By Dr. Mercola
If you're already off to a good start on a healthy fitness plan, and you're looking for ways to take it to the next level, then you might want to consider a form of fasting called Scheduled Eating, or intermittent fasting.
In essence this fitness-enhancing strategy looks at the timing of meals, as well as when NOT to eat. This isn't one of those fad plans, where you eat just one or two things for several days in a row.
In fact, the longest time you'll ever abstain from food is 36 hours, although 14-18 hours is more common. You can also opt to simply delay eating. For example, skipping breakfast may be just the thing to kick-start you off a plateau in your fitness routine.
But hypoglycemics and diabetics beware—there is a proper way to implement fasting, and hypoglycemic and/or diabetics need to be particularly careful in order to not worsen their health.Ditto for pregnant or breastfeeding women.
The plan is supported by a growing body of evidence showing that certain forms of fasting are good for you, and Mark Sisson's excellent series on this topic on his blog on marksdailyapple.com, delve into this topic at some depth.
For me, the issue of fasting is a major shift from my typical recommendations.
I've not been a major advocate for it in the past, but as many of you who have been reading this site for years know, I am always learning. Life is a journey, and no one has all the answers.
I seek to explore the best concepts out there to maximize learning.
To that end, I've been playing around with various forms of fasting for about a year and a half, and I now feel I'm ready to make some suggestions based on my experience.
First of all, I believe that fasting is not something you should undertake willy-nilly. You need to pay careful attention to your body, your energy levels, and how it makes you feel in general—especially if you're diabetic, hypoglycemic, or pregnant. I'll share some precautionary notes in a moment.
Furthermore, remember that the type of diet and/or form of fasting that might be best for you will vary depending on your weight, health, and fitness goals. Is your goal to live a longer, healthier life? Or are you a competitive or elite athlete? It may surprise many to learn that you cannot achieve maximum fitness and maximum longevity and fertility at the same time.
Each goal requires a different strategy, and will not provide you with equal end results. For example, elite female athletes typically have a difficult time getting pregnant—their fitness has been maximized at the expense of their fertility, as female hormones depend on sufficient amounts of body fat.
While most people need to address the foods they DO eat, before considering skipping meals, fasting can provide you with many benefits, and is another tool you can experiment with to help you reach your goals. However, please keep in mind that proper nutrition becomes even MORE important when fasting, so addressing your diet really should be your first step. Common sense will tell you that fasting combined with a denatured, highly processed, toxin-rich diet is likely to do more harm than good, as you're not giving your body proper fuel to thrive when you DO eat.
Intermittent Fasting for Weight Loss
In part 1, Mark Sisson discusses the merits of using fasting—in whatever form—to achieve weight loss. Overall, the research is very favorable for this goal. He lists three studies from recent years into fasting for weight loss, all of which showed positive results:
- Non-obese patients lost an average of four percent of their total fat with alternate-day fasting for 22 days. Their fasting insulin also decreased.i
- Alternate-day fasting was also effective for obese patients in a 2009 study. On fasting days, participants consumed 25 percent of their daily calorie needs. On average, they lost just over 5.5 pounds in eight weeks, and about three percent of their total body fat. Total cholesterol and LDL ("bad") cholesterol decreased, while HDL ("good") cholesterol remained unchanged. Systolic blood pressure also decreased.ii
- In young, overweight women, alternate-day fasting was just as effective as calorie restriction for promoting weight loss and improving metabolic markers.iii
One of the mechanisms that makes fasting so effective for weight loss is the fact that it provokes the secretion of human growth hormone (HGH), which is a fat-burning hormone. It also plays an important role in muscle building. Fasting also increases catecholamines, which increases resting energy expenditure, while decreasing insulin levels, which allows stored fat to be burned for fuel. Together, these and other factors will turn you into an effective fat-burning machine.
Hence, if like many tens of millions of people, your goal is to shed excess fat, fasting can be both effective and beneficial for improving many disease markers. The type of fast you choose appears to be less important, so pick whichever one fits your lifestyle, schedule, and temperament the best.
