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Quick Start Guide to 18:6 Fasting

author avatar Dr. Eric Berg 05/02/2024

Intermittent fasting has profound health benefits, and a growing body of research supports its effectiveness in improving metabolic health, boosting weight loss, and promoting longevity.

Here’s a complete guide to 18:6 fasting to get you started and practical tips and tricks to transition smoothly into extended fasting periods.  

Intermittent fasting concept

What is 18:6 fasting?

An 18:6 fast involves alternating between an 18-hour fasting period and a six-hour eating window. 

Because of its simplicity, 18:6 fasting is one of the most popular intermittent fasting schedules that has helped many individuals lose weight, improve their metabolic balance, and enhance their overall health.

During fasting periods, the body is forced to utilize stored body fat instead of blood glucose to generate energy. This metabolic switch from using sugar as a fuel source to burning fat triggers ketosis.

Ketosis is a metabolic state that enhances the body’s ability to burn fat. This not only helps weight loss but also has been linked to improved energy levels, mental clarity, and better blood sugar control.  

Watch the video below to discover why fasting for 18 hours can dramatically spike brain power. 

Dramatically Spike BRAINPOWER with an 18 Hour Fast

Is it safe?

The 18:6 fasting regime has gained widespread popularity due to its impressive health benefits, and research repeatedly confirms the effectiveness and long-term safety of intermittent fasting.

A study published in Diabetes Care evaluated the safety of intermittent fasting in diabetic patients. The authors summarized that adherence to a time-restricted eating pattern is a safe and feasible therapeutic strategy to promote metabolic and hormonal health.

“From an evolutionary point of view, the human body is well adapted to intermittent fasting, which mimics the natural feast-and-famine cycles that our ancestors experienced,” explains Dr. Berg.

Although the 18:6 fast is considered safe for most people, it’s crucial to understand that some people should avoid fasting

Who shouldn’t do 18:6 fasting

Intermittent fasting can increase the risk of unhealthy eating patterns in individuals with eating disorders.  

In addition, those who are underweight or at risk of malnourishment could lose excessive body fat or develop nutrient deficiencies when limiting food intake to restricted time periods.  

Pregnancy and breastfeeding are periods of increased caloric needs, and pregnant or breastfeeding mothers shouldn’t practice intermittent, prolonged, or alternate-day fasting. 

Fasting can trigger profound metabolic changes, and it’s crucial to consult a healthcare professional if you have underlying medical conditions such as poor liver function, kidney disease, or low blood sugar, also known as hypoglycemia, before starting the 18:6 fasting routine. 

Clock in front of a salad

Health benefits of 18:6 fasting

Although many individuals start practicing intermittent fasting to achieve a healthy weight, time-restricted eating has various other health benefits beyond weight loss.

Research published in The New England Journal of Medicine investigated the health benefits of the 18:6 fast and concluded, “The 18:6 fasting pattern can trigger a metabolic switch from glucose-based to ketone-based energy, with increased stress resistance, increased longevity, and a decreased incidence of diseases, including cancer and obesity.”

Here are five health benefits of 18:6 fasting. 

1. Promotes a healthy body weight 

Time-restricted eating patterns naturally limit calorie intake, which helps avoid weight gain and promotes weight loss. 

However, the benefits of intermittent fasting for weight management aren’t just linked to calorie restriction during fasting windows. 

Fasting stimulates growth hormone production, which can boost muscle mass and enhance the body’s capacity to utilize stored fat as a fuel source, thereby promoting fat-burning and weight loss.  

2. May help reverse diabetes 

Fasting for 18 hours keeps blood sugar levels balanced, which helps prevent insulin resistance linked to metabolic syndrome, obesity, and diabetes. 

Intermittent fasting has been extensively studied as a potential therapeutic tool to prevent, manage, and even reverse diabetes. 

A study published in JAMA Network Open found that time-restricted eating improved weight status, long-term blood glucose control, insulin sensitivity, and other metabolic health markers in diabetic individuals. 

In fact, 18:6 fasting has such profound benefits for metabolic health that intermittent fasting could replace insulin for diabetes, potentially providing an effective and safe alternative to pharmaceutical diabetes treatments.    

