PDF Summary:Fast. Feast. Repeat., by Gin Stephens

In Fast. Feast. Repeat., Gin Stephens explains how intermittent fasting (IF) can help you lose weight, feel better, fight disease, and live longer. Stephens breaks down the cutting-edge science that supports fasting as a powerful practice for overall health, and she explains how to implement intermittent fasting as a sustainable, flexible lifestyle choice.

After Stephens, a former educator, lost over 80 pounds with intermittent fasting, she created online support groups to bring IF to others. Soon after, she self-published Delay, Don’t Deny, her first book about IF, and followed it up with Fast. Feast. Repeat. In our guide, you’ll learn why fasting beats traditional dieting, how to think like an intermittent faster, how to fast and feast for your unique body, and how to follow a four-week quickstart program to adapt to this new lifestyle.

We’ve also fleshed out Stephens’s ideas with perspectives from The Obesity Code and In Defense of Food, and we’ve noted where her ideas appear to come from earlier works such as Intuitive Eating.

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Fast Properly and Feast Well

Now that you know how to think like an IFer, we’ll explain the “clean fast”—Stephens’s approach to fasting—and her “delay, don’t deny” approach to feasting. Afterward, we’ll detail how to time your fasting/feasting cycles with various rhythms.

Fast Cleanly by Avoiding Foods or Flavors

According to Stephens, you must do a clean fast to get the full benefits of fasting. The main three purposes of clean fasting are insulin regulation, ketosis, and autophagy:

Purpose #1: Regulate your insulin. Since insulin prevents effective fat burning, you’ll want to avoid eating, period. Further, avoid consuming any flavors—sweetness, sourness, and umami flavors all activate the insulin response.

(Shortform note: While Stephens approves coffee for her clean fast, some studies indicate that coffee consumption may briefly increase insulin levels. As such, abstaining from coffee could result in a cleaner fast than not doing so.)

Purpose #2: Activate fat-burning. Fasting burns fat by activating ketosis—using fat stores for fuel. Don’t consume anything that gives your body an external source of fuel.

(Shortform note: Healthline reports that if you want to activate ketosis, eat fewer carbohydrates. Carbs convert directly into blood glucose, which your body will use for fuel. The fewer carbs you eat, the less glucose and glycogen you’ll need to deplete each time you fast in order to reach ketosis.)

Purpose #3: Activate autophagy. Many of fasting’s benefits come from autophagy, so avoid eating anything, including vitamins and supplements. Research found that taking supplements may reduce autophagy and increase insulin levels.

(Shortform note: While fasting is the main way to activate autophagy, you may also be able to do so by following the keto diet. In short, keto involves eating minimal carbs and increasing your fat intake. This stimulates ketosis, during which autophagy ramps up—so fasting combined with keto may be the best way to regularly benefit from autophagy.)

In short, to fast cleanly means to eat nothing that hinders the above purposes. Stephens provides the following breakdown of what you can and can’t eat on a clean fast:

Can Eat	Unflavored water, black coffee, plain tea made from camellia sinensis, mineral, sparkling, and seltzer waters, club soda, salt and electrolytes, doctor-approved medications	According to Stephens, bitter flavors from coffee or tea don’t activate the insulin response. Nor do non-flavored beverages, salt, or medications.
Gray Area	Peppermint oil, herbal teas, vitamins and supplements	These items may activate the insulin response. After adapting to IF, try them out one at a time.
Can’t Eat	Any food, flavored waters and drinks, diet sodas, coffee creamers or fatty add-ins, sweeteners (even if zero calorie), gum, mints, breath strips, workout supplements	All of these items activate the insulin response. There’s no need to eat while fasting—that’s the point!

(Shortform note: While Stephens asserts that you’ll only reap the full benefits of fasting by following her guidelines, other practitioners allow for some consumption during the fasting period. This is because different IFers have different goals: Martin Berkhan, author of The Leangains Method, recommends taking BCAA supplements prior to exercise—his goal is bodybuilding. To better understand how you should fast and feast, consider your own goals: Do you want to lose fat, gain muscle, or simply maintain good health? Depending on the answer, you have more or less room to compromise with Stephens’s relatively strict plan.)

Feast on Quality Foods Plus Some Treats

Stephens explains that when it’s time to eat, you can eat whichever foods you want. She recommends following her “delay, don’t deny” principle and eating mainly quality foods.

• To delay means to wait until your fast is over and it’s time to eat. Most often, this means waiting until your daily fast ends. However, you might also delay consuming a given food that would hinder your weight loss efforts—such as pizza—until you reach your goal.
• Don’t deny means that there’s no list of banned foods. When it’s time to eat, enjoy what you’d like to—whether it’s a cheeseburger or a salad is up to you.

