Is Fasting Good For You? The Pros & Cons - Old School Labs
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Home » OSL Blog » Is Fasting Good For You? The Pros & Cons

Is Fasting Good For You? The Pros & Cons

January 11, 2020

Key Takeaways

  1. Fasting methods have been around for centuries, especially water fasting.
  2. There are documented studies that show both mental and physical benefits to water and intermittent fasting.
  3. People with certain health conditions may not be suitable for fasting.
  4. Always consult your doctor before trying any fasting method, to make sure it’s right for you.

Obesity rates in American continue to climb year over year. As of the most recent data compiled from 2018, 48 states have a minimum of 25% of adults who are obese. This means they have a BMI of 30 or more. 

Let’s put that into perspective: just 2 states and the District of Columbia have obesity rates lower than 25 percent. What’s worse, the lowest number doesn’t go below 20 percent:

  • Hawaii – 24.9%
  • Colorado – 24.7%
  • D.C. – 23.0%

This data, collected by the Behavioral Risk Factor Surveillance System (BRFSS) of the CDC, shows upward trends in obesity. Every single state, including the District, have increased obesity rates almost continually. Only Alaska showed a decrease from 2017 to 2018.

Obesity and Fasting

Regardless of the reason for these numbers, many try and are unsuccessful at losing weight. Some people may feel they have tried everything, with little to no results. Many have turned to fasting as an option for weight loss, with the most popular currently being intermittent fasting.

Though it’s popular now for weight loss, fasting has been done for religious reasons for centuries and has documented health benefits. Water fasting and intermittent fasting both have physical and mental benefits, but isn’t for everyone.

Today, we’re going to try to determine if fasting is good for you. We’ll discuss:

  • The benefits, both physical and mental
  • The types of fasting methods
  • How to safely break a fast
  • Why some think fasting is bad or shouldn’t be recommended

The Physical Benefits of Fasting

One of the main physical benefits of fasting is weight loss. However, there are other benefits to the body that make fasting a method to heal body systems.

Doctors advising Fasting

Some studies indicate that the following health ailments have been helped by different fasting methods:

  • Improves liver function
  • Decreases the effect of chemotherapy
  • Asthma
  • Rheumatoid arthritis
  • Improve gut microbiota
  • Coronary artery disease

This study specifically highlights intermittent fasting as a way to “flip the metabolic switch” in the body. As the body switches from using food as energy to using the body’s own ketones, it also improves physiological function.

This is one reason that IF is so popular for weight loss – it allows for fat burning while retaining muscle mass. While the premise is similar to the keto diet, people who use intermittent fasting tend to eat differently.

The focus of fasting is to eat highly nutritious foods like fruits and vegetables, avoiding fats and oils. The body stores the food as fuel and then does a “clean burn” during the fasting period of the food ingested.

The Mental Health Benefits of Fasting

While the physical benefits of fasting are enough for many, there are also some impressive mental benefits.

Fasting and Mediation

Fasting is a method used by some in meditation, and it also has many medical applications. The metabolic switch reset discussed previously is just as much a mental benefit as it is a physical one.

Some mental benefits to note:

Types of Fasting

There is not just one way to fast, regardless of the reason for doing so.

Fasting means that you will abstain from food, and sometimes drinks for a set time period. This is usually anywhere from 24 – 72 hours, though the fasting period can last longer than that.

Here, we’ll discuss several different types of fasting and how they are performed.

Water Fasting

This fasting method is one that has been studied for years with close clinical observation. Using this method, a person would only drink water for a certain time, then reintroduce food slowly once completed.

This meta-analysis reviewed over 700 medical charts during a five year period (2006 – 2011). All patients participated in water fasting, some as short as two days, some as many as 40 days. The average amount of time was seven days.

Water Fasting

Quality of life, prevention, and fatigue were the most common reasons patients entered the facility. Others came for treatment to fix a wide array of health issues in their systems:

  • Cardiovascular
  • Musculoskeletal
  • Gastrointestinal
  • Endocrine

Most had mild to moderate effects early on and noted benefits and improved wellness from water fasting. Only two elderly patients had severe effects from dehydration. They were treated with IV electrolytes and fully recovered.

Water-only fasting has had therapeutic applications for years and has been popular for some time in Europe. In Germany, the Buchinger Willhelm clinic has a long history with fasting, dating back to the early 1900s. 

A study released in early 2019 from the clinic showed many positive benefits in the over 1,400 patients studied:

  • Ketones permanently present in urine throughout the fast
  • Lower cholesterol and lipid levels
  • Significant weight loss
  • Improved blood pressure
  • Lower blood sugar levels, improved diabetes
  • Fatty liver improvement
  • Improved mental wellbeing

Almost all of the patients saw substantial improvements, both mentally and physically. Studies like these show the benefits of water fasting with close monitoring by experienced professionals.

Intermittent Fasting

This type of fasting is done using time on/time off method, most often 16:8. This means that the person fasting will only eat within an eight-hour window, and drink only during the remaining hours.

