Complete Guide to Intermittent Fasting

by | Jan 15, 2020 | Last updated Feb 15, 2022

Intermittent fasting is a practice where you abstain from all or certain foods for a period of time, a fast is a centuries-old practice in many cultures and religions. In more recent times, different fast methods have gained popularity as a way to regulate calorie intake and force the body to use stored fat.

Intermittent fasting should not be confused with a diet, as it has a pattern of cycling between periods of eating and fasting. Very little behavior changes are necessary with an intermittent fast. So, what is intermittent fasting? You must have enough self-control to restrain any inclination to eat during fasting periods. Lack of self-control with body hunger and mental hunger is the mental barrier that often prevents people from a successful fast.

When using intermittent fasting, tracking food intake, especially nutrients, is critically important. Noom offers an extensive food database to make it easy.

Neuroscience Research on Intermittent Energy Restriction

Stanford University’s Center for Law and the Biosciences referenced neuroscience research associated with intermittent energy restriction, or IER. Weight loss, lower blood pressure, reduced body fat, and a lower resting heart rate are a few of the benefits associated with intermittent energy restriction.

Intermittent energy restriction shows promising signs of reducing the risk for developing cardiovascular disease, cancer, and diabetes even when the overall consumption of calories in a week is the same in a faster and non-faster.

For centuries anecdotal information stated that taking a break from eating was good for the human body. Now, medical science has started catching up with centuries-old folklore to prove why a fast is a smart thing to do.

Neuroscience research recently found that intermittent energy restriction appears to improve elderly people’s performance on memory tests and may decrease the chances someone will develop Parkinson’s disease or Alzheimer’s disease, raising hope for people at risk for developing those and other neurodegenerative diseases.

If you already have a neurodegenerative disease, intermittent energy restriction can increase brain or cognitive functioning and help you lead a life richer in quality than you otherwise might have had. Intermittent energy restriction spurs new neurons to grow, which is a tremendous development for brain health in general.

IER encourages an increase in brain activity after someone has a traumatic brain injury or a stroke. People with anxiety, depression, or other mood disorders report intermittent energy restriction has a positive impact and can even prevent those debilitating mood disorders.

The root of the positive impact intermittent energy restriction has on the brain lies in its ability to increase biological markers associated with memory and learning called synaptic plasticity. If neuroscientists gain a way to harness the growth of synaptic plasticity, the implication for mitigating or even curing many brain injuries and diseases has no limit.

Another way to state why fasting helps the body and brain is that controlled food deprivation periodically pushes and challenges the body’s biological systems and network of cells. Think of it as a gardening technique. If plants are constantly fed, watered, and pampered, they never get the chance to “harden,” so to speak, so their growth remains limited, and they really cannot withstand challenges from weather, pests, or other elements.

The same thing happens to your body. When your body’s cells and systems that control biological and metabolic functions get challenged on a regular basis, they gain efficiency, strength, and the ability to deal with daily stressors.

So, how does intermittent fasting work? Now, science shows that the brain reacts the same way the body does. An intermittent fast challenges brain cells to grow new neurons and find alternate pathways to make connections it normally has no incentive to do.

Change When You Eat – Not What You Eat

Practicing intermittent fasting does not mean you change your food habits, it just means you change when you eat the same food. So, is fasting safe? Your caloric intake on a weekly basis is the same as usual. When the weekly caloric intake was the same for an intermittent faster and a non-faster, the intermittent faster still lost weight and gained the benefits that fasting offered.

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Fasting Schedules Differ for Men and Women

When practicing fasting on a daily basis, different results happen between men and women. Daily fasting during certain hours can also be called the Leangains diet. Men eat during eight hours of the day and fast for the other 16 hours. This is called the 16:8 method of intermittent fasting.

Men get the best results from the 16:8 method. Typically, a fast with the 16:8 method starts with your first meal being eaten at noon. The feeding period lasts until the end of the evening meal at 8:00 p.m. From 8:00 p.m. until noon the next day, the fast period takes place, and no food is eaten. This method may not be the most effective way to fast for men who feel that skipping breakfast leaves them less functional for the day.

Women get better results using the 14:10 method. Women practicing the 14:10 fast method start eating at 10:00 a.m. and finish with the end of their evening meal at 8:00 p.m. The fast period starts at 8:00 p.m. and lasts for 14 hours until 10:00 a.m. the next day. Just like men, if women feel more functional starting their day with breakfast, the 14:10 method is probably not the best method for the woman to use.

History of Intermittent Fasting

Throughout the history of the world, humans have always practiced intermittent fasting. Our earliest ancestors practiced it because they had no choice. Often, fasting for a week was not unheard of if no food could be located.

While fasting for a week is certainly not recommended, our ancient ancestors who survived became stronger because of it.

Humans Have Fasted Throughout the History of Earth

As S.B. Eaton suggests, “An evolutionary perspective on human physical activity: implications for health,” Western society has strayed far from what he states was the origin of our genetic makeup, the Paleolithic standard. He states that our original genetic makeup depended on daily physical exertion and energy expenditure. Our physiology and biochemistry are not designed for the sedentary lifestyle more Westerners live.

Because of this, he feels serious health problems arise because of the conflict between our genetic makeup and our behavior. Cardiovascular disease, diabetes, age-related problems, and obesity are high on that list. If we patterned our daily habits after the original ancestors, we would fast every other day or at least several times a week.

