One of the most common reactions I get to my advice to try intermittent fasting is:  I could never do that!

Like the Jackson Browne song “Running on Empty,” the word “fasting” often conjures up dire images of starvation and energy deprivation.  Many of you reading this post may have experienced strong hunger pangs, headaches, tiredness, sweating and even shaking or wooziness when going without eating for even part of a day, much less a whole day.  So it is natural to extrapolate such experiences into the thought that going without food for a day, or even several hours, would invariably lead to uncomfortable or even dangerous hypoglycermic symptoms. That, together with the negative image of fasting as something unhealthy or associated with eating disorders, leaves most people pale at the thought of even attempting a short fast.

But I tell you, if you don’t try fasting you are missing out on an enjoyable, incredibly energizing experience that will put you in control of your eating and improve your health, your energy and your outlook.  Many people, myself included, have learned to fast for up to a day or even longer, on a regular basis and without negative repurcussions. Done correctly, short-term fasting is not dangerous, it’s actually health-promoting and greatly helps to retrain your appetite.  If you need to lose weight, the fast helps both in reducing basal insulin and retraining your appetite to be smaller. I’ve written about the benefits of intermittent fasting extensively on this site. Many of the Diet Links listed in the right-hand panel, such as fast-5 and Eat-Stop-Eat, amply document the safety and health benefits of fasting, dispelling the myths about “starvation mode”, slowing of metabolism,  and loss of lean muscle mass.  So I won’t reiterate here the voluminous evidence supporting the benefits of intermittent fasting.  Our bodies are designed to last many days with out food, without great discomfort, and in fact it is beneficial to our health to forgo food periodically. But many of you are asking: Am I really up to this?  How do I get started?

To clarify, by intermittent fasting (IF), I mean forgoing eating for at least 12-20 hours in a day, at least one or two days each week. For many of us, it is a daily practice. Water and unsweetened, non-caloric beverages are allowed, but I exclude “juice fasting” or any solid snacks from true fasting. Others have written about the virtues of juice fasts for “detox” or “cleansing”, but IF has a different purpose, namely insulin reduction, appetite reduction, and mental clarity and focus.

Tips for getting started. So this post is not about the benefits of intermittent fasting, but rather about how to get started with it.  I’m basing this largely on my own personal experience, combined with what I’ve learned about what has worked for others. Fasting is not that hard or unpleasant to do. The reality is that, like skydiving, the contemplation of it is probably far worse than the experience.  You will experience some periods of discomfort, but you may be surprised at how great you’ll feel most of the time you are fasting, especially once you are past the first few hours.  People on low carbohydrate diets often (but not always) experience the pleasurable energy that comes with ketosis; I’ve found that the ketosis of fasting is deeper, and more reliable that that from low carb.  Several people who experience brain fog on low carb  find fasting to provide greater clarity and energy.

Here are 7 practical suggestions to help you get through the transition:

1. Start with a mini-fast. How long do you go between meals without eating? Two hours? Five hours? Start there and try to increase it by a few hours. The easiest way to start is to cut out eating anything between dinner and bedtime. Then go to cutting out afternoon snacks 2 or 3 days a week. And increase from there in increments. Of all my suggestions, I think this is the most important. It’s one of the core principles of using Hormetism to improve your strength and resilience in any challenging endeavor. You have to walk before you can run.

A very common mistake that many people make when embarking on fasting is to go straightaway from a typical pattern of 3 meals per day with snacks, to a day-long fast.  That’s a terrible idea, and yet it forms the main reason that so many people reject fasting as impractical or unhealthful.  I’ll repeat here the comments I made in an earlier post on Calorie restriction and hormesis about a researcher’s conclusions in a 2006 study of calorie restriction in mice, in the journal Biogerontology:

Calorie restriction is doomed to fail, and will make people miserable in the process of attempting it,” said Dr. Jay Phelan, an evolutionary biologist at the University of California, Los Angeles, and a co-author of the paper. “We do see benefits, but not an increase in life span.” Mice who must scratch for food for a couple of years would be analogous, in terms of natural selection, to humans who must survive 20-year famines, Dr. Phelan said. But nature seldom demands that humans endure such conditions. Besides, he added, there is virtually no chance Americans will adopt such a severe menu plan in great numbers. “Have you ever tried to go without food for a day?” Dr. Phelan asked. “I did it once, because I was curious about what the mice in my lab experienced, and I couldn’t even function at the end of the day.

