There’s a buzz about intermittent fasting in the news, magazines, Instagram, and blogs. It seems everyone is doing it. But, what is it exactly? Is it safe? What are its health benefits? Does it speed up keto progress? Is it worth doing? Let’s demystify the practice with this beginner’s guide so you can confidently answer these questions and determine whether intermittent fasting is right for you.
What is Intermittent Fasting
Fundamentally, fasting is more than just planning to skip breakfast. It’s a voluntary prolonged abstinence from food, beverage, or both, for a specific amount of time, ranging from hours to weeks with the intention of helping jumpstart your body toward optimal health. It involves following an eating pattern of planned eating periods and fasting periods and can be short-term or long-term and every day or alternate day fasting. It also involves managing your calorie intake, usually with calorie restriction; while intermittent fasting isn’t always associated with a high-fat diet or low-carb diet, it is popular among the keto community. It’s also popular form of dieting with an aim for fat loss, but it has other health benefits as well (Hello, autophagy.).
Though intermittent fasting is a white-hot trend in the health and fitness world, it’s not a remotely new concept. In fact, fasting has been practiced for thousands of years in Christianity, Judaism, Islam, Buddhism, Hinduism, and native tribal religions/spirituality, and beyond as a ritual to heal the body and soul, as a form of penance/sacrifice, and to purify. (Think Ramadan for Muslims, Uposatha for Buddhists, and Ash Wednesday and Good Friday for the Roman Catholic church.) But fasting has also always had clinical health-related appeal to physicians and philosophers, dating as far back as the times of Hippocrates, Plato, Socrates, and Aristotle.
Hippocrates, generally regarded as the father of medicine, said, “Everyone has a doctor in him or her; we just have to help it in its work. The natural healing force within each one of us is the greatest force in getting well. Our food should be our medicine. Our medicine should be our food. But to eat when you are sick, is to feed your sickness.” This quote embodies the core philosophy of the keto diet: feed your body food that promotes health. It also nods to the role of fasting, or refraining from eating to help fight sickness and promote wellness.
Intermittent fasting, or alternating cycles of fasting and eating, is a way of making fasting an ongoing part of a health-minded lifestyle. We’ll discuss how and for how long below, but first let’s explore the benefits.
What are the Benefits of Intermittent Fasting
Following are the benefits of intermittent fasting. You’ll see they’re similar to those of a keto diet, where meal plans ensure you maintain high ketone levels and use ketones for energy rather than glucose (sugar). If used in conjunction with a keto lifestyle, fasting heightens the benefits you’re already getting.
- Mental clarity
- Increased energy levels
- Weight loss / lower body weight
- Reduced body fat percentage (fat burning)
- Lowered blood insulin levels
- Lower glucose (blood sugar) levels
- Lower cholesterol levels
- Reduction and possible elimination of diabetes medications (as prescribed by a healthcare provider)
- Reduction of inflammation
- Increased level of ketosis (In the fasted state, your body depletes your glucose stores and turns to fats for fuel, pushing most people who don’t even follow a ketogenic diet into ketosis for at least a brief period of time. Between this and the decrease in insulin you are setting your body up for optimal ketosis.)
How to Intermittent Fast
There are all kinds of fasts, from one day fasts to 24-hour fasts to fasts that last a week or more. But intermittent, or eat-stop-eat plans, create fasting windows. Some of the more popular intermittent fasting methods/schedules are the following:
- 16:8 (16 hours fasting per day followed by eating within an eight hour window)
- 14:10 (14 hours fasting per day followed by eating over a ten hour time frame)
- OMAD (one meal a day)
- 5:2 (eating 5 days per week, then conducting a partial fast for 2 days)
Let’s break these intermittent fasting plans down.
The 16:8 method of intermittent fasting works by fasting for 16 hours, then consuming your meals/macronutrients (macros)/calories during an eight hour period of time. During this time regardless of diet preference it is suggested to eat lower glycemic foods such as vegetables, fruits, meats, nuts, and some dairy and ensure you are getting plenty of fiber. The same is true for the 14:10 schedule of intermittent fasting; you go 14 hours without eating, then eat your meals/calories during a 10 hour period of time. During both the 16:8 and 14:10 schedules you should be able to fit in 2 to 3 meals, and you’ll want to maintain proper hydration and keep up your electrolytes.