Doctors Used the Intermittent Fast in the Early 1900s

Doctors practicing in the early 1900s often prescribed an intermittent fast to treat hysteria, nervous disorders, digestive problems, diabetes, epilepsy, and others.

Since biblical times, fasting and other methods were used to treat epilepsy. Starting in the 1920s, doctors started using intermittent fasting and ketosis to treat epilepsy unaffected by other treatments. Intermittent fasting ketosis fell out of favor as new anticonvulsants came on the market. Recently, physicians rediscovered intermittent fasting and ketosis and began using intermittent fasting ketosis to treat unresponsive epilepsy.

Since at least 500 BC, a fasting diet was the preferred treatment method for epilepsy. For 6000 years, it remained the only treatment for epilepsy. Early in the 20th-century, researchers found that a ketogenic diet mimicked the metabolism of a fasting diet. This introduced a new method of treating epilepsy that, in the past 25 years, has caused an upsurge in interest and research into the ketogenic diet. Its ability to mimic the metabolism that happens during a fast is uncanny.

How Intermittent Fasting Works?

Does fasting work? You might want to learn how to start fasting if you have one of the following conditions:

  • You are a die-hard carb junkie.
  • If you are pregnant or trying to become pregnant, however, do not follow how to start fasting unless your doctor agrees and approves.
  • If you are taking medication that impacts blood sugar. Is intermittent fasting safe? Definitely discuss it with your doctor before following any fasting tips.
  • If you are taking medication that needs to be taken with food in the morning and before bed – be sure to ask your doctor, is intermittent fasting bad? Get input before following any intermittent fasting tips.

Glycogen is the most easily accessible energy source. Glycogen is easily broken down into glucose molecules to provide energy for the other cells, which can provide energy for 24-36 hours. Here’s a breakdown of how it works.

Once sugar links into a long chain of glycogen, it is stored in the liver. The liver only has a certain amount of room. Once the liver runs out of room, the De-Novo Lipogenesis process begins. What is the De-Novo Lipogenesis process? An intermittent fasting how-to guideline often explains this process as the liver turning excess glucose into fat.

When it has finished, the liver sends fat to various deposits in the body. Two food energy systems are stored in our bodies. The first one is glycogen, which is an easily accessible energy source that is broken down into glucose molecules to provide energy for the other cells, which can provide energy for 24-36 hours.

After that point, the body begins breaking down fat to use it as energy. Does fasting work? The only way for the body to break down hard to reach fat storage is through a fast.

Different Types of Intermittent Fasting

Intermittent fasting schedules are as widely varied as there are hours in the day and days in the week. Practically every conceivable time period is touted as being a good intermittent fasting model by those who practice it.

Some are science-based intermittent fasting plans, but others use mythical anecdotes to back up their intermittent fast method rather than relying on scientific research that might prove their claims are embarrassingly lacking clinical evidence of any benefit to be achieved by following their ideas.

In no particular order, here are some of the intermittent fasting schedules and fasting rules you might hear about.

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  • Daily Intermittent Fasting

This is one of the most popular methods to intermittent fast and does have scientific studies to back its claim that it is effective for many people. The fast periods are different for men than they are for women.

Women who practice this intermittent fast method tend to get the best results by practicing a 14-hour fast period with a 10-hour feeding period. Women who wake up hungry for breakfast may want to practice a feeding schedule that starts at 8:00 a.m. and ends at 6:00 p.m. If you do not mind skipping breakfast, you might want to follow a schedule where you start eating at 10:00 a.m. and stop eating at 8:00 p.m. Follow the schedule that works best for your hunger patterns as well as being a good fit for your family and social schedule.

Men follow a 16-hour fasting period followed by an eight-hour feeding period. This schedule is very similar to the Leangains model of intermittent fasting, which is referenced further under number four on this list. There is no emphasis as to the timing of the eight-hour feeding period. If you are a big breakfast eater, you might want to start at 8:30 a.m. and end at 4:30 p.m. if you can handle a 16-hour fast window that begins that early.

Many men who follow this guide to fasting tend to loosely follow an eating schedule that begins at 12:00 p.m. and ends at 8:00 p.m., which often coincides with finishing dinner in the evening. The 16-hour fasting period starts at 8:00 p.m. and goes until 1:00 p.m. the next day. Does fasting work? You can adjust it to whatever time period works best for you, your family, and your social schedule.

Most people currently eat around the same time each day, and they are not on an intermittent fast schedule. Practicing intermittent daily fasting becomes the same thing with the only difference being you learn to practice not eating during certain time periods, a rather simple routine to follow. This fasting schedule becomes an easy habit to fall into because intermittent daily fasting is already done every day, naturally.

Because you typically trim a meal out of your usual eating patterns, a potential disadvantage of an intermittent daily fast is that it becomes tougher to consume that same number of calories on a weekly basis that you normally had eaten. This can result in weight loss when following this intermittent fasting protocol. If your goal is to use intermittent fasting for weight loss, then this may be a positive result.

However, if intermittent fasting bulking is your goal, you may consider this potential side effect to be a disadvantage. You may have to concentrate on eating bigger meals consistently during the feeding period.

Proponents of a daily intermittent fasting schedule point out that it is healthy to avoid using a fanatical approach to change your dieting behavior. Building a set of healthy behavior habits with your diet the majority of the time is appropriate. If you choose to eat pizza and ice cream with your kids outside of your feeding period the other 10 percent of the time, they suggest enjoying it without berating yourself for breaking your fast.

