Is Fasting for You? Upsides and Downsides to Keep in Mind

Article at a Glance:

Fasting has a lot of physical and mental benefits, but that doesn’t mean it’s the right choice for everyone.
Fasting has potential downsides like the loss of nutrients, the discomfort of hunger, the potential for dehydration, and the possibility of slowing your metabolism.
When planned well, however, fasting can help you lose weight, improve insulin sensitivity, reduce inflammation, enhance heart health, support brain health, and slow cellular aging.
There are a variety of approaches you can take to fasting, including the 5:2 diet, the 16/8 fast, a 24-hour fast, and juice fasting, among other options.
Choosing the right approach for your goals and lifestyle is the best way to reap the benefits of fasting without experiencing many (if any) downsides.

Many of us hear the word “fast” and immediately bolt for the fridge to inhale the leftover take-out, expired milk, and anything else even remotely edible. We hear “fast” and we think “hunger.” And who wants to feel hungry? We eat three meals per day and carry snacks around with us everywhere to avoid feeling hungry because hunger is uncomfortable. When taken to the extreme, hunger even threatens our survival. Why then have so many people throughout the centuries subjected themselves to self-inflicted hunger by fasting?

There are a lot of reasons. Some people fast as a spiritual practice that delays physical gratification and provides spiritual insight. In spiritual fasts, people may even abstain from food and water, making the fast even more challenging. Other people fast because of the mental benefits. It makes their minds sharper and helps them function at their peak. And if you’ve been following the latest scientific research on fasting, you know that fasting offers some pretty impressive physical benefits too, like more balanced blood sugar, reduced inflammation, and even slower cellular aging.

So there are some very solid reasons to embrace hunger, at least temporarily, no matter how uncomfortable it feels. But if you’re new to this whole fasting thing, you should know that just because fasting can have benefits doesn’t mean everyone should do it. The fasting lifestyle is better suited to some people than others, and it’s important to understand the upsides and downsides of fasting before you make it a part of your life.

Summary: Fasting is the deliberate abstinence of food and/or drink as a means to help an individual achieve a specific physical, mental, or spiritual goal, but it may not be for everyone.

Reasons Not to Fast

It’s important to talk to your doctor before diving headfirst into fasting (especially if you have any health issues) because fasting affects everyone differently. It’s also important to carefully consider what type of fasting is best for your lifestyle and to be aware of the downsides of fasting. Here are a few of the downsides of fasting to consider before starting a fast.

Potential Dangers of Fasting

For many people, it’s safe to fast for a few days. In fact, the body can go quite a while without food as long as it stays hydrated. Some research shows that people on hunger strikes can go between 21 and 40 days without food before they begin to experience life-threatening symptoms. Still, there’s no denying that going without food for long periods is stressful on your body.

Your body not only needs calories for energy, it needs the minerals and vitamins you get in your diet to keep your organs and tissues functioning the way they’re supposed to. Denying your body vital nutrients for too long can lead to dangerous nutrient deficiencies that impact critical processes in your body.

Fasting for up to three days is safe for most people because it gives your body enough time to experience the benefits of fasting without depleting your nutrient reserves too severely.

The Discomfort of Fasting

Severe hunger is the most common side effect of prolonged fasting. Big surprise, right? Hunger is uncomfortable enough on its own, but it’s even worse when you throw dehydration into the mix, which can lead to dizziness, headaches, sluggishness, and a bunch of other not-so-fun symptoms.

Even people who aren’t abstaining from water during their fast are more likely to become dehydrated because they’re not getting hydration from food (most of us get about 20 percent of our hydration from the food we eat). You also lose something called glycogen when you fast. Glycogen is a stored form of glucose that’s bound to about three or four grams of water. So as your glycogen levels drop, your hydration levels do too.

Some people give up food and water for spiritual fasts, but if you’re fasting for health purposes, we recommend just abstaining from food and keeping yourself well hydrated throughout the process. That will make the experience much safer and less uncomfortable.

Slows the Metabolism

Though it’s possible to lose weight through fasting since you’re reducing the number of calories you’re taking in, it may not be the best approach. That’s because eating less or not at all for a long period can actually slow your metabolism. When the body isn’t receiving any new energy, it kicks into starvation mode and dials down the metabolism to hold onto whatever energy remains.

In fact, fasting frequently and/or for long periods can even slow down your metabolism beyond just when you’re fasting. That means when you start eating normally again, your body could be burning calories slower than it did before. A slow metabolism will make it difficult to lose weight and may even contribute to weight gain.