I'll summarize the four different types of intermittent fasting programs that are covered very well in Mark Sisson's excellent series on this subject (see Sources below for links to his blog). Mark is particularly well qualified to report on this topic as he's a leading blogger in the Paleo community, and a former elite Olympic Trials athlete.
Intermittent Fasting for Athletes
One 2008 study that evaluated the effect of fasting during the Muslim observance of Ramadan found it had a positive effect on body mass and other health markers in trained athletesiv.
While athletes are certainly concerned with shedding excess fat, another overriding concern is the optimization of muscle growth. For this, you need protein. As a general guideline, you'll want to consume a high quality protein 30-60 minutes after finishing your workout—whey being one of the most ideal for this purpose, as it helps your body build muscle and lose fat simultaneously. Research has also shown that high quality protein from meat and whey has a positive effect on blood sugar, muscle building, changing body composition, and sparing muscle while losing fat.
Many find it works out well to break their fast after working out, which would allow you to get the best of both worlds: the benefits of working out in a fasted state, and protein-loading about half-an-hour to an hour afterward. This is my new strategy. I will typically delay my breakfast until 11 or 12 and workout around 9 AM. Since my last meal is typically around 7 PM, I will fast for about 14-17 hours before I eat my first meal. The fact that you are sleeping during most of this time makes it relatively painless and easy to do.
Avoid grain carbs, however. Although popular with many, "carb loading" is a mistake, particularly for people engaged in intense strength training, as you will burn carb fuel very quickly and then "hit the wall." The same goes for most people who start their day with muffins, bagels, or pancakes for example. This type of breakfast typically ignites a vicious cycle of hunger and snacking on even more carbs. And the more you continue eating these carb snacks, the more insulin resistant you become.
Part of what makes working out in a fasted state so effective is that your body actually has a preservation mechanism that protects your active muscle from wasting itself. So if you don't have sufficient fuel in your system when you exercise, you're going to break down other tissues but not the active muscle, i.e. the muscle being exercised. According to Ori Hofmekler, author of The Warrior Diet, you can quite literally re-design your physique using a combination of under-eating and exercise. However this really only works well once your metabolism has become proficient at burning fat. Mark discusses this in his series.
What about competitive sports athletes who may be exerting themselves in competitions several times a week—should they fast, and if so, when? Mark Sisson offers the following advicev:
"Personally, I would eat on game days. It might be fun to try out a few fasted games, just to see how you perform, but the likely optimal way to integrate fasting into competition is to save the fasting days for your training days. By doing this, you'll be "training low, playing high," which should result in some beneficial adaptations after training and improved performance in the game (when you're "high" or fully replete with nutrients and calories)."
If you're an athlete, keep in mind that fasting can be contraindicated with overtraining, so be cautious if you're more or less in constant training.
Intermittent Fasting for General Health and Longevity
Fasting is historically common-place as it has been a part of spiritual practice for millennia. But modern science has confirmed there are many good reasons for fasting, including:
- Normalizing your insulin sensitivity, which is key for optimal health as insulin resistance (which is what you get when your insulin sensitivity plummets) is a primary contributing factor to nearly all chronic disease, from diabetes to heart disease and even cancer
- Normalizing ghrelin levels, also known as "the hunger hormone"
- Promoting human growth hormone (HGH) production, which plays an important part in health, fitness and slowing the aging process
- Lowering triglyceride levels
- Reducing inflammation and lessening free radical damage
There's also plenty of research showing that fasting has a beneficial impact on longevity in animals. There are a number of mechanisms contributing to this effect. Normalizing insulin sensitivity is a major one, but fasting also inhibits the mTOR pathway, which plays an important part in driving the aging process. The fact that it improves a number of potent disease markers also contributes to fasting's overall beneficial effects on general health.
Interestingly, one recent study that included more than 200 individuals, found that fasting increased the participants' low-density lipoprotein cholesterol (LDL or "bad" cholesterol) and high-density lipoprotein cholesterol (HDL, the "good" cholesterol) by 14 percent and 6 percent, respectivelyvi. Why would fasting raise total cholesterol? Dr. Benjamin D. Horne, PhD, MPH, director of cardiovascular and genetic epidemiology at the Intermountain Medical Center Heart Institute, and the study's lead author, offers the following explanation:
"Fasting causes hunger or stress. In response, the body releases more cholesterol, allowing it to utilize fat as a source of fuel, instead of glucose. This decreases the number of fat cells in the body... This is important because the fewer fat cells a body has, the less likely it will experience insulin resistance, or diabetes."