  • Weekly Intermittent Fasting

If you are new to the intermittent fast, one of the easiest ways to begin is using a weekly intermittent fasting schedule. Although this method may not cut out quite as many calories, you still receive many of the health benefits associated with an intermittent fast.

An example of weekly intermittent fasting would be starting a fast at noon on Friday and not eating anything until noon on Saturday. While you still eat every day of the week, there is a 24-hour window to fast that gives you some great health benefits. It also has the advantage of letting beginners get used to the idea of a fast to realize that they will not shrivel away and die by going 24 hours without food.

Essentially, you are cutting out two, maybe three meals out of your week, so if you are not practicing intermittent fasting dieting methods, you do not have to worry over losing weight. If intermittent fasting bulking is your goal, and you want to keep weight on or even gain weight, then a weekly intermittent fasting schedule might be a good choice for you.

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Weekly fasting is good for your health; it helps you mentally overcome any ingrained fear or resistance you have to go without food voluntarily, and it gives you a good sense of self-discipline. If you travel long distances a lot, it is easy to work in a 24-hour fast. After a big holiday or family celebration, you might feel better going 24 hours before starting to eat again.

  • Alternate Day Intermittent Fasting

This method uses alternating days with longer fasting periods throughout the week. One example of this method is to eat dinner on Wednesday evening then not eat again until Thursday evening. The advantage of alternate day intermittent fasting is that it allows you to eat every day while you fast for 24 hours in-between. You end up eating at least one meal each day and sometimes two.

Some drawbacks to this intermittent fasting plan include the realities of trying to eat enough nutrients in one meal to stay healthy and avoid losing weight unless using it as a weight-loss tool is your goal. People who have followed an intermittent fasting pattern of eating for many years report it can be quite difficult to teach yourself to eat more during eating periods. Especially when required to do that every single day at one meal. A lot of cooking, consistent eating periods, and planning go into the alternate day fast.

People just learning how to do fasting may be better off practicing intermittent fasting Leangains style rather than an alternate day fast. Food fasting one day a week might also be a better way to learn how to do fasting. Trying to cram too much into eating periods can overwhelm someone practicing fasting for beginners. Periodic fasting is easier to practice that intermittent fasting every day on an alternate day fast guide to fasting.

  • Leangains Model of Intermittent Fasting

According to the person who designed it, Martin Berkhan, Leangains is tailor-made specifically to strength and fitness training. If you want to get as strong and lean as possible, Martin Berkhan states intermittent fasting Leangains is how intermittent fasting should work.

He further states that when comparing the Leangains model to practice your intermittent fast with other intermittent fasting schedules, you will find that there is a difference. The Leangains model of intermittent fasting places much more value and emphasis on complete pre-workout and post-workout nutritional needs, according to Martin Berkhan. Specific guidelines exist, he says, for macro composition, meal timing, and caloric cycling.

  • The 16:8 Method

The 16:8 method is part of the daily intermittent fast period where you choose an eight-hour window for eating and a 16-hour time period for your fast. This follows the Leangains model and is a sensible method to practice. Women should follow a 14:10 time period.

  • Eat-Stop-Eat

The eat stop eat diet is a fast once or twice a week that lasts for a 24-hour period. An example would be not eating from lunch one day until 24 hours go by, and it is lunch the next day. On the eat stop eat diet you can eat lunch on the second day. What time does fasting start? On this plan, you can do morning fasting, an evening fast, or basically any fasting hours you choose for 24 hours.

  • The 5:2 Diet

How to start fasting using the intermittent fasting 5:2 plan involves eating your normal diet during five days of the week. Using the intermittent fasting 5:2 plan leaves you with no concerns about what time fasting starts, or what to eat when fasting. Two days of the week, you restrict your eating to 500 to 600 calories each day.

What to eat on fasting days? Most people who practice this suggest eating two small meals with a protein serving, salad and fruit. Make sure there are foods high in fiber as that will help you feel full as well as aid digestion.

It is important that you do not attempt to complete two days of fast in a row. At least one day should separate them. Intermittent fasting every day is only practical if you fast using the 16:8 or 14:10 method.

  • The Warrior Diet

The Warrior Diet is a rather radical method to fast. It is not an intermittent fast according to the strictest sense because the author, Ori Hofmekler, allows fruits and vegetables in small meals during the intermittent fast period. Based on something he calls survival science, these intermittent fast schedules a ratio of 20 hours to fast per day to four hours of feeding.

He advises an extremely limited selection of food to choose from for the feeding period. There is a risk that people on this diet will not get enough nutrients, such as fiber and essential vitamins and nutrients. This can increase the risk of cancer and have an adverse effect on digestive and immune health.

With so many options out there for intermittent fasting, confusion abounds. But, you don’t have to be confused about losing weight.

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Step-by-Step Intermittent Fasting Guide

Some methods involve daily 16-hour fasts or 24-hour fasts. The following example gives an idea of how to start fasting on a 12-hour schedule.

Fast for 12 hours a day.

Fasting tips for this method are fairly simple. Choose a 12-hour window during which you plan to fast. Follow it post fast with eating.

Some researchers indicate following a fast for 10–16 hours can cause the fat stored in the body to change into energy, which releases ketones into the bloodstream. This, in turn, encourages weight loss, so do not follow this method if you would rather practice intermittent fasting for bodybuilding.