However, don’t deny does not mean that you can eat as much as you please. If you overeat, you’ll store excess blood glucose as glycogen and fat. If you can’t empty your glycogen stores in each fast, your body won’t be able to access and burn fat as fuel. In this case, you’ll maintain or gain weight.

(Shortform note: In Intuitive Eating, Tribole and Resch recommend that you honor your hunger as a key step to healing your relationship with food. If you deny your hunger, you’ll reinforce the dieting mindset that causes yo-yoing between self-deprivation and bingeing. Instead, give yourself “unconditional permission to eat” and pay attention to your hunger signals to learn when you’ve had enough.)

While Stephens’s approach allows you to eat as you choose, the quality of your food does matter. So while desserts aren’t off-limits, you can’t exclusively eat treats and expect to feel good or lose weight. This is because not all calories are equal: 100 calories of candy is empty of nutrition while 100 calories of vegetables is nutrient-rich.

(Shortform note: While Stephens allows for some ultra-processed foods in her lifestyle, Michael Greger argues in How Not to Die that highly refined foods are never good for us. They’re at the root of numerous modern diseases, and they desensitize your palate so that normal foods don’t taste as good. Given this, it might be easier to go cold turkey from ultra-processed foods rather than trying to eat them in moderation. After all, they’re engineered to encourage overeating, which Stephens acknowledges—so if you keep them in your diet, you might find yourself struggling to eat in moderation.)

Stephens recommends using the NOVA classification system to choose what you eat:

• Food Type #1: Unprocessed or minimally processed foods—This includes whole foods such as fresh fruits and vegetables, meats, fish, nuts, and dried or crushed foods like nuts.
• Food Type #2: Processed culinary ingredients—This includes foods prepared with traditional processing methods such as milling, grinding, or churning. Flours, sugars, butters, and salts fall in this category.
• Food Type #3: Processed foods—These foods result from the combination of unprocessed foods and processed culinary ingredients, and they resemble whole foods. Think homemade bread, yogurt, tofu, or pickles.
• Food Type #4: Ultra-Processed foods—This category includes highly processed food-like items made primarily from food-derived ingredients, preservatives, flavors, and other chemical compounds. Think Cheetos, chicken nuggets, ice cream, grocery store bread, or Twinkies-style snack foods.

The Purpose of the NOVA Classification System

NOVA—a term, not an acronym—originates from a group of researchers at the University of Sao Paulo, Brazil. Developing their research and ideas in papers since 2009, the group advocates for the NOVA system to clarify the nature of ultra-processed foods and leave no room for doubt about whether they’re healthy.

In their view, ultra-processed foods are by nature unhealthy and we shouldn’t eat them. The researchers argue that such “foods” are created from industrially derived and processed ingredients that leave no real food intact. They argue that a global food industry is steadily replacing traditional, less-processed diets with convenient, cheap, and heavily-processed “food products.”

By creating and advocating for their NOVA system, these researchers intend to shine a spotlight on the negative effects of ultra-processed foods, which include increased obesity and type 2 diabetes. In addition, NOVA provides a framework for policymakers to assess the dietary habits of a given population and work toward positive change.

Stephens explains that ultra-processed foods contribute to overeating and obesity, and she recommends eating them infrequently, if at all. Instead, eat mainly foods from the first three categories, shop in the produce and deli sections of the grocery store, and avoid eating things that your great-great-grandparents wouldn’t recognize as food.

(Shortform note: In Fast Food Nation, Eric Schlosser explains that in addition to their contribution to obesity and food addiction, the ultra-processed foods created by fast food companies and agribusiness have decimated independent farmers and exploited workers for decades. Farmers receive a pittance for the food they produce, while laborers in fast food chains and slaughterhouses withstand poor working conditions and an aggressively anti-union environment. To overcome this, Schlosser suggests that the federal government needs to pass antitrust laws and put the power back with the people.)

How to Time Your Fasts

According to Stephens, there are multiple “rhythms” or patterns of fast, feast, repeat that you can use. The two main categories are time-restricted eating and alternate-day fasting. Each has its own benefits and suitable use cases.

Time-Restricted Eating (TRE)

This is a popular fasting rhythm wherein you divide each day into a fasting period and a feasting period. For example, you might fast for 18 hours and feast for six (notated as 18:6). Stephens explains that TRE works well for weight maintenance.

