by Dave Asprey
Make your one meal count: balanced and diverse, with a full range of macro- and micronutrients.
Adjust the schedule. If it’s more comfortable for you to spread your large meal out over more than an hour, do it. Maintaining your composure (and your sanity) is more important than a strict timeline.
Break your fast mindfully. After fasting all day, you may feel that you want to eat the biggest meal possible as quickly as possible—not a good idea because you’ll feel sick at first. That said, the goal of intermittent fasting is not to limit your calorie intake. If you normally consume 2,000 calories in a day, you can eat a 2,000-calorie dinner of high-quality, high-calorie food.
Listen to your body, and recognize when to stop. OMAD may simply not agree with your metabolism, your exercise regimen, or your lifestyle. That’s okay. Don’t force a schedule without listening to your body’s cues. If you’re not sleeping well, or if you’re feeling sluggish, weak, or constantly tired, your body is telling you that it needs more energy more often.
Women should be especially attentive to their responses to an OMAD diet. Studies show that excessive intermittent fasting can interfere with women’s insulin response.8 If you notice negative changes in how you feel or shifts in your menstrual cycle, fast less. See a doctor for a hormone test if things don’t level out as they should.
Remember that fasting can cause more than just physical stress. This is true of all types of fasting, but especially of OMAD because it is the longest fast you can do in one day. Restricting yourself to one meal a day can be taxing to your mind if you obsess over food all day. Take care of your stress levels by practicing yoga, meditating, exercising—really, whatever helps you find your Zen. You are not in a race. You are not trying to prove something. More difficult fasts do not equal better results; they won’t automatically get you there more quickly. Make sure that your schedule feels right, and keep in mind that it’s fine to try different styles of fasting and to take breaks from fasting entirely.
OTHER TYPES OF FASTING
People have recently become very creative in inventing and naming new styles of fasting. That’s a good thing—it means that lots of folks are experimenting and personalizing their strategies—but all the terms can get a little confusing, especially when you start googling fasting. So in the hope of dispelling some of that confusion, let’s look at some of the other most popular fasting methods. I recommend starting with the 16:8 intermittent fast and then working up from there.
Spontaneous meal skipping: Strictly speaking, this is not fasting, but it is a great way to prepare your mind and body for a more regimented approach to fasting. Simply skip a meal now and then, overriding the hunger pains and that silly voice telling you that you’re going to starve to death. If you live a hectic lifestyle, you may do this sometimes already. When you skip meals deliberately, you begin to break the habit of eating because it’s “mealtime.” Then you allow your body to learn to go without from time to time, just as our ancestors did for many thousands of years. This style of fasting will not put you into ketosis, and it won’t turn on autophagy, but it will increase your cortisol level as your body uses it to generate some blood sugar quickly. When your metabolism is flexible and working well, this won’t be an issue for you.
Crescendo fast: This is the gentlest form of intermittent fasting. It is basically a 16:8 fast, but you fast only every other day, and on fasting days you don’t exercise strongly.
Eat stop eat: The primary focus of this fast is two twenty-four-hour periods of complete fasting per week, generally lasting from one dinner to the next. Then you would eat normally the other five days of the week, alternating days so that you never have two fast days in a row. You may be asking yourself what the difference is between eat stop eat and just doing OMAD twice per week. The answer is . . . good marketing! They’re the same thing. Eat stop eat is different from 5:2 fasting because on fasting days, you actually fast with eat stop eat, and on 5:2 you’re allowed to consume 600 calories. Many people, including me, start OMAD with a cup of Bulletproof Coffee.
Alternate-day fast: As the name suggests, this program has you fasting for twenty-four hours every other day. Some people prefer to go completely without food on fast days, while others eat minimally, restricting their intake to a few hundred calories, in the style of the 5:2 fast. This is another pretty extreme approach that is not recommended for fasting newcomers. I would also not recommend doing alternate-day fasting for extended periods of time because it places too much stress on the body.
Now we come to a couple truly extreme versions of fasting.
Water fast: Should you drink nothing but water during a fast? I would recommend against this unless it’s part of a spiritual journey for you. Most water fasts are one to three days long and allow no other liquid or food. People tend to combat their hunger pangs by overdoing it on the water, chugging multiple liters a day. You simply must add salt or electrolytes to the water, or you can get sick or even die. Some people do up to ten-day water fasts, but you should attempt that only under medical supervision. Since you are eliminating calories entirely, you will lose a lot of weight, but you may also suffer from dizziness and a significant drop in blood pressure, technically known as orthostatic hypotension. Strangely, a water fast may also leave you dehydrated, because a lack of bulk in your colon means your colon can’t absorb liquid the way it normally does.
