Intro to Intermittent Fasting

With intermittent fasting, you’re not just skipping breakfast here and there, but rather, you’re sticking to a schedule that allows for extended periods without food so your body can focus on cleaning up other systems. 

Many cultures worldwide have been using fasting to attain physical, mental, and spiritual health for thousands of years. However, it’s only more recently that scientific research has helped us understand how going without food for a while can truly benefit your body on multiple levels

Fasting can impact your health on a cellular, tissue, organ, and systemic level. Here are some of the most well-researched benefits of fasting:

Stimulates Autophagy

Autophagy is a process of cellular repair and rejuvenation. It’s the cleaning out and recycling of old cell parts to allow for the production of new healthy cells. 

Dysfunctioning autophagy may contribute to diseases like cancer and neurodegenerative disorders. Therefore, stimulating autophagy in your body is crucial to maintaining homeostasis and optimal health. 

Increases Human Growth Hormone 

When you fast, the levels of human growth hormone (HGH) in your body increase significantly.

HGH is involved in growth and development, boosts protein production, and promotes the utilization of fat. Research shows that this hormone can help to balance out blood lipids, maintain healthy muscle mass, and reduce weight gain around the middle—the most dangerous type of fat.

What’s more, HGH also plays a role in healthy brain function, with one of the symptoms of low HGH being anxiety and depression. 

Improves Insulin Sensitivity

Another hormone tied to metabolic health that’s significantly influenced by fasting is insulin. 

Insulin plays a vital role in the regulation of blood sugar, helping to shuttle glucose into your cells and out of your blood after meals. When insulin is working properly, your blood sugar remains relatively stable, and your cells are able to utilize glucose as fuel.

Unfortunately, many people experience some form of insulin resistance, where their cells no longer respond to insulin messages and blood sugar can become erratic. Ultimately, this can lead to type 2 diabetes. 

Research shows that fasting can help to sensitize your cells to insulin and improve glycemic control (blood sugar control), thereby offering a potential preventative strategy against diabetes and other related metabolic concerns. 

Enhances Mitochondrial Health 

Your mitochondria are the part of your cells where all energy production takes place. These crucial power generators are vital for converting the fuel into usable energy and play a role in almost every cell in your body.

Unfortunately, lifestyle factors and aging can negatively impact the health and function of your mitochondria over time. Poor diets can be particularly taxing, exhausting your mitochondria and increasing the production of reactive oxygen species (ROS) in your body that contribute to oxidative stress. That means there are too many free radicals and not enough antioxidants to counter their damage to your cells. 

Research shows that IF supports your mitochondria by protecting them against the harmful impact of aging and poor lifestyle factors. As a result, this leads to better energy production and healthier cells. 

Reduces Inflammation 

Chronic inflammation is at the root of many (if not all) modern diseases. Cardiovascular disease, diabetes, autoimmune disease, and metabolic syndrome are just some examples.

When you fast, research shows that levels of an important inflammatory marker, C-reactive protein, significantly drop. This indicates that the act of fasting has a positive impact on inflammation throughout your body.

Furthermore, when you refrain from eating, it creates a shift in your metabolism as your body gets used to not having an influx of glucose from food. Instead, your body starts to rely on ketone bodies (which come from your fat stores). Ketones not only serve as an excellent alternative fuel source, but they’re also highly anti-inflammatory. 

By lowering your inflammation, you’re supporting both your physical and mental health and promoting a stronger immune response.

Supports Heart Health

Fasting may support heart health in a handful of ways. 

First, since heart disease goes hand in hand with inflammation, the anti-inflammatory impact of fasting creates a supportive environment for optimal cardiovascular health. 

Second, many people find that they lose weight when fasting, which puts them into a healthy BMI range (a designation crucial for heart health). 

Third, research shows that fasting can promote a healthy blood lipid profile. Specifically, fasting can reduce LDL cholesterol (the bad kind) and triglycerides while maintaining HDL cholesterol (the good kind) levels. 

And fourth, fasting has been shown to reduce blood pressure. High blood pressure is directly related to cardiovascular disease risk. 

Improves Cognitive Function

Young and old, it seems that everyone is looking for a way to improve their cognitive function these days. 

IF offers a unique strategy for improving brain health due to its impact on the brain hormone called brain-derived neurotrophic factor (BDNF). BDNF has been shown in animal models to increase the resistance of brain cells to the degeneration caused by neurodegenerative disorders like Alzheimer’s and Huntington’s disease. 

Research also shows that IF increases antioxidant activity in the brain, further protecting and enhancing the function of neurons (brain cells) while also supporting the synthesis of new brain cells. 

Supports Weight Loss 

It may seem like a no-brainer: If you don’t eat for a while, you’ll lose weight, right?

