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Intermittent Fasting Diet Explained

Intermittent Fasting Diet Explained
Dr. Constance Odom, MD Picture of Dr. Constance Odom, MD

Medically reviewed by

Written by our editorial team.

Last Edited 6 min read

The term intermittent fasting has surfaced frequently over the past decade when discussing weight loss. While fasting has long been a familiar concept, intermittent fasting takes a different approach. Although there are many different methods one can take to pursue intermittent fasting, all of them show promising results in decreasing belly fat and overall weight. 

What is Intermittent Fasting?

Intermittent fasting simply refers to a pattern of eating. Unlike traditional fasting where zero calories are consumed for days or even weeks, intermittent fasting alternates between periods of eating and not eating. While most diets focus on the foods that are eaten, this approach is all about the timing instead of the foods. For instance, some may choose to fast for an entire day and then eat the next. Others may opt to eat for a short period of time each day and fast for the remainder. In either scenario, people who use the method swear by this approach for achieving and maintaining an ideal, healthy weight.

Intermittent Fasting Methods

Intermittent fasting simply refers to restricted eating schedules. Within this group, there are subcategories of fasting methods that those who participate in the practice use. The chosen method is a matter of preference and many who are just getting started experiment with a variety of them before deciding which works best for their preferences and lifestyle. The most popular fasting methods include:

  • The 16/8 Method: This approach to intermittent fasting is one of the most popular methods. Although this specifically focuses on fasting for 16 hours per day and eating during 8, it can be altered in any number of ways. Some people chose to fast for 12 hours and eat for 12 or any combination of eating/fasting hours throughout the day. 

  • Alternate Days: Throughout the week, the participant alternates between eating and not eating for 24 hours. For example, they will eat whenever they’d like on Monday, fast all day on Tuesday and then eat again on Wednesday. 

  • The 5:2 Approach: The 5/2 method of intermittent fasting is more drastic than the alternate days or 16/8 approaches. With this schedule, a person eats their typical diet for 5 days of the week and then restricts their caloric intake to around 500 calories for the remaining 2 days. A lot of people use this approach and eat what they want throughout the week but then restrict their intake on the weekends. 

  • Eat Stop Eat: Eat, stop, eat is similar to alternate day fasting; however, it involves fewer fasting days. Here, people typically eat as normal for most days of the week but opt for a fasting period of 24 hours once or twice each week. The amount of fasting days that you choose to include is a personal decision but each day of fasting should be surrounded by a day of eating before and after to follow this approach.

  • The Warrior Diet: Another popular intermittent fasting approach is known as the warrior diet. It avoids total fasting days and instead focuses on a very limited food intake for 20 hours each day. During these 20 hours, very small amounts of fruit, vegetables or nuts can be consumed. The remaining 4 hours of the day; however, followers can eat as much as they wish and there are no restrictions on the types of foods that can be eaten during this timeframe. Essentially, it is a mixture of under-eating throughout the day followed by a small window of overeating at night. 

What Foods Should Be Avoided While Intermittent Fasting?

Because intermittent fasting is a scheduled eating pattern, there are no specific foods that must be avoided. Some people enjoy this portion because they find it difficult to stick to specific diets like low-carb, keto or high protein. You can eat whichever foods that you prefer, but keep in mind that a healthy diet is still recommended. If you eat fried or fatty foods during eating times, fasting for several hours afterwards may not make much of a difference in terms of your weight. Likewise, this type of diet is detrimental to your overall health. Instead, it is recommended that those who are fasting follow a healthy, well-balanced diet that contains proteins, vegetables, and fruits. They can also indulge in a sweet treat or guilty pleasure from time to time, so long as their other nutritional needs are being met and they are not over-indulging in unhealthy treats.

Likewise, many people who are struggling with obesity also have weight-related health issues. In these cases, participants should exercise caution and follow any dietary restrictions that have been recommended by their health care providers. 

Can You Drink Water During Fasting Times?

Staying hydrated is essential and decreasing fluid intake is never recommended for anyone. Those who fail to stay adequately hydrated can experience a number of problems like dehydration, headaches, dry mouth, muscle cramps, fatigue, constipation and others. In extreme cases, a lack of hydration can lead to hospitalization and serious illness. 

The average adult should drink between 8-13 cups of water each day, depending on their weight and level of physical activity. When following intermittent fasting, you should continue to drink this amount of water whether you are fasting or not fasting during that time period. During fasting times, you are also permitted to drink other beverages that do not contain calories such as black coffee and hot teas without sweeteners. Consuming an adequate amount of water during fasting periods can also help to alleviate hunger pangs and make your stomach feel fuller for longer in between meals. 

