How Does Intermittent Fasting Work?

With intermittent fasting, your body operates differently when "feasting" compared to when "fasting": When you eat a meal, your body spends a few hours processing that food, burning what it can from what you just consumed. Because it has all of this readily available, easy to burn energy in its blood stream (thanks to the food you ate), your body will choose to use that as energy rather than the fat you have stored. This is especially true if you just consumed carbohydrates/sugar, as your body prefers to burn sugar as energy before any other source.
During the "fasted state," your body doesn't have a recently consumed meal to use as energy, so it is more likely to pull from the fat stored in your body, rather than the glucose in your blood stream or glycogen in your muscles/liver.
Burning fat = win.
The same goes for working out in a "fasted" state. Without a ready supply of glucose and glycogen to pull from (which has been depleted over the course of your fasted state, and hasn't yet been replenished with a pre-workout meal), your body is forced to adapt and pull from the only source of energy available to it: the fat stored in your cells!
Why does this work? Your body reacts to energy consumption (eating food) with insulin production. Essentially, the more sensitive your body is to insulin, the more likely you'll be to use the food you consume efficiently, which can help lead to weight loss and muscle creation. Along with that, your body is most sensitive to insulin following a period of fasting.
Your glycogen (a starch stored in your muscles and liver that your body can burn as fuel when necessary) is depleted during sleep (fasting), and will be depleted even further during training, which can further increase insulin sensitivity. This means that a meal immediately following your workout will be stored most efficiently: mostly as glycogen for muscle stores, burned as energy immediately to help with the recovery process, with minimal amounts stored as fat.
Compare this to a regular day (no intermittent fasting). With insulin sensitivity at normal levels, the carbs and foods consumed will see full glycogen stores, enough glucose in the blood stream, and thus be more likely to get stored as fat. Not only that, but growth hormone is increased during fasted states (both during sleep and after a period of fasting). Combine this increased growth hormone secretion, the decrease in insulin production (and thus increase in insulin sensitivity), and you're essentially priming your body for muscle growth and fat loss with intermittent fasting.

Fasting the Way That's Right for You

    There are many considerations to take note when fasting intermittently:

    • Intermittent fasting is not a form of extreme calorie restriction. It's a practice that should make you feel good. If your fasting strategy is making your feel weak, you need to reevaluate it.
    • Typical fast time ranges from 14 to 18 hours, and the longest you'll ever abstain from food is 36 hours. You may also opt to delay eating, which is what I've been personally doing. I advise that you skip breakfast and eat your lunch and dinner within a six to eight-hour time frame, and stop eating three hours before you go to bed.

      Fasting will help your body adjust from burning carbs to burning fat. Eating on a six- to eight-hour window can take a few weeks and should be done gradually. Once your body has successfully shifted into fat burning mode, it will be easier for you to fast for as much as 18 hours and still feel satiated. Your craving for sugar will slowly dissipate and managing your weight will be easier.
    • It is not advisable to practice intermittent fasting if your daily diet is filled with processed foods. Addressing the quality of your diet is crucial before you venture into fasting. It's critical to avoid the wrong calories, including refined carbohydrates, sugar/fructose, and grains.

      Within the six to eight hours that you do eat, you need to eliminate refined carbohydrates like pizza, bread, and potatoes. Fill your diet with vegetable carbohydrates, healthy protein, and healthy fats such as butter, eggs, avocado, coconut oil, olive oil, and raw nuts. 

      On the days that you work out while fasting, it's best to consume a recovery meal—ideally consisting of fast-assimilating whey protein—30 minutes after your workout. Finding out what schedule works for you may take some trials and errors.
    • Intermittent fasting is not something you should carelessly undertake. ALWAYS pay close attention to your body and your energy levels. Individuals who are hypoglycemic, diabetic, or pregnant (and/or breastfeeding) should avoid any type of calorie restriction until your blood sugar or insulin levels are regulated.