Well, weight loss isn’t always that simple, and restricting your calories can actually backfire. 

With that being said, when you do an intentional fast, the impact it has on your hormones, blood sugar, and metabolism creates the perfect symphony for lasting weight loss.

As previously mentioned, when you fast, your cellular health and energy utilization improves due to enhanced mitochondrial function and autophagy. Your hormones that support weight loss are upregulated, and your ability to use (instead of store) glucose is improved.  

For many people, this combination of factors results in steady weight loss.

24-Hour Fast

A 24-hour fast is a pretty popular method for fasting. When following this type of schedule, you would pick one or two days a week to fast for a full 24 hours. 

The trick to a 24-hour fast is to split the fast between two days. For example, you might start your fast on a Tuesday after lunch, where you’ll finish eating by 2pm. Then, you fast until 2pm the following day.

This way, much of your time spent fasting will coincide with the time you’re sleeping. 

Example 24-hour fasting schedule:
Monday: Eat normally
Tuesday: Eat breakfast and lunch, finish by 2pm, skip dinner
Wednesday: Skip breakfast, eat a late lunch at 2pm, and then have a light dinner
Thursday: Eat normally
Friday: Eat breakfast and lunch, finish by 2pm, skip dinner
Saturday: Skip breakfast, eat a late lunch at 2pm, and then have a light dinner
Sunday: Eat normally

Of course, you can shift your eating schedule however you like, and if you want to just stick to one 24-hour fast per week, that will also yield results. 

16:8 Method (Eating Windows)

The 16:8 method, or “eating windows,” is one of the most popular ways to start fasting for beginners. With eating windows, you’re able to eat every day; you’re just blocking off several hours where you don’t consume food each day. 

The 16:8 method is the most popular of the eating window formulas, where you fast for 16 hours and then allow yourself an eight-hour eating window. You repeat this schedule each day of the week. 

Some people like to start off with 14:10, which (as you can imagine) is 14 hours of fasting, followed by a 10-hour eating window. Again, carrying this through each day of the week.

This method allows people to dip a toe into fasting without having to cut calories too much or go too long without food. With that being said, it still offers some fantastic health benefits. 

Example 16:8 fasting day:
Skip breakfast
Lunch at 11am
Finish dinner by 7pm

Example 14:10 fasting day:
Late breakfast at 10am
Regular lunch
Finish dinner by 8pm

The 5:2 Diet

The 5:2 diet involves five days of normal eating each week, with two days of calorie restriction (around 500 to 600 calories). 

With the 5:2 diet, there are no set eating windows; you’re really just tracking the number of calories you consume on your “fasting” days. Some people choose to skip a meal or two on their fasting days, while others just make two or three small meals—whatever works best for you is the way to go. 

Example week on the 5:2 diet:
Monday: Eat normally
Tuesday: Cut calories to 500–600 for the day (skip breakfast, small lunch, and small dinner)
Wednesday: Eat normally
Thursday: Eat normally
Friday: Cut calories to 500–600 for the day (skip breakfast, small lunch, and small dinner)
Saturday: Eat normally
Sunday: Eat normally

Alternate-Day Fasting (ADF)

Alternate-day fasting is a more advanced fasting technique.

With traditional alternate-day fasting, it’s pretty straightforward: You’ll fast every other day. Alternatively, you could do a modified ADF where you restrict calories every other day, kind of like a hybrid between the 5:2 diet and ADF. 

Keep in mind that you’re actually fasting for around 36 hours at a time with the traditional format, as you’ll have to include two full nights of sleeping into the equation. 

Example of alternate-day fasting (traditional format):
Monday: Eat normally
Tuesday: Fast all day
Wednesday: Eat normally
Thursday: Fast all day
Friday: Eat normally
Saturday: Fast all day
Sunday: Eat normally

Example of alternate-day fasting (modified format):
Monday: Eat normally
Tuesday: Cut calories to 500–600 for the day (skip breakfast, small lunch, and small dinner)
Wednesday: Eat normally
Thursday: Cut calories to 500–600 for the day (skip breakfast, small lunch, and small dinner)
Friday: Eat normally
Saturday: Cut calories to 500–600 for the day (skip breakfast, small lunch, and small dinner)
Sunday: Eat normally

Extended Fasts

Extended fasts are fasts that last longer than 24 hours. For instance, if you were to do the traditional alternate-day fast, it would be considered an extended fast as you would go for about 36 hours without food. 

Extended fasts are recommended only for seasoned fasters, and you should always consult with your healthcare provider before embarking on an extended fast. 

Some people will fast for 48 hours, 72 hours, or longer. While it may seem intimidating, after a day or so, you’ll notice that your food cravings drastically plummet, and the fasting process becomes much easier. 

While there are many health benefits associated with extended fasts, they can also be hard on your body, which is why you should only do them under the supervision of a healthcare professional.

