more about my simple metabolic trick to lose weight daily…

Alternatively, you can use literally any ratio of fasting and feeding to fit your individual needs. The only caveat is that a majority of the day should be devoted to abstaining from consuming calories.

Intermittent Fasting Benefits


Insulin Sensitivity

Despite the fact that most foods, including protein, induce an insulin response, typically the largest increase of insulin is in response to consuming carbohydrate.

When you consume foods such as carbohydrate and digestion commences,(converting it to the usable form of energy in the body, called glucose), levels of glucose in the blood rise. As a response, insulin is secreted from the pancreas, which drives the blood glucose into various tissues such as muscle and fat.

Over time with chronic, high increases in insulin, this can lead to a disorder termed insulin resistance. Insulin resistance is a state in which insulin is unable to successfully pull glucose from the blood and store it, leading to further issues such as obesity and type 2 diabetes.

Interestingly, studies have revealed that using periods of intermittent fasting may help increase insulin sensitivity, thus reducing resistance.

In order to test insulin sensitivity, many researchers use a technique called a euglycemic clamp in which glucose is directly infused into the blood.

Over time, the researchers observe how much glucose is needed in order to maintain a constant level in the blood. If insulin is working, we can expect that more and more glucose will be needed in order to maintain a constant level since it should be removed from the blood.

If blood glucose levels rise, this is a good indication of insulin resistance, meaning that insulin isn’t working properly.

These researchers used the above technique and discovered that participants using intermittent fasting required increased rates of glucose infusion, in order to maintain constant levels of blood glucose.

In observing this phenomenon, it’s safe to conclude that even short periods of fasting may have a significant impact on improving insulin sensitivity.

While there are many potential reasons that intermittent fasting may result in improved insulin sensitivity, it’s highly likely that the fasting periods allow insulin levels to decrease significantly.

As mentioned, consistent high levels of insulin can cause resistance, or the inability of insulin to remove glucose from the blood and deposit it into body tissues.

By spending significant portions of the day fasting, and thus not inducing an insulin spike, you allow tissues of the body to become “sensitized” and ready to accept glucose. In essence, fasting enables insulin to work a bit better.

Doing so may help the body regulate glucose better, reducing the risk or symptoms of disorders such as type 2 diabetes, or extreme insulin resistance leading to obesity.

Increased Adiponectin

Adiponectin is a protein that is actually secreted from fat tissue, which plays a large role in how glucose and fatty acids are metabolized and stored in the body.

Unfortunately, when adiponectin levels are low, this leads to issues such as increased storage of fatty acids and increased resistance to insulin, making it a major player in whether or not you have further issues such as obesity.

Studies have revealed that the use of intermittent fasting may actually increase the amount of adiponectin that is released into both the brain and circulation, where it can decrease storage of fat and also produce a thermogenic effect or increase in metabolic rate. 

In fact, one study indicated that there might be a positive correlation with fasting and levels of adiponectin.

This study revealed that during days of fasting for roughly 20 hours, levels of adiponectin were increased by 37% relative to days that included a shorter fasting period and days without fasting.

Based on this finding, it may be quite beneficial to periodically increase the duration of fasting or ensure that your daily fasting periods are at least 16 hours long.

Increased AMPK and Mitochondrial Biogenesis

Additionally, higher levels of adiponectin, as witnessed with intermittent fasting, have been associated with increasing levels of an enzyme called AMPK.

The body’s main source of energy, ATP is required for most processes. ATP is a compound of adenosine attached to three phosphates called adenosine triphosphate.

When phosphate is removed from the compound, it releases energy. Additionally, the compound is then transformed into what is called ADP or Diphosphate. Further, when the process continues, it becomes adenosine monophosphate, indicating only one phosphate remaining.

When levels of ADP and AMP rise within the cell, this signals the body that energy availability is beginning to become limited.

The signal initiates the increase of a special enzyme called AMPK, which is considered to be the major energy gauge within cells.

Interestingly, when AMPK is increased in the cell, it initiates a myriad of different effects, including the breakdown of fatty acids to be used for energy, as well as improving the ability of glucose to enter the cell, so that it can be used as energy.

In essence, increasing AMPK allows you to use fat as fuel, in addition to sensitizing tissues to carbohydrates you ingest, so that they are shuttled towards muscle for energy usage rather than being stored and converted to body fat.

If that’s not enough, AMPK is also an enzyme that increases a receptor co-activator called PGC-1a.

This is important because PGC1a is a major regulator of mitochondrial biogenesis or the creation of new mitochondria, the body’s fat burning powerhouses.