Extended fast: It is generally considered safe to go up to four or five days of fasting without needing any sort of special accommodations. Some people will do up to ten days, but a four-day fast, like the one I did in the cave, is more common. During an extended fast, you would not eat any sugar, artificial sweetener, or any other form of carbohydrate or starch or any form of protein. Even healthy protein will definitely break the fast. The longer the fast, the more important it is to maintain your electrolytes, the critical electrically charged minerals in your body. An electrolyte drink shouldn’t be a sugary sports drink. What you really want is to get your essential doses of magnesium, calcium, sodium, and small amounts of potassium. A zero-calorie electrolyte drink mix is your best bet. At a very minimum, put a pinch of salt into your water. When I do an extended fast for up to five days, I usually have Bulletproof Coffee on the first two or three days and switch to black coffee in the morning after my body is fully adapted to the fast.
At the other end of the spectrum are quasi-fasting diets that have health and psychological benefits, even though they don’t involve a full break from digestion. These include the following.
Protein fasting: I introduced this concept ten years ago in The Bulletproof Diet. Once a week, you consume no more than 15 grams of protein in an entire twenty-four-hour period. Studies show that restricting your protein intake to near zero will turn on autophagy. This is hard to do, because even most vegetables have some protein in them, and those little bits add up quickly. You end up eating some rice, some coconut milk, and some veggies for a day, usually about 1,000 calories. This approach is fantastic if you want to eat on a social occasion, because you can easily transform an intermittent fasting 16:8 day into a protein-fasting day by having a light lunch and dinner. Or you could just do an OMAD fast, which definitely contains less than 15 grams of protein. In practice, OMAD is easier to do because it requires less thinking than a protein fast does. On the other hand, a protein fast lets you feel less deprived and be more social. One day a week is fine, and it stacks well with anything from 16:8 to OMAD.
Fasting-mimicking diet: This eating plan tricks your body into thinking it is fasting, even though you eat specific low-carb, low-protein, high-fat foods for five consecutive days. Some people like to criticize this approach and say that it’s not really a fast. Here’s my take: if it does the same thing, or most of the same things, as a fast, it’s a fast but probably not a gut-healing fast. A recent study by gerontologist Min Wei and his colleagues at the University of Southern California found that the fasting-mimicking diet is highly effective for weight loss.9 It is likely to
be less effective at activating autophagy than the other fasting techniques discussed here. But for all the other reasons you would fast, including longevity, fasting mimicking is legit. The only reason people say it’s not a fast is because of a misguided, puritanical belief that fasting should make you miserable.
The fasting-mimicking diet allows up to 400 calories a day several days in a row, which is why you get a lot of the benefits of fasting. You’re consuming fewer calories than normal during that time, and I would argue more satiety, the feeling of being full. Don’t fall into the trap that says fasting has to be 0 calories or else it’s not a fast. That is not how fasting actually works. If you’re getting the results of fasting, including weight loss and metabolic benefits, and feel stronger and more in control, that’s cool. Suffering, on the other hand? Not cool.
Seasonal eating: This is a pleasantly primal method of eating, focused on eating only foods that are available each season. Summer is a time of eating fresh fruit and vegetables, with more carbs and little if any fasting, while winter has more fasting and is mostly keto, based on the idea that our ancestors could hunt in winter but had little ability to store lots of carbs for winter. You can combine seasonal eating with any of the patterns of fasting. Mainly, this approach is a good way to steer yourself toward eating fresh, unprocessed foods—which generally happen to be both delicious and healthy.
Dopamine fast: This falls into the broad category of nonfood fasts that I mentioned earlier. The purpose of a dopamine fast is to abstain from anything that causes your body to secrete dopamine, a neurotransmitter that is closely associated with our pleasure sensors and can play a role in reinforcing addictions. Eating spicy or sweet food causes a dopamine spike. So does having lots of social interaction, in person or on social media. Just about all of life’s pleasures give you a dopamine hit: gaming, watching TV or pornography, gambling, shopping, and having sex. Oh, and drugs and alcohol. The intent of a dopamine fast isn’t to make yourself miserable, it’s to allow your dopamine receptors to take a break so that when they come back online, they’ll become more sensitive to dopamine. When you stop the fast, which normally lasts two to seven days, you will find that everything you do feels more pleasurable. Training your body to go without all of its various cravings will make you stronger and more directed. My fasting in a cave for four days was an intense dopamine fast, among other things.
THE FASTING TRAP
I’ve just spent almost an entire book sharing everything I know about fasting and extolling its virtues. Now take a minute to balance out that elation with a cautionary note about what I call the “fasting trap.” It’s a consequence of the natural habit formation pathways in our brains. Pay attention, because to get the most out of fasting you need to beware of this trap.
Once upon a time, I was a raw vegan. That meant not eating any food or products coming from animals, no processed foods, and no foods cooked at temperatures above 118 degrees in the belief that foods are more nutritious if they are only minimally cooked—hence, the “raw” part. At first I felt amazing. After about six weeks, I lost some weight. I thought the diet was miraculous, so I committed to it completely.
It turned out that six weeks is a very significant number. B. J. Fogg at Stanford University, a behavioral scientist who specializes in studying habit formation, has shown that six weeks is the amount of time it takes to form a habit. (In the Bible, many significant events and fasts last forty days and forty nights, which is suspiciously similar to six weeks. People have had an intuitive feel for this process for a very long time.) Soon after that, my raw vegan habit started not working so well anymore. My body started to feel strange. My teeth became temperature sensitive, and then I cracked a tooth. I was cold all the time. I started getting new joint pain and new allergies. But I didn’t stop, because I knew how good I felt on the diet.