Intermittent Fasting

The number of hours is defined, but the actual hours in a 24-hour window are up to the individual and can change.

Spontaneous meal skipping is another intermittent fasting method. This is an intuitive method where you skip a meal if you aren’t hungry and eat again when you are.

Most fasting methods that are widely used today are different variations of intermittent fasting. This is where you cycle between eating and fasting periods, either on the same day or over the course of a week.

Intermittent fasting is a popular method because it’s easier to follow and has impressive results for some. Check out our article all about intermittent fasting to learn more.

One Meal a Day (OMAD)

During this fasting method, as the name suggests, one meal a day is consumed. This means that for 23 hours per day, a person would not consume any food, eating only during a 1-hour window.

OMAD Fasting

Most will choose to eat during the evening, a few hours prior to sleep, while others prefer eating breakfast. 

4:3 Diet

This method of fasting is also called alternate day fasting. Bodybuilders and other people dedicated to their fitness schedule may find this fasting method attractive.

4:3 Diet Fasting

Rather than have a specific time frame or window for eating, you would fast every other day. During the fasting days, some calories can be consumed but should be limited to no more than 500 calories.

There are no restrictions on eating days and water should be increased on fasting days. Though there aren’t restrictions, clean and healthy eating should be observed for the best results.

The Warrior Diet

This diet is similar to the OMAD fasting method, though it has a larger window for eating. Eliminate or greatly reduce calories for 20 hours per day and eat during a four-hour window.

Warrior Diet

Emphasis is placed on high-nutrient foods, focusing on fruits and vegetables. To get the most benefit out of the diet, overeating is not recommended during the “feeding” window. 

We will be doing an in-depth review of the warrior diet soon, so stay tuned for that! We’ll tell you all about the origins of the diet, what you can and can’t eat, and why it might be right for you.

5:2 Diet

This is similar to the 4:3 diet, but instead, you would eat five days a week and then fast for two. There is more flexibility here, allowing you to choose if the two fasting days are consecutive or not.

You can choose to fast completely or limit to no more than 500 calories on those days. If calories are consumed on fasting days, you can work out, though nothing high-intensity. 

Religious Fasts

Many people around the world choose to fast to honor their respective religious convictions. Some religions only have a day of fasting while others have a month or more.

For example, the month of Ramadan brings a fast from dawn until sunset. Lent is also a popular time to fast, spanning 40 days. Others may have a day of fasting, while some religions offer suggestions and leave it up to their followers to choose.

religious fasting

Most religions allow exceptions for health issues, including:

  • Diabetes
  • Pregnancy/breastfeeding
  • Heart conditions

Fasting is also popular as part of meditation practices to allow better dissociation with oneself. It has also been used over the years as part of protests. Mahatma Gandhi was one who used this method of protest, among others.

How to Break a Fast Safely

When ready to break your fast, you may want to binge eat and get right back into eating the foods you love.

However, there is a general process to follow to ease your body back into eating. These tips are most often used when ending water fast but can be used with other methods.

Checking fasting results

 If you don’t refeed properly, you could:

  • Gain back the weight you lost, and potentially even more
  • Recreate health issues that were resolved from fasting
  • Create new health concerns
  • Potentially create dangerous eating habits or develop an eating disorder

Here are some general rules to follow at the end of your fast:

  1. Expect the refeeding process to last for at least half the time you fasted (fasting for 20 days means refeeding for 10 days)
  2. Start off with just drinking liquids, this can include:
    1. Water
    2. Juices (best from raw fruits and vegetables)
    3. Liquid supplements
  3. Gradually reintroduce solid foods while avoiding sugars, oils, and additional salt
  4. Once eating solid foods, gradually reintroduce light, then moderate, exercise

The amount of time each step will take will depend on the length of the refeeding process. 

The benefits to your wellbeing, both physical and mental, can be seen even after fasting for a day. While some may have temporary side effects, overall fasting can help regulate the body’s systems so they reset and work correctly.

Is Fasting Bad for You?

While there do seem to be a lot of benefits to fasting, it isn’t recommended for everyone. In fact, there are certain groups of people who have higher risks of adverse effects if they participate in fasting.

Even those who are in good health can have negative effects when fasting if not careful. Dehydration can happen if you don’t get enough water intake. Some also believe that fasting doesn’t have any further benefits than other methods to lose weight.

In the early days, the most common negative effects are tiredness and fatigue. Some also deal with mood swings, irritability, and even anxiety when fasting. Though most negative effects are not long-term and usually resolve in a few days, it’s not for everyone.


Anyone who has diabetes, whether type 1 or 2, should proceed with extreme caution before considering fasting. There can be serious health implications, from seizures to a coma and even death if you aren’t careful.