During times of fasting, the body begins to turn to stored body fat for energy. In order for this to occur efficiently, the body requires ample amounts of mitochondria to contribute to energy production.

This not only enables the generation of large amounts of energy quickly, but may also significantly alter body composition as the use of fat for energy increases.

Decreased hunger

Paradoxically, intermittent fasting has been linked with actually decreasing hunger.

I know what you’re thinking, there’s no way not eating can actually decrease hunger.

Truth is, many things regulate hunger. However, most importantly, a peptide hormone called ghrelin is primarily in charge.

Secreted from cells within the gastrointestinal tract, ghrelin is often secreted in response to the stomach being empty and then ceases, once food is ingested and the stomach stretches.

However, research is beginning to reveal that these two factors are likely not the only reasons for ghrelin secretion.

Interestingly, one study indicates that cells within your stomach, called oxyntic cells that secrete ghrelin, actually operate on a circadian rhythm, much like your sleep-wake cycle.

As with falling asleep and waking, you can train your body,and thus its cells, to act on a specific schedule. These cells within your stomach act exactly the same except in response to when you normally eat or don’t eat.

With a normal schedule of eating throughout the day, these cells secrete ghrelin according to normal eating patterns, creating feelings of hunger encouraging you to find food.

Once you manage to have a regular schedule of fasting, these cells become entrained to this schedule and thus won’t secrete ghrelin.
In essence, by fasting on a regular schedule, you train these ghrelin secreting cells to not secrete ghrelin in the first place, leading to reductions in feelings of hunger.

Based on the ability of these cells to have a schedule of secretion, you can expect that, for the first few days of using a fasting plan, you’ll feel quite hungry during the fasting period at times when you would normally consume food.

However, the adaptation period seems to be quite short and these feelings of hunger should subside within a week or two.

Hormones That Promote Fat Burning

During periods of fasting, the body still requires energy to function.

This energy can come from various different sources such as glycogen (stored glucose) from the muscle and liver, or it can come from fat.

When you fast, and blood glucose drops low, this forces the secretion of a hormone from the pancreas called glucagon.

When glucagon levels rise, this initiates a process called gluconeogenesis in which the body converts glucose from non-carbohydrate sources such as protein, or releases glucose from the liver.

Alternatively, this increase in glucagon can initiate a process of metabolizing fat for energy, one of the main benefits of intermittent fasting.

Interestingly, fasting also increases levels of hormones called catecholamines.

These catecholamine hormones are able to attach to receptors located on the membranes of fat cells. Once attached, fatty acids stored in these cells are released into circulation, to ultimately meet their fate of being oxidized, or “burned.”

This process of releasing fatty acids into blood is called lipolysis and studies indicate that intermittent fasting is especially proficient at inducing it.

Together, this increase in glucagon and lipolysis is a perfect combination for increasing the amount of weight that is lost specifically from fat tissue.

Improved Body Composition

Intermittent fasting is an easy way to reduce calorie intake and thus decrease body weight and fat mass.

Fortunately research is beginning to reveal that when intermittent fasting is used, subjects not only reduce body weight but also seem to reduce body fat and retain lean muscle mass to a greater extent than those who use only calorie restriction.

It’s highly likely that,due to intermittent fasting’s transient effects on the ability to metabolize fat, a greater portion of body weight is lost from body fat, with a preservation of lean mass.

In fact, one of the first studies evaluating a 16 hour fasting regimen in trained individuals indicated that using intermittent fasting does actually help reduce body fat by up to 17.4% while maintaining lean body mass.

In addition to the obvious benefit of increasing the amount of fat being metabolized, increasing ketone levels have many different potential health-promoting benefits and have been implicated in being especially beneficial for disease states such as metabolic disease, cancer and neurodegenerative disorders such as Parkinson’s and Alzheimer’s.

Why Intermittent Fasting Works 

In addition to all of the aforementioned benefits, intermittent fasting is especially proficient at allowing you to consume fewer calories, partition nutrients to the body tissue you want and to reduce hunger.

The first of these is the most important.

When attempting to lose body weight, the number one measure you’ll need to take is to ensure you have a negative energy balance.

Energy balance is the idea of either consuming more calories than you expend or expending more calories than you consume; the latter will result in weight loss while the former will result in weight gain.

When it comes to creating a negative energy balance (expending more calories than consumed), intermittent fasting is especially good at allowing this to happen with ease.

In fact, studies have shown that intermittent fasting does generally lead to a reduction in calorie intake.

