A 16-hour fast is another kind of intermittent fasting popular among those seeking healthy eating habits and weight loss. But is it really helpful for weight loss? What are its benefits and results? What are the best foods to eat and avoid during 16-hour fasting? This article will answer these questions and many more to help you decide if it’s something you need to try. Let’s dig in!
Table of Contents
A 16-hour fast is a popular kind of intermittent fasting, where individuals fast for 16 hours and eat during an 8-hour period.
Different studies have indicated that intermittent fasting, including the 16-hour fast, can result in weight loss and fat burning.
A 16-hour fast offers various health benefits, including improved insulin sensitivity, cardiovascular health, brain health, and reduced inflammation.
Staying hydrated is essential during the fasting period. You can drink water, black coffee, or herbal tea.
To reach the best results, choose nutrient-dense foods, including vegetables, fruits, lean proteins, healthy fats, and whole grains, and avoid sugary and processed foods.
What Is a 16-Hour (16:8) Fast?
A 16-hour fast or 16:8 is another common form of intermittent fasting tried by many dieters. Generally, intermittent fasting is so popular for various reasons, and there’s a huge body of research about it.
Let’s speak science and have a sneak peek into recent research about intermittent fasting, its effects, and people’s opinion.
It’s so popular, as a survey shows 80.17% of respondents knew about intermittent fasting.
Another survey by YouGov conducted in 2020 revealed that 24% of US adults had done intermittent fasting for weight loss, which means it has been the most popular diet in the US with the Atkins diet.
Different studies have reported that intermittent fasting decreased the waist circumference of participants by about 1.18 to 3.15 inches.
A review of 40 different studies indicated that those doing intermittent fasting for ten weeks had lost 7–11 of body weight.
A global survey done in 2022 found that 41.81% of respondents got used to intermittent fasting and felt less hungry in less than a week.
Another study on participants for 12 weeks found a 23% increase in sleep quality after intermittent fasting.
Another survey has found that 80% of respondents find intermittent fasting an inexpensive diet than many other diets.
Many celebrities have tried intermittent fasting, including Jennifer Anniston, Nicole Kidman, Hugh Jackman, Reese Witherspoon, Halle Berry, Margot Robbie, Elsa Pataky, Kourtney Kardashian, Jennifer Lopez, Giselle Bündchen, Elsa Pataky, Scarlett Johansson, Vanessa Hudgens, and Mindy Kaling.
A randomised controlled trial conducted in 2013 found that the alternate-day fasting group lost more weight (about three times) than the exercise group.
Another 2016 study revealed that intermittent fasting helps regain lean body mass - not fat - which results from calorie restriction.
Also, a review published in the journal Nutrients in 2019 indicated that intermittent fasting improves weight loss and decreases the risk factors of heart disease, i.e., diabetes, high blood pressure, unhealthy blood lipid levels, and inflammation.
Science aside, a 16-hour fast is quite simple to do. Let’s take a look at its main principles and rules.
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Principles and Rules
16-hour fasting, aka the 16:8 fasting or time-restricted eating, is a kind of intermittent fasting that includes avoiding food (calorie intake) for 16 hours and eating for 8 hours.
The main rules and points you need to know about the 16-hour fast are as follows.
Set Eating Window Carefully: Set a specific time for the daily 8-hour eating period. The 12 pm to 8 pm or 1 pm to 9 pm is common, but you can choose a time that suits your situation best.
Drink Lots of Water: It’s necessary to stay hydrated during the fasting period. In addition to water, you drink black coffee, tea, or other non-caloric beverages during fasting.
No Calorie Intake During Fasting Period: No calorie can be consumed during the fasting period, i.e., you need to avoid food, sugary beverages, and snacks. This process will keep the insulin levels low and make your body burn fat for energy.
Nutrient-Dense Meals: You must provide the necessary nutrients in the 8-hour eating period. You can consume vegetables, fruits, lean proteins, healthy fats, and whole grains.
Control Portion Sizes: Eat in moderation, i.e., avoid overeating and undereating during the eating period.
