Fast. Feast. Repeat. is a practical self-help guide that explains intermittent fasting (IF) as a lifestyle and approach to overall well-being. Among other benefits, Gin Stephens argues that IF can help you lose weight, feel better, fight disease, and live longer.
Stephens is a teacher-turned-researcher who lost over 80 pounds through intermittent fasting. She then wrote Delay, Don’t Deny, her first book about IF, and she created online support groups to help others on their IF-based weight-loss journeys. Our guide explains Stephen’s perspective on intermittent fasting in four parts:
We also expand and compare her work with ideas from The Obesity Code by Jason Fung, In Defense of Food by Michael Pollan, and Intuitive Eating by Evelyn Tribole and Elyse Resch.
To start, we’ll explain what intermittent fasting is and what it can do for you.
Stephens explains that intermittent fasting is simply a way of eating—it’s about changing how you eat. This distinguishes it from diets, which restrict what you eat. For instance, keto is a diet since it has a yes/no food list, while intermittent fasting doesn’t require you to restrict what you eat.
(Shortform note: As another example of a “way of eating” versus a diet, consider the standard “three square meals” pattern. It’s a way of eating, not a diet, in that it prescribes three daily meals, spaced roughly equally throughout the day. It doesn’t prescribe what you can eat—just when. Using this standard pattern, you can follow many different diets—keto, the standard American diet, paleo, Atkins, and so on. The same is true for intermittent fasting.)
To do intermittent fasting, you simply cycle between periods of fasting and periods of “feasting” or eating. Regular fasting yields benefits such as increased energy and fat loss, and the feasting periods allow you to eat without the stringent rules of a typical diet.
Stephens stresses that intermittent fasting is not a diet. Instead, IF will help you relearn to eat intuitively, enjoy special occasions without guilt, and achieve a healthy relationship with eating.
The History of Fasting and Eating
Proponents of intermittent fasting often argue that it’s good for us because our ancestors fasted, but historians explain that this isn’t the whole story. Our ancestors fasted out of necessity, not as part of a routine followed for health benefits. Further, food may not have been as scarce as we think—people tended to live where natural resources were abundant, and only events like natural disasters or plagues caused long periods of fasting.
When the agricultural revolution began around 10,000 years ago, we became reliant on staple crops such as wheat and rice and learned to store the surplus. Since we had plenty of food, the population boomed and we began eating three meals a day. This was likely when our modern way of eating—“three square meals”—originated.
Voluntary fasting originates from religion, including daily Ramadan fasts for Muslims and Christian fasting during Lent. More recently, the modern search for health-via-dieting created a new surge of interest in fasting as a health-promoting way of eating. IF is now a popular lifestyle—a voluntary choice that our ancestors didn’t necessarily have or make.
In this section, we’ll explore how our bodies store and use energy, and we’ll present Stephens’s argument for why fasting is a better approach to weight loss than traditional dieting.
Stephens explains that when we eat, our blood glucose (blood sugar) levels increase. In response, our bodies release insulin, a hormone that stores excess glucose in the liver and muscles as glycogen. If any blood glucose remains after this step, insulin converts it into fat and stores it away.
By storing this glucose-based energy, insulin lowers your blood glucose. When your blood sugar runs out and you need energy, the pancreas signals for your liver to release some of its stored glycogen to use as energy. When those glycogen stores run out, you enter the fasted state.
In the fasted state, your body converts your fat stores into ketones, a fat-based energy source. Put another way, you’ll burn your fat as fuel (a state called ketosis). We evolved to burn fat for energy when food was scarce, so you’ll do so only after depleting your blood glucose and glycogen stores.
Your Glycogen “Wallet” and Fat “Bank”
In The Obesity Code, Jason Fung explains this process in more detail. When you eat, the body breaks down each macronutrient—proteins, fats, and carbohydrates—into materials for the body to use. Carbohydrates are sugar molecules, so they become glucose, a simple sugar that every cell in the body can use for energy.
This rise in blood sugar stimulates the release of insulin, a key hormone (molecules that deliver messages or resources to cells). Insulin acts like a key, fitting into the insulin receptor on a given cell and “opening the door” for glucose to enter the cell. If there’s more glucose than needed, insulin chains together glucose molecules into glycogen and stores them in the liver. Later, they’ll break back down into glucose when the body needs more energy.
Fung compares glycogen stores and fat stores to your wallet and bank account, respectively. Glycogen is easier to access, but your liver stores a limited amount. Conversely, your fat stores are difficult to access but hold far more potential energy.
Fung also explains that ketosis doesn’t activate as quickly as Stephens suggests. Your body won’t start breaking fat down into ketones until one to three days into a fast, he says. In the first 24 hours, your body instead breaks fat into glycerol, from which it produces new glucose.
According to Stephens, the modern habit of eating continually causes high blood glucose levels—that is, the body never gets a break from converting food into glucose. This leads to chronically high insulin levels, since insulin releases to store all that glucose. Since we’re never out of glucose or glycogen, the body can’t access its fat stores, burn them, and lose weight.