For the one meal a day or OMAD method of fasting, you eat only one meal a day and fast until the next day’s meal. This means you are getting all, or at the very least most, of your calories, vitamins, and minerals in that one meal.
With the 5:2 intermittent fasting schedule, you eat 5 days of the week and do a 500 to 600 calorie fast for the remaining 2 days.
With each of these diet-plan options, you are still allowed to drink black tea, black coffee, and water during the fasting state. This helps to keep you hydrated and, in some cases, wards off hunger. It’s also thought in many circles that you can add additions to your water, coffee, or tea and not break your fast as long as they are under 50 calories.
See the timelines below for example fasting schedules, but note that fasting is very personal and you need to take your own bio-individuality into consideration when determining what works for you.
Tips For Intermittent Fasting
If you’re considering fasting, we recommend you heed the following advice:
- Consult your healthcare provider or dietitian before making any dietary changes, whether you have type 2 diabetes, medical risk factors, or consider yourself optimally healthy.
- Make sure to stay properly hydrated.
- To mitigate possible side effects, ensure you get the appropriate amount of electrolytes each day regardless of intermittent or extended fasting.
- Feel free to experiment with different fasting times to see what works best for you.
- Start slowly! Try intermittent fasting one day a week and slowly work up to the amount of days a week you would like to implement intermittent fasting.
- When you’re in the eating window/feeding state, choose low-glycemic (foods low in carbohydrates or sugars) and nutritious foods that are high in fiber, minerals, and vitamins to maintain optimal health.
- For optimal results, pair intermittent fasting with your low-carb or ketogenic lifestyle, which naturally uses fat for fuel in a similar way that fasting does.
How Long Should You Fast
The duration of any intermittent fast is based on your individual desires, needs, and body; it’s great for anyone interested in weight loss, blood glucose control, or therapeutic benefits in relation to cancer, autoimmune disorders, and inflammation. It can be done for one day or a few days per week (women are generally said to benefit most from 14 hour fasts) or for as long as you like and as long as it feels right for you.
Within the first week, you’re likely to experience heightened appetite control and improved blood-glucose control, with the additional benefits following shortly thereafter. For those new to intermittent fasting, starting out fasting 10 to 16 hours fasting two days a week, then see how you feel. Depending on your goals, you may want to step this up to five days a week or even seven days a week.
Extended fasting is going for 24 hours or more on a “wet” fast (liquids only). While fasting days may have therapeutic benefits (to address cancer, obesity, and neuroprotective properties), the research is still in its infancy and this type of fasting is not for the newbie. Dr. Jason Fung, one of the most cited physicians around fasting and the author of The Complete Guide to Fasting, explains why: “Instead of undertaking shorter fasts and gradually extending it, [people new to fasting] immediately opt for a full on water-only extended fast. This is like a rookie mountaineer that decides that he/she will tackle Mount Everest, without oxygen and push on to the summit irregardless of weather.”
Extended fasts should only be done under medical supervision with the use of monitoring through blood tests, urinalysis, and physician physical exams and supplementation of vitamins, minerals, and hydration.
Who Should Not Fast
Fasting isn’t for everyone, especially people who are any of the following:
- Underweight with a BMI of 18.5 or less (no need to burn fat or lose weight)
- Experiencing eating disorders
Note: While intermittent fasting can be quite beneficial for the diabetic, it’s best to work closely with your healthcare provider to ensure that it’s implemented in a safe and healthy way.
Inspiration for You if You Want to Fast
Want to try intermittent fasting but worried you can’t handle extended periods without food? You may want to reframe your thinking. In his book, Dr. Fung makes a great point: “We talk a lot about what you should eat and what you shouldn’t eat. But people never talk about meal timing — making sure you have long periods where you’re not eating. Look at the word ‘breakfast’ in English. That’s break fast. That’s the meal that breaks your fast. This implies that fasting is a part of everyday life. We’ve forgotten that. We think it’s some sort of Herculean effort, but it’s not. We should be fasting every day.”
Want more info? Watch this quick video explaining ketosis and fasting.