By Dr. Mercola
Intermittent fasting or “scheduled eating” is one of the most powerful interventions I know of to shed excess weight and reduce your risk of chronic diseases like diabetes and heart disease.
These health benefits are more or less beneficial “side effects” of shifting your body from burning sugar to burning fat as its primary fuel. I’m really pleased to see this approach now receiving more mainstream media attention, as it’s such a potent health-promoting tool.
Most recently, The Wall Street Journal1 did a write-up on intermittent calorie restriction, specifically mentioning the 5:2 diet, promoted by Dr. Michael Mosley2 in his book The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting.
The 5:2 strategy involves eating regularly five days a week, and fasting for two. On fasting days, Dr. Mosley recommends cutting your food down to ¼ of your normal daily calories, or about 600 calories for men and about 500 for women, along with plenty of water and tea.
As reported by featured article:
“Some research shows that this more radical-sounding approach may be a struggle at first but ends up being easier to stick with compared with the typical route of cutting calories each day. Some animal studies suggest it also offers other health benefits, including cognitive improvements.”
There are many different variations of intermittent fasting, however. If you are like 85 percent of the population and have insulin resistance, my personal recommendation is to fast every day by simply scheduling my eating into a narrower window of time each day. I find this method to be easier than fasting for a full 24 hours or more, twice a week.
Once you are at your ideal body weight, don’t have diabetes, high blood pressure, or abnormal cholesterol levels, you can eat more at other times. However, it is probably best to regularly resume some type of scheduled eating regimen on a regular basis.
‘Intermittent Eating’ May Be Easier Than Day-Long Fasts
In order to understand how you can fast daily while still eating every day, you need to understand some basic facts about metabolism. It takes most people eight to 12 hours for their body to burn the sugar stored in your body as glycogen. Now, most people never deplete their glycogen stores because they eat three or more meals a day. This teaches your body to burn sugar as your primary fuel and effectively shuts off your ability to use fat as a fuel.
Therefore, in order to work, the length of your fast must be at least eight hours. Still, this is a far cry from a 24-hour or longer fast, which can be quite challenging. I believe that, for most people, simply restricting the window of time during which you eat your food each day is far easier.
For example, you could restrict your eating to the hours of 11am and 7pm. Essentially, you’re just skipping breakfast and making lunch your first meal of the day instead. This equates to a daily fasting of 16 hours—twice the minimum required to deplete your glycogen stores and start shifting into fat burning mode.
Please keep in mind that a proper nutrition plan becomes even more important when you’re fasting and/or cutting calories, so you really want to address your food choices before you try any form of fasting.
This includes minimizing carbs and replacing them with healthful fats, like coconut oil, olive oil, olives, butter, eggs, avocados, and nuts. Many would benefit from getting as much as 50-85 percent of their daily calories from fats. (While this may sound like a lot, consider that, in terms of volume, the largest portion of your plate would be vegetables, since they contain so few calories. Fat, on the other hand, tends to be very high in calories. For example, just one tablespoon of coconut oil is about 130 calories—all of it from healthful fat.)
Three Reasons Why Intermittent Fasting Works
One of the primary mechanisms that makes intermittent fasting so beneficial for health is related to its impact on your insulin sensitivity. While sugar is a source of energy for your body, it also promotes insulin resistance when consumed in the amounts found in our modern processed food diets. Insulin resistance, in turn, is a primary driver of chronic disease—from heart disease to cancer. Mounting research confirms that when your body becomes accustomed to burning FAT instead of sugar as its primary fuel, you rather dramatically reduce your risk of chronic disease. Becoming fat adapted may even be a key strategy for both cancer prevention and treatment, as cancer cells cannot utilize fat for fuel—they need sugar to thrive.
In short, fasting increases insulin sensitivity along with mitochondrial energy efficiency, thereby retarding aging and disease, which are typically associated with loss of insulin sensitivity and declined mitochondrial energy. Two additional mechanisms by which fasting benefits your body include:
- Reducing 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.
- Increasing 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.
Watch Cravings ‘Magically’ Vanish While Excess Weight Falls Off...
Intermittent fasting is one of the most effective ways I know of to shed excess weight. And, although it might be challenging in the beginning, once you’ve adapted to burning fat, you’ll typically find that sugar cravings vanish without a trace.
The featured article3 cites a recent study4 comparing the effectiveness of intermittent fasting versus daily calorie restriction to produce weight loss in overweight women with a history of breast cancer. All in all, intermittent fasting was determined to be more effective for weight loss and improving insulin resistance than daily calorie restriction:
“Participants were divided into groups and instructed to eat a diet for three months in a way that reduced their typical calorie intake by about 25 percent. The first group ate only low-carbohydrate foods for two consecutive days, while the second was limited to two straight days of low-carbohydrate, low-calorie foods. The third group restricted calories daily.