All that said, it is possible to lose weight from a fasting lifestyle. Some people do it very successfully. But it’s a tricky business. You need to take the right fasting approach to promote weight loss rather than weight gain (read more on that below).

People Who Shouldn’t Fast

There are certain groups of people who should avoid fasting altogether. Pregnant and nursing women shouldn’t practice fasting, since they need all the nutrients and nourishment possible to help their baby develop properly and keep themselves healthy. People with a history of eating disorders should also avoid fasting since it could trigger unhealthy eating patterns and mindsets.

Summary: Fasting, especially for longer periods, can take a toll on your body’s nutrient supply, trigger uncomfortable symptoms due to hunger or dehydration, and slow your metabolism. Each person is different and should consider all the physical, mental, and emotional aspects of their life before starting a fasting lifestyle.

Benefits of Fasting

After reading about all those downsides, you might be thinking: forget fasting! But the truth is, a properly planned fast can have serious benefits that have a great impact on your health and life. Here are a few of the best fasting benefits.

Weight Loss

Yes, we just told you not to rely on fasting for weight loss. However, you can lose weight through fasting if you take the right approach. Intermittent fasting, for example, is proven to help you shed pounds.

Intermittent fasting is the process of cycling between short periods of fasting and eating every day. That means you’re never going too long without eating and are less likely to slow down your metabolism. In fact, this pattern of eating can actually help boost the metabolism.

In a 16/8 intermittent fast, you fast for 16 hours per day and eat for eight hours. Going 16-18 hours in a 24 hour period without eating can reduce calorie intake and increase metabolic function if you practice it consistently. So give that a try if weight loss is your goal.

Promotes Increased Insulin Sensitivity

Fasting can increase your body’s sensitivity to insulin, which can help it regulate blood sugar levels better. Increased insulin sensitivity makes the transport of glucose from the body’s bloodstream to the body’s cells more efficient. This is good news for people at risk for diabetes because it means that periodic fasting is probably an effective diabetes prevention tactic.

Fights Inflammation

Another benefit of fasting is that it can help decrease inflammation levels.

Inflammation is a natural byproduct of a healthy immune system. When you have an injury or infection, your body sends out immune cells to repair damaged tissue and fight off pathogens, but they trigger inflammation in the process. Short-term inflammation is fine, but if the inflammation goes on for too long or occurs unnecessarily, it can cause disease.

In fact, chronic inflammation has been linked to serious conditions, like cancer, heart disease, and autoimmune diseases like rheumatoid arthritis and Crohn’s disease. Even musculoskeletal disorders have been linked to inflammation. So you can thank inflammation for that annoying back pain you’re feeling.

Diet plays a big part in inflammation. Avoiding highly processed and sugary foods can help reduce inflammation. Fasting can also lower levels of inflammation. In fact, recent research shows that fasting can reduce the amount of pro-inflammatory cells circulating in the blood without impairing the body’s ability to respond to infections when necessary.

Lowers Risk of Heart Disease

Heart disease is the leading cause of death pretty much everywhere in the world. Luckily, there are a lot of lifestyle changes that can reduce your risk, including fasting.

Research shows lifestyle changes, like exercising regularly, not smoking, and eating a well-balanced diet are the best ways to reduce the risk of heart disease. But the occasional fast could help you maintain a happy and healthy heart too.

In certain studies, occasional, alternate-day fasting lowered levels of LDL or “bad” cholesterol and blood triglycerides, which are both risk factors for heart disease. Fasting is also linked to a lower risk of coronary artery disease and diabetes, and those conditions are both major risks for developing heart disease too.

Brain Boost

Thought we were done talking about inflammation? Not quite. Inflammation occurs everywhere in the body, and the brain is no exception. In fact, chronic neuroinflammation is often found in people with Alzheimer's disease and depression.

As we already mentioned, fasting helps reduce inflammation in the body, but research shows it reduces neuroinflammation too, which means it could help protect against neurodegenerative diseases.

Studies also show that intermittent fasting improves overall brain function and slows cognitive decline in mice. We suspect it does the same for humans based on anecdotal reports from fasters, but there aren’t enough scientific studies in humans yet to know for sure.

Slow Cell Aging

Some studies show that a 48-hour fast can improve cellular repair by promoting a process called autophagy. Autophagy cleans out old or damaged cells and makes room for healthy new cells. By promoting more effective cellular repair, autophagy may help to prevent age-related diseases such as cancer and Alzheimer’s.