The reason for this is largely due to restricting the amount of time that you are able to consume food, in addition to generally consuming larger meals when you do eat.

When you fast, and then feed within a restricted time window, it is very likely that you will be unable to consume a similar amount of calories compared to what you normally would when eating throughout the day.

This is in addition to the inability to compensate for the calories expended during the fasting period.

Secondly, intermittent fasting may allow you to partition nutrients to the body tissue you desire.

By fasting during the day when you are not exercising, you aren’t consuming calories that could potentially contribute to fat gain.

Once you exercise and then begin your feeding period, you’re ensuring that the food you are eating is shuttled towards muscle tissue for repair and growth.

Interestingly, when your muscle contracts, within the cell certain components actually migrate to the outer edges of the cell’s membrane.

These components, known as GLUT 4 transport proteins, actually help shuttle glucose (what carbs are converted to in the body) into the muscle cell for storage and energy.

By abstaining from food prior to exercise and then consuming afterwards, you ensure that the food you’re eating is shuttled where you want it.

Lastly, as already mentioned, the “hunger hormone” called ghrelin largely regulates hunger.

When you fast, cells that secrete this hormone may become suppressed, preventing ghrelin secretion. In addition to other potential factors, most people who practice IF indicate that doing so does, in fact, decrease hunger.

Having a reduction of hunger while calorie restricting is one of the best ways to effectively continue reducing calories and stay on track.

For reference, the traditional dieting group within this study only observed a 2.8% reduction in fat mass. Unsurprisingly, this is not the only study to show these results.

Other studies also indicate that using fasting may decrease fat mass while having a minimal effect on lean body mass.

It’s highly likely that all of the potential benefits of intermittent fasting contribute to the body’s ability to use stored body fat as energy, rather than tapping into other sources such as muscle, for sustenance.

Based on the evidence, intermittent fasting seems to be a strong candidate for those looking to favorably change body composition, while posing a minimal threat to lean body mass (muscle mass).

Increased Autophagy

Autophagy is a process in which damaged or unneeded cellular components, or cells themselves, are recycled to make way for new, healthy cells and components.

During this process, the damaged or unneeded components are flagged by the immune system for disposal. Once flagged, these marked components are engulfed by what are called phagocytes, which breakdown and dispose of them.

During times of constant feeding, this process can be halted or severely diminished. This is primarily due to the fact that when energy from food is present in the body, it causes a cascade of events that initiate growth processes; the opposite of autophagy.

It seems that by spending a significant portion of the day, with little energy intake, growth processes become down-regulated while degradation responses, such as autophagy, become up-regulated (18).

In essence, by spending time fasting, you give your body the time and ability to hold off on growth processes while allowing for increased cellular clean up.

In doing so, there is potential that the body will be better equipped and responsive when damaged cellular components or threats are introduced into the body. 

Increased Levels of Ketones

Ketones are byproducts of increased fat metabolism.
Under normal circumstances, the body is fairly optimized to use glucose as a primary source of fuel, in particular if you normally consume carbohydrates.

When you begin to primarily metabolize fat, the fatty acids are broken down into different components, which can be metabolized within cells. However, eventually these cells are unable to keep up and eventually begin producing byproducts of fatty acid metabolism called ketones.

The liver is not capable of metabolizing ketones so they are sent into circulation where they can be used by various different tissues in the body.

Interestingly, this process is exactly what occurs when individuals practice a ketogenic diet, which is often referred to as a fast-mimicking diet.

As mentioned earlier, intermittent fasting stimulates various different processes that stimulate the release of fatty acids into the bloodstream for metabolism. Increasing levels of these ketones is simply a byproduct of this fatty acid release during the fasting window. 

So Should You Try Intermittent Fasting?

While research on intermittent fasting is still in its infancy, the studies which have been carried out indicate that it’s not only beneficial for changing body composition but also has potent effects on a number of different markers of health in terms of metabolism and disease prevention.

Despite the fact that intermittent fasting still abides by the laws of energy balance, it does seem to provide many of its benefits to a greater extent than traditional calorie restriction and also even in the absence of caloric deficit.

Based on the current evidence regarding IF’s benefits, its use to optimize body composition and health are very impressive and future research will continually highlight it’s unique place in countering the current obesity epidemic.

Now that you understand the science and what benefits intermittent fasting may provide for you, continue reading to understand how to optimize the diet, based on the style you choose and the schedule you’ll be able to sustain.

I’ve meticulously laid out the standard format for each style of intermittent fasting to help you find what suits you best in order to be successful, regardless of preference and schedule.

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