PDF Summary:Fast This Way, by Dave Asprey

In Fast This Way, biohacker Dave Asprey argues that intermittent fasting is more than just a way to lose weight: It transforms you into your best self by optimizing how your mind and body function and helping you gain a sense of control over your life. Going without food can be challenging, so Asprey created an intermittent fasting method that makes it easier and more enjoyable—“Bulletproof Intermittent Fasting.” By following Asprey’s advice, you can lose weight, think more clearly, and live longer and healthier.

In this guide, we’ll explain what intermittent fasting is and how our modern eating habits differ from our bodies’ naturally evolved eating patterns. We’ll also discuss the many benefits of fasting and examine Asprey’s Bulletproof fasting method. Throughout the guide, we’ll supplement Asprey’s insights with those of other health and nutrition experts and provide additional tips to help you in your fasting journey.

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2. Fasting lifts your mood. During a fast, your body produces chemicals such as dopamine and adrenaline that enhance your mood and energy. These chemicals allowed our ancestors to survive: They gave them energy when they were hungry and helped them stay motivated to hunt for food.

Harnessing the Benefits of BDNF Through Fasting

In Fast. Feast. Repeat., Gin Stephens explains that fasting boosts your brain power and mood by boosting the levels of a compound called brain-derived neurotrophic factor (BDNF), which protects your neurons from wearing down. Fasting raises your BDNF levels, which helps you think better and lowers your risk of diseases like Alzheimer’s and Parkinson’s.

BDNF also regulates your mood: Lower levels of the compound are linked to depression, and some research suggests that one reason antidepressants work is that they increase BDNF levels.

Fasting Enhances Your Workouts

Another benefit of fasting is that it enhances your workouts by making your body more metabolically flexible and resilient. Asprey explains that normally when you work out, your body first turns to carbohydrates—derived from food—for energy. When you fast, however, you don’t have a supply of carbohydrates to use as fuel, so your body burns fat instead. This has two advantages for your workouts: First, fats provide more energy than carbohydrates. Second, fats are anti-inflammatory, so they speed up your muscle healing with less ache and soreness.

(Shortform note: Working out while in ketosis can not only help you burn more fat and recover post-workout, but it can also improve your body composition by optimizing your hormones: In particular, fasting while sprint-training raises human growth hormone (HGH) production and insulin sensitivity, which gives you a more youthful and lean body. However, experts caution that your performance may dip at first until your body gets used to burning fat and not carbohydrates for fuel. It could take up to six months before you become metabolically flexible and have adapted to using fat as a fuel source.)

Fasting Improves Sleep

Asprey writes that fasting can improve the quality of your sleep, which can have a number of benefits for your health: Sleep reduces stress and inflammation, accelerates healing, increases your sex drive, helps with weight loss, and improves your memory and thinking.

(Shortform note: In Why We Sleep, Matthew Walker agrees with Asprey that there’s a long list of benefits quality sleep can bring. Walker notes, further, that sleep deprivation can lead to a host of negative health outcomes, including not only the opposites of sleep’s benefits but also decreased emotional control and an increase of many diseases not typically associated with sleep, such as cancer and heart disease.)

According to Asprey, improper eating habits can interfere with your body’s sleep patterns. If you eat close to your bedtime, your stomach will signal to your body that it’s still time to be awake, and you’ll have trouble sleeping soundly. This is not only because your digestive tract is actively consuming energy but also because your blood sugar and insulin levels are increasing, which can cause you to awaken during the night.

Asprey recommends that you stop eating at least three hours before going to bed. He writes that this gap of time allows for enough digestion that your blood sugar won’t be overly elevated as you settle down for the night.

(Shortform note: Most experts agree with Asprey’s recommendation to refrain from eating a large meal before bedtime and to allow around three hours to pass after eating before you go to sleep. However, some caution there are exceptions to this advice. If you struggle to maintain a stable blood sugar level, eating a small, nutrient-dense snack before bedtime may help you sleep better as it can prevent your blood sugar from either rising or falling sharply during the night. In addition, some nutritionists contend that an evening snack of foods rich in melatonin (such as cherry juice), magnesium (like almonds), or anti-inflammatory antioxidants (like kiwi fruit) can improve your sleep.)

Tips for Intermittent Fasting

Now that we’ve discussed the many benefits of fasting, we’ll look at how you can start intermittent fasting. According to Asprey, one of the biggest obstacles people face when they start to fast is the psychological struggle of going without food. However, he argues that fasting doesn’t have to be a struggle. It can actually be enjoyable and easy—the secret is learning how to avoid hunger pangs. To do this, Asprey presents a simple and effective way to keep hunger pangs at bay while you fast: In the morning, drink a special blend of coffee, grass-fed butter, and a teaspoon or two of C8 MCT oil.

Asprey calls this blend Bulletproof Coffee, and he maintains that the combination of these ingredients allows you to enjoy all the benefits of fasting without feeling hungry. Here’s how each of the ingredients works:

• Black coffee: Provides caffeine, which doubles your ketone production. Higher ketone levels reduce your hunger by suppressing a hormone called ghrelin which stimulates your appetite.
• Grass-fed butter: Provides high-quality fats that keep you satiated while still allowing your body to burn fat and undergo autophagy.
• C8 MCT oil: Unflavored coconut oil that suppresses your hunger and boosts your energy by converting directly into ketones.

