(How Many Hours Per Day Should You Fast And When Should You Eat?)
By Ori Hofmekler
The intermittent fasting approach has been getting increased recognition these days. But 10 years ago, it was a different story.
When I introduced The Warrior Diet concept about 12 years ago, it was highly criticized by mainstream fitness authorities as an “extreme and dangerous” approach to dieting. Telling people to skip breakfast and lunch was like committing dietary heresy.
The Warrior Diet book was the first to offer a diet plan based on intermittent fasting. Yes, at that time, it felt like I was the only person in the world arguing for substituting the frequent feeding approach of several meals per day with 1 meal per day.
Then, a few years later, studies on intermittent fasting (conducted by Dr. Marc Mattson/NIH) shocked the world with the news that that “radical” pattern of eating yielded a substantial increase in the lifespan of rodents along with outstanding improvements in major health markers including insulin sensitivity, body composition and neuro-regeneration capacity.
And since then, a growing number of health and fitness gurus have been jumping into the IF wagon. Just Google intermittent fasting and check for yourself.
Multiple websites and many bloggers are now claiming credit for their IF plan.
The variations include fasting all day, every other day, every third day, twice per week, once per week, or once every other week. Some recommend skipping breakfast or skipping dinner, whereas others advise ‘eating only when hungry’ or ‘not eating when not hungry’. Incredibly, even Andrew Weil is now blogging in favor of IF. According to Weil, simply eating three meals per day with no snacks should be called in America “a form of intermittent fasting”…yes indeed, to be popular in this country, a diet plan must be easy to follow…
But fasting is never easy. And there is always a reason to avoid fasting. Virtually all IF websites are happy to give you these reasons.
Plenty of reasons (or perhaps excuses) why not to fast
They tell you: don’t fast if you’re hypoglycemic; don’t do that if you’re diabetic; don’t skip meals if you suffer from heartburn, or don’t get yourself overstressed with fasting if you’re already overstressed.
It is also very popular these days to say, “fasting is not for everyone”… hence, if you’re looking for a reason why not to fast, that’s the easiest one to pick.
Note that there are cases that may prohibit long term fasting such as with young children, type I diabetics (on insulin medication), or in the case of clinical myopathy (muscle wasting disease). Nonetheless even in these or similar cases, the exclusion of fasting is not necessarily wise, as fasting could be potentially useful as a therapeutical strategy. Fasting has shown to improve conditions of metabolic disorders, lower the need for insulin medication, and help relieve inflammation.
So how can fasting benefit you? To figure that out, you need to take a look at the science behind fasting. You need to know how fasting induces its beneficial effects on your body, and what meal frequency allows you to take maximum advantage of that.
How fasting benefits your body
Scientists have been acknowledging three major mechanisms by which fasting benefits your body as it extends lifespan and protects against disease:
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.
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.
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.
There is only one fasting regimen that makes sense in practice. The rest simply don’t.
So given the above, what kind of fasting regimen will benefit you most? If you learn the facts behind human biology and how your body is programmed to thrive, you will realize that almost every popular IF program today including alternate day fasting, once or twice a week fasting and once every other week fasting are in the best case only partial beneficial. Most IF programs cannot and will not yield the results you’re looking for.
The reason: Your body operates around a 24 hour cycle which dictates your innate circadian clock. Most IF programs are not designed to accommodate that cycle.
Most IF programs disregard your innate clock.
Your innate clock is an essential factor in your life as it controls all your circadian rhythms. Called the Suprachiasmatic Nucleus (SCN), it is located in your hypothalamus, where it regulates how your autonomic nervous system operates along with your hormones, your wake and sleep pattern, your feeding behavior and your capacity to digest food, assimilate nutrients and eliminate toxins.
What happens when you go against your innate clock?
If you’re routinely disregarding your innate clock – working during sleeping hours, or feeding at the wrong time – you’ll sooner or later pay the consequences with symptoms that may include disrupted sleep, agitation, digestive disorders, constipation, chronic fatigue, chronic cravings for sweets and carbs, fat gain, and lower resistance to stress.
Note that chronic disruptions in circadian rhythms have been linked with increased risk for chronic inflammatory disease and cancer. Most IF programs overlook this issue. Their timing of feeding is either random or wrong.
But the timing of your feeding is not something you can afford overlooking. There is a dual relationship between your feeding and innate clock. And as much as your innate clock affects your feeding, your feeding can affect your innate clock. Routinely eating at the wrong time will disrupt your innate clock and devastate vital body functions; and you’ll certainly feel the side effects as your whole metabolic system gets unsynchronized.
Your biological feeding time is at night.