Diabetics and Fasting

If you are thinking about fasting for other health reasons, consider the precautions you’ll have to take:

  • Checking your blood sugar more often
  • Recognizing the symptoms of low or high blood sugar, and keeping glucose tablets/gels or injections with you at all times
    • Hypoglycemia (low blood sugar) – when your blood sugar drops below 70 mg/dl
    • Hyperglycemia (high blood sugar) – when your blood sugar goes above 300 mg/dl
  • Always wearing a medical alert bracelet identifying you as a diabetic, in case you become unconscious
  • Provide easy access and always carry your doctor’s information so it’s available to anyone who may need it

Fasting prior to a medical procedure prescribed by a doctor is generally considered safe, as long as they know you’re diabetic.

Resting at gym

You should bring food to eat as soon as your procedure is done. Also, be sure to follow the instructions provided by your doctor completely to maintain your health.

Always speak with your doctor before trying any method of fasting. If they approve, stop immediately if you go above or below the threshold listed above. The inability to maintain safe blood sugar levels could mean that fasting isn’t right for you.

Women who are Pregnant or Breastfeeding

Much like diabetics, fasting for religious reasons typically exempts pregnant and breastfeeding women. They understand the health of the mother and baby are more important than observing a religious fast.

Ultimately, the risks of fasting during pregnancy are different depending on the individual. The trimester you are in and any medications also change the risk factors.

If you are in general good health and so is the baby, there may be no negative health effects.

Fasting can greatly reduce the number of nutrients taken in by the breastfeeding mother.

This can cause reduced nutrients in the breast milk and could also affect the lactation supply. While it may not show any immediate ill effects, fasting during breastfeeding is generally not recommended.

Children and Teens

Fasting for children and teens is typically done for religious purposes. These age groups are going through spurts of rapid growth, so fasting is usually not recommended.

If weight is an issue, it can often be resolved with better eating habits and more exercise. 

Yoga mat exercises

Some children and young adults will go on a hunger strike at some period. While this can be frustrating and possibly alarming, they shouldn’t be forced to eat.

This also goes for times where they say they aren’t hungry. Children are in tune with the hunger center of their brain, and only eat when they are hungry. They may unintentionally go through periods of IF but most grow out of it.

Teens and pre-teens may see reduced sleep patterns but also could see improvement in memory and spatial planning when fasting.

People with a History of Eating Disorders

Risk factors are much higher in people with a history of eating disorders. The amount of risk can change depending on the type of disorder and the thought process behind it.

Anorexia nervosa is the eating disorder most commonly associated with fasting and starvation as a form of control. Even if you have never had an eating disorder before, fasting can be a slippery slope.

Eating Disorder and Fasting

Fasting may actually create an eating disorder where there wasn’t an issue before.

If you choose to fast, especially with a mental health condition, really consider the reason behind your choice. Consider another option, if one is available, to meet your goal instead of in a safer manner.

Working with your doctor and mental health professional is the only way to know if fasting is a risk. When determining a treatment plan for dealing with an eating disorder, psychologists are urged to consider the reason for fasting.

People Taking Certain Medications

Fasting may not be an option for people who take certain medications. Depending on the method of fasting, or reason for doing so, you can only take medication at certain times. 

During Ramadan, for example, eating and drinking are prohibited between dawn and sunset. This can put an additional burden on people taking medications, especially for:

  • High blood pressure (hypertension)
  • Heart disease or other heart-related issues
  • Migraines
  • Diabetes 

If medications can’t be safely adjusted to comply with fasting, then it is generally not safe to fast. It’s best to work with your doctor to determine if fasting is an option based on your medical needs.

Consult your doctor

If you do choose to try out fasting to see if it’s a good choice for you, always consult your doctor first.

Let them know:

  • What type of fasting you are thinking of following
  • Why you think fasting is right for you
  • The benefits you hope to gain from fasting
  • Any concerns you might have for physical, mental, and/or medication interactions

You want to make sure you aren’t jeopardizing your health or potentially creating a greater risk of serious health concerns.  

Final Thoughts on Fasting

Fasting seems to have a lot of benefits, including weight loss, which can be enticing for a lot of people. As more studies are done on humans, we are seeing some of the same benefits only shown in animal testing previously.

Fasting is a difficult process to do on your own without close interaction with medical professionals.

Fasting difficulties

Many people start out with good intentions, only to give in and go back to old habits, or binge eat. It takes a strong will and a lot of support from those around you to successfully fast for any length of time.

If you are interested in any of the fasting methods, make sure to consult your doctor first. Be aware of the risks, look out for any adverse events, and get treatment immediately if needed.

Water fasting is not for everyone and should be approached only after research and doctor approval. Intermittent fasting is usually easier to tolerate. Water fasting should never be combined with heavy workouts, as the risks are just too high.

Have you tried fasting before? Which method did you try and did you see successful results? Would you try it again in the future? Let us know your thoughts in the comments section below.

Disclaimer: None of the individuals and/or companies mentioned necessarily endorse Old School Labs or COSIDLA Inc. products or the contents of this article. Any programs provided for illustration purposes only. Always consult with your personal trainer, nutritionist and physician before changing or starting any new exercise, nutrition, or supplementation program.
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