Listen to Your Body: Stay alert to your body’s reactions in the early hours and days of fasting and modify it accordingly.
Exercise Regularly: Regular exercise can increase the metabolism and multiply the positive effects of the 16-hour fast.
Be Patient: You need to stay patient to see the results, as it may take time based on your body status, eating habits, and many other factors.
Consult a Healthcare Professional: Before starting fasting, and if you see any problems during fasting, consult a physician or dietitian to make the best decisions and avoid health problems.
What Happens to Your Body During a 16-Hour Fast?
During a 16-hour fast, your body tries to adapt to changes, so various physiological changes happen. Here are the highlights based on time:
Early Hours (0-4 hours): Early hours after eating the last meal of the 8-hour eating period, the body starts to burn glucose to provide energy. Insulin levels decrease, so the fat cells release stored energy as fatty acids.
Some Hours Into Fasting (4-8 hours): When the glucose is used up and finished, the body starts to use glycogen (glucose stored in the liver and muscles) to maintain blood sugar levels.
Transition to Ketosis (8-12 hours): When glycogen is finished, the ketosis process starts. It is a metabolic state where the liver produces ketones from fatty acids, meaning that ketones substitute glycogen to provide energy.
Ketosis and Fat Burning (12-16 hours): After a couple of hours into ketosis, the body relies on fat for energy, so ketone production increases. Fat is broken down into fatty acids and glycerol to produce energy.
As a result of all these processes, your body experiences positive changes. To know what they are, keep scrolling to the next section.
Weight Loss: Intermittent fasting, including the 16:8 fasting, helps weight loss and decreases body fat. Fasting makes the body use fat for energy, which results in fat burning.
Source: Varady KA, Bhutani S, Klempel MC, et al. Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutr J. 2013 Nov 12;12:146. doi: 10.1186/1475-2891-12-146. PMID: 24215592; PMCID: PMC3833266.
Insulin Sensitivity: Intermittent fasting can improve insulin sensitivity and decrease the risk of insulin resistance and type 2 diabetes.
Source: Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661-74. doi: 10.1093/nutrit/nuv041. Epub 2015 Sep 15. PMID: 26374764.
Cardiovascular Health: Intermittent fasting can decrease cardiovascular risk factors, including blood pressure, triglycerides, and LDL cholesterol.
Source: Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Transl Res. 2014 Oct;164(4):302-11. doi: 10.1016/j.trsl.2014.05.013. Epub 2014 Jun 5. PMID: 24993615.
Cellular Repair and Autophagy: Intermittent fasting improves autophagy by removing damaged components of cells, which helps cellular repair and promotes longevity.
Source: Alirezaei M, Kemball CC, Flynn CT, et al. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010 Aug;6(6):702-10. doi: 10.4161/auto.6.6.12376. Epub 2010 Aug 19. PMID: 20534972; PMCID: PMC3106288.
Brain Health: Intermittent fasting can improve neuroprotective effects and cognitive function and decrease the risk of neurodegenerative diseases.
Source: Martin B, Mattson MP, Maudsley S. Caloric restriction and intermittent fasting: two potential diets for successful brain aging. Ageing Res Rev. 2006 Aug;5(3):332-53. doi: 10.1016/j.arr.2006.04.002. Epub 2006 Jun 5. PMID: 16899414.
Anti-Inflammatory Effects: Fasting can decrease inflammation markers, which promotes overall health and decrease the risk of chronic diseases.
Source: Li L, Messina JL. Acute effects of dietary constituents on motor skill and cognitive performance in athletes. Nutr Rev. 2009 Mar;67(3):119-31. doi: 10.1111/j.1753-4887.2009.00176.x. PMID: 19267851.
Blood Sugar Regulation: Intermittent fasting can regulate blood sugar, which is good news for those with prediabetes or type 2 diabetes.
Source: Halberg N, Henriksen M, Söderhamn N, et al. Effect of intermittent fasting and refeeding on insulin action in healthy men. J Appl Physiol (1985). 2005 Dec;99(6):2128-36. doi: 10.1152/japplphysiol.00683.2005. Epub 2005 Jul 21. PMID: 16036904.