So when should be your right feeding time? Your body is programmed for nocturnal feeding. All your activities, including your feeding, are controlled by your autonomic nervous system which operates around the circadian clock. During the day, your sympathetic nervous system (SNS) puts your body in an energy spending active mode, whereas during the night your parasympathetic nervous system (PNS) puts your body in an energy replenishing relaxed and sleepy mode.
These two parts of your autonomic nervous system complement each other like yin and yang. Your SNS, which is stimulated by fasting and exercise, keeps you alert and active with an increased capacity to resist stress and hunger throughout the day. And your PNS, which is stimulated by your nightly feeding, makes you relaxed and sleepy, with a better capacity to digest and replenish nutrients throughout the night. This is how your autonomic nervous system operates under normal conditions.
But that system is highly vulnerable to disruption.
If you eat at the wrong time such as when having a large meal during the day, you will mess with your autonomic nervous system; you’ll inhibit your SNS and instead turn on the PNS which will make you sleepy and fatigued rather than alert and active during the working hours of the day. And instead of spending energy and burning fat, you’ll store energy and gain fat. This is indeed a lose-lose situation. (more information and science references on the human circadian clock in the end of the article) Unfortunately, most IF programs fail to recognize that.
Most IF programs miss the boat.
Let’s take a brief look at some of the most notable IF regimens.
Alternate day fasting
This program seems to be the most difficult to handle. Followers of this regimen have been complaining of a significant increase in hunger and a chronic excruciating desire to eat on their fasting day. But what makes this IF program even more problematic is the adaptability issue – as followers seem to be just as hungry on the last day of fasting as on their first day. There have also been reports of side effects such as sleeping disorders, constipation, and a persistent fatigue among the followers.
The alternate day fasting has one major caveat: the 24 hours fast seems too long to handle (both physically and mentally). This regimen has been shown to cause sleeping issues due to the fact that night fasting turns on the SNS which keeps you alert and anxious rather than relaxed and sleepy during the night – thereby disrupting your sleep-wake cycle.
Furthermore, based on epidemiological evidence, it seems that the human body is programmed for a daily cycle of 24 hours and its optimum fasting threshold should be within the range of 18 hours. Anything beyond that may put your body in a starvation-catabolic mode which if done chronically, may lead to metabolic shutdown’s symptoms such as underactive thyroid, decreased sex hormones, loss of muscle mass, and declined energy.
Once a week or twice a week fasting
Both once or twice a week seem to be easier to follow than the alternate day fasting, only that these regimens are less effective than the alternate day fasting. Eating 3-4 square meals every day for most of the week is a serious compromise of the original IF concept, as it minimizes the weekly impact of fasting to merely 1-2 days per week.
Fasting every other week or every month
Worse than that is “fasting every other week” or every month. These IF programs seem to target the typical American dieter who is constantly looking for an “easy to follow” program to lose weight or improve health. The motto “better fasting once or twice per month than not fasting at all” is just an excuse to choose mediocrity over excellence.
The skipping dinner approach goes against your innate clock. This regimen may cause sleep disorders and similar side effects as the alternate day fasting diet, only that skipping dinner is less effective than the alternate day fasting due to its shorter fasting time.
Advocates of skipping dinner argue that breakfast is an important meal and should not be skipped. Nonetheless, the science clearly indicates the opposite – breakfast antagonizes the SNS and disrupts healthy circadian rhythms.
There is growing evidence that the typical breakfast is the most harmful meal of the day. A study by the Human Nutrition Research France (British Journal of Nutrition, 2000; 84:337-344) indicated that the typical high energy breakfast caused major adverse effects in the short and long terms. These included a strong inhibition of fat burning throughout the day, increase in serum triacylglycerol, decrease in HDL (good cholesterol), and over-glycemic reactions. The researchers concluded that high-energy breakfast does not appear to be favorable to health; they also indicated that the study’s results do not support the current advice to consume more energy at breakfast.
Note that the average consumption of energy at breakfast among breakfast eaters is between 15-20% of total daily energy intake. The typical breakfast composition: 12% of calories from protein, 25% from fat and 63% from carbohydrates.
Other reports coming from epidemiological surveys have been indicating that the consumption of high energy breakfast leads to a significant higher energy consumption for the whole day. Furthermore, big breakfast has shown to yield only a limited satiety effect which lasts merely 2 hours after breakfast. Overall, science confirms that the typical high carbohydrate breakfast tends to increase fat storage, increase body weight, and increase the risk for cardiovascular disease and long term health.
Note that some of the healthiest societies in the past did not eat breakfast. The word breakfast was not part of their vocabulary. The typical breakfast did not exist during Biblical times. In the original Hebrew text of the Bible, breakfast is called “pat shacharit” which meant a tiny piece of bread at dawn – nothing more. And there isn’t a single mention of breakfast in the new testimony; supper was the main meal of the day (hence, the Last Supper). The ancient Greeks and Romans were very particular about eating their main meal at night. According to Plutarch and Cicero, only slaves and farm animals were fed breakfast and lunch, as contrary to free men and soldiers who ate one meal per day at night.