(Shortform note: Asprey’s advice to drink coffee as part of the Bulletproof Intermittent Fast might interfere with your ability to get the quality sleep he also recommends. According to Walker in Why We Sleep, caffeine has a half-life of five to seven hours, meaning it will remain in your system for 10 to 14 hours depending on your genetics. Therefore, although caffeine may aid your fasts, it can make it harder for you to sleep at night, even if you drink it in the morning.)

If You Drink Bulletproof Coffee, Are You Still Fasting?

While Asprey says you can drink Bulletproof coffee and still receive the full benefits of fasting, other experts have contrasting perspectives. In Fast. Feast. Repeat., Gin Stephens says you can consume black coffee because it doesn’t activate your insulin response, but she disapproves of adding fats like butter or MCT oil. If you ingest fats during your fast, you prevent your body from burning your own stored fat, she explains. This can reduce your weight loss potential.

Experts present another caveat you should consider before drinking Bulletproof Coffee: Butter and MCT oil are high in saturated fats, which can increase LDL cholesterol and raise your risk of heart disease. Because of this, they caution against drinking Bulletproof Coffee daily or at all if you have certain health disorders like diabetes, heart issues, or gastrointestinal diseases.

Decide Which Type of Fasting Works for You

According to Asprey, there are different intermittent fasting windows you can try, each with its unique health benefits. If you’re new to fasting, Asprey recommends you start with the 16:8 Bulletproof intermittent fast. This involves fasting for 16 hours and eating during an eight-hour window, with the addition of Bulletproof Coffee. For example, after a night’s sleep, you could drink a cup of Bulletproof Coffee in the morning, eat lunch at noon (or later), eat dinner, and stop eating at around 8:00 p.m.

Other types of intermittent fasting include:

• The 5:2 fast: Eating normally for five days of the week and eating 500 to 600 calories on the other two days.
• One Meal a Day (OMAD): Fasting for 23 hours and only eating in a one-hour window.
• Alternate-day fast: Fasting every other day.
• Multi-day fasts: Fasting for four to five days or even longer—typically for people who are more experienced with fasting.

Understanding the Intermittent Fasting Rhythms and Getting Started

Asprey suggests beginners start intermittent fasting with the 16:8 rhythm, but if you’re looking for a more detailed guide to follow, Fast. Feast. Repeat.’s Stephens outlines three plans you can choose from to map out your first month of intermittent fasting:

Option 1 (Easy): Follow a 12:12 pattern (fasting for 12 hours and eating for 12) in Week One, 14:10 in Week Two, 16:8 in Week Three, and 18:6 in Week Four.

Option 2 (Medium): Follow a 16:8 pattern in Week One, 17:7 in Week Two, 18:6 in Week Three, and 19:5 in Week Four.

Option 3 (Hard): Follow an 18:6 pattern in Weeks One and Two, 19:5 in Week Three, and 20:4 in Week Four.

Throughout these four weeks, Stephens encourages you to maintain your usual diet, since changing the foods you eat can make it harder for you to adjust to intermittent fasting.

The different types of intermittent fasting Asprey lists all fall into one of two patterns of fasting—time-restricted eating and alternate-day fasting. According to Stephens, each offers unique benefits:

Time-restricted eating (TRE): For this type of fasting, you divide each day into a fasting period and an eating period. This includes the 16:8 and OMAD fasts, as well as others like 18:6 (fasting for 18 hours and eating for six). According to Stephens, TRE is effective if you want to maintain weight.

Alternate-day fasting (ADF): For this type of fasting, you alternate between days of fasting and days of eating normally. This includes the 5:2 fast and “True ADF,” which is fasting every other day. Stephens writes that ADF is more effective for intensive fat loss. Like Asprey, she approves of eating a 500-calorie meal on fasting days but says going without food entirely can enhance fat burning.

While Asprey says multi-day fasts can be beneficial for more experienced practitioners, Stephens recommends you don’t try anything beyond a 72-hour fast without medical supervision because fasting can be hard on your body. She says extended fasts can often have negative consequences because when your body thinks it’s starving, it reduces your metabolism and triggers strong hunger signals. This can lead people to binge eat after a long fast, resulting in rapid weight gain.

Embrace Inconsistency to Become Resilient

Asprey suggests you switch up your fasting routines and avoid sticking to a single variation. This will make your body more flexible and adaptive, and will give you better results. In addition, it will prevent possible problems from arising—Asprey notes that some of the extreme fasts (like OMAD or multi-day fasts) can cause health problems if you do them all the time. Thus, experiment with different fasting windows and sometimes take breaks from fasting altogether.

(Shortform note: While Asprey recommends you be flexible and inconsistent with your fasts, other experts argue that sticking to consistent eating times is better for your health. They argue that eating at regular times helps you maintain a healthy circadian rhythm (the body’s internal 24-hour clock) and that irregular eating can lead to obesity, high blood pressure, and type 2 diabetes.)