Longevity and Ageing: Some animal studies indicate intermittent fasting can decrease ageing and support longevity. But further research needs to be done on humans to ensure the results.
Source: Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017 Oct;39:46-58. doi: 10.1016/j.arr.2016.10.005. Epub 2016 Oct 31. PMID: 27810402; PMCID: PMC5411330.
Intermittent fasting comes in different types. A 16-hour fast is a common one, but there is another popular type good for starters called a 14-hour fast. Let’s compare the two and find out the differences and similarities.
16-Hour Fast vs 14-Hour Fast
As mentioned above, the 16-hour fast includes fasting 16 hours a day and eating 8 hours on the same day. The fasting period includes avoiding calorie intake to make the body rely on fat for energy and melt fat. You can drink water and other non-caloric beverages during the fasting period.
The 14-hour fast is another type of intermittent fasting, where you need to fast for 14 hours and eat for 10 hours. This method has a shorter fasting period and is more suitable for beginners who find it challenging to avoid food for an extended period.
The Difference Between 16- and 14-Hour Fast
Fasting Duration: The 16-hour fast includes fasting for 16 hours each day, while the 14-hour fast means fasting for 14 hours each day.
Eating Window: A 16-hour fast provides an 8-hour eating period, while the 14-hour fast lets you eat during a 10-hour period.
Adaptation Period: You may need a longer time to adapt to a 16-hour fast than the 14-hour fast, which is more suitable for beginners.
Flexibility: The 14-hour fast is slightly more flexible, providing a longer eating period.
Caloric Intake: A 16-hour fast can result in faster weight loss as it restricts calories for a longer period.
Is a 16-Hour or a 14-Hour Fast Better?
Choosing one of these fasting methods as better is highly dependent on your personal needs, goals, and status, as both can be effective in health and weight loss.
However, as mentioned earlier, a 14-hour fast can be better for beginners, and a 16-hour fast can be better for more experienced dieters who need faster results.
Another popular intermittent fasting method is the 12-hour fast. The following section will compare it with the 16-hour fast to see which one can be a better option.
The 16:8 or 16-hour fast includes consuming no calories for 16 hours and eating during an 8-hour period.
The 12-hour fast divides a day into two equal periods of fasting and eating.
The Difference Between 12- and 16-Hour Fast
Fasting Duration: The 16-hour fast involves fasting for 16 hours a day, while the 12-hour fast includes fasting for 12 hours per day.
Eating Period: The 16-hour fast allows an 8-hour eating period, while the 12-hour fast gives you a 12-hour eating period.
Caloric Intake: Longer fasting in the 16-hour fast means a slightly greater calorie deficit, which helps faster weight loss.
Adaptation Period: The 12-hour fast is a better option for beginners who can’t fast for longer hours, and it’s easier to adapt.
Flexibility: The 12-hour fast is more flexible in terms of meal timings.
Is 16- or 12-Hour Fast Better?
If you’re a beginner or have a busy schedule and can’t fast for longer periods, a 12-hour fast can be a better option. However, if your goals and lifestyle allow a longer fasting period, you can try a 16-hour fast.
Another common fasting method is the 18-hour fast, which is tried by many dieters worldwide for health and fitness reasons. Let’s review it and compare it with the 16-hour fast to see which one is better for us.
16-Hour Fast vs 18-Hour Fast
A 16-hour fast means avoiding calories for 16 consecutive hours and consuming the necessary nutrients in the 8-hour eating period.
The 18-hour fast includes an 18-hour fasting period and a 6-hour eating window.
The Difference Between 18- and 16-Hour Fast
Fasting Duration: The 16-hour fast includes fasting for 16 hours, while the 18-hour fast includes fasting for 18 consecutive hours.
Eating Window: The 16-hour fast allows 8 hours of eating, while the 18-hour fast includes a 6-hour eating period.