This is a good beginning intermittent fast plan. This is because the fasting window is relatively small, much of the fast occurs during sleep. Usually, the same number of calories get consumed each day.

The easiest way to do the 12-hour fast is to include the period of sleep in the fasting window. For example, you could fast between 8:00 p.m. and 8:00 a.m. Most people practice this type of fast without realizing it.

Intermittent Fasting, Grazing, and Starvation

Many people who are unfamiliar with intermittent fasting tend to confuse it with terms such as “grazing” and “starvation.”

Intermittent Fasting versus Grazing

Grazing is a term that refers to eating many small portions of food throughout the day, as well as the night in some cases. It gained prominence within the last three decades as a way to control hunger, keep glucose on an even level, decrease calorie intake, and avoid the highs and lows of blood sugar swings. Additionally, studies found it could decrease high cholesterol.

While grazing is quite effective for a certain portion of the population, it has nothing to do with how an intermittent fast works. In one study, one group ate a large breakfast at one meal. The other group at the same breakfast broken up into five small portions eaten once every hour for five hours. Both groups then ate lunch.

After the food consumed at lunch was measured, the group that ate five small meals had less food and consumed fewer calories at lunch than the group that had breakfast in one large meal. Therefore, researchers concluded that smaller meals eaten more often led to consuming less food and fewer calories.

However, another study conducted with rats found that those allowed to graze on food when they wanted ate 30 to 40 percent more food and calories than rats who were fed every other day. Yet another study with mice and rats found that those who were not fed for a day then allowed to self-graze on alternate days lived 30 percent longer than the group allowed to graze at will daily.

Intermittent Fasting versus Starvation

For many centuries, our hunter-gather ancestors survived on one large meal a day, if they were lucky. Often, they went for several days without food. They had no eating window. They ate when food was available, or they starved.

Starvation is the inability to obtain adequate nourishment. When you cannot eat because you do not have any food that is not considered part of the intermittent fast protocol. Our hunter-gather ancestors did not participate in spontaneous meal skipping. They would have found the idea of an eating window or mental hunger astounding. Intermittent fast schedules were unplanned. Their idea of spontaneous meal skipping was giving food to their children instead of consuming it themselves.

The Difference Between Noom and Other Plans and Programs

When it comes to learning how to eat and how to live for weight loss, Noom works from a psychological perspective. According to the Chief of Psychology for Noom, Dr. Andreas Michaelides, “By understanding the past behaviors and attitudes of all types of users, we know the best way to meet our users where they are in their journey to help them maximize their change of long-term weight-loss success.” Noom, as a weight-loss platform, uses the power of food logging, among other advanced technologies, to teach simple, key behaviors for lasting change. Behavior changes that include self-efficacy, motivation, and knowledge are just the start of how psychology can interact with food, so you lose more weight in a way that lasts a lifetime.

Noom works with tech-based tools partnered with support from real-life coaches in a structured program that connects the user with the social support and positive reinforcement needed to change behavior in a way that increases the likelihood of success.

Not all dietary changes are for everyone, and no two weight-loss plans should be the same, which is precisely how Noom works.

By identifying specific areas where changes can be made to reach goals of weight loss and health improvement successfully, users realize where their best changes are to be made and how those changes are incorporated into a lifestyle they can adopt for the long-term.

Fed State Vs. Fasted State

If you have questions like, how does fasting work, this might give an answer and explanation to that question.

Fed State

When your body is absorbing and digesting food, it is in the “fed state.” A body in the fed state has high insulin levels. Elevated insulin levels make it difficult to burn fat. As you begin eating, your body begins the fed state and continues in this mode for three to five hours.

During this time, your body burns little fat. Once the fed state completes, your body starts a postabsorptive state, which starts the metabolic process of the fasted state. During the eight to ten hours, your body stays in the postabsorptive state; it is not processing food.

Fasted State

Your body reaches the postabsorptive state about four hours after your last meal. This starts the body’s transition to a fasted state. Approximately 8-12 hours after eating, your body transitions into a full “fasted state.” A body in the fasted state contains low insulin rates. This allows your body to burn body fat that was not accessible for about 12 hours.

People rarely go 12 or more hours without eating a snack or meal, so the body seldom reaches a fasted state. This accounts for weight loss in people who start an intermittent fasting program. You may achieve weight loss without changing your diet, the amount of food you eat, or increasing your exercise program. Your body reaches a fat-burning fasted state that seldom occurs with normal dietary habits.

Post-Absorptive State

A relatively healthy individual typically eats three meals each day on a fairly fixed schedule. So, each 24-hour period can be divided into three periods:

The postprandial period – meaning after eating a meal. This period lasts four hours after each meal, accounting for a full 12 hours out of each 24-hour period.

The fast period – while the postabsorptive period overlaps and segues into the fast period, the only real fast takes place in the last three to four hours of sleep before you wake up and eat breakfast.

The post-absorptive period – the postabsorptive period often overlaps with the postprandial period, leading some researchers to assert that the postabsorptive period accounts for any remaining daytime periods and possible nearly all of the 24-hour period, leaving no real fast time.

Absorptive State

During the absorptive state, your stomach is full because you recently finished eating. When your stomach is full, anabolism synthesizes glucose and requires energy input. That exceeds catabolism, which releases energy as it is used up. The absorptive state is critical for the body to function, as vital nutrients present in the intestines and stomach are being absorbed by the body.