During the fasting period, follow Stephens’s clean fasting guidelines. Lipolysis (fat-burning) activates between hours 12 and 16, and increases between hours 18 and 24. During the feasting period, eat according to the principles in the previous section. Spread your eating between one or two meals and a snack or two.

Popular timings include 16:8, 19:5, 20:4, and One Meal a Day (OMAD), which usually features a two- to four-hour eating window. Stephens encourages you to pick a timing that works for your goals: Longer fasts burn more fat while shorter fasts work well for maintenance.

Time-Restricted Eating Isn’t a Panacea

Research suggests that a 16:8 TRE timing has a limited to negligible effect on weight loss versus eating with normal meal timing. In the study, which took place over 12 weeks, researchers found that the group who ate during an eight-hour period lost an average of two pounds, while the control group lost an average of 1.5 pounds.

At the same time, other research has found a significant effect: In one study on fasting during Ramadan, a Muslim holy month that involves fasting daily from dawn to dusk, subjects lost weight, lowered their BMI, and decreased their waist circumference.

Considering the conflicting research, it’s probable that whether TRE works for weight loss depends on additional factors—such as what you eat and how much. While Stephens decries dieting, it’s unlikely that intermittent fasting works independently of a good diet.

Alternate-Day Fasting (ADF)

Alternate-day fasting involves alternating days of fasting and days of eating normally. For instance, a 5:2 ADF rhythm means that you eat normally on five days of the week and fast on two days of the week. According to Stephens, ADF works well for intensive fat loss.

On your fasting days, you can fast completely or eat a 500-calorie meal to keep yourself going. The first option increases fat burning due to the longer fast, while the second still works but is easier. Either way, fast cleanly to ensure that you burn fat, activate autophagy, and lower insulin.

On your eating days, eat slightly more than you need—around 110% of your typical intake—and don’t restrict your eating in any way. Research indicates that “overfeeding” temporarily increases metabolism while restricting your eating can slow down your metabolism.

Popular patterns include 5:2, 4:3, and “True ADF,” which means alternating up-and-down nonstop. A 5:2 pattern is the most flexible since you can adjust the days on which you fast, while the 4:3 pattern and “true ADF” are more rigorous. Whichever pattern you choose, avoid ever having two fasting days in a row—always follow a fasting day with an eating day.

Alternate-Day Fasting Has a Larger Impact Than TRE

Research suggests that alternate-day fasting has potential as a powerful clinical intervention for weight loss and improvement to overall health. In the study, researchers found that over a four-week period, fasting for 36 hours every other day led to fat loss, increased heart health, and a reduction in inflammatory molecules that cause aging. These effects persisted on non-fasting days. The researchers also note that ADF seems to be safe for healthy adults.

Other researchers found similar results and recommend ADF as a way for obese people to lose weight. However, they don’t recommend it for just anyone, noting that it’s an extreme way of restricting your diet. As Stephens explains above, it may be risky not to eat for longer than 36 hours, especially if your body isn’t used to fasting.

Start Fasting: The Quickstart and Beyond

Having covered the science, mindset, and guidelines of intermittent fasting, let’s put what we’ve learned into action. We’ll outline how to start intermittent fasting by committing to a four-week adaptation period, and we’ll explore the changes you’ll experience while adapting to IF.

Commit to a Four-Week Quickstart

To get you started, Stephens lays out a four-week program during which you’ll adapt to IF by depleting your glycogen stores and teaching your body to access your fat stores. While adapting, be consistent and patient. Follow through with the full four weeks once you start. If you dabble, your body will struggle to adapt and you’ll delay the benefits of IF.

Keep your fasting clean: Follow Stephens’s clean fasting guidelines to teach your body to access its fat stores. You’ll gradually deplete your stored glycogen and cue your body to search for an alternate source of fuel—your fat.

Do not change what you eat during this four-week period. Adapting to IF is a large change, and another—such as diet change—can overwhelm you and hinder the process.

Build the IF Habit

While Stephens gives plenty of information about fasting, she doesn’t dive into how you can successfully change your behavior. In Tiny Habits, BJ Fogg explains that successful behavioral change occurs when you have sufficient motivation, ability, and a prompt that gets you started. He explains this as Behavior = MAP.

The core of Fogg’s approach is to make the change as small as possible. He argues that motivation is unreliable, so we need to make sure our new behaviors are small enough that we won’t find excuses to avoid them. Create a “tiny habit” by finding just the first step of the behavior you want to learn—for instance, putting on your socks and shoes to start a running habit. For intermittent fasting, you might commit to one day of fasting and build momentum from there.

Lastly, celebrate your success each time you perform the new behavior. According to Fogg, this reinforces the behavior in your brain and helps make it automatic. Plus, feeling good about yourself is healthy for its own sake.