Also, Asprey advises you to be gentle with yourself if you aren’t able to fast as long as you want. Being flexible and listening to your body is ultimately better for your health. Embracing inconsistency allows you to enjoy the diverse benefits of different kinds of fasts while adding in an element of variability that trains your body to become more resilient and adaptive.

(Shortform note: While Asprey recommends you switch up your fasting routines regularly, Stephens suggests, in Fast. Feast. Repeat., that you wait two weeks before trying out a different rhythm. This way, you can see how your body reacts and find what suits you best. However, Stephens does agree with Asprey on the importance of flexibility: If you feel nauseous or unwell, you should listen to your body and eat, or take a break from fasting as Asprey suggests.)

Take Supplements to Upgrade Your Fast

Asprey suggests you take supplements while fasting to provide your body with the nutrients it needs. He explains that modern foods aren’t as healthful as those our ancestors ate, and we therefore can’t rely on food alone to meet our nutritional needs: Today’s foods contain toxins, chemicals, and stressors that weren’t present years ago, and they contain more calories and fewer nutrients.

(Shortform note: Although it’s true that the nutritional content and toxin levels of individual foods may have changed since ancient times, some argue that a bigger shift, that’s had a more significant effect on modern nutrition, is the change in the breadth of foods we eat today as compared to our ancestors. Ancient foragers ate a wide variety of foods from diverse sources (the mummified body of an Iron Age man, for example, revealed his last meal of porridge consisted of 40 different grains and seeds). Today, agricultural practices have narrowed our food choices down to a handful of staples (sugar, corn, wheat, and rice) and eliminated much variety within vegetables and fruits, resulting in a more limited range of nutrients available to us.)

Asprey recommends several supplements in particular that can provide you with nutritional support and improve your fasting results:

1. Activated charcoal: This type of charcoal traps toxins in your gut and prevents your body from absorbing them. It can help you avoid gut pain while fasting, and it also reduces your hunger cravings.

(Shortform note: Activated charcoal is more commonly used as an emergency treatment for poisoning under medical supervision. However, there isn’t much research to support the efficacy of activated charcoal for your gut health. While mostly safe, activated charcoal can cause side effects like vomiting, diarrhea, constipation, black stools, and sometimes intestinal blockages.)

2. Proteolytic enzymes: These enzymes improve your body’s autophagy process, helping clear out unwanted proteins and other cellular debris. They also improve digestion and blood flow.

(Shortform note: While Asprey suggests you get proteolytic enzymes from supplements, they’re also naturally found in foods such as papaya, pineapple, kiwi, and fermented foods. Supplements are more likely to cause side effects (which include diarrhea, nausea, and vomiting), so some experts suggest consulting your medical provider before taking them.)

3. Adaptogens: These are herbs (such as ashwagandha and ginseng), mushrooms, and other substances that can make your fasts less painful by reducing your stress response and helping you relax.

(Shortform note: For a plant or mushroom to be an adaptogen, it must satisfy three requirements: It must be non-toxic in normal doses, help your body manage stress, and help your body return to homeostasis (an internally balanced state). However, like other vitamins and supplements, adaptogens aren’t regulated by the FDA, so you should research products carefully.)

How Beneficial Are Supplements, Really?

Asprey argues that supplements are essential to counteract the harmful effects of modern processed foods, but other experts question the effectiveness of supplements for three reasons:

First, the perceived benefits of supplements might be misleading, according to Michael Pollan in In Defense of Food. He says that although supplement users tend to be healthier, they typically already lead healthier lives—they’re generally more educated, wealthier, and more informed about their health. Thus, their good health might not be caused by the supplements they’re taking.

Second, according to T. Colin Campbell and Thomas M. Campbell II in The China Study, supplements and vitamins are poorly regulated and can have unintended consequences or side effects. They also lack the holistic nutritional value that can only come from consuming the range of vitamins, minerals, and fibers in whole foods.

Third, in Fast. Feast. Repeat., Stephens cautions against taking vitamins and supplements during your fast because some may activate the insulin response and can reduce autophagy. Also, most supplements have protein, and some may contain sweeteners or added flavors that would break your fast.

Be More Mindful if Fasting as a Woman

According to Asprey, women shouldn’t do intermittent fasting every day, but instead, every other day. He explains that fasting affects men and women differently. Women’s bodies are designed to support reproduction and tend to be more sensitive to dietary changes because a lack of food or nutrients could endanger a potential child. Fasting too much or too often can trigger a stress response more quickly than in men and can be harmful to their health. Thus, Asprey recommends that women be attentive to their bodies and adjust their fasting frequency, duration, and intensity according to their individual needs.

(Shortform note: Other experts echo Asprey’s suggestion to be more thoughtful about your approach to fasting if you’re a woman, adding that fasting can cause female sex hormones (estrogen and progesterone) to drop, which can cause headaches, moodiness, changes in your menstrual cycle, and other symptoms. They suggest you start slow with a milder 12-hour fast and gradually work up to a 16-hour fast if you feel OK. They also recommend you avoid fasting a week before your period, which is when your body is more sensitive to stress.)