Caloric Intake: The 16-hour fast provides a good calorie deficit, but the 18-hour fast provides a longer calorie restriction, which may result in faster weight loss.
Is 18-Hour Fast Better Than 16-Hour Fast?
While the 18-hour fast can result in faster weight loss, it may not be sustainable or suitable for everyone, especially for beginners or those with certain health concerns. You need to choose a method that best suits your situation and goals.
Now that we’ve learned about different types of intermittent fasting, let’s see how to do the most popular one, i.e., the 16-hour fast.
How to Do 16-Hour Fasting?
Here is a step-by-step guide to starting a 16-hour fast.
Choose Your Fasting Window:
Decide when you will eat the meals. 12 pm to 8 pm or 1 pm to 9 pm are common time frames, but choosing a time depends on your goals and preferences.
Eat Balanced Meals:
Ensure to consume balanced, nutrient-dense meals to provide the necessary nutrients during the eating period. You can have vegetables, fruits, lean proteins, healthy fats, and whole grains.
Start with Dinner:
If you're a beginner, fasting can be easier after dinner, as a long time will pass during sleep. For example, if you finish dinner by 8 pm, you won't eat until 12 pm the next day.
Stay Hydrated During Fasting Period:
Drink enough water during the fasting period. You can also drink other non-caloric beverages like black coffee and tea, which curb hunger and help hydration.
Avoid Calories During Fasting:
Consume no calories during the fasting period, i.e.; you can’t eat food, sugary beverages, and snacks.
Manage Hunger and Cravings:
Manage hunger by keeping yourself busy and taking your mind off fasting. Do your favourite activities, and remind yourself of your health and fitness goals.
Break the Fast Gradually:
Break the fast with a balanced meal. Avoid overeating and undereating, and let your body adapt to the new eating style.
If your body and the healthcare professional allow, try weekly fasting to help your body adapt sooner and get the best results.
Listen to Your Body:
Monitor your body’s reactions and make modifications to make the most of the fasting. Seek medical help if you see extreme or unusual reactions.
Preservation of Lean Body Mass (Source: https://pubmed.ncbi.nlm.nih.gov/26892521/)
Sustainable Weight Loss (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6471313/)
How Much Weight Can You Lose in a 16-Hour Fast?
It’s no secret that different individuals have different body composition, calorie intake, health status, diet quality, physical activity, metabolism, starting weight, and consistency, among many other differences that affect the fat loss results.
Monitoring your weight before and after fasting in specific intervals, like after a week, a month, etc., can help determine your weight loss rate.
Just remember that the recommended weight loss rate is around 0.5 to 2 pounds per week.
How Much Fat Is Burned in a 16-Hour Fast?
The amount of fat you can burn during a 16-hour fast depends on many personal factors, and there isn’t any fixed rate for it. Calorie restriction during fasting, in addition to lower calorie intake and more physical activity, helps you burn more fat in a shorter period.
Will a 16-Hour Fast Put Me in Ketosis?
Yes, a 16-hour fast can put the body into a mild state of ketosis, especially near the end of the fasting period. Remember that ketosis caused by 16-hour fasting is lower than longer fasting periods or strict ketogenic diets.
Is a 16-Hour Fast Enough?
16-hour fasting is the most popular type of intermittent fasting. The speed of achieving the results varies among individuals, but it’s popular for a reason, and it is fast enough for average dieters!
Will I Lose Weight If I Fast 16 Hours a Day?
Yes, based on the studies provided in this article and according to personal reports, a 16-hour fast can help you melt fat and lose weight by calorie deficit and ketosis.
Following a balanced diet, doing regular physical activity, staying hydrated, keeping consistency, and planning a personalized approach help you achieve your health and fat loss results faster.
Who Should Avoid Doing 16-H Fasting?
It’s necessary for everyone to consult a healthcare professional before making significant changes in their eating habits. However, the following groups need constant supervision and personal care to get the best results and avoid medical problems.