To fix my problems, I decided, I needed to be an even more committed raw vegan. Obviously I wasn’t committed enough! But things only got worse. I became really unhealthy, damaged my thyroid, and my joints started creaking. My memory became impaired. Eventually, I realized that lifestyle just wasn’t working for me anymore. I had to undo the damage done to my body.
After that, I was determined to develop my own healthier and more constructive way to eat so I would never be fat again and never have the energy crashes that had plagued me my entire life, including all through the vegan time. That was the birth of my Bulletproof Diet. Along the way, I learned that going into ketosis can have some of the same habit-forming risks as a diet like raw vegan. In the late 1990s, when I was first experimenting with fasting, I tried the Atkins diet—or dirty keto, as it’s called today. This protein-heavy, high-fat diet put the body into ketosis, which I loved. I ate a steak every night and really restricted my carb intake. I lost half the weight I wanted to, felt the glow of success, and became convinced that that was the only way to do it.
When my weight loss stalled, I resolved to be even more keto, not understanding that I was inflaming my body by eating the wrong foods. By that point, my ego was so bound up in succeeding that I didn’t want to admit I needed to rethink my entire approach. I was also a victim of what behavioral scientists call the “sunk cost fallacy.” I couldn’t get my time and effort back, so I was determined to put in even more time and effort until I succeeded. It’s the same psychological glitch that convinces people to keep investing more money into failing businesses or to continue gambling to make up for their ever-mounting losses. You may know the common saying “throwing good money after bad.” It never leads to success, and it sure didn’t work for me while I was doing the wrong kind of diet.
My troubles with the raw vegan and Atkins diets—aka the vegan trap and the keto trap—had a lot in common. If you do something for six weeks and it feels good, you tend to get hooked. At that point, you stop questioning whether it works. You keep doing it even if it messes with your health. People who eat dirty keto without breaks end up dropping their sex hormone levels, shedding hair, and ruining their sleep. People who go raw vegan get oxalic acid poisoning in their tissues and break the cell membranes in their brains by missing out on fatty acids from animals. They feel good and lose weight in the short term, so they get hooked on the habit. By the time allergies and metabolic dysfunction kick in, it’s hard for them to stop.
Getting short-term benefits for six weeks makes you think that a strategy will always work—and just like me, you’ll double down on something once you believe in it. It’s a function of how people make decisions.
When I first started writing about intermittent fasting a decade ago, it was fairly esoteric knowledge. Some of the early Bulletproof followers, especially younger men, got very excited that they had found something new and powerful. They would say they were committing to doing intermittent fasting every day for the rest of their lives. Having been in two diet traps already, that made me nervous. So I’d like to pause for a moment and specifically address younger readers.
If you are eighteen to twenty-five years old, you probably have abundant energy (unless you have a serious illness or a metabolic dysfunction as I had at that age), so you can handle all kinds of self-destructive behaviors without feeling the consequences. You can go out drinking four nights a week, you can smoke or vape, and the next day you don’t feel terrible. You can eat a bunch of junk food and brag, “I don’t know how I do it, but I stay thin.” None of those is a good idea, and you probably know that, but you can do them without having to reckon with the consequences right away.
In the same way, the resilience of youth may make intermittent fasting feel a little too easy. Strange as it sounds, you might enjoy it so much that you’re tempted to do it frequently, which will create too much strain on your body over time. Creating an obsessive habit is never a good idea, even if it is an obsessive habit about intermittent fasting. You can overdo it, just as you can with any other type of behavior. Don’t fall into the fasting trap.
The solution to the fasting trap is self-awareness.
Expanding your self-awareness is one of the main goals of fasting anyway, so it’s really important to work on it. If you do decide you’re going to fast all the time, take a pause. STOP. Consciously consider that there is a serious risk of fasting too much. You don’t want to fast when you’re in physical pain, such as when you’re sick or injured. The pain response chews through calories, making it hard to fast. If you’re really addicted, you may be tempted to double down. STOP.
Every type of fast can do fantastic things for you. There’s nothing wrong with going all in and doing one meal a day, which is a very powerful form of fasting. But here’s the deal: even if you think of yourself as super-OMAD, every couple of weeks on Saturday, have some damn gluten-free waffles for breakfast.
If you’re under eighteen, I urge special caution and restraint with fasting. Your body is still growing. Your brain’s critical prefrontal cortex is not fully baked until about twenty-four years of age. An intermittent fast done one to three times a week, with adequate calories at the end of the fast, can provide benefits. But daily OMAD or daily 16:8 fasting can stunt your growth or your brain development. It’s not worth the risk. You need high-quality food, and you need to send a strong signal to your body that there is zero risk of a famine. Long fasts may change your epigenetic signaling in a negative way that can take years to undo.