    Tips for Fasting and Exercising Safely: A Post-Workout Recovery Meal is Crucial

    An effective exercise program that incorporates high-intensity interval training combined with intermittent fasting can help counteract muscle aging and wasting, and boost fat-burning. If at any point you don't have enough energy or don't feel good, then it is likely time to shift your experiment and reduce the hours of fasting. Intermittent fasting should make you feel better, and if it doesn't then it is best to reevaluate your strategy.
    Make sure to keep the following two points in mind:
    1.Timing of meals: Intermittent fasting is not extreme calorie restriction. You're not supposed to starve yourself. Rather it's simply a matter of timing your meals properly by abstaining from food during much of the day, and limiting your eating to a small window later in the evening. If you were to limit eating to say 4-7 pm, you are effectively fasting for 21 hours. Ideally, you'll want to fast for at least 12-18 hours.
    If you can't abstain from food entirely during the day, limit it to small servings of light, low-glycemic, mostly raw foods such as fruits, vegetables, whey protein or lightly poached eggs every 4-6 hours. Whatever times you choose, it will be very helpful to avoid having any food or calories for three hours prior to going to bed as this will minimize oxidative damage to your system and give your body a major jumpstart in intermittent fasting.
    2.Break your fast with a recovery meal on workout days: On the days that you work out while fasting, you need to consume a recovery meal 30 minutes after your workout. Fast-assimilating whey protein is ideal. Then fast again until you eat your main meal at night. It's very important that you eat an appropriate recovery meal after your workout session, as this will prevent brain and muscle damage from occurring, so do NOT skip this meal.
    If the thought of fasting for 12-18 hours is too much, you can get many of the same benefits of fasting and exercise by simply skipping breakfast and exercising first thing in the morning when your stomach is empty. This is because eating a full meal, particularly carbohydrates, before your workout will inhibit your sympathetic nervous system and reduce the fat burning effect of your exercise. Instead, eating lots of carbs activates your parasympathetic nervous system, (which promotes energy storage – the complete opposite of what you're aiming for).

    Fasting for a Few Days Can Regenerate Your Immune System

    In related news, another recent study has found that a three-day long fast can regenerate your entire immune system, even if you're elderly. The researchers described the findings as "remarkable." Fasting for a few days, they found, has the power to kick-start your stem cells into producing more white blood cells, which are part of your body's natural defense arsenal. As reported by Daily Life: 
    "Scientists at the University of Southern California (USC) say the discovery could be particularly beneficial for those suffering from damaged immune systems, such as cancer patients on chemotherapy. It could also help the elderly whose immune systems become less effective...
    ''And the good news is that the body got rid of the parts of the system that might be damaged or old, the inefficient parts, during the fasting. Now, if you start with a system heavily damaged by chemotherapy or ageing, fasting cycles can generate, literally, a new immune system."
    They discovered that longer fasts (two to four days) led to the reduction of an enzyme called protein kinase A (PKA), which previous research has linked to life extension in simple organisms. Starving the body for a couple of days turns off the gene for PKA, and this is the trigger that tells your stem cells to shift into regeneration mode. According to Valter Longo, professor of gerontology and biological sciences at the University of Southern California, this is what "gives the OK for stem cells to go ahead and begin proliferating and rebuild the entire system." Fasting for three days also led to a reduction of IGF-1, a growth factor hormone linked to aging, cancer, and tumor growth. According to co-author Tanya Dorff:9 ''The results of this study suggest that fasting may mitigate some of the harmful effects of chemotherapy."

    Three Reasons Why Intermittent Fasting Works

    For people who loathe the idea of dieting, intermittent fasting offers a simple alternative that doesn't involve calorie counting or starvation. In fact, I prefer to think of intermittent fasting as a lifestyle shift rather than simply a diet change. It's a way of living and eating that can help you live a longer, healthier life without feeling like you sacrificing too much. If you're still skeptical, there are three major mechanisms by which fasting benefits your body, as it extends lifespan and protects against disease, including:
    1. Increased insulin sensitivity and mitochondrial energy efficiency – Fasting increases insulin sensitivity along with mitochondrial energy efficiency, and thereby retards aging and disease, which are typically associated with loss of insulin sensitivity and declined mitochondrial energy.
    2. Reduced oxidative stress – Fasting decreases the accumulation of oxidative radicals in the cell, and thereby prevents oxidative damage to cellular proteins, lipids, and nucleic acids associated with aging and disease.
    3. Increased capacity to resist stress, disease and aging – Fasting induces a cellular stress response (similar to that induced by exercise) in which cells up-regulate the expression of genes that increase the capacity to cope with stress and resist disease and aging.