It’s not surprising that Dr. Phelan’s personal “one day experiment” failed and that he “couldn’t function” after suddenly downshifting gears so rapidly. As anyone who has taken the time to research calorie reduction or intermittent fasting realizes, a dietary change of this sort should be approached gradually, allowing time for deconditioning of previous dietary habits and hormonal responses. These changes typically take weeks or longer to become comfortable. But that does not mean that a reduced calorie diet is “extreme”. By historical standards, it would be more accurate to characterize the typical hypercaloric American diet as extreme.

2.  Schedule your fasts. Intermittent fasting works best when you are in control of the timing.  I like being able to spontaneously decide when I’ll start my next fast and I plan exactly when I’ll break the fast and eat.  That really frees me from thinking about food and making choices, because I know that at 4 p.m. Friday or noon Sunday I’ll have my next meal. Associating the start and stop of a planned fast with definite events or times of day takes advantage of the well-known behavioral principle of “putting on cue”.  For a fuller explanation, check out the work of Karen Pryor, the renowned animal behaviorist and dolphin trainer.  I’ve also written about this on the Psychology page of this blog.

3. Cheat using high fat “training snacks”. If you’re having trouble fasting, it is likely that you are lacking the ability to readily shift to fat burning and ketosis.  When you are fasting, after initially depleting your glycogen stores, you will be literally “living off your fat”, as well as fat byproducts like ketones.  To do that, you’ll need to get your insulin level very low and upregulate your catabolic hormones and enzymes: glucagon, adrenaline and hormone sensitive lipase.  But if you are used to eating 3 or more meals and snacking frequently, then you are not used to metabolizing your own fat stores, and you have difficulty shifting quickly from energy storage (anabolism) to energy release (catabolism) .  You literally have weeks of “meals” stored beneath your skin and within your abdomen.  You just can’t access them.  It’s literally like having a locked pantry on your body, so when you get hungry you have to eat food supplied externally, instead of what is already within you.

So train yourself to burn fat by eating pure fat or oil!  The easiest way to train your body to get it used to burning fat, is to “jump start” it with a small high-fat “training snack”.   You don’t need much to get started: 5 to 10 grams of fat is plenty.  Don’t worry, this is not a “high fat diet”, it serves only to provide some satiety and let your metabolism get used to fat burning. The amount of fat you’ll snack on is trivial compared to your overall weekly diet, and you’ll go back to your “normal” diet after the fast. The best approach is to wait until you would normally have a meal or snack and substitute the high fat training snack.  This will tend to suppress your appetite for at least a few hours.  If you start to get hungry again, take another training snack — but wait at least 3-4 hours between these snacks. The training snacks must be virtually free of any carbohydrates or protein and must be small.  Good examples include:

• “Carbless cream soda”. Pour a few tablespoons of heavy whipping cream into a glass (check to make sure it has less than 1 gram carbs) over ice cubes and add sparkling water or herbal tea.
• “Platinum” tea or coffee. To an unsweetened cup of hot tea or coffee, add a tablespoon or two of heavy whipping cream or coconut oil.  The heavy cream has the advantage of easily blending with the tea or coffee, but some people find the coconut oil to be more energizing.  It comes as a solid but readily melts in the hot beverage; it tends leave some oily droplets on the surface because it does not emulsify as well as cream, but most people have no problem with that.  It is important not to add any sweeteners; even artificial sweeteners will tend to psychologically induce a conditioned preprandial insulin response (See Diet page).
• Macademia nuts.  These are high in fat with very few carbs.  Eat no more than a half dozen.
• A small piece of cheese. This is a great training snack, but keep it to one or two small slices of cheese.
• A tablespoon of oil. It may not sound very palatable, but a spoonful or two of extra light olive oil or other vegetable oil can be a great appetite suppressant and kick you into fat burning mode rather effortlessly. The oil works best if flavorless, or if you pinch your nose to avoid tasting it before rinsing.  This is the basis for the popular Shangri-La Diet of Seth Roberts. Roberts attributes the effect to breaking the connection between flavor and calories.  I propose an alternative explanation in my post on Flavor Control Diets.  and also in a long discussion thread on the Shangri-la Diet forum. In any case, flavorless or not, a small dose of oil is a very effective “bridge” to fasting.

