A Beginner’s Guide to Intermittent Fasting
Intermittent fasting (IF) has become a popular method for losing belly fat, increasing energy, and improving cognitive function. It’s also said to protect against cancer, improve insulin sensitivity, and lower your risk of type 2 diabetes (1). With all of these benefits, you may be thinking of giving intermittent fasting try.
While intermittent fasting is safe and effective for most people, there are a few important things to consider before you dive in. Read on to learn more about what intermittent fasting is, how it works, the benefits you can experience, and who should (and shouldn’t) practice it.
What is Intermittent Fasting?
It may be considered a health trend, but intermittent fasting is nothing new. We’ve been fasting since the beginning of time, and throughout most of history during periods of famine. Many cultures practice fasting for religious reasons, and we’re willing to bet you’ve fasted before, too. If you’ve gone more than 12 hours without eating anything (yes, sleep counts) then you’ve fasted.
However, when it comes to using intermittent fasting as a tool for weight loss, there is some strategy behind it. To understand how and why intermittent fasting works, it helps to know the difference between the fed state and fasted state, and how your body responds to both.
The Fed State vs The Fasted State: Why Do They Matter?
Your body is in one of two states at all times: the fed state or the fasted state.
The fed state is the one you’re in when you consume calories and your body is busy digesting, absorbing, and assimilating nutrients from the foods you eat. Under normal circumstances, you’re in the fed state for most of the day, except for when you’re sleeping, which is when you enter the fasted state.
The fasted state is where the magic happens (so to speak) when it comes to losing weight and experiencing the other health benefits of intermittent fasting. This is because when you’re not taking in any calories, your body can focus on burning fat instead. The idea behind intermittent fasting is to be intentional with the window of time you fast, so that you can be in the fasted state — and therefore, a fat burning state — for a longer period of time.
The most common fasting windows are 12, 14, 16, and 18 hours, but you can fast for up to 48 hours. If you fast for less than 24 hours, you’ll have an eating window, as well as a fasting window.
For example, let’s say you decided to go with a 16-hour fasting window. This means your eating window is 8 hours, so you would eat all of your meals between 12 to 8pm or 10am to 6pm (or whichever 8 hour window works best with your schedule).
There is no right or wrong eating and fasting window (however, there are certain precautions women should take when practicing intermittent fasting). The beauty of intermittent fasting is that you get to choose and experiment to find the method that works best with your lifestyle, and discover the fasting sweet spot that helps you feel your best physically.
Now that you have a basic understanding of how intermittent fasting works, let’s get into the benefits and how-to’s of doing it on the keto diet.
How Intermittent Fasting Works
Intermittent fasting simply means you go a period of time without eating, anywhere between 12 to 48 hours (any period longer is generally discouraged). This length of time is known as your fasting window, where you only consume liquids such as water, herbal tea, or broth.
Some experts recommend drinking low-calorie green vegetable juices and taking supplements while fasting to help keep vitamin and mineral intake consistent, while others believe only water should be consumed. Like many topics in the health realm, the rules around intermittent fasting are subjective, depending on who you ask and your personal health profile.
If you fast for less than 24 hours, you’ll also have an eating window. This is the time allotted for meals before you begin your fast. For most people practicing intermittent fasting, their eating window is between 6 to 12 hours. The most common fasting times are 12,14,16, and 18 hours.
Let’s say, for example, you were to do a 12-hour fast. Your eating window would be 12 hours. You could start your eating window at 7am and end at 7pm. You would break the fast the next day at 7am.
Although some of the intermittent fasting methods online seem more intense than others (some can last upwards of 48 hours), the beauty of intermittent fasting is that you get to choose and experiment with how long you fast. This not only allows you to determine how intermittent fasting can fit in within your lifestyle, but to discover the fasting sweet spot that helps you feel best physically.