    Intermittent Fasting Is Not a Diet – It's a Lifestyle

    While most people would think that intermittent fasting is a fairly new approach to healthy living, this type of lifestyle has actually been practiced even during the early times. For example, our hunter-gatherer ancestors rarely had access to food 24/7 – this may mean that our genes are likely optimized to consume sporadic, intermittent meals as opposed to regular cycles of feasting. During the 1940s, the benefits of intermittent fasting have also been widely appreciated. There are also religious sects that consider fasting a tradition, even until today.
    In my opinion, intermittent fasting is very different from fad diets that are widespread today. It's actually a lifestyle shift – it allows you to live and eat well, but without making you feel as if you are sacrificing too much.
    There are three major mechanisms by which fasting benefits your body:
    • It increases your mitochondrial energy efficiency and insulin sensitivity. This helps retards aging and disease, which are both associated with loss of insulin sensitivity and declined mitochondrial energy
    • It reduces oxidative stress. The decreased accumulation of oxidative radicals in your cells helps ward off oxidative damage to lipids, cellular proteins, and nucleic acids
    • Increased resistance to stress, disease, and aging. It induces a cellular stress response that upregulates the expression of genes, helping increase your capacity to cope with stress and resist disease and aging
    Aside from these benefits and the apparent weight loss, one of the most wonderful effects of intermittent fasting is its ability to eliminate your hunger and sugar cravings. You lose the desire to eat unhealthy processed foods – a definite advantage that will help you achieve your health and fitness goals.
    Another boon of intermittent fasting that I would like to stress on: you're not going to starve yourself. You don't even have to restrict the amount of food you eat. However, please note that you have to be careful in choosing healthy foods. Avoid or minimize your intake of carbs and replace them instead with healthy fats like olive oil, olives, eggs, butter, coconut oil, avocados, and nuts.
    It may take a few weeks for your body to shift to fat-burning mode, but once you become "fat adapted," your body will be able to burn your stored fat and you will not need to rely on new carbs for fuel.

    Intermittent Fasting Reduces Your Diabetes and Heart Disease Risk

    Did you know that aside from helping you lose weight and supporting your fitness goals, intermittent fasting can also reduce your risk of chronic diseases, particularly heart disease and diabetes?
    According to a 2013 review published in the British Journal of Diabetes and Vascular Disease, obese or overweight individuals with type 2 diabetes who fast on consecutive or alternate days not only lost more weight, but also acquired cardioprotective benefits and experienced better heart health.
    I believe that this clearly supports the notion that going against the customary "three square meals" a day in favor of intermittent fasting may have superb benefits for your overall health.

    Research Confirms How Intermittent Fasting May Be the Key to Fighting Obesity and Diabetes

    The report, which evaluated the various approaches to intermittent fasting, particularly its benefits and limitations in fighting type 2 diabetes and obesity, found that fasting had a broad range of therapeutic potential. These effects were seen even though the total calorie intake of the subjects did not change or was only slightly reduced.
    The review suggests that intermittent fasting may also play a role in:
    • Limiting inflammation
    • Improving circulating glucose and lipid levels
    • Reducing blood pressure
    • Helping prevent or reverse type 2 diabetes (or even slowing its progression)
    • Causing significant reductions in body weight (especially in obese individuals)
    • Improving metabolic efficiency and body composition
    • Improving insulin levels and insulin sensitivity
    • Improving pancreatic function
    • Reducing LDL and total cholesterol levels
    • Helping modulate levels of visceral fat, the dangerous fat that gathers around your internal organs

    Eating Breakfast Does Not Improve Metabolism, Study Finds

    Skipping breakfast is one form of intermittent fasting in which you restrict your daily eating to a specific window of time, say between 11am and 7pm, as an example. This type of eating schedule typically does promote weight loss—but what you eat is another important factor.
    This is especially true if you're severely overweight and eat a standard American processed food diet. Many people find that eating breakfast leads to feeling hungry again soon thereafter, which can lead to unnecessary snacking. This is reflected in another recent study4 into the metabolic effects of eating or skipping breakfast.
    As reported by Time Magazine
    "...contrary to popular belief, having breakfast every day was not tied to an improvement in metabolism. Prior thought—supported by research—has shown that eating early in the day can prevent people from overeating later out of hunger, and it boosts their metabolism early. The new study which examined causal links between breakfast habits and energy balance couldn't prove that."
    The study found that eating breakfast was linked to a greater overall dietary energy intake. And again, the type of foods you eat for breakfast may be the key ingredient that is being overlooked in this type of research—both past and present. Typically, you will find that eating a carbohydrate-rich breakfast will tend to make you hungry again far sooner than a low-carb, high-fat breakfast will. The reason for this is because if your body is using sugar as its primary fuel, it will need a "refill" at regular intervals, as sugar is a very fast-burning fuel.
    Fat, on the other hand, is a slow-burning fuel, allowing you to feel satiated longer, and the more important fact is that you have loads more fat available than sugar stored as glycogen in your muscles and liver. While glycogen stores will only last for less than a day, your fat store can last for weeks. In addition to that, eating first thing in the morning also coincides with your circadian cortisol peak, which has an exaggerated impact on your insulin secretion. When you eat during this time, it leads to a rapid and large insulin release and a corresponding rapid drop in blood sugar levels, more so than when you eat at other times of the day.
    If you're healthy, your blood sugar level won't drop dangerously low (such as can occur with hypoglycemia) but they can drop low enough to make you feel hungry again, even though you recently ate. This effect is amplified when eating a carbohydrate-rich breakfast, such as pancakes, muffins, cereal, or bread, with a large glass of juice for example.