It’s important to note that fasting works a bit differently for women, and therefore a woman’s protocol may not look exactly the same as a man’s. 

When some women try fasting, they find that they come up against some issues such as extremely low energy, loss of menstrual cycle, or an inability to concentrate or function optimally when going long hours without food. 

The reason for this is simple: Women’s bodies are very different from men’s from a hormonal perspective. 

Modern societal norms aside, women’s bodies are meant to reproduce, and the reproductive cycle is very energy-intensive. Whether pregnant or not, the drastic and constantly changing hormonal structure of a female body requires lots of energy to flow optimally. 

From an ancestral perspective, when food was scarce, it was not a time to reproduce. There simply wasn’t enough fuel in the form of food around to sustain a woman and her child if she were to get pregnant. So, as an act of self-preservation, a woman’s body would shut down the reproductive process, and she would go into amenorrhea (her period would stop). 

In other words, vital processes that keep a woman’s body in balance and fertile had to take the backburner when food was scarce. 

As you can imagine, losing your menstrual cycle can create a lot of imbalance in a woman’s biochemistry. In fact, animal research shows that excessive fasting can lead to masculinization, a heightened stress response, lowered sex hormones, and reproductive shutdown.

So, how exactly should women go about fasting? The best way to start is slow and steady. Don’t jump into extended fasts or push yourself beyond what feels comfortable. A great IF plan to start with is the 14:10 eating window. If this feels good, maybe you increase to 16:8 but only do what feels good to you. And if you notice you’re not feeling well as you slowly extend your fast, always cut it back.

Before beginning a fasting protocol, a few areas of confusion need to be cleared up. 

Exercise

Many people believe that when you fast, you need to hold off on working out—this is shortsighted. Although you may not have the energy to go all-out, exercising in a fasted state is an excellent way to increase the production of anti-inflammatory ketones. 

High-intensity interval training (HIIT) is a popular type of exercise to pair with fasting as it can kickstart your production of ketones. This is also an excellent method for boosting metabolism as quick hits of high exertion can offer lasting metabolic benefits throughout the day.

The best time to exercise is right before you break your fast. This allows you to replenish your nutrients (especially protein) after your workout so that you can start rebuilding muscle.  

As always, however, listen to your body before working out in a fasted state. If you feel extra lethargic or tired, you can always skip your workout. 

If you’re doing an extended fast, you may want to avoid exercise altogether. Light walking or stretching is always good, but anything high-intensity may be too much for your body.

Beverages

It’s pretty clear what you can eat during a fast: nothing. 

Beverages, on the other hand, can be a bit more tricky. 

As a rule, water is always allowed on a fast (unless you’re doing a water fast, which is a whole other thing and really doesn’t apply here).

In addition, you can enjoy beverages like tea, black coffee, and soda water. You just want to make sure that anything you drink does not include any added sugars or calories. 

That means soda, juice, and alcohol are all off-limits. 

Some people will make Bulletproof-style coffee, where they add butter or MCTs to enhance ketone production. There is some debate as to whether this will interfere with some of the benefits of fasting, but it does help to curb cravings and hunger pangs. 

Supplements

Most supplements won’t interfere with a fast as long as they don’t contribute a significant amount of calories. 

However, one thing to note is that fat-soluble supplements like vitamins A, D, E, and K all need fat to be optimally absorbed. Also, some supplements will instruct you to take them with food. If this is the case, it’s likely for absorption reasons or because they’ll cause digestive unrest on an empty stomach. 

The best approach with supplements is to experiment and see which ones you can take on an empty stomach and which ones you should wait to take with food. 

How to Break Your Fast

A common mistake that many people make when breaking their fast is to plan a big meal and overeat. This is the last thing you want to do, as your body won’t be able to handle the influx of food, and you’ll likely feel sick. 

If you make a habit of this behavior, it could even mess with your digestive system after a while. Instead, plan a nutrient-dense meal with high-quality protein and healthy fats, accompanied by a hefty portion of veggies.

While we won’t go super in-depth on the types of foods that keep you fuller, clear-headed, and energized, you can learn the basics of healthy eating in our Intro to Nutrition guide. Or if you’re interested in exploring a particular diet in conjunction with fasting, you might be interested in our Keto or Paleo guides.

You’ll want to feel satisfied and enjoy your first post-fast meal, but you don’t want to overindulge and combat some of the benefits you just gained from fasting.

Breaking a fast is also an excellent time to practice mindful eating. Eating mindfully means paying attention to both your meal and how it affects your body. Take the time to enjoy each bite and pay attention to how you feel. When you eat slower, your body has a chance to signal that it’s full once your nutrient needs have been satisfied.

