Pros and Cons of Intermittent Fasting: An Unbiased Guide

Intermittent fasting has become a popular topic in the health and wellness community but no one seems to know for sure if we should or should not be doing it. 

Like any diet pattern, there are pros and cons. 

Below is an unbiased look at intermittent fasting, the differences between types, what the research says, and more.

What is Intermittent Fasting

Intermittent fasting (IF) is a type of eating pattern that involves periods of fasting and periods of eating. 

Although it is normal to go through periods of fasting during the time that we are asleep, IF uses strategic fasting and eating cycles. 

This process can reduce total calorie intake without changing the types of foods you are eating. 

IF is also believed to help balance out hormones and metabolism as we rotate between a fed-fast state. 

During fasting periods you are limited to no foods, only water, and sometimes black coffee or tea and other non-caloric beverages. 

Some forms of IF do allow low-calorie foods during fasting periods while others are more strict to avoid prematurely breaking the fast before the set time. 

Most fasting windows can extend between 12 to up to 40 hours at a time [1].

Different Types of IF

As mentioned above, there are many different forms of IF. 

The differences are usually limited to the eating and fasting ratio each day or each week. 

Some of the most well-known and well-researched IF forms include Time-Restricted Eating, 5/2, Eat Stop Eat, and Alternate-Day fasting [2]. 

Time-Restricted Eating (16:8, 20:4) 

Time-restricted IF involves fasting at a specific time and eating at a specific time. 

For example, 16:8 time-restricted eating is when you fast for 16 hours and then have an 8-hour window for eating.

Let’s say someone may IF from 8 pm to 12 pm and then be able to break their fast and have meals between 12 pm and 8 pm each day. 

Similar to 16:8 fasting, 20:4 involves a 20-hour fasting window and only a 4-hour eating window. It’s a more restrictive form of IF that can severely reduce overall caloric intake throughout the day. 


The 5/2 form of IF is more lenient and involves eating normally for 5 days out of the week and fasting for 2. 

During this fasting time, you are still able to eat however, you are limited to no more than 500-600 calories per day.

Eat Stop Eat 

Eat Stop Eat is a form of fasting that you can do once or twice per week at your discretion. Each fasting day will last 24 hours at a time.

Alternate-Day Fasting

As you might have guessed, alternate-day fasting rotates periods of eating with periods of fasting with a goal to fast every other day.

Which is the Most Effective Type of IF?

The research is mixed on what form of IF is considered the most effective. 

This also depends on what it is considered most effective for. 

For example, some argue that the Eat Stop Eat method is the most effective IF method for weight loss while other research shows more support for Alternate-Day fasting in the form of 16:8 to be more effective for blood sugar management. 

The jury is out regarding the most effective form of IF. Some might argue it is whatever works best for the individual. 

Some people don’t do well limiting their eating time to short periods, such as with the 20:4 Alternate-Day IF method, while others may thrive on this because it benefits their current lifestyle or schedule.

Why Do People Do IF?

The biggest reason many opt for IF is because it is believed to help with weight loss. 

Shortening your periods of eating or going through periods of fasting throughout the week is hypothesized to reduce your overall caloric intake. 

It’s also believed that going through periods of fasting will help our body utilize stored fat for energy instead of keeping it in our fat cells. 

In addition to that, many people have seen research on IF that claims to help with balancing blood sugar levels, boost heart health, improve blood pressure, and more.

Additionally, IF has become somewhat of a fad over the last few decades. 

Many people have started doing IF because a friend or family member told them to or because they saw it on the cover of a magazine. 

Doctors have even been found guilty of specifically recommending IF to their patients as an eating pattern. 

Many consumers aren’t aware of the perceived benefits of IF but have started it because someone told them they should [3].

Is Intermittent Fasting Actually Backed By Research?

There is promising research available on various forms of IF benefiting health; however, most research available has been conducted on mice and human trials are very limited. 

Some of the current research available supports that IF may provide benefits in reducing blood pressure, improving blood sugar, and supporting brain health but further trials are warranted [4, 5, 6, 7].

Are There Risks to Intermittent Fasting?

IF is considered safe for most adults however, there are some things to look out for if you are considering this eating pattern. 

Because many forms of IF consist of going long periods without eating, those who have difficulty with hypoglycemia may want to avoid doing IF. 

This diet can result in low blood sugar episodes that can be dangerous. 

Certain IF methods can also be very restrictive which may trigger or exacerbate certain eating disorder behaviors, such as binge eating. 

Does IF Work for Weight Loss?

When it comes down to it, there are currently no strong studies using human trials that suggest IF is more effective for weight loss than traditional calorie-restrictive diets. 

This is not to say that you cannot lose weight during IF however, it is not considered any more effective than traditional methods [1, 8, 9].

Does IF Help With Gut Health?

There is some research available to suggest that IF may help with gut health. 

It’s hypothesized that periods of fasting may work to improve our gut microbiota however, it’s important to note that studies on this are also limited. 

Further research involving the long-term use of fasting and its effects on our gut microbiome is still needed [10].

Who Should Avoid Intermittent Fasting?

Like most diets, IF is not for everyone. 

Certain people should avoid practicing the IF method, including women who are pregnant, breastfeeding, or planning to become pregnant along with children and those who suffer from diabetes or hypoglycemia. 

You should also avoid IF if you are at a risk for developing an eating disorder or currently struggling with an eating disorder, such as binge-eating disorder (BED). 

Certain IF methods, specifically Time-Restricted eating methods, can increase the likelihood of binge eating in some individuals due to their restrictive nature. 

Some IF methods are not recommended for those who struggle with gastrointestinal conditions. 

Doing Time-Restrictive IF at 20:4 for example can result in gastrointestinal upset due to the heavy caloric load of consuming one or more large meals in a short period. 

On the flip side, other forms of IF have been used to help treat conditions such as Irritable Bowel Disease (IBD). 

Always speak to your doctor or healthcare provider before trying IF to make sure it is safe for you to do so, especially if you are taking any medication for a chronic condition.

Who Should Give Intermittent Fasting a Try?

Anyone healthy adult can do IF but whether or not you should do it depends on what your goals are. IF has the potential to help burn fat and improve metabolism. 

Although the research for this is still underway, someone who finds it easier to restrict the times they eat instead of counting calories throughout the day to create a deficit may find IF beneficial for weight loss.

Is it OK to Take Supplements During IF?

It is ok to take certain supplements during IF as long as they don’t result in an insulin spike which would be considered “breaking” the fast. 

For example, taking certain electrolytes such as potassium and magnesium are ok, however, a gummy multivitamin sweetened with sugar is likely to cause an insulin spike and should be avoided during periods of fasting. 

What is the Best Way to Break a Fast?

If you are doing IF, you might want to consider how you plan to break a fast. Choosing a high-quality first meal can help to set you up for greater success. 

Although the goal of most IF methods is to help to create a caloric deficit, we must be still getting adequate nutrients throughout the day to avoid deficiencies and potential losses in muscle mass. 

A great way to boost our nutrient intake without filling up too quickly is to include a shake or smoothie immediately following our fast

Below is a collagen smoothie recipe that provides a variety of essential vitamins, minerals, and protein to help make sure you meet your needs during your eating window. 

Avocado Kale Collagen Smoothie Recipe

Serves 2


  • 1 scoop collagen peptides 
  • ½ of a medium frozen avocado 
  • 1 large handful of fresh kale
  • ½ cup frozen pineapple
  • ½ cup frozen strawberries
  • ½ - ¾ cup coconut water 


Combine ingredients in a large blender or food processor and blend until smooth. Add more or less liquid to reach desired consistency.