4.  Savor flavored calorie-free beverages. To satisfy your need for flavor, enjoy herb teas and black coffee.  Decaf is preferable, but if you have a caffeine habit, go with it for now.  Don’t add any sugar or artificial sweeteners, since these can induce an insulin response that shuts down fat burning. Flavored beverages are a great boon to fasting because they satisfy the urge for flavor and provide some pleasure that can be a big help.

5.  Smell something aromatic while fasting. This is an old aromatherapy trick to turn off your appetite, but it has a scientific basis.  A strong aroma from herbs, spices, flowers or perfumes can rapidly dampen a craving by saturating the cephalic phase insulin response, as explained in my post on Flavor control diets — but you must not eat within 30 minutes after smelling. It is also useful to repeat the smelling frequently and cycle between very different aromas. This has been exploited in devices such as the SlimScents odor inhaler, but a few minutes with your spice rack, perfume bottles or flower garden may do the trick.  The good news is that the effect is long lasting and will permanently decondition your cravings.  Try it!

6.  Drink water frequently. This is an old standby and may seem boring compared to the above two suggestions.  But it works well in two ways: it tends to suppress hunger, and it keeps you hydrated. Keep in mind that the effect is often delayed, so wait 15-30 minutes after drinking the water before you pass judgement on it.

7.  Exercise briefly when hungry or tired. This is one of the more surprising ways to fight cravings, tiredness, mental fog, or borderline hypoglycemia. It may seem counterintuive to expend energy just at the point you are feeling hungry or tired. But it works incredibly well! The key is to do it at the first sign of a cranky or tired feeling, and you’ll head off it off at the pass.  By “exercise” I don’t necessarily mean going to the gym — unless you are used to that. Walking around for 5-15 minutes at a brisk pace is good enough, particularly if you can elevate your heart rate a bit. If you have been fasting, walking or other brief exercise will stimulate your liver to release glucose and free fatty acids, giving you an energy boost. It really is just about as good as eating a meal, for providing energy, and it has the benefit of providing a more sustained form of energy.  You’ll find that “after lunch” meetings are less soporific.

Getting out for a lunch time walk is an excellent alternative to eating lunch.  It gets you away from the kitchen or cafeteria, changes the scene and restores energy.   I probably eat only two lunches a week at work; the other days I go walking either outside or inside, depending on the weather.  Make it social and enlist a friend or start a small walking group – it is just as easy to converse while walking as while eating at a table.

When you get more experienced with fasting, the addition of extended, more intense exercise is very energizing and beneficial. With lower basal insulin levels and upregulated catabolic hormones and enzymes, you’ll find that a long run or workout with weights provides lasting energy and suppresses your appetite. Eating before or after the fast ruins the benefits. Wait at least several hours after the workout before breaking the fast. This may seem paradoxical, as it is virtually the opposite of what many experience who are not used to fasting.  But I have found it to be my experience.  For those interested in fasted workouts, checkout Martin Berkhan’s Leangains blog, as well as a recent article in Running Times on the benefits of glycogen-depleted exercise for greatly increasing your endurance; it appears to be a great strategy for learning to burn fat and weaning yourself off carb dependence,

A final word. The above approach, which emphasizes gradualism, should give your metabolism time to adapt.  For most people, this is enough to avoid any health issues with hypoglycemia or diabetic complications.  In fact, Lee Shurie cured his diabetes, normalized his blood sugar, and increased his energy level by carefully monitoring his blood glucose and gradually transitioning to intermittent fasting.  He found that all the traditional advice to eat low glycemic foods and exercise was insufficient to normal his blood glucose. Eventually, by delaying meal time and allowing his blood glucose to drop into the normal range, he found himself eating only at dinner time, and all the happier for it.  So transition to IF gradually. However, if you have any concerns, stop the fast and eat.  Consult with your physician if you have concerns.  Otherwise, check out the discussion of Intermittent fasting on the Getting Stronger Discussion Forum, to read others’ experiences.

Happy Thanksgiving!

Studies on calorie restriction in primates or humans are as yet inconclusive. Controlled primate studies only started in the late 1980s and have yet to be completed, although the preliminary indications are very promising. And in humans it is more difficult to conduct controlled studies for both ethical and compliance reasons. An additional factor to consider is that animals raised post-weaning on calorie restricted diets typically have much smaller adult body sizes that animals not restricted in their eating.  Because of the social and physical implications of this consequence, advocates of calorie restricted diets for humans advise that they be started only upon reaching adulthood.