Human brain illustration

3. Boosts brain function 

Evidence published in Nutrition Reviews suggests that fasting directly stimulates the release of brain-derived neurotrophic factor (BDNF).

BDNF is a crucial protein supporting neuronal cell growth and functionality. Higher concentrations of BDNF in the central nervous system are associated with improved cognitive function, memory recall, and mood regulation.

4. Triggers autophagy 

Fasting for prolonged periods triggers autophagy, a cellular recycling and repair mechanism that removes damaged or dysfunctional cell organelles.

Autophagy is a crucial process that helps maintain cellular health and functionality, which is associated with a lower risk of various chronic diseases, including cancer, atherosclerosis, and neurodegenerative conditions such as Alzheimer's disease and dementia.     

5. Supports heart health

Metabolic and cardiovascular health are intricately connected. 

Obesity, blood sugar imbalances, and insulin resistance are all established risk factors for heart disease, significantly increasing the chances of cardiovascular issues such as high blood pressure, heart attacks, and strokes. 

Intermittent fasting has been shown to restore balanced metabolic functions effectively. This makes time-restricted eating a powerful strategy for promoting a healthy heart and reducing the risk of cardiovascular disease.

18:6 fasting illustration

How to start an 18:6 fast

The key principle of the 18:6 fast is to avoid food and calorie-containing beverages during an 18-hour fasting period.

While it may be tempting to start with 18-hour fasting periods immediately, it’s crucial to remember that your body needs time to adapt to prolonged caloric restriction. 

Fasting for too long too quickly is one of the most common intermittent fasting mistakes and can lead to unpleasant side effects, including headaches, dizziness, irritability, and disrupted sleep.   

If you are new to intermittent fasting, it’s recommended to start with a 14-hour fast followed by a ten-hour eating window and gradually prolong your fasting periods until you reach an 18:6 schedule. 

How quickly you can achieve a consistent 18:6 fasting routine depends on your metabolic health and overall dietary pattern. While some individuals can fast for 18 hours within a few days, others may require several weeks to comfortably restrict their eating periods to six hours.

Woman drinking water

What can you drink while fasting?

During the initial stages of adapting to caloric restriction, fasting can lead to temporary fluid loss and disruptions in electrolyte balance. 

Adequate fluid intake during fasting periods is crucial to minimize the risk of dehydration. However, it’s vital to consume calorie-free beverages that won’t break your fast. 

Here are fasting-friendly drink options:

  • Plain water

  • Sparkling or carbonated water

  • Lemon water 

  • Black coffee 

  • Black and green tea

  • Herbal tea 

  • Diluted apple cider vinegar 

In addition, replenishing electrolytes during fasting periods with a sugar-free electrolyte powder is an excellent option for maintaining the body’s fluid and electrolyte balance. This supports overall well-being and helps prevent fatigue, dizziness, and muscle cramps.

Many people who practice intermittent fasting drink bulletproof coffee during their fasting period to help curb hunger, boost energy levels, and enhance mental focus. 

Although bulletproof coffee does contain calories, it’s considered fasting-friendly as it’s made with black coffee, butter, and coconut oil, none of which interfere with the body’s natural fasting state. 

Ketogenic foods

Tips and tricks 

While time-restricted eating has various metabolic advantages, it’s equally important to consider what you eat during your eating windows. 

Combining an 18:6 fast with a healthy diet can speed up fasting success and help you achieve your health and fitness goals more effectively.

Here are four tips and tricks to smoothly transition into an 18:6 fasting regime.

1. Eat plenty of healthy fats

Consuming plenty of healthy fats during your eating window plays a critical role in providing your body with fuel and can help maintain fat-burning even when you break your fast. 

Obtaining the majority of your daily calories from fats while limiting carbohydrate intake keeps blood sugar levels low and forces your body to continue using fat to generate energy. 

Limiting carbs keeps your metabolism in ketosis, which explains why a nutritious high-fat diet such as Healthy Keto® is an ideal intermittent fasting diet meal plan. 

Combining keto with intermittent fasting is an excellent strategy to maximize the health benefits of ketosis and helps curb hunger and cravings during your 18-hour fasting period.  

There are plenty of healthy fat sources on the keto food list to choose from, including olive and coconut oil, full-fat cheese, butter, heavy cream, seeds, and nuts. 