(Shortform note: In The Obesity Code, Jason Fung argues along these lines in more detail. Continuing the “wallet and bank” metaphor, he argues that, as with money, we prefer to use our wallets (glycogen)—and when we deplete them, we’d rather fill them back up than get money from the bank (fat stores). By eating without long breaks, you prevent your body from accessing fat stores, and at the same time you keep your insulin levels high, which promotes increased storage of glucose as fat. In Fung’s view, this leads to obesity.)
Stephens explains that diets don’t lower insulin levels enough to deplete your glycogen stores and start burning fat. This is because diets work on the logic of “calories in, calories out”—that is, eat less than you need and you’ll lose weight.
(Shortform note: Fung agrees, and he argues that dieting doesn’t lower insulin levels because it doesn’t address insulin resistance. In short, chronically high insulin levels—such as from constant eating—cause your cells’ insulin receptors to become insulin resistant: They need more stimulation (more insulin) for glucose to enter the cell. Eating less doesn’t solve this because any eating stimulates the release of insulin. The solution, he asserts, is to regularly fast for 24 to 36 hours, since fasting gives your body extended time to break down insulin.)
While dieting or eating less works temporarily, it also causes metabolic adaptation, a scenario wherein your metabolism slows down to deal with perceived starvation. It works like this: When you eat fewer calories than you need to maintain your weight, your body thinks you’re starving. Then, Stephens says, it makes three changes to handle the situation:
Diet for long enough, and your metabolism settles in at that slower pace—that’s the “adaptation” in metabolic adaptation. Then, you’ll need to eat even less to continue losing weight, since you aren’t burning as much energy—creating a downward spiral of hunger and slowing metabolism.
Dieting Also Poses Psychological Difficulties
In Intuitive Eating, Evelyn Tribole and Elyse Resch explain the psychological dimensions of why dieting doesn’t work. As they say, dieting fails because of both your body’s reactions to deprivation and because it creates a downward spiral in your emotional health. The more you try to diet, the more diets inevitably fail you. If you remain unaware that it’s dieting’s fault, not yours, you’ll continually blame yourself and feel wracked with guilt.
Bingeing is one symptom of this “diet backlash.” Binging is a psychological condition wherein you fixate excessively on food, feel frequent cravings for “bad” foods, overeat to an extreme level, and lose trust in your ability to eat well.
To overcome this, realize that dieting simply doesn’t work. It fails to take into account the power of the hormones that regulate our appetite and weight—and you can’t overcome such hormonal imbalance with willpower. Instead, drop the idea that whether or not you diet “successfully” has any bearing on your character. It isn’t a moral issue, it’s a biological one. The solution is to learn to eat enough (not too much or too little) while trusting yourself to make the right eating choices.
Dieting typically doesn’t involve fasting, so when you diet, you never use the built-in fat burning mechanism your body already has. Here’s how to access it.
Since our bodies are used to overeating, we need to teach them to access our fat stores again. According to Stephens, when you start fasting, your body won’t yet know how to burn fat and will instead slow your metabolism to save energy until you can eat again.
Since insulin releases when you eat, fasting allows insulin levels to decrease. Then you can use up your liver’s stores of glycogen and begin to access your fat stores. If you fast often enough, your body will “remember” it has fat stores to burn for energy.
Unlike dieting, where you never stop eating long enough to start fasting, intermittent fasting promotes sustainable fat loss. Each time you burn fat for fuel, you’ll lose some weight—and with fasting, you’ll also eat enough each day, so you won’t cause your metabolism to slow down.
Fasting May Heal Insulin Resistance
In The Obesity Code, Jason Fung argues that periods of extended fasting (24 to 36 hours) are the key to healing insulin resistance and beating obesity. As he explains, our modern eating habits of three meals a day, plus regular snacking, never allow insulin to drop much. These chronically high insulin levels lead to insulin resistance.
Fasting heals insulin resistance because it’s the most reliable way to lower insulin levels. The longer you fast, the more insulin levels decrease. Insulin levels must be both high and persistent to produce insulin resistance, so if you regularly fast, you prevent persistently high insulin. Over time, you’ll increase your insulin sensitivity, and that enables your body to make do with less insulin—which slows down fat storage and helps with fat loss.
Stephens explains three main health benefits of intermittent fasting, in addition to fat loss:
Benefit #1: Fasting promotes autophagy, which Stephens calls your body’s natural recycling process. Autophagy takes damaged or aging cellular materials and breaks them down into raw material that can become new cells and compounds. Autophagy is a key bodily process that helps prevent disease—everything from cancer to aging and neurodegenerative disorders.
Benefit #2: Fasting is great for your heart and brain. Research has linked fasting to improvements in various aspects of cardiovascular health, including reduced blood pressure, cardiovascular stress response, and your heart tissue’s ability to heal damages.