Whether or not a restricted calorie diet extends the human lifespan, the evidence is becoming overwhelming that a nutritionally complete diet with reduced calories has the potential to greatly improve our health, particularly as we age. But is it practical and possible for humans to happily adhere to such a diet?

Monkeys on calorie restriction (left) and normal diet (right)

Benefits. The benefits of calorie restriction in animals are wide-ranging. For example, studies on rhesus monkeys and macaques at the University of Wisconsin have found that the calorie-restricted monkeys have significantly less diabetes, cancer, cardiovascular disease, and neurodegenerative diseases. Their fasting insulin and glucose levels are greatly reduced, and they have higher insulin sensitivity and excellent lipid profiles. While the study is yet to be completed, at the 20 year point, 80% of the calorically restricted monkeys were still alive, compared to only half of the controls.

In a study of humans who restrict their calories by 10-25% relative to baseline, but supplied with adequate vitamins and minerals, similar benefits have been seen, with significantly lower blood pressure, insulin, fasting glucose, triglycerides and LDL cholesterol; and significantly higher HDL cholesterol.

Mechanisms. Nobody knows for sure why calorie restriction works, but there are a number of theories with varying degrees of confirmation. They are not mutually exclusive, so it is possible that more than one, or all of them, are true:

• Autophagy (“Self digestion”) is a phenomenon whereby the cells degrade and digest damaged or non-essential contents within the cell membrane. During nutrient starvation, autophagy basically “cleans house”: it breaks down non-vital components and releases nutrients, ensuring that the vital processes can continue. How does this come about? Calorie restriction is known to dramatically lower the concentrations of insulin, IGF-1 and growth hormone. Reduced levels of these hormones in turn activates the genes and pathways for autophagy or catabolism. Basically this involves the cell producing enzymes that specifically degrade oxidized or otherwise damaged intracellular molecules. This is an interesting process.During autophagy, the  cell actually builds a special membrane encircling these damaged components, forming a “vesicle”. The cell then fuses the vesicle to the lysosome — a reservoir of digestive enzymes — and digests and removes the contents of the vesicle. This reminds me of how certain insects like spiders or wasps wrap up their prey and then digest them.  The cell is digesting and recycling accumulated “cellular junk” that would otherwise gum up its metabolic machinery, producing extra energy as a consequence.  How clever!
• Mitohormesis is defense response, which is believed to occur within the mitchondria, the energy factory of the cell.  The mitohormesis theory proposes that calorie restriction is a type of “low-intensity stress” that activates genes involved in defensive responses against aging processes such as oxidation. The mitohormesis concept has been demonstrated in studies of the worm Caenorhabditis elegans, which showed that limiting the amount of glucose being fed to the worm resulted in oxidative stress, to which the organism responded by adapting so as to resist further oxidative stress.  This extended its lifespan. The genetics of mitohormesis have started to be uncovered. Studies at the molecular level have shown that several genes in the sirtuin class, including SIRT1, SIRT3, and SIRT4, create enzymes that increase the activity of the mitochondria and slow the cell’s aging process
• BDNF. In addition to these general mechanisms, calorie restriction activates some important specific pathways in higher animals. One of the more intriguing and potentially important of these is the connection between calorie restriction and mental health.  An excellent review paper by Gomez-Panilla, linked here, documents how fasting, diet and exercise can stimulate a neuroprotective factor called Brain-Derived Neurotrophic Factor (BDNF). This key neurotransmitter plays a key role in neuroplasticity, the ability of the brain to adapt, learn and respond to stress. Depressed levels of BDNF are associated with deficits in memory and learning, and with a number of psychiatric disorders. BDNF also provides a strong defense within the brain against reactive oxygen species (ROS), and is protective against degenerative neurological conditions such as Alzheimer’s disease. BDNF is induced by calorie restriction, but also by intense exercise and omega-3 fatty acids. Conversely, it is suppressed by a high calorie diet, particularly one high in sugar and fat content. Low BDNF levels can be reversed within a few months: a study by Araya et al showed that BDNF increases significantly in insulin-resistant overweight and obese subjects after three months of a diet in which calories are restricted by 25%.