The two intermittent restriction groups lost twice as much weight as the chronic restriction group, but the intermittent groups didn't differ from each other. In addition, more people in the intermittent groups lost weight: 65 percent of intermittent restrictors, compared with 40 percent in the chronic restriction group.”
Keep in mind that while most people will successfully switch over to burning fat after several weeks of intermittent fasting, you may need several months to teach your body to turn on the fat-burning enzymes that allow your body to effectively use fat as its primary fuel. So don’t give up!
Once you’ve become fat adapted and are of a normal weight, without high blood pressure, diabetes, or high cholesterol, you really only need to do scheduled eating occasionally. As long as you maintain your ideal body weight, you can go back to eating three meals a day if you want to. I restricted my eating to a six- to seven-hour window each day until I got fat adapted and lost about 10 pounds. Now, I still rarely ever eat breakfast, but several days a week I will have two meals instead of just one.
Other Health Benefits of Intermittent Fasting
Aside from removing your cravings for sugar and snack foods and turning you into an efficient fat-burning machine, 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 Orleans5 showed that fasting triggered a 1,300 percent rise of human growth hormone (HGH) in women, and an astounding 2,000 percent in men.
HGH, 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 over train 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"
Reducing inflammation and lessening free radical damage
Lowering triglyceride levels
Preserving memory functioning and learning
Intermittent Fasting May Boost Your Brain Health
With Alzheimer’s incidence on the rise, it’s well worth noting strategies that can help prevent such a fate, and intermittent fasting appears to be a particularly effective one. As reported in the featured article:
“... [F]asting for periods of as short as 16 to 24 hours seems to induce a state of mild stress in the body. The brain releases additional neurotrophic proteins that help stimulate and support the growth of neurons and other cells, heightening their responsiveness and activity. Just as exercise makes muscles stronger, fasting makes the brain stronger, Dr. Mattson says. The body chemicals produced by fasting and exercise also could help boost people's moods.”
The brain-boosting protein referred to here is called brain-derived neurotrophic factor (BDNF). Dr. Mattson, mentioned in the paragraph above, is a senior investigator for the National Institute on Aging, which is part of the US National Institutes of Health (NIH). He has researched the health benefits of both intermittent fasting and calorie restriction, and his research suggests that fasting every other day can boost BDNF by anywhere from 50 to 400 percent,6 depending on the brain region.
This is great news, as 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.
Interestingly, 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 helps explain why a physical workout can have such a beneficial impact on your brain tissue—and why the combination of intermittent fasting with high intensity interval training appears to be a particularly potent health-boosting combination.
Are You Ready to Boost Your Health Potential?
Based on my own phenomenal experience with scheduled eating, I believe it’s one of the most powerful ways to shift your body into fat burning mode and improve a wide variety of biomarkers for disease. The effects can be further magnified by exercising while in a fasted state. For more information on that, please see my previous article “High-Intensity Interval Training and Intermittent Fasting - A Winning Combo.”
To get started, consider skipping breakfast, and avoid eating at least three hours before you go to sleep. This should effectively restrict your eating to an 8-hour window or less each day.
When you do eat, make sure to minimize carbs like pasta, bread, and potatoes. Instead, exchange them for healthful fats like butter, eggs, avocado, coconut oil, olive oil, and nuts—essentially the very fats the media and “experts’ tell you to avoid. You may also want to restrict your protein a bit if you’re typically a big meat eater. I strongly suggest eating only high-quality pastured protein, and limiting it to about one gram of protein per kilogram of lean body mass (about one-half gram of protein per pound of lean body weight) may be appropriate for most people. (Note: if your body fat mass is 20 percent, your lean mass is 80 percent of your total body weight.)
These kinds of food choices, in combination with intermittent fasting, will help shift you from carb burning to fat burning mode. Last but not least, intermittently fasting will also help support healthy microorganisms in your gut. Your intestinal health, as you may know, in turn has a tremendous influence on your overall health, as 80 percent of your immune system resides in your gut.
Remember, it usually does take a few weeks, and you have to do it gradually, but once you succeed to switch to fat burning mode, you’ll be easily able to fast for 18 hours and not feel hungry. The “hunger” most people feel are actually cravings for sugar, and these will disappear, as if by magic, once you successfully shift over to burning fat instead of sugar.
Some caveats: If you're hypoglycemic, diabetic, or pregnant (and/or breastfeeding), you are better off avoiding any type of fasting or timed meal schedule until you've normalized your blood glucose and insulin levels, or weaned the baby. Other categories of people that would be best served to avoid fasting include those living with chronic stress and those with cortisol dysregulation.