Is It Hard to Maintain Over Time?

The more extreme the diet or restrictions are, the more difficult it becomes to maintain these standards over time. Those who commit to methods like alternate day fasting, the warrior diet or eat stop eat are less likely to follow the restricted pattern for a long period of time than those who take a more realistic approach to intermittent fasting, like with the 16/8 method. This is because it seems fairly restrictive but is typically easier to maintain because many of the fasting hours are overnight while sleeping. It still enables participants to eat everyday; however, it can be helpful in avoiding late night snacking or overindulgences.

Despite this, it is important to note that everyone is different. In some cases, people may find it easier to maintain other approaches based on their personal schedules or lifestyles. If you are able to experiment with intermittent fasting, it is best to try out several different patterns at first to see which one is easiest to maintain. If you struggle to maintain fasting times during intermittent fasting, keep in mind that the biggest component of this approach is that calories are restricted. You can also experiment with other diets that are less restrictive in terms of time but allow you to consume the same amount of calories each day. 

Who Should Avoid Intermittent Fasting?

For most individuals, intermittent fasting is a safe and effective way to lose weight and maintain it over time. Despite this, some people should not use this approach to lose weight as it may be dangerous. People who should avoid intermittent fasting, include:

  • Women who are pregnant or breastfeeding as intermittent fasting may affect the growing fetus or the nutrients found within the breast milk.

  • Those who have been diagnosed with certain health conditions, like Type 1 or Type 2 Diabetes.

  • Infants and children under the age of 18.

  • Anyone with a history of eating disorders.

  • Those who take medications on a regular basis to treat a myriad of health conditions.

  • Elderly or immunocompromised individuals.

  • Those who are underweight or malnourished.

  • People with certain mental health conditions, like dementia.

This list is not conclusive and anyone with pre-existing health conditions should discuss their desire to partake in intermittent fasting with their health care provider before beginning to ensure that it will not negatively impact their health. If severe side effects occur while participating in intermittent fasting, discontinue the fasting regime until you are able to speak with a doctor and determine if it is safe to continue. 

Is Intermittent Fasting Effective?

Those who have practiced intermittent fasting for any period of time report promising weight loss results. The amount of weight that a person can expect to lose while fasting varies greatly, depending on their chosen method of fasting as well as the type of food that they eat during eating periods. An individual who also incorporates healthy foods like lean meats and salads will likely experience better results than one who chooses to consume pizza or fried foods during eating periods. Additionally, their level of physical activity should be considered. To get the most effective results from intermittent fasting (like any diet), regular exercise and a healthy diet is recommended.

A review of intermittent fasting studies conducted by Harvard University revealed that the average weight loss for all individuals following the eating pattern was between 7-11 pounds over the course of 10 weeks. Despite this, when results were reviewed after a period of one year, most participants reported a total weight loss of 14-18 pounds. 

Are There Any Side Effects?

Whenever a person’s eating habits or overall diet are significantly altered, there can be side effects. When it comes to intermittent fasting, there can be certain side effects which are most prevalent during fasting periods. Some of these side effects, include:

  • Headache

  • Lightheadedness

  • Hunger

  • Stomach Pains

  • Fatigue

  • Irritability

  • Changes in Mood

  • Low Energy Levels

  • Bad Breath

  • Dehydration

  • Malnourishment (when taken to extremes)

While there can be unwanted side effects with intermittent fasting, some of these symptoms only last for a few days after starting. For instance, a study that took place in 2020 showed that hunger and cravings only lasted among fasting participants during the initial days of fasting periods between 4-21 days in length. While these side effects are unpleasant initially, not all of the effects are negative. According to research, intermittent fasting provides a number of health benefits. While weight loss is one of them, it can also improve metabolic health, gut microbiome health and the circadian rhythm which affects sleep patterns. 

Is Intermittent Fasting Right For Me?

Each person has a unique lifestyle, health concerns and preferences. There are a multitude of ways that can be used to lose weight and keep it off effectively. Many experience success with intermittent fasting, but it may not be right for everyone. If you have health concerns, take certain medications or have a history of eating disorders, you should consider other methods for weight loss. If you try intermittent fasting and discover that it isn’t right for you, look into methods that are easier to incorporate into your lifestyle, such as eliminating sweets and breads. 

It can also be helpful to experiment with all of the different methods of intermittent fasting before making a final determination in whether or not it is right for you.


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This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your physician about the risks and benefits of any treatment. Nu Image Medical may not offer the medications or services mentioned in this article.