Even more remarkable, the study also found that fasting triggered a dramatic rise in HGH—1,300 percent 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 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. If you're over the age of 30, especially if you lead an increasingly sedentary lifestyle, you've likely entered a phase known as somatopause (age-related growth hormone deficiency). As your HGH levels decrease, your levels of insulin-like growth factor-1 (IGF-1) also decrease, and this is yet another important part of what drives your body's aging process.
Variations of Fasting
In his blog on marksdailyapple.com, Mark Sisson delves into four different variations of fasting, and how to implement them. The variations he includes are:
- LeanGains (a fasting protocol by Martin Berkhanvii )—A daily 14-16 hour fast, during which time you consume nothing, with the exception of non-caloric fluids. Sleeping time is included in this time-frame, leaving an 8-10 hour window during the day when you're allowed to eat.
This protocol is designed with regular exercise in mind, with specific nutrient ratios for workout days and rest days, and is geared for those who want to shed excess fat and gain muscle mass. Hence, it's best suited for those who are actually exercising and lifting weights each week and can tolerate working out in a fasted state.
- Eat Stop Eat (created by Brad Pilonviii)—In this protocol, you fast for a full 24 hours once or twice a week. Your fast should be broken with a regular-sized meal (i.e. avoid gorging when coming off your fast), and you can maintain a regular exercise program without any special diet recommendations for workout days.
Fasting for 24 hours can be tough for some people, but I would agree with Mark's advice that eating a high-fat, low-carb diet can make 24-hour fasting easier, as a higher fat diet will tend to normalize your hunger hormones and provide improved satiety for longer periods of time.
- The Warrior Diet (by Ori Hofmekler)—This is another protocol designed to improve your fitness by exercising in a fasted state. I've interviewed Ori and posted detailed articles on this in the past. His plan calls for 20 hours of fasting, and four hours of "feasting." You exercise during the day in a fasted state. Raw vegetables are allowed during your fast, but no protein, which is reserved for "feasting" or post-exercise recovery meals.
To learn more about the Warrior Diet, please see this previous interview with Ori.
- Alternate Day Fasting—This fasting protocol is exactly as it sounds: one day off, one day on. When you include sleeping time, the fast can end up being as long as 32-36 hours.
As Mark notes, this may be the most difficult of all types of fasting, as it will require you to go to bed with an empty stomach a few times a week. It's definitely not for everyone.
Mark rounds off his list with one last suggestion: to simply let your hunger guide you and skip meals if you're not hungry. While this should work really well for those who are otherwise healthy and are not struggling with food cravings, it may not work if you're constantly craving food. Food cravings is a sign that you're not providing your body with proper nutrients in the appropriate ratios, so following your hunger in this case could be staggeringly counterproductive.
Who Should Use Extra Caution when Fasting, or Avoid it Altogether?
As I mentioned earlier, if you're hypoglycemic, diabetic, or pregnant (and/or breastfeeding), you need to be extra cautious with fasting, and may be best served to avoid it entirely, until you've normalized your blood glucose and insulin levels, or weaned the baby.
Hypoglycemia is a condition characterized by an abnormally low level of blood sugar. It's commonly associated with diabetes, but you can be hypoglycemic even if you're not diabetic. Common symptoms of a hypoglycemic crash include:
As your blood glucose levels continue to plummet, more severe symptoms can set in, such as:
- Confusion and/or abnormal behavior
- Visual disturbances, such as double vision and blurred vision
- Loss of consciousness
One of the keys to eliminating hypoglycemia is to eliminate sugars, especially fructose from your diet. It will also be helpful to eliminate grains, and replace them with higher amounts of quality proteins and healthful fats, However it will take some time for your blood sugar to normalize. You'll want to pay careful attention to hypoglycemic signs and symptoms, and if you suspect that you're crashing, make sure to eat something. Ideally, you should avoid fasting if you're hypoglycemic, and work on your overall diet to normalize your blood sugar levels first. Then try out one of the less rigid versions of fasting and work your way up to a full 24-hour fast.