Other studies found that intermittent fasting increases levels of brain-derived neurotrophic factor (BDNF), a compound that helps neurons resist degeneration. This improves cognition and reduces risks related to Alzheimer's disease, Parkinson’s disease, and depression.
Benefit #3: Fasting may fight aging. According to Stephens, research found that fasting can increase metabolites—compounds produced by metabolic processes—that help maintain muscles and promote anti-aging antioxidant activity.
Autophagy Is the Key Benefit
At present, research shows that intermittent fasting is an effective way to induce autophagy, supporting Stephens’s argument. Further, autophagy may be the root benefit that promotes the rest:
Many degenerative diseases—everything from Parkinson’s and Alzheimer's to arthritis and polio—occur due to cellular and tissue degeneration.
Since autophagy is how the body recycles and reuses degenerating cellular material, it stands to reason that autophagy would combat degenerative diseases.
Researchers have linked autophagy to decreased risk of some cancers and obesity as well as neurodegenerative diseases. In other words, fasting indirectly promotes a variety of positive health outcomes through the restorative effects of autophagy.
Now that we’ve covered how intermittent fasting works with the body to promote weight loss, let’s look at how to leave behind the dieter’s mindset and instead adopt an IF mindset.
Stephens explains that decades of contradictory advice about how and what to eat has created immense confusion, a tangle that she calls “diet brain”: When you no longer have any clue how to eat “properly.”
“Nutritionism” and Diet Confusion
In In Defense of Food, Michael Pollan argues that when Americans began looking to medical experts to guide how we eat, we lost touch with tradition that once guided us to eat well. Pollan explains that the doctrine of “nutritionism,” or looking for the magic nutrient-based solution to health problems, produced conflicting views about what is healthy.
This is because such research focuses on nutrients rather than the whole-food contexts in which they exist. Because studies have concluded that certain nutrients are problematic instead of certain foods, we’ve had trends such as the low-fat era, the anti-cholesterol era, the anti-carb era, and so on—and oddities like low-fat ice cream.
Pollan stresses that so long as we remain confused about diets and nutrition, we’ll struggle to reclaim our health and to change our lifestyles for the better. To change this, his rule of thumb is to eat real, mostly plant-based food in moderation and to listen to your body to know when you’re full.
Recent research suggests that there’s no such thing as a universally optimal diet. Instead, different individuals seem to respond differently to the same foods. This is called “bio-individuality.” For instance, you might do well with whole wheat bread while a friend doesn’t.
Stephens explains that this gives us good reason to stop thinking about dieting as a moral issue. As she explains, dieting causes you to think in terms of “good” or “bad” behavior, and we’ve learned to punish ourselves for being “weak,” if we fail at dieting. But since there’s no universally perfect diet, there’s nothing to fail at. You’re simply learning how your body works, and you can stop worrying about whether you’re “falling off” the diet.
(Shortform note: The idea of bio-individuality originates from the Institute of Integrative Nutrition, a for-profit organization that teaches a course in “Health Coaching” and advocates for bio-individuality. In the update we’ve linked, the IIN explains that the National Institutes of Health (NIH) has begun to study the value of precise, individualized health plans—lending credibility to the concept. They also note that the studies used to produce the standard blanket diet recommendations—such as the food pyramid—used only 3% of participants from African or Hispanic ancestry.)
Since there’s no perfect diet, Stephens says we can stop worrying about the conflicting diet advice. Instead, learn to intuitively regulate your eating by getting back in touch with your body’s natural appetite signals.
Ghrelin signals when we’re hungry, and leptin signals when we’re satisfied. As infants, we can easily sense these signals and know when we’re hungry or full. But we lose touch with them as we age, making it easy to overeat and gain weight. According to Stephens, intermittent fasting helps you tune back into your appetite signals. When you’ve tuned back in, you can use those natural signals to eat what feels best to you and to “stop when satisfied.”
(Shortform note: The notion of “intuitive eating” originates from a 1982 book called Diets Don’t Work by Bob Schwartz. He advocated, simply, to eat only when you’re hungry, to eat slowly, and to stop eating when you’re full. The idea was popularized in 1995 in Intuitive Eating by Evelyn Trible and Elyse Resch, who detailed how to overcome the “dieter’s dilemma”—the conflicting desires to be thin and to binge on treats—by rejecting the “diet mentality.” Given the similarity of these terms to Stephens’s (“diet brain”), it’s likely she lifted her ideas from this earlier work.)
When tuning back in, it takes time for your appetite signals to reset. To help get you there, Stephens offers the following tactics:
(Shortform note: In Intuitive Eating, Tribole and Resch argue that one key to healing your relationship with food is to focus on the process. In this view, weight loss isn’t the goal so much as a side-effect of your commitment to eating well. As you learn to listen to your body and eat when you’re truly hungry—and to eat what your body truly wants and needs—you’ll naturally trend toward a healthy weight for your body.)
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.
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! |