Stephens offers three approaches to begin fasting: An easy, medium, and hard approach. In each, you’ll build from shorter fasts and longer feasts to longer fasts and shorter feasts. Below, we’ve notated the fast/feast windows with the x:y ratios explained in “How to Time Your Fasts.” Pick one and follow the fasting/feasting patterns prescribed for each week.

• Approach #1: Easy—In week one, 12:12. In week two, 14:10. In week three, 16:8. In week four, 18:6.
• Approach #2: Medium—In week one, 16:8. In week two, 17:7. In week three, 18:6. In week four, 19:5.
• Approach #3: Hard—In weeks one and two, 18:6. In week three, 19:5. In week four, 20:4.

(Shortform note: In Tiny Habits, Fogg also argues that we should treat behavioral change as a scientific experiment instead of a judgment of motivation or willpower. If the approach you choose is too tough, consider that you might’ve asked yourself to make too big a change with too little motivation, ability, or no good prompt. Reflect on what didn’t work, and then use Fogg’s technique: Brainstorm several behaviors that could help you adapt to IF, and pick the “golden behavior”—the option that’s both feasible and impactful.)

Common Changes While Adapting

Once you begin, your body needs to get used to fasting instead of having the glucose from consistent eating. When that glucose isn’t available, you might experience lethargy, headaches, and fatigue. This means your body is depleting your glycogen stores. After a few weeks (usually three to four, or eight at most), you’ll experience heightened energy and ease during your fasts.

Stephens stresses that it’s fine if you get hungry during your fast—this happens to everyone. Know that hunger tends to come in waves that pass. It won’t build forever or overwhelm you. However, your appetite will likely increase since your body can’t access your fat stores very well yet. Once your body learns to access fat for energy, your appetite will settle down.

(Shortform note: Harvard Health explains that alternate-day fasting causes headaches and lethargy more often than time-restricted eating. If you experience severe pains, they recommend using TRE instead of ADF or fasting less frequently. In addition, they note that fasting often causes overeating since your appetite hormones ramp up while you aren’t eating. To avoid this, they recommend easing into IF by gradually decreasing your eating window over a period of several months—much more gradually than Stephens prescribes.)

Adjust Your Approach

If your first approach doesn’t work out, Stephens recommends you switch to another. If it was too easy, pick a harder plan. If it was too hard, pick an easier plan.

(Shortform note: While Stephens suggests an evening eating window, other studies indicate that a morning eating window may be better. Research found that people’s cognition and memory were stronger when they’d eaten breakfast. Those who fasted early in the day also struggled to exercise on an empty stomach, and eating late has been linked to weight gain.)

After finishing the four-week adaptation period, you can further adjust your approach. Stephens explains that it’s up to you to customize your fasting lifestyle and find what works best. This is as simple as trying out different fasting rhythms, paying attention to how you feel, and adjusting until you feel great.

Each time you make an adjustment, give your body at least two weeks to adjust before judging how something works for you. Listen to your body’s signals—if you feel great, that’s a good sign. If you feel moody or nauseous, try adjusting your approach again.

(Shortform note: In The 4-Hour Body, Tim Ferriss argues that self-experimentation is the best route to knowing yourself. By experimenting extensively with his diet, exercise habits, and more, he learned how to rapidly build muscle, improve his sleep, and lengthen his life. Ferriss recommends finding the “minimum effective dose” to change something in your life, and he advises changing only one aspect of your lifestyle at a time.)

Lose Weight With Intermittent Fasting

Let’s look at how to use intermittent fasting to lose weight. We’ll cover measurement tactics, how to overcome plateaus, and how to maintain your weight once you reach your goals.

According to Stephens, you will not experience rapid weight loss with IF. Instead, expect that your body will take time to adjust and know that weight loss will ramp up over time. In addition, intermittent fasting doesn’t produce linear weight loss due to body recomposition. You’ll lose fat and gain muscle due to increased human growth hormone. Because muscle weighs more than fat by volume, you’ll drop sizes while remaining heavier than you expected.

(Shortform note: Intuitive Eating recommends putting weight loss on hold and first reclaiming a healthy relationship with food. If you lose weight as a consequence of eating more intuitively, that’s wonderful. But if you focus on weight loss rather than getting back in tune with your body’s natural signals, you aren’t truly losing a dieting mindset.)