Pro’s and Con’s of Intermittent Fasting
As it stands, most of the information and studies we have on intermittent fasting are done on rats rather than humans. However, here’s what research suggests the benefits of intermittent fasting may include:
- Sustainable weight loss
- An increase in lean muscle mass
- Hormonal balance
- More energy
- An increase in cell stress response (which could increase resistance against some diseases)
- A reduction in oxidative stress and inflammation
- Improved insulin sensitivity (which could protect against or reverse type 2 diabetes)
- Increased production of neurotrophic growth factor (which could relieve depression, boost cognitive function, and protect against neurodegenerative diseases, such as Alzheimer’s)
Side Effects of Intermittent Fasting
- Poor cognitive function (this is more common in the beginning stages)
There are a few additional side effects that can be primarily experienced by women. This is because women’s bodies are naturally more sensitive to signs of starvation than men.
Types of Intermittent Fasting
There are several different intermittent fasting methods discussed online. Here are a few of the most popular ones.
The Crescendo Method is one of the best ways to ease into intermittent fasting without shocking your body or aggravating your hormones. It doesn’t require you to fast every day, only a few days per week, spaced throughout the week. For example, Monday, Wednesday and Friday.
Fasting Window: 12-16 hours
Eating Window: 8-12 hours
Safe for Women: Yes
The 16/8 method, sometimes called the “leangains method,” is another brief intermittent fasting routine that’s used specifically to target body fat and improve lean muscle mass (a.k.a. your gains!).
Fasting Window: 16 hours
Eating Window: 8 hours
Safe for Women: Yes
24 Hour Protocol (a.k.a. “Eat-Stop-Eat”)
The 24 hour protocol, also known as “eat-stop-eat” requires you to do a 24-hour fast once or twice a week. You can choose the time you start fasting. Some people prefer to fast from 8pm to 8pm the following day, or begin their fast after breakfast.
Fasting Window: 24 hours
Eating Window: 0
Safe for Women: Yes, when done a maximum of 2 times per week
The 5:2 Diet
The 5:2 diet, also known as the “Fast Diet,” involves restricting calories two days a week to 500 calories per day (with two 250 calorie meals), while eating normally for the other five days. For example, you might eat all of your regular meals Saturday through Wednesday, and eat 500 calories per day on Thursdays and Fridays.There isn’t a ton of research to back up this diet, although it was publicized by Michael Mosley, a British journalist and doctor. Since it doesn’t completely restrict food on the fasting days, it may also be an effective way to ease into fasting without shocking your system. The Fast Diet is considered safe for men and women.
Fasting Window: No fasting window, just calorie restriction to 500 calories per day for 2 fasting days per week
Eating Window: Assume regular caloric intake 5 days per week
Safe for Women: Generally considered safe for women, but studies are lacking on this diet
|Method||Eating Window||Fasting Window|
|Crescendo Fasting||8-12 hours||12-16 hours|
|The 5:2 Diet||Regular meals 5 days per week||500 calories per day for 2 days per week|
Who Shouldn’t Practice Intermittent Fasting?
During certain life stages, intermittent fasting can be dangerous and cause or worsen health problems. You shouldn’t consider intermittent fasting if you are:
- Under chronic stress
- Have a previous history of disordered eating, such as bulimia or anorexia
- Struggle with sleep disorders, or have difficulty sleeping
- Have been diagnosed with a heart condition
- Have a blood sugar imbalance (such as hypoglycemia or diabetes) and feel faint when you don’t eat
Therefore, some of the cons due to hormonal imbalances brought on by intermittent fasting in women may also lead to:
- Irregular periods and amenorrhea (complete loss of period)
- Metabolic stress
- Shrinking of the ovaries
- Anxiety and depression
- Fertility issues
- Difficulty sleeping
This doesn’t mean women can’t practice or reap the benefits of intermittent fasting. We’ve explained all you need to know about intermittent fasting for women in great details here.
Adding a few windows of intermittent fasting to your routine can help break weight loss plateaus and allow you to reach your health goals quicker. However, it’s a method that’s meant to complement a healthy diet and lifestyle, as no dietary protocol can replace the benefits of eating whole, unprocessed foods.