2. Focus on nutrient-rich foods

Processed foods can increase the risk of nutritional deficiencies as they typically lack vitamins, minerals, fatty acids, and other vital nutrients necessary for overall health. 

It's crucial to prioritize nutritious foods to ensure your body gets the nutrients it needs to function optimally, especially during fasting periods. 

Healthy Keto focuses on nutrient-dense organic vegetables, grass-fed meats, wild-caught fish, and pasture-raised eggs, making it a perfect addition to an 18:6 intermittent fasting schedule.  

Woman declining sugary foods

3. Limit carbohydrates

Sugar and carbohydrate-rich foods, such as bread, rice, and pasta, are rapidly broken down and absorbed, which raises blood sugar levels.

Elevated blood sugar will stop ketosis and fat burning, as the liver prioritizes using blood glucose as a fuel source. Consuming carbs and sugars when you break a fast can slow fasting success and hinder weight loss.  

In addition, sugar and refined carbs can cause blood sugar imbalances and energy fluctuations. This can trigger hunger and cravings during your fasting window, making it more challenging to achieve an 18-hour fast. 

4. Avoid snacking 

Breaking a snacking habit is crucial to smoothly transitioning into intermittent fasting and helps prolong fasting periods. 

Consuming any foods that raise blood sugar levels, even low-calorie or healthy snacks, can break the fasting state and disrupt ketosis and fat-burning. 

Although it might seem challenging to avoid snacking during the initial stages of adapting to intermittent fasting, hunger, and cravings will decrease as your body adjusts to using body fat for fuel.

Clock and ketogenic foods

Key takeaways

Intermittent fasting has profound health benefits, and the 18:6 fast is a popular mealtime schedule that alternates between an 18-hour fast and a six-hour eating window.

To maximize fasting success, it’s crucial to slowly ease into an 18:6 fasting routine to allow the body to adapt to the metabolic changes triggered by time-restricted eating.

Combining intermittent fasting with a nutritious high-fat diet such as Healthy Keto while limiting carbs and avoiding snacking can help quickly ease the transition into an 18:6 fast. 


1. How effective is 18:6 fasting?

An 18:6 fast is a highly effective intermittent fasting schedule. Fasting for 18 hours forces the body to burn fat instead of sugar to generate energy. 

This promotes a healthy body weight and boosts energy levels while improving metabolic health, which is linked to a lower risk of heart disease and diabetes. 

2. Is it safe to fast for 18 hours every day?

Yes, fasting for 18 hours every day is safe for most people. However, it’s crucial to combine an 18:6 fast with a balanced diet that provides adequate nutrients to prevent potential nutritional deficiencies. 

Intermittent fasting isn’t recommended for individuals with an eating disorder, pregnant or breastfeeding mothers, and those with chronic kidney disease.  

3. What is the best time to start an 18:6 fast?

Many people start their fasting periods in the evening after dinner, fast for 18 hours, and have their first meal until around lunchtime. 

4. Can you drink during the 18:6 fasting?

Yes, you can drink during an 18:6 fast. In fact, it’s crucial to stay hydrated during your fasting period to prevent dehydration.

However, it’s important to avoid sugar-sweetened drinks and opt for calorie-free beverages such as water, carbonated water, lemon water, black coffee, and black, green, or herbal tea, which won’t break a fast or interfere with fat-burning. 

5. How do I start 18:6 fasting?

It’s recommended to slowly ease into an 18:6 fast by fasting for 14 hours and gradually extending your fasting periods until you can comfortably fast for 18 hours. 

Combining an 18:6 fast with a nutritious high-fat diet such as Healthy Keto® helps transition into intermittent fasting, prevents nutritional deficiencies, and can curb hunger and cravings during fasting periods.   

6. How long does it take 18:6 fasting to work?

Most people notice weight loss and improved energy within two weeks of starting an 18:6 fasting routine. However, it can take up to four weeks of consistent intermittent fasting to experience enhanced mental clarity, stronger immune defenses, and overall better health and well-being. 


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9887629/ 

  2. https://www.nejm.org/doi/full/10.1056/nejmra1905136 

  3. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2811116

  4. https://academic.oup.com/nutritionreviews/article/81/9/1225/7116310 

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