Skipping breakfast is certainly a better idea than skipping dinner. This protocol seems to be particularly viable for those who exercise during the morning hours. In this case a specially modified high protein lunch can serve as a post exercise recovery meal. The skipping breakfast regimen is nevertheless problematic.
Proponents of this approach speculate that skipping breakfast after a night fast yields about 16-18 hours of fasting including sleeping time. That seems good in theory but in reality this regimen doesn’t yield as many hours of fasting as claimed.
Here is why:
What really counts is your net fasting time, the gap between your meals minus digestion time. It typically takes your body between 6 – 8 hours to fully digest a hearty evening meal (depends on your meal density – content of protein and fat, etc). If for instance you start your evening meal at 8pm and finish eating at 9-10pm, your body will only shift into a fasting state by the early morning hours (about 3-6am). Hence, your body will not be in a fasting state for most of the night.
So when you skip your morning meal until noon, your net fasting time is merely 6 – 9 hours. That might be good but not enough to grant maximum impact. So what is the ideal way to fast? What should be your right meal frequency?
The 1 meal per day
The 1 meal per day is the only regimen that can accommodate your innate clock and maximize the beneficial effects you get from IF on a daily basis. That’s if your food choices and meal timing are adequate.
The 1 meal per day yields 14-16 hours of net fasting time provided that you have a window of about 2 hours to finish eating. And in the case that you have a feeding window of 4 hours, you’re still left with 12-14 hours of daily net fasting – sufficient to get you the results you’re looking for.
Other IF regimens yield a net fasting time which is either too long or too short. And most of these programs cause adverse side effects as they fail to accommodate your innate clock.
Can the 1 meal per day regimen satisfy your physical needs?
The 1 meal per day can accommodate your physical needs but you need to know how to modulate this regimen to fit your specific condition. For instance, if you routinely exercise during the day you’ll need to feed your muscle after your workout with a low glycemic recovery meal made with fast assimilating protein such as from quality whey. You can also feed your muscle before your workout as this will help increase your capacity to sustain intense exercise.
Can the 1 meal per day regimen accommodate super intense training?
If you’re engaged in max strength conditioning or MMA training, you should feed your muscle before and after your workout. Only that in this case your pre-workout meal should consist of protein and carbs. Note that max strength exercise work your fast glycolytic muscle fibers (Type IIB white fibers) which are inherently carb dependent. Having fast assimilating protein and carbs before your workout can help load glycogen in your muscle, nourish your fast fibers; and boost your max strength performance.
Your best choice for pre-exercise and post-exercise meal is quality whey protein, derived from raw milk of pasture fed or grass fed cows. For pre-workout carbs use nutrient dense fruits such as berries which can swiftly fuel your muscle with carbs and antioxidants and thereby enhance your performance while reducing the oxidative stress in your muscle to allow a faster recovery after your training.
Having an oatmeal or porridge an hour before training can be a viable option in case that you’re engaged in prolonged intense training sessions. Again, make sure your post-exercise recovery meal is low glycemic with no sugar added – to support your insulin and accommodate your IF. High glycemic meals negate the benefits you get from fasting.
So is it ok to eat whey protein during fasting? What other foods could be safely consumed during the fast? How often can you eat these foods and how much?
Foods that can be safely consumed during fasting
In the Warrior Diet Book, I introduced the concept of “undereating” as a viable alternative to water fasting. Undereating means minimizing your food intake to small servings of specific foods, which you’re allowed to consume in a certain frequency during your fast. If done properly, undereating can yield the same benefits of fasting and even more. Let me explain.
Most foods negate the effects of fasting, but there are some exceptions. Some foods can be safely eaten without compromising your fast. These include fast assimilating nutrient dense foods such as quality whey protein, green vegetables and berries. But you need to know how much you’re allowed to consume and how often. What makes these foods complimentary to fasting are the following properties:
They’re rich in antioxidant and anti-inflammatory nutrients
They target the same genes as fasting
They induce similar effects to those you get from fasting
Having small servings of whey protein, green vegetables or berries during your fast isn’t just ok, it may actually increase the benefits you get from fasting.
Being fast assimilating, these foods nourish your body without taxing your digestion, as they enhance the anti-inflammatory and metabolic modulating effects of your fasting. They also increase your body’s antioxidant defenses against reactive oxygen species (ROS) which tend to accumulate in your body during fasting and exercise as byproducts of fat breakdown and detox. ROS are unstable and highly reactive molecules which search, bind to, and destroy cellular lipids, proteins and DNA. The above foods help protect your body from that oxidative damage.