Once absorbed, the anabolic process uses these nutrients to feed the body’s immediate need for energy. During this time, glucose gets synthesized into energy. The body remains in the absorptive state for four hours. Here is what happens to the metabolic systems during the absorptive state.

The liver processes amino acids to keto acids. The body can convert this to fat or direct it to other body cells to create necessary proteins or allow it to be used in the Krebs cycle to produce ATP. The Krebs cycle refers to all of the body’s aerobic organisms using a series of chemical reactions as a way to make energy. It does this by oxidizing a substance called acetate. Acetate comes from fats, carbohydrates, and proteins. Once the body’s energy oxidizes these acetates, they become carbon dioxide.

Anabolic body processes use glucose for energy and other things during the absorptive state.

Fat digestion products are called chylomicrons. During the absorptive state, chylomicrons get reconstituted to become fat again. The body then stores that fat in adipose tissue or uses it as a source of energy in a low-carb environment.

The bloodstream carries glucose to cells for use as energy providers for all of the body’s cellular processes.

Glucose converts to fat or glycogen in the liver. Glycogen stores energy for the body to use in the future. Glycogen fats get stored in muscle tissue, other fats are stored in adipose tissue.

Post-Absorptive State

The metabolic period that happens once the intestines and stomach are empty is the postabsorptive state. The body continually demands energy for normal functioning, so it acquires the energy it needs from energy stored previously. Typically occurring four to five hours after absorption of a meal, post absorption signals the beginning of metabolic changes that lead the body to a fasting state.

Once the body exhausts the nutrients in the intestines and stomach, it turns to other sources for energy. During the postabsorptive state, the body needs glucose for energy, so it converts fat to glucose. Soon, the body depletes fat reserves, so it starts synthesizing proteins stored in muscle tissues. The body’s secretion rate of insulin drops as blood glucose slowly diminishes, and glucagon begins to secrete from the pancreas.

For physiological purposes, fasting can be the metabolic state of the body reached after complete absorption and digestion of a meal, to the metabolic state of the body when an individual has not eaten overnight.

How the Body Works in the PostAbsorptive State

Bile acids (BA) activate a nuclear receptor called a Farnesoid X receptor (FXR). BAs contain fat solubilizer molecules that work in the intestine after we finish eating.

  • Glucose, lipids, and amino acids are metabolisms regulated and transported by BA synthesis.
  • BA synthesis relies on hepatocytes to signal the feedback to begin that transport and regulation.
  • Hepatocytes wait on BAs to bind FXR, so it can send the signals.
  • BAs can only bind with FXR when the body is in a post-absorptive state.

So, the four processes listed above clearly have a domino effect. If the body does not reach a postabsorptive state, these intricate processes cannot work together to regulate the metabolic effects of amino acids, glucose, and lipids.

Fats, proteins, and sugars are the nutrients the rely on FXR to act as a stabilizing factor. When FXR is viewed as metabolizing nutrition, a study looked at its role in being a stabilizing factor for liver energy when:

  • The body is postprandial or just finished eating.
  • The stability provided in the postabsorptive state.
  • The role of FXR during the fast or starvation states.

The study showed the following results:

  • FXR regulates proliferative cells by controlling their metabolic needs.
  • Autophagy repression occurred due to FXR in nutrient abundant conditions.
  • The impact inflammation has on metabolizing nutrients was directly affected and regulated by FXR.

Therefore, researchers felt that FXR could be an effective therapy to use in combating liver diseases.

The Post Absorptive State Lasts 8-12 Hours After the Last Meal

The post-absorptive state lasts eight to 12 hours after you finish your last meal. The first four hours are used by the absorptive state. After that, the postabsorptive state starts the metabolic changes that signal the body to begin the fast mode. During the postabsorptive fast state energy expenditure, contributors change. Instead of carbohydrate oxidation being the main contributing source toward energy expenditure, fatty acid oxidation gives proportionately higher contributions to energy expenditure.

Higher counter-regulatory hormone concentrations levels and lower insulin levels cause plasma non-esterified fatty acid to rise in their place. These fatty acids contain a lower amount of carbohydrates available for use but provide higher lipid levels for fatty acid oxidation to use for contributing to the body’s expenditure of energy.

Intermittent Fasting and Weight Loss

A study in 2000 indicated the researchers’ goal was to understand the link between increased energy metabolism and restricting food intake, as they felt it should be better quantified after more than a century of investigations.

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Using healthy subjects, they had them fast for 84 hours. Measurements of metabolic rates were performed on days one, two, three, and four. On the first day of the fast, energy expenditure while at rest had increased, which, in turn, increased norepinephrine concentration, serum glucose levels decreased, but insulin levels had no significant change. By day four, resting metabolic rate had increased 14 percent, and norepinephrine concentration increased to nearly double the amount found the first day.

Researchers concluded that the 84-hour fast led to a decline in serum glucose, which triggered an increase in norepinephrine (plasma). In turn, this led to the greatly increased resting metabolic rate, which burns fat and sheds body weight.

Intermittent Fasting for Weight Loss and an Intermittent Fasting Diet

While many exercise and diet trends begin with a legitimate scientific premise, by the time the information reaches the general population, science barely recognizes the exaggerated version. Human nature and the desire to make a lot of money on the way to reaching the best-seller list leads to minimizing risks associated with the diet and embellishing and inflating its associated benefits.