Summary: Weight loss, increased insulin sensitivity, reduced inflammation, lower risk of heart disease, increased cognitive function, and slower cellular aging are just a few of the benefits of fasting.

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Different Methods of Fasting

If you’re ready to give fasting a try, the first step is to figure out what type of fasting is right for you. There are a lot of options to choose from, some more restrictive than others. Do your best to choose a method that works for your goals and lifestyle.

Here are a few fasting methods to consider. Keep in mind that there are many more ways to incorporate fasting into your life. These are just some examples.

5:2 Diet

The 5:2 diet is a form of intermittent fasting that’s gained popularity in recent years. The diet involves eating normally five days a week, then significantly restricting calories two days per week.

This could mean that a person who regularly eats 2,000 calories a day would limit calories to about 500 hundred for two days per week.

The two fasting days don’t need to be consecutive. In fact, the best way to practice the 5:2 diet would be to space the fasting days between normal eating days, so you don’t disrupt the body’s energy supply and slow your metabolism.

This isn’t a fast in the truest sense of the word, since it just involves restricting calories and not totally abstaining from food. But it’s still been shown to have a lot of benefits.

16/8 Fast

In a 16/8 fast, you fast for between 14 and 16 hours per day and eat normally for 8 to 10 hours per day.

This method is one of the most popular types of intermittent fasting because it’s a very simple way to fit fasting into your lifestyle but still has a lot of benefits, including weight loss.

24-Hour Fast

A 24-hour fast is just what it sounds like— not consuming any food for 24-hours. This can be done weekly or done spontaneously as a simple detox.

Juice Fast

Juice fasting (also known as juice cleansing) involves only drinking fruit or vegetable juice, typically for up to 72-hours.

There are several different ways to approach a juice fast. You can choose to drink just vegetable juice, just fruit juice, or a combination of both.

The idea behind a juice fast is that it allows the body to absorb the vitamins, minerals, and phytonutrients from fruits and vegetables more easily and quickly. When juice is extracted, the natural fiber from fruits and vegetables is lost. This gives the digestive system a little break and allows it to absorb the remaining nutrients more easily.

Alternate Day Fasting

Alternate day fasting is a form of fasting where you fast every other day. An example would be eating Monday, fasting Tuesday, eating Wednesday, fasting Thursday, and so on.

You can approach this type of fasting in two different ways. You can completely abstain from food on fast days or limit calories to about 500 on fast days.

Alternate day fasting is a more extreme approach to fasting and is difficult for a lot of people to maintain. But people who practice it often experience a wide range of benefits, including weight loss and better heart health.

Summary: There are a number of ways you can tailor fasting to your goals, health, and lifestyle. Choose the method that works best for you.

Exercise and Fasting

The body requires calories for energy and energy for exercise. So when you’re not taking in any calories during a fast, there’s obviously less energy available for exercise. But that doesn’t mean you can’t exercise during your fast. It all depends on the type of fast you’re doing and the intensity of the exercise.

Intermittent fasting, for example, pairs perfectly with exercise because you’re only fasting for short periods and still taking in enough calories to keep up with a vigorous workout routine. But if you’re doing one of the more intense types of fasting, approach exercise with care and caution.

In a fasted state, your body’s glycogen (the carbs stored in your tissues) is most likely depleted. This makes it possible for your body to burn fat instead of carbs when exercising, which would be good. However, it’s also possible that instead of burning carbs, your body may turn toward another form of energy to fuel your workout— protein. Your body could potentially break down muscle to use protein, which would be bad.

That’s why, if you choose to do a long fast of any kind, you should probably avoid vigorous exercise. Stick to light forms of exercise like walking and always listen to your body if it’s telling you to rest.

If you’re trying to implement a healthy, long-term lifestyle, then some form of intermittent fasting could be a good choice for you. This will allow you to reap the benefits of fasting while continuing to make exercise a daily part of your life.

Breaking a Fast

When it’s finally time to end a fast, start by eating easily digestible foods. If you eat something too heavy right away, your stomach might not be happy with you. It’s been off digestion duty for a while and needs time to get back into the swing of things. Soft fruits such as avocado and berries or steamed vegetables are good options to help ease your body back into your usual diet. Many people also enjoy breaking their fast with bone broth, lean meats, or fish.

Fast With a Purpose

Overall, fasting is a healthy practice that can be done safely, as long as you fast with a purpose and with education. Choose a style of fasting that fits your goals and lifestyle and talk to a trusted healthcare professional if you have any questions. If you approach fasting with care and attention, you can safely enjoy all the mental and physical benefits without experiencing many (or any) of the downsides.