Pregnant and Breastfeeding Women
Children and Adolescents
Individuals with Eating Disorders
Those with Chronic Health Conditions
Individuals Taking Specific Medications
Those Doing Heavy Physical Activity
Those Experiencing Uncontrolled Stress and Sleep Issues
A 16-Hour Fast Diet and Autophagy
A 16-hour fast can boost autophagy, a cellular process helping the body's cellular maintenance and repair. Autophagy cleans damaged or dysfunctional cells and recycles cellular components to improve the cells’ health and longevity.
During a 16-hour fast, insulin levels are decreased, and glucagon secretion increases. This hormonal shift stimulates metabolic changes that can result in autophagy.
The whole process includes:
Low Insulin Levels
Blood Sugar After a 16-Hour Fast
Blood sugar levels vary after a 16-hour fast based on personal diet, physical activity, and overall health status.
The blood sugar levels usually stay stable or slightly decrease for most individuals in the fasting state as the body tries to adapt to the fasting status.
A 16-Hour Fast and Growth Hormone
Intermittent fasting, including a 16-hour fast, can influence the secretion of growth hormone (GH), a peptide hormone produced by the pituitary gland. Growth hormone positively affects growth, metabolism, and body composition.
The Salt Intake on a 16-Hour Fast
There is no special guideline or restriction for consuming salt in a 16-hour fast. However, keeping it low is good for preventing heart conditions or hypertension. Pay attention to the following considerations about consuming fat on 16-hour fat.
Hydration: While drinking water helps pepper hydration, it's also essential to keep electrolyte balance. Sodium is a necessary electrolyte, and eating moderate salt maintains proper fluid balance.
Avoid Excessive Salt Intake: While some salt is necessary to maintain electrolytes, too much salt can cause high blood pressure and other health issues.
Choose Nutrient-Dense Foods: Consume fresh fruits, vegetables, lean proteins, whole grains, and healthy fats to provide enough sodium and essential vitamins, minerals, and other nutrients.
Personal Health Considerations: If you have certain health conditions like hypertension or kidney problems, consult a healthcare professional to know the exact amount of salt to consume.
The Best Supplements to Take on a 16:8 Fast Diet
While intermittent fasting, including the 16:8 fast, provides the necessary nutrients, you may need to take some supplements in some cases, such as the following.
Multivitamin and Mineral Supplement
Omega-3 Fatty Acids
A 16-hour fast has been tried by numerous people in search of a healthy method to lose weight or regain health. This type of intermittent fasting comes with various long-term and short-term benefits.
However, deciding if this common method is right for you depends on various personal factors, including health status, body composition, body weight, fat content, goals, and preferences.
You can check all this and make the final decision after consulting a healthcare professional and doing the necessary tests. So, talk to a doctor before drastically changing your eating habits.
The following Q&As help you find answers to the most frequently asked questions about a 16-hour fast.
What Fats to Consume After a 16-Hour Fast?
Plant-based fats like olive and coconut oil, avocado, nuts and seeds, salmon and fatty fish, nut butter, chia pudding, and full-fat dairy are healthy fats to consume after a 16-hour fast.
How Long Does It Take to See Results from 16-Hour Intermittent Fasting?
The time it takes to see results from 16-hour intermittent fasting can vary among individuals. Some people may notice changes in weight, energy levels, and overall well-being within a few weeks, while others may take longer. Consistency and adherence to a balanced diet and lifestyle are significant in achieving noticeable results.
How Often Should You Do a 16-Hour Fast?
The frequency of doing a 16-hour fast is based on your preferences and goals. Many individuals do 16-hour fasts once or twice a week.
How Many Calories Do You Burn in a 16-Hour Fast?
The number of calories you burn in a 16-hour fast relies on many factors, including age, weight, metabolism, and physical activity.
What Is The Best Meal to Break a 16-Hour Fast?
The best meal to break a 16-hour fast is a balanced and nutrient-dense meal containing protein, healthy fats, fiber, and micronutrients.
What Is Dry Fast 16-Hour?
Dry fasting is another kind of intermittent fasting where no liquid is allowed during the fasting window.