As for pregnant and/or lactating women, I don't think fasting would be a wise choice. Your baby needs plenty of nutrients, during and after birth, and there's no research supporting fasting during this important time. Sisson lists three studies on fasting during pregnancy, and all three suggested it might be contraindicated, as it can alter fetal breathing patterns, heartbeat, and increase gestational diabetes. It may even induce premature labor.
My recommendation would be to really focus on improving your nutrition during this crucial time. A diet with plenty of raw organic, biodynamic foods, and foods high in healthful fats, coupled with high quality proteins will give your baby a head start on good health. You'll also want to be sure to include plenty of cultured and fermented foods to optimize your—and consequently your baby's—gut flora. For more information, please see this previous article that includes specific dietary recommendations for a healthy pregnancy, as well as my interview with Dr. Natasha Campbell-McBride.
Others categories of people that would be best served to avoid fasting include those living with chronic stress, and those with cortisol dysregulation.
Fasting—Is it Right for You?
I understand it can get confusing at times, trying to determine when and what to eat in order to optimize your health. Unfortunately, besides a few basic principles that will apply to virtually everyone, such as strictly limiting consumption of sugars (particularly fructose) and grains, the rest is really a matter of figuring out what works for your individual biochemistry. This requires some trial and error.
For example, there is good evidence supporting the recommendation to eat a protein-heavy breakfast if you want to lose weight, and even more so if you exercise first thing in the morning to optimize muscle growth and recovery. But there may be times when you feel like you've hit a plateau, and while your diet and exercise routine may be good, the simple act of skipping breakfast and exercising on an empty stomach could be just the thing that will kick start you onto that next level.
Personally, I skip breakfast and exercise in a fasting state whenever I've gained a few pounds and want to get them off. I find this works well for me. While I'm not eating breakfast, I don't really eliminate that meal entirely; rather I'm simply delaying it until noon or later, in order to reap the metabolic rewards of exercise combined with calorie restriction.
While I have not widely promoted calorie restriction in the past (as I believe most people need to address the foods they DO eat, before considering skipping meals), it is an important piece of the puzzle, and intermittent fasting may be helpful for many, especially if you've already mastered a nutritious diet, which really should be your first step. Fasting combined with a highly processed, toxin-rich diet is not going to do your health any favors. In fact, you may be making things worse, since you're not giving your body proper fuel when you DO eat.
Also remember that fasting does not mean abstaining from ALL food for extended periods of time, but rather a dramatic reduction of calorie intake at regular intervals—whether you opt for a 16, 20, or 24 hour fast once or twice a week, or fasting every other day, or simply delaying certain meals, such as skipping breakfast and exercising on an empty stomach. As always, listen to your body, and go slow; work your way up to full day fasts if your normal schedule has included multiple meals a day. Also be sure to address any hypoglycemic tendencies, as it can get increasingly dangerous the longer you go without eating to level out your blood sugar.
I will finish off with Mark Sisson's "bottom line," practical, and sound recommendations, as he sums it up nicelyix:
"... [T]here is no concrete, objective law regarding the suitability of intermittent fasting for a particular person.
If you're truly hungry, eat. Failing to do so will add stress.
If you're stressed, don't IF (intermittent fast). You don't need another stressor.
If you're training six days a week, don't IF. Unless you're genetically blessed, you'll need lots of fuel to prevent overtraining.
If you're not hungry, don't eat. If coffee's enough, skip breakfast.
If life is good, try fasting.
In the end, the prudent path is to simply listen to your body. Don't let CW grazing propaganda drive you to eat when you aren't hungry; don't let the IF dogma make you feel guilty about grabbing a handful of macadamia nuts and jerky in between meals when you are fasting. Try it out, skip a meal, go fourteen hours or so (you already do eight every night) without eating, get a workout in, go for a walk, go about your day and see how you feel. A quick trial is not going to kill you...
Are you lightheaded?
Are you weak?
Did your workout suffer?
Then maybe it's not for you. Maybe you need to fix a few things (Primal eating, sleep, chronic stress) and then try again..."