    Intermittent Fasting and Low-Carb Diet – A Powerful Combo

    If you're obese or severely overweight, I believe the first thing that you should do is to cut back on your overall sugar and grain consumption. I highly recommend keeping your total sugar or fructose intake below 25 grams a day, or as little as 15 grams a day if you have any health problems related to insulin and leptin resistance, such as high blood pressure, diabetes, or heart disease, until your insulin-leptin sensitivity has been restored.
    Fructose is particularly troublesome, as it triggers a key enzyme, fructokinase, which in turn activates another enzyme that causes your cells to accumulate fat. This is especially true if you are overweight, but far less of an issue if you aren't. Likewise, grains also break down into sugar in your body, thereby promoting insulin and leptin resistance just like other sugars, which in turn promotes obesity and makes losing weight a real struggle.
    After getting rid of sugar in your diet, you can take your weight loss efforts further by practicing intermittent fasting and exercising in a fasted state. The simplest way to get started is to skip breakfast, make lunch the first meal of your day, and have your dinner no later than 7PM or at least three hours before you hit the sack. I typically suggest sticking to this type of eating schedule, however for those who have schedules that do not allow this, eating breakfast and skipping dinner is an acceptable alternative.
    The general rule is to limit your eating to a specific and narrow window of time each day (about six to eight hours), instead of eating every two to three hours all throughout the day. By providing ample amount of time in fasting, your body empties its glycogen stores, which rarely happens when you're eating three times a day, and turns on its natural fat-burning mode.
    Warning: I strongly advise against fasting without your doctor's consent if you are hypoglycemic, living with chronic stress, have cortisol dysregulation, or have an existing medical condition. Pregnant women or nursing mothers are also not good candidates for any type of fasting, as babies need generous amounts of nutrients before and after birth.

    Top Breakfast Myths – Debunked!

    The belief that breakfast is the most important meal of the day is now a thing of the past, as mounting research continues to support the benefits of intermittent fasting, a dietary pattern that promotes longer bouts of fasting by limiting your food intake to a specific timeframe.
    Here are some common breakfast misconceptions that were proven incorrect by a study from the University of Alabama, Birmingham:
    • Eating breakfast helps you lose weight – In an effort to find out whether eating or not eating breakfast truly had an impact on weight loss, researchers divided 309 overweight and obese but otherwise healthy adults into two random groups. Some were told to eat breakfast, while the others were told to skip it. After 16 weeks, the researchers found no difference in weight loss between the groups. 

      In essence, it didn't matter if they ate breakfast or not. However, it's important to note that they didn't control the food intake of the participants involved. The reason why there may be no significant weight loss between the two groups is that all of them may have been eating a standard American diet – refined carbs and processed fructose – which hinders your body from effectively burning fat.
    • Eating breakfast improves your metabolism – In an article by Time magazine, it was revealed that eating your breakfast regularly does not improve your metabolism. Disputing the previous notion that eating breakfast will actually prevent you from overeating later in the day because their metabolism was boosted earlier, many people find that eating breakfast leads to feeling hungry again soon afterwards, which can lead to unnecessary snacking.

      Again, this may have something to do with the type of food the participants in the said study were eating. Typically, you will find that eating a carbohydrate-rich breakfast will make you hungry again far sooner than a low-carb, high-fat breakfast will. The reason for this is that if your body is using sugar as its primary fuel, it will need a "refill" at regular intervals, as sugar is a very fast-burning fuel.