Intermittent Fasting Benefits Can Get Lost in the Weight-Loss Hype

Such is the case with the intermittent fast, which is one of the latest trends to lose weight. People tout the benefits of a fast or refrain from ingesting food, up to a 24-hour period once or twice a week. Unfortunately, the latest trends tend to get the label of “fad diets.” A fad diet is one that takes the world by storm suddenly and becomes extremely popular for a short time period.

Intermittent Fasting and Ketosis

Ketosis used to treat epilepsy, especially in children, does so specifically to attain the same metabolic response you receive in a dietary fast.

Ketogenic Diets Mimic Metabolism Present in a Dietary Fast

Since biblical times, fasting and other methods were used to treat epilepsy. Starting in the 1920s, doctors started using intermittent fasting and ketosis to treat epilepsy unaffected by other treatments. As new anticonvulsants came on the market, intermittent fasting ketosis fell out of favor. Recently, physicians rediscovered intermittent fasting and ketosis and began using intermittent fasting ketosis to treat unresponsive epilepsy.

In another brief history of epilepsy, the author mentions that a fasting diet and other methods were used to treat people with epilepsy since 500 BC or before. He states that the ketogenic diet was introduced in the 1920s, specifically to mimic the metabolism of a fasting diet. For about two decades, this was the preferred method for treating epilepsy, until antiepileptic drug treatment was introduced. However, the past 25 years have seen a return to researching and using a ketogenic diet, especially for childhood epilepsy.

The Ketosis State Naturally Present in a Dietary Fast

Increased production of ketone bodies happens with a dietary fast. A comparison to calorie-restricted diets shows intermittent fasting is more open to ketogenesis as an energy production pathway. This allows the body to develop an increased concentration of fasting serum. When a ketogenic diet was fed to rats, they showed better resistance to seizures. (Ageing Research Reviews)

The importance of this preventative treatment cannot be overstated. When untreated, the degradation of toxic neuronal damage is devastating, especially in children.

Intermittent Fasting Results

While many results are listed for intermittent fasting, the best results are clinically-based studies where the results are evidence-based.

Evidence-based benefits for health when you practice intermittent fasting can be life-changing.

Powerful brain and body benefits exist if you practice an eating cycle that alternates between periods of eating and a fast period. This eating pattern is called an intermittent fast.

The Function of Genes, Hormones, and Cells Change when You Practice Intermittent Fasting

Positive Human Growth Hormone Changes

Growth hormone blood levels can increase up to five times the normal rate. Muscle gain, fat burning, and many additional positive benefits occur when there is an increase in growth hormone blood levels.

Cells Repair More Effectively

An intermittent fast spurs the body’s cells to repair, in part, by shedding waste material from inside the cells. The upregulation of autophagy is enhanced by a fast as well as when food is restricted. The liver benefits from this, and in 2010 a study found that the brain benefits as well.

Levels of Insulin Change

Fat burning is facilitated by a significant drop in insulin blood levels.

Your Brain Benefits from Intermittent Fasting

Improving the metabolic rate turns out to be excellent for the brain as well as the body.

Clinical studies have shown the growth of new nerve cells in rats who were placed on an intermittent fast schedule. Several studies in rats have shown that an intermittent fast may increase the growth of new nerve cells, which benefits brain function. Neural stem cells in the adult brain can multiply in a process called neurogenesis. This takes place in the hippocampus. Neurogenesis in the hippocampus reacts and affects physical and mental activity and can help brain injuries.

Although prior studies showed that restricting one’s diet could curb deficits in memory and learning that are age-related, this study found that maintaining a diet restriction with rats caused a noteworthy upsurge in neural cells newly produced in the dentate region of the hippocampus.

Metabolic rate changes improve brain health by reducing blood sugar levels (in men), oxidative stress, insulin resistance, and inflammation.

Intermittent Fasting Increases Brain Hormone Levels Of Brain-Derived Neurotrophic Factor (BDNF).

Brain-derived neurotrophic factor deficiency contributes to depression and several other brain issues. Practicing intermittent fasting has been shown to counteract that effect.

Certain animal studies show that practicing an intermittent fast can protect the brain against strokes.

Find out more about how Noom can help you work toward a healthier, lighter life with small changes.

Studies in Animals Suggest Intermittent Fasting Results in Less Cancer

Highly promising clinical research studies have found a link between lowering cancer risk with the effects of an intermittent fast. Unfortunately, these studies have involved only animals, so the human factor is not yet known.

However, when you know that due to family history or your lifestyle that you are at risk for certain cancers, it certainly cannot hurt to try an intermittent fast method before clinical studies are complete.

Even Short-Term Intermittent Fasting Can Help Tumor Survival Rate

A research study used rats and placed them on an alternate day fast regimen one week before injecting them with tumor cells. The rats who had their dietary intervention with an intermittent fast survived longer than the rats in the control group.

However, this was a small study using just 24 rats, and the survival rate was one day longer (10 days) than the control group (9 days). Although it showed benefits for starting an intermittent fast just one week prior to tumor injections, these clinical evaluations need human subjects to determine the full effect on people.

Intermittent Fasting Versus Chemotherapy Versus Both

Another short-term study used slightly more extreme methods of short-term starvation in cancer-free rats. Once exposed to cancer cells, rats on the short-term fasting diet were kept on it while the control group had chemotherapy.