Starting a new fasting protocol can feel overwhelming, but there are really just a handful of things to keep in mind:

Make a Plan

Once you’ve chosen which fasting protocol you’re going to follow, make a meal plan that supports your fast. For instance, if you’ve decided to do a 24-hour fast, plan ahead which meals you’ll be skipping and what you’ll eat to break your fast. 

Alternatively, if you’re going for the 5:2 diet, choose which days are your fasting days and which days you’ll eat normally. By planning your fasting days ahead of time, you’ll know which days to schedule social activities and which days you’ll be keeping it more low-key.

The same goes for physical activity. If you’re planning a 10-mile hike, it’s probably not the best day to do a 24-hour fast. 

Beware of Common Mistakes 

Some of the most common mistakes with fasting include:

Starting off with an extended fast

Although working up to an extended fast can reap wonderful benefits, this is definitely not the place to start. In fact, the shorter the fast, the better when you’re beginning. The reason for this is simple: Your body isn’t acclimated to fasting yet.

Moreover, your mind isn’t acclimated to fasting yet. 

Your body could be totally on board, but your mind plays a significant role in how well a fast is going to go for you. All too often, people try to jump into fasting with a 24-hour or 36-hour fast and find that they give up because it was just too hard. 

Begin with a fast of about 14 to 16 hours; this will give you plenty of time in a fasted state while not overwhelming you. Once you feel solid on a 16-hour fast, then you may want to consider extending your fasts for longer periods. Or maybe you stick to 14 or 16 hours—you’ll benefit either way. 

Breaking your fast with a binge

This one was mentioned previously, but it bears repeating. If you don’t plan your meals ahead of time, the likelihood of going overboard with your fast-breaking meals exponentially increases. 

Before you break your fast, choose a meal that is going to be nutrient-dense and satisfying (without tempting you to stuff yourself). Eating to excess is really hard on your digestion, and it will leave you feeling lousy instead of full of energy.

Starting your fast with a binge

Many people go into “last supper mode” before starting a fast. The idea of going without food for an extended period of time brings on a little anxiety, or maybe a “license to cheat” type of feeling. Either way, if you’re getting last supper vibes, reel it in. 

The meal you eat before your fast should be full of nutrient-dense foods that are going to keep your blood sugar stable. For instance, imagine you ate a big bowl of ice cream with some cookies before your fast. Can you imagine how you’re going to feel three hours in? That’s right—sugar roller coaster. You’ll be craving sugar for the first half of your fast, which will only make the whole experience that much more difficult. 

If, on the other hand, you decide to have a salad with some salmon and an olive-oil based dressing, you’ll be satisfied for hours due to the protein and fat content, and you won’t wake up in the middle of the night craving sugar. 

Forgetting to drink water

When you’re avoiding food, it can become easy to avoid water as well. However, thirst can often be confused for hunger, so staying hydrated while you fast is crucial for keeping you on track.

It’s always important to consult with your healthcare practitioner before starting a fasting routine, no matter how healthy you are. With that being said, there are a handful of individuals for whom fasting is not a good idea.

People With History of an Eating Disorder

If you have a history of disordered eating, fasting may not be the best idea for you. For some people, fasting can mimic eating disorder behavior and send you into a spiral of shame.

If you find that you are incredibly hard on yourself when you fall off a program, fasting may be too much for you. Fasting should only serve to benefit you—if it becomes a physical or emotional drain, it’s not working. 

If You’re Pregnant

Pregnant women need as much nutrient density as they can get. While you’re pregnant, this is not the time to fast. As explained earlier, the female body requires consistent nourishment to signal healthy fertility. When meals are sporadic, it may cause hormonal imbalances that could lead to infertility or complications with the pregnancy.

Those With Serious Health Conditions 

This is a case where you must speak with your doctor before starting. Health issues not only create uncertainties in your biology, but many people with health conditions are on medications that won’t work well if you’re fasting. 

With that being said, some metabolic conditions can benefit from fasting, which is why running it by your doctor is always a good idea.  

If You Are Underweight 

If you’re already underweight, fasting may make things worse. Although research shows that fasting can help people drop pounds, this won’t be healthy for underweight individuals. Unless you are under supervision of a nutritionist or doctor that can ensure you’re still getting the calories you need to gain or maintain your weight, fasting should be avoided for this group.

Research shows that intentionally skipping meals on a regular basis can support heart health, metabolic health, weight loss, inflammation, cognitive function, and much more. 

If you’re new to fasting, the best way to begin is with a relatively short 14- or 16-hour fast. These protocols are excellent for training your body and mind to go without food while still allowing you to eat every day. 

Many people stick to this type of intermittent fasting because it works so well for their lifestyle. Others may decide to extend their fasts to 24 or even 36 hours—it just depends on what works for you. 

The key is to always listen to your body and don’t overdo it (especially if you’re a woman).