    How Intermittent Fasting Benefits Your Brain

    Your brain can also benefit from intermittent fasting. As reported in the featured article:
    "Mattson has also researched the protective benefits of fasting to neurons. If you don't eat for 10–16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory and learning functionality, says Mattson, as well as slow disease processes in the brain."
    Besides releasing ketones as a byproduct of burning fat, intermittent fasting also affects brain function by boosting production of a protein called brain-derived neurotrophic factor (BDNF). Mattson's research suggests that fasting every other day (restricting your meal on fasting days to about 600 calories), tends to boost BDNF by anywhere from 50 to 400 percent, depending on the brain region. BDNF activates brain stem cells to convert into new neurons, and triggers numerous other chemicals that promote neural health. This protein also protects your brain cells from changes associated with Alzheimer's and Parkinson's disease.
    BDNF also expresses itself in the neuro-muscular system where it protects neuro-motors from degradation. (The neuromotor is the most critical element in your muscle. Without the neuromotor, your muscle is like an engine without ignition. Neuro-motor degradation is part of the process that explains age-related muscle atrophy.) So BDNF is actively involved in both your muscles and your brain, and this cross-connection, if you will, appears to be a major part of the explanation for why a physical workout can have such a beneficial impact on your brain tissue — and why the combination of intermittent fasting with high intensity exercise appears to be a particularly potent combination.

    Intermittent Fasting Is as Good or Better Than Continuous Calorie Restriction

    According to Dr. Stephen Freedland, associate professor of urology and pathology at the Duke University Medical Center, "undernutrition without malnutrition" is the only experimental approach that consistently improves survival in animals with cancer, as well as extends lifespan overall by as much as 30 percent. 

    Interestingly enough, intermittent fasting appears to provide nearly identical health benefits without being as difficult to implement and maintain. It's easier for most people to simply restrict their eating to a narrow window of time each day, opposed to dramatically decreasing their overall daily calorie intake.

    Mark Mattson, senior investigator for the National Institute on Aging, which is part of the US National Institutes of Health (NIH), has researched the health benefits of intermittent fasting, as well as the benefits of calorie restriction. According to Mattson, there are several theories to explain why fasting works:

    "The one that we've studied a lot, and designed experiments to test, is the hypothesis that during the fasting period, cells are under a mild stress, and they respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease... There is considerable similarity between how cells respond to the stress of exercise and how cells respond to intermittent fasting."

    In one of his studies, overweight adults with moderate asthma lost eight percent of their body weight by cutting their calorie intake by 80 percent on alternate days for eight weeks. Markers of oxidative stress and inflammation also decreased, and asthma-related symptoms improved, along with several quality-of-life indicators.

    More recently, Mattson and colleagues compared the effectiveness of intermittent fasting against continuous calorie restriction for weight loss, insulin sensitivity and other metabolic disease risk markers. The study, published in the International Journal of Obesity in 2011, found that intermittent fasting was as effective as continuous calorie restriction for improving all of these issues, and slightly better for reducing insulin resistance. According to the authors:

    "Both groups experienced comparable reductions in leptin, free androgen index, high-sensitivity C-reactive protein, total and LDL cholesterol, triglycerides, blood pressure and increases in sex hormone binding globulin, IGF binding proteins 1 and 2. Reductions in fasting insulin and insulin resistance were modest in both groups, but greater with IER [intermittent fasting] than with CER [continuous energy restriction]."

    The Health Benefits of Intermittent Fasting

    Aside from removing your cravings for sugar and snack foods and turning you into an efficient fat-burning machine, thereby making it far easier to maintain a healthy body weight, modern science has confirmed there are many other good reasons to fast intermittently. For example, research presented at the 2011 annual scientific sessions of the American College of Cardiology in New Orleansshowed that fasting triggered a 1,300 percent rise of human growth hormone (HGH) in women, and an astounding 2,000 percent in men.

    HGH, human growth hormone, commonly referred to as "the fitness hormone," plays an important role in maintaining health, fitness and longevity, including promotion of muscle growth, and boosting fat loss by revving up your metabolism. The fact that it helps build muscle while simultaneously promoting fat loss explains why HGH helps you lose weight without sacrificing muscle mass, and why even athletes can benefit from the practice (as long as they don't overtrain and are careful about their nutrition). The only other thing that can compete in terms of dramatically boosting HGH levels is high-intensity interval training. Other health benefits of intermittent fasting include:

     Normalizing your insulin and leptin sensitivity, which is key for optimal health
     Improving biomarkers of disease
     Normalizing ghrelin levels, also known as "the hunger hormone"
     Lowering triglyceride levels
     Reducing inflammation and lessening free radical damage
     Preserving memory functioning and learning