The researchers reported short-term fast periods proved just as effective as chemotherapy in delaying the progression of cancers. When both a short-term fast and chemotherapy was administered, the result was a long-term survival rate and in a cancer-free state.

This study is extremely promising if it can be duplicated in human subjects.

Alternate Day Fast Significantly Decreased Cancer Risk

A 2005 study used aged mice to study the specific cancer of lymphoma. Mice were placed on an alternate day fast for a four-month period. Then, all mice were exposed to lymphoma.

Significant differences occurred between mice on the alternate day fast and the control group. The control group had 33 percent of the mice develop lymphoma cancer. The alternate-day fast mice had a cancer lymphoma rate of 0 percent. Not one mouse on the fasting schedule developed lymphoma.

Another item of note is that no calorie restriction was placed on either group. Further studies found the mice who were placed on the fast routine generated increased mitochondria activity that lowered oxidative stress normally associated with aging.

Long-Term Fasting Lowers Cancer Risk in Rats

A 2002 study placed rats on a 52-week fast regimen of 48 hours each week. When the rats were studied, researchers found the fasting rats had greatly decreased tumor growth compared to the control group.

Fasting May Decrease Side Effects of Chemotherapy

In 2009 a study using 10 cancer patients looked at the potential benefits of a fast before chemotherapy treatment. They wanted to determine if a pre-treatment fast helped with the side effects of chemotherapy in humans.

Studies on animals had already proven the benefits of a fast before chemotherapy and showed the aftereffects were lessened in the fasted animals.

Researchers report the 10 patients reported many of the side effects normally associated with chemotherapy were greatly diminished or gone when they used an intermittent fast prior to chemo treatment.

This is significant not only because it reduces human suffering but potentially could allow for increased chemotherapy at closer intervals.
Benefits of Intermittent Fasting

As already outlined, there are numerous intermittent fasting health benefits. However, intermittent fasting health benefits are not the only benefits of fasting.

Dieting is Harder than Intermittent Fasting

Dieting involves changing patterns in many areas of your life. While some of those patterns are easy to change and adjust, many others are not. Eating special foods might require cooking two meals: One for yourself and another for your family. Going out to dinner becomes an exercise in frustration. Going to a dinner party? Forget about it!

Dieting does not only affect you and your life. It affects the lives of your family, friends, roommates, coworkers, and casual acquaintances. Anyone who bears the brunt of a dieter’s mood swings and cranky behavior knows the effect dieting can have on your life. Dieting is changing your behavior.

Anyone who has ever started a diet knows it is easy to start one. Following a diet on a long-term basis is nearly impossible for most people, especially with the wrong diet. The idea of starting a diet is easy to consider. The reality is the opposite.

On the other hand, this study researched obese people who agreed to practice alternate day modified fasting to see if it was effective for weight loss. Surprisingly, researchers discovered that individuals quickly adapted to changes in their food intake. While initially, the subjects were hungry, they reported soon not feeling hungry or feeling like they needed to eat on fasting days. They were able to maintain increased physical activity without feeling deprived.

A Quick Look at More Fasting Benefits

Intermittent Fasting Can Prolong Your Life

As research indicates, restricting calorie intake through intermittent fasting contains a mechanism that can potentially prolong your life.

Simplify Your Life

Meal planning, shopping for food, putting the food away, preparing the food, cleaning up after meals – all of this is time-consuming and can leave you feeling drained. Intermittent fasting makes your life far simpler by reducing the amount of food you have to buy and prepare.

Get Lean

Intermittent fasting muscle gain is a positive side effect, as is losing belly fat. When you finally reach a fasting state, about 12 hours after last eating, your body goes into a fat-burning state that most people seldom reach when following a normal eating schedule.

Potentially Lower Your Cancer Risk

Studies performed on animals prove that alternate fasting reduces cancer risk. While those studies have not yet been duplicated in human subjects, it certainly cannot hurt to try alternate fasting to lower your risk of getting cancer. This is especially appropriate for people with a family history of cancer.

The main intermittent fasting health benefits, according to Healthline, are numerous and varied in their extent.


Inflammation is a strong marker for many chronic diseases. Studies of Muslims during Ramadan show some positive health effects after prolonged intermittent fasting like the month-long daytime fast of Ramadan. Researchers found one of those positive effects was on the inflammatory issues in the body. Another positive benefit was lowered risk factors for CRP, TC/HDL ratios, and homocysteine, which are all markers for cardiovascular diseases.

Improves Brain Health

By increasing the brain hormone BDNF, intermittent fasting helps brain health and people with Huntington’s Disease. New nerve cells may generate, which was once thought impossible. Evidence is encouraging for protecting against Alzheimer’s disease and may reverse some of the effects of that devastating disorder.

Potentially Help Prevent Cancer

Several studies in animals show intermittent fasting’s benefit in reducing the risk of cancer. These studies need human subjects for better understanding and clinical findings.

Intermittent Fasting’s Effect on Insulin Resistance

A study found intermittent fasting helped subjects lower blood sugar by three to six percent, reduce insulin resistance, and lower fasting insulin levels by 20-31 percent. This could prove significant in treating type II diabetes.

May Promote Weight Loss

Intermittent fasting has been shown to promote the loss of belly fat and weight without consciously undergoing calorie restriction. This study has significant value as belly fat is an indicator and risk factor for diabetes and cardiovascular problems.