Most importantly, non-denatured whey protein, green vegetables and berries contain nutrients (antioxidant polyphenols, flavons, resveratrol, cyanidins, indoles, in plants; leucine, calcium and immune factors in whey) that target the same genes, transcriptional factors and pathways as fasting and exercise. Most notable among these are the SIRT-1 gene (the longevity gene) and the transcriptional co-activator PGC-1a, known to counteract oxidative stress and inflammatory pathways associated with declined health and increased mortality. SIRT-1 and PGC-1a increase mitochondrial biogenesis and thereby prevent the typical decline in mitochondrial function and cellular energy associated with aging and disease.
How much and how often can you eat these foods?
You can have small serving of whey protein (20-30g net protein) every 3-6 hours, depending on your level of physical activity. Those who do not exercise can have one or two servings of whey protein during their daily fast.
Similarly, you can have 8oz of berries or green vegetables (or freshly squeezed green vegetable juice) every 3-6 hours while you fast. Do not mix berries with whey unless you use that blend as a preworkout meal to support your strength conditioning.
Having a small serving of whey protein, berries or greens will hardly affect your body’s negative energy balance throughout the fast. Hence, if you eat them at the right amount and frequency, the above foods will not compromise your IF.
It may take science another 10 – 15 years to figure out the difference between water fasting and that mode of undereating. Nonetheless, based on what we know today about the nutritional properties of whey, berries and greens, and based on testimonials coming from Warrior Diet followers, and my own experience, I can tell you that having these foods during the fast isn’t just making it easier, but also makes it more effective and beneficial to your body than a sheer water fast.
The one meal per day is the only regimen that can maximize the benefits of your IF on a daily basis.
Eat your main meal at night to accommodate your innate clock.
Whey protein, berries and greens compliment your fast if you know how much to consume and how often.
If you exercise during the day, have a recovery meal after your workout consisting of whey protein with no sugar added.
If you’re engaged in super intense training, have a pre-workout meal consisting of whey protein and berries.
If you’re engaged in prolonged intense training, have a bowl of oatmeal with your whey protein about an hour before your workout.
The science behind circadian rhythms
Circadian regulation of immune response and resistance to disease
Recent studies published by the PNAS, January 2012, revealed the existence of a specific nuclear receptor that mediates circadian regulation of innate immunity and resistance to disease. This circadian regulation is controlled by an internal mechanism which is highly conserved in humans and animals and orchestrates the daily patterns of diverse physiological processes such as wake/sleep cycles, feeding, and metabolism. According to the researchers, many diseases exhibit a disrupted circadian rhythmicity in their pathology…and lifestyles that disrupt the inherent timing system, such as chronic shift work, are associated with increased risk of cancer, metabolic disorders, cardiovascular disease and cerebrovascular disease. The researchers indicated that inflammatory diseases in particular exhibit strong time-of-day symptoms. They concluded that in humans, circadian rhythms are driven by a complex of feedback loops that mediate gene activities throughout a period of 24 hours and speculated that daily risk of infection is likely to be a direct consequence of wrong timing of activity and feeding.
The 24 hours cycle
A study by Czeisler et al. at Harvard University found that the range for normal healthy adults of all ages to be quite narrow: 24 hours and 11-16 minutes. This innate clock resets itself daily to the 24 hour cycle of the Earth’s rotation.
The sympathetic/parasympathetic division
Based on biology textbook (see Wikipedia – autonomic nervous system), the sympathetic and parasympathetic divisions typically function in opposition to each other. Consider sympathetic as “fight or flight” and parasympathetic as “rest and digest” or “feed and breed”. The sympathetic nervous system – corresponds with energy generation, and inhibits digestion. The parasympathetic nervous system – promotes “rest and digest” response, along with calming of the nerves.
Light and the innate clock
According to a 2010 study, completed by the Lighting Research Center, daylight has a direct effect on performance and wellbeing. The research showed that students who experience disruption in lighting schemes in the morning experienced disruptions in sleep patterns. Removing circadian light in the morning delays the dim light melatonin onset by 6 minutes a day, for a total of 30 minutes for five days.
Feeding and the innate clock
The feeding clock mechanism is the same as the light/dark driven clock controlled by the innate master clock – the suprachiasmatic nucleus (SCN) which is a cluster of neurons in the hypothalamus. But the machinery that inter-regulates feeding and the innate clock is located in a different part of the hypothalamus (DMA).
Recent studies reveal that mice on a daily 4 hours feeding window shifted their circadian rhythms so that their peak physical activity was before feeding and not after. This rhythm continued even if the mice were kept in constant darkness. Hence, the animals are inherently programmed for post action feeding and not the other way.
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