Scare tactics. First, let us be clear that nobody who is serious in the field of calorie restriction is advocating extreme calorie reduction of the sort that would lead to starvation or eating disorders. All of the responsible advocates of CR base their recommendations on the emerging science, which indicates that a calorie reduction of 10-25% versus the standard American diet, is not only tolerable, but healthful, so long as it is accompanied by adequate micronutrients — vitamins, minerals, and essential fatty acids.  Yet this has not stopped skeptics from attacking calorie restriction. A particularly irresponsible, but not atypical, example is that of Jay Phelan, whose 2006 article in the journal Biogerontology used mathematical models to argue that CR can at best deliver only modest benefits:

Calorie restriction is doomed to fail, and will make people miserable in the process of attempting it,” said Dr. Jay Phelan, an evolutionary biologist at the University of California, Los Angeles, and a co-author of the paper. “We do see benefits, but not an increase in life span.” Mice who must scratch for food for a couple of years would be analogous, in terms of natural selection, to humans who must survive 20-year famines, Dr. Phelan said. But nature seldom demands that humans endure such conditions. Besides, he added, there is virtually no chance Americans will adopt such a severe menu plan in great numbers. “Have you ever tried to go without food for a day?” Dr. Phelan asked. “I did it once, because I was curious about what the mice in my lab experienced, and I couldn’t even function at the end of the day.

Dr. Phelan’s personal “one day experiment” was ill-conceived and his conclusion is not to be taken seriously, in my opinion.  It is no surprise he “couldn’t function” after suddenly downshifting gears so rapidly.  As anyone who has taken the time to research calorie reduction or intermittent fasting realizes, a dietary change of this sort should be approached gradually, allowing time for deconditioning of previous dietary habits and hormonal responses. These changes typically take weeks or longer to become comfortable. But that does not mean that a reduced calorie diet is “extreme”. By historical standards, it would be more accurate to characterize the typical hypercaloric American diet as extreme.

Dietary alternatives. There is no single preferred mode of approaching calorie restriction. People have had success in many different ways in adapting CR to different cultural backgrounds and personal preferences. Here are a few approaches worthy of investigation if you are considering a reduced calorie diet as a means of hormetic stimulus and improved health:

• Okinawa diet. One of the oldest and best studied traditional diets is that which predominates (or used to predominate) on the island of Okinawa, Japan. This is a diet high in fish, rice, and yellow and green vegetables, many of them fermented.  The Japanese as a whole eat fewer calories than do Americans.  But the Okinawans eat even less. Compared with the average Japanese caloric intake, the Okinawa diet has:
  • 20% fewer calories
  • 25% fewer grains
  • 75% less sugar
  • 300% of level of green/yellow vegetables, especially sweet potatoes
  • small amounts of fish and pork, including pig organs
  • no eggs or dairy
• The CRON-diet (Calorie Restriction with Optimal Nutrition) was developed by Roy Walford, Lisa Walford and Brian Delaney. They advocate a plan involving three meals per day. Two of these meals are “free choice” recipes. The third is prepared in advanced according to recommended recipes to ensure adequate micronutrients. Meals are carefully weighed and assesed for calorie content. The CRON-diet is popular among members of the Calorie Restriction Society.

Intermittent Fasting. A number of studies have shown that fasting for short periods of time, generally less than 2-3 days, produce many of the same health benefits as general calorie reduction, without having to reduce the average number of calories consumed per week.  However, many adherents of intermittent fasting find that their average calorie intake tends to decrease voluntarily; in other words, they tend not to “make up for lost time” on their non-fasting days.  And many people (myself included) feel that it is psychologically more tolerable to alternate fasting with the ability to eat to fullness, rather than restricting calories at every meal.  In addition, there are some scientific arguments that favor a “cycling” approach for optimizing the secretion of hormones such as leptin, and for avoiding a long term adaptive reduction in basal metabolic rate.  If you are afraid that skipping meals will cause your metabolism to shut down and shift into “starvation mode”, dispel that thought. A study by Zauner et al in the Journal of Clinical Nurtrition showed metabolic rate actually increases during fasting up to 4 days, due to a more than doubling of norepinephrine.  So fasting for 6-24 hours hours has no downside.
There are several variations of intermittent fasting:

• Alternate day fasting (ADF) as described in a post by Dr. Michael Eades.
• Occasional fasting (for example, Brad Pilon’s Eat-Stop-Eat program of 1-2 fasting days per week)
• Partial daily fasting (for example, Fast-5, which restricts eating to a flexible 5 hour daily “window”)