Intermittent Fasting and Anti-Aging Potential

A study in rats showed intermittent fasting extends rats’ lifespan. Another study showed rats survived about 36 to 83 percent longer than rats who did not do intermittent fasting.

Intermittent Fasting Food List – Allowed

What to eat when fasting? Part of it depends on your plan for morning fasting, evening fasting, and what intermittent fasting foods you like. Intermittent fasting how to guides suggest some of the following foods make you feel full for a longer period.

Soups – eating the same foods blended in the form of soup can be more satisfying. Cauliflower, miso, vegetable, tomato, or whatever soup you like is helpful. One study done in 1990 experimented with serving the soup right before a regular meal versus serving melon, with the third option being cheese on crackers.

The subjects were non-dieting males of normal weight. Results showed that tomato soup eaten before the second course reduced intake significantly more than the melon or cheese on crackers. Subjects found it more satisfying.

A second study in 2007 looked at the soup’s form to see if blending the ingredients in different ways made a difference. Men and women with normal weight came to the lab once a week for five weeks. Each week they were given one of four different soup blending, or no soup, before being served a regular meal. Chunky vegetable soup, pureed vegetable soup, broth, and vegetables served separately, or chunky-pureed vegetable soup were the four blends. Subjects eating soup in any form reduced their test meal by 20 percent compared to the no soup preload subjects. It did not matter what way the soup was served or blended, the results stayed the same.

Vegetables – some particularly healthy vegetables include:

Carrots, which can reduce the risk of prostate cancer;

Kohlrabi, a type of cabbage/turnip that can be cooked or eaten raw. It contains high amounts of antioxidants, which is a good weapon against diabetes and inflammation;

Brussel’s Sprouts may be particularly helpful in protecting cells from damage. It contains a component that provides protection from free radicals, which contribute to and cause chronic disease. They help detoxify the body as well;

Sweet Potatoes are a root vegetable containing two grams of protein and four grams of fiber, as well as a slew of vitamins. One of those is vitamin A, which has beta-carotene. One study in 1994 found beta carotene reduced the risk of lung cancer in non-smokers. A second study found beta carotene reduced the risk of postmenopausal breast cancer;

Spinach, which can help your heart. A 2015 study found spinach lowers blood pressure, thereby helping your heart health;

Collard Greens, one cup has four grams of protein and five grams of fiber. It also contains 27 percent of your recommended daily allowance of calcium.

A Final Take on Intermittent Fasting

Adopting a schedule of intermittent fasting has been linked to various health benefits, and, with plans like then 16:8, 14:10 and 5:2 options, you can choose just how long and how often to fast. Whether you’re trying to lose weight, improve overall health, or fight inflammation, there’s something in intermittent fasting for everyone.

You don’t have to fast to lose weight. You can make healthy, natural lifestyle changes and see what it looks like to live a life where weight loss is something that happens naturally and the weight stay off.

Try Noom today for a fresh look into what weight loss should look like.

Questions and Answers (QA)

Q: How much weight can you lose in a month with intermittent fasting?
A: There’s no universal answer to this question. After the initial water weight loss, you can safely lose up to two pounds a week while fasting. Depending on your diet before fasting, you may notice more significant weight loss in the beginning weeks.

Q: What can you eat on intermittent fasting?
A: Yes, you eat while intermittent fasting. Men typically follow 16-hour fast with an 8-hour window of eating. Women have seen more success following a 14-hour fast with a 10-hour window of eating. The eating phase is not defined by specific foods. You are free to eat as desired.

Q: What are the benefits of intermittent fasting?
A: The benefits of intermittent fasting include neuroprotection, improve cardiovascular health, balanced mood, reduced hunger, and weight loss, to name a few.

Q: Is intermittent fasting bad for you?
A: Intermittent fasting is not “bad” per se, but it is not an eating plan for everyone. Depending on your medical status, you may not benefit from fasting for extended periods. Seek the advice of your physician before any extreme dietary change.

Q: What happens to your body when you fast for 16 hours?
A: If you break the fasting state into three sections, the first is when the body finishes digesting the food you last ate. The section of time goes to using up glycogen stores for energy. And finally, by the last few hours, the body switches to burning fat for fuel as it enters the state of ketosis.

Q: How long do you have to fast before you start burning fat?
A: During the last few hours of the 16-hour fast, your body has switched over to burning fat for fuel. This process is called ketosis. When you eat your first meal, your body switches back to burning carbohydrates.

Q: Can I eat rice during intermittent fasting?
A: Yes, intermittent fasting doesn’t require eliminating any specific foods.

Q: Should you intermittent fast every day?
A: Some people choose to fast for a day or two and others have adopted intermittent fasting as part of their lifestyle. For significant weight-loss and health benefits, you have to fast regularly.

Q: Is it better to skip breakfast or dinner in intermittent fasting?
A: There are no strict rules when it comes to the fasting step of intermittent fasting. Many people find skipping breakfast to be a better option because they don’t typically eat early in the morning. Plus, going to bed feeling hungry, at least until your body adjusts to the fasting state, is not desirable.

Q: What are the negative effects of intermittent fasting?
A: Not everyone will experience negative side effects while intermittent fasting. Men and women with underlying medical conditions, like liver disease, kidney disease, or type 2 diabetes, should seek medical advice and guidance before fasting.