Use at least one of the following measurement tactics to track your progress:

• Tactic #1: Calculate your average weight loss. If fat loss is your main goal, track it by calculating your weekly average drop in weight. This shows you the trend of your weight loss—it’ll go steadily downward, even if daily numbers fluctuate. If weighing stresses you out, Stephens says you can drop the scale altogether and rely on other measurements.
• Tactic #2: Use “goal” clothing. Buy a pair of pants that you’d like to fit into—a size or two down—and check each week to see how they fit. Once they fit, you know you’ve made progress, and you can aim to drop another size or two.
• Tactic #3: Take regular photos. Wearing the same clothes each time, take weekly pictures from the front, back, and sides. By comparing these, you’ll see clearly the progress you’ve made.

Weight Loss Isn’t Everything

While many people come to intermittent fasting for weight loss, others argue that you can be “healthy at every size” (HAES). The basic premise of HAES is that you can have healthy lifestyle habits, such as exercise or practicing affirmations for self-esteem, at any size.

That is, being heavier doesn’t mean you can’t love yourself, build skills, or lead a satisfying life. Rather, HAES proponents contend that it’s the negative stigma against fatness that causes heavier people to feel discontented with themselves.

Taking this as the case, you might still benefit from intermittent fasting. While Stephens’s above measurement techniques would no longer apply, you might still reap other benefits—such as the positive effects of autophagy and insulin reduction.

Overcome Plateaus by Adjusting

Stephens explains that as you lose weight, your body might settle into a new set point—a default weight that your body wants to maintain—and resist further weight loss. When this occurs, the solution is usually to adjust your fasting or your feasting.

• Adjust your fasting. First, make sure you’re fasting cleanly. Second, switch up your fasting rhythms: Try going from TRE to ADF, changing the length of your fasting window, or adjusting when you fast and when you feast.
• Adjust your feasting. Recognize if you’re overeating or eating too many ultra-processed foods, and try delaying these foods for a month or two. In addition, try switching up your eating style by getting more whole foods or adjusting your macronutrient intake.

Do Gut Bacteria Affect Your Weight?

If you’re having trouble losing weight and Stephens’s adjustments don’t work for you, consider the health of your gut microbiome. In recent years, research on the link between gut bacteria and everything from mood and personality to obesity and appetite hormones has expanded.

In one study, researchers implanted mice with bacteria from the guts of lean or obese women, and the mice that received the obese women’s bacteria became obese. Conversely, the lean-bacteria mice remained lean. When the mice were allowed to mix, those that had received the obesity-causing bacteria remained lean—likely because they acquired additional bacteria from close contact with the lean mice. The researchers speculate that the gut microbiomes of the obese mice lacked the diversity of bacteria types to fill every role in a well-functioning digestive system.

Lastly, diet plays a large role in keeping your gut healthy. In Gut, Enders recommends taking probiotics and prebiotics, which fill your gut with healthy bacteria and feed them, respectively. She also advises against taking antibiotics unless strictly necessary, since they kill off both good and bad bacteria and can cause antibiotic resistance.

Maintain Your Weight

Once you’ve approached your goal weight, Stephens recommends choosing a “goal body” to maintain. Your weight will naturally fluctuate a bit, so stressing about maintaining an exact number isn’t helpful. Instead, trust that your body will reach a healthy weight and stay there.

To maintain your goal body, keep up with good IF habits. If you gain weight, check your eating habits and adjust them a bit to settle back down. If you lose too much, eat a bit more. It’s okay to enjoy a bit more food from time to time, and it’s okay to eat less when you need to.

You can also use your “goal” clothing to keep perspective. If you still fit in your goal pants, you’re doing fine. If you feel a little tight in them, that’s a gentle signal to ease back a bit on the feasting.

Celebrate Your New Set Point

In The Obesity Code, Jason Fung explains that, contrary to popular understanding, obesity isn’t caused by overeating. Instead, overeating is a symptom of obesity. In Fung’s view, the term obesity doesn’t refer to being overweight—rather, it refers to a hormonal imbalance with side effects including persistent hunger and intractable weight gain. It also drives up your set point, the body’s preferred default weight. This imbalance is likely caused by ultra-processed foods.

Fung explains that your set point is like the setting on a thermostat: It’s the balance-point your weight naturally works to maintain, and it returns there if you gain or lose too much weight. Your body maintains its set point via a complex balance of hormones such as insulin, leptin, and cortisol. Obesity throws this balance off, but when you fast regularly, you give your body daily time to heal hormonal imbalances—such as the insulin resistance that corresponds to obesity—and lower the setting on your body’s “thermostat.”

As Stephens implies above, reaching a new set point is worth celebrating. Further, you can relax about weight loss: Your body will naturally maintain its set point, and you now have the tools and knowledge to adjust and enjoy the lifestyle you want.