What is 16/8 and 12/12 Intermittent Fasting?


Fasting diets have become increasingly popular in recent years due in large part to the fact that they do provide noticeable results. But with so many different types of fasting diets, it can be difficult to choose the one that best works for you. Extensive research is required to learn all there is to know about these diets. You probably don’t have time to conduct that research, so here’s a breakdown of two of the most popular fasting diets, the 16/8 and the 12/12 intermittent fasting diets. 

What are Fasting Diets And How Do They Work?

Fasting is the dietary practice of cycling between periods of fasting and eating. It should be noted that the vast majority of fasting diets do not say anything about which foods to eat or not eat, but rather when you should eat them. We already ‘fast’ every day while we’re sleeping, taking a 6-10 hour break from eating. Sometimes, fasting can be as simple as extending that period a little longer. 

Fasting has become a popular diet trend in recent years, but it has been commonplace in certain cultures for centuries. For example, religions and philosophies that practice fasting include Buddhism, Christianity, Islam, Judaism, Taoism, Jainism, and Hinduism. These fasts can last for a few hours or even a few weeks. During these religious fasts, most practitioners will eat at night and fast during the day. 

Is It Healthy to Fast?

If you are relatively healthy and stay hydrated during a fast, fasting for a few days shouldn’t cause any issues. Most fasting diets, such as the 16/8 and 12/12 intermittent fasting diets, are safe for healthy individuals. However, most doctors do not recommend fasting for a long period of time. 

This is because your body needs vitamins, minerals, and other nutrients from food in order to function properly. If you don't get enough, you can have symptoms such as fatigue, dizziness, constipation, dehydration, and not being able to tolerate cold temperatures. Fasting too long can be life-threatening. If you have diabetes, you should avoid even short fasts as it can lead to dangerous dips and spikes in blood sugar. Women who are pregnant or breastfeeding should also avoid fasting. 

Comparing 12 Hour and 16 Hour Intermittent Fasting

What is the ideal intermittent fasting time? Intermittent fasting has become one of the most popular dietary trends in recent years with the two most common forms being the 12/12 and 16/8 intermittent fasting diets. The main difference, and really the only difference, between the two diets, is the intermittent fasting times. As you can probably tell by the names, the 12/12 diet has a 12-hour eating window and a 12-hour fasting window. The 16/8 diet has an 8-hour eating window and a 16-hour fasting window. 

Later in this article, we will discuss what the research says regarding which one works more than the other. Keep in mind, however, that the diet that best works for you will largely depend on personal preference. Many people do not wish to go on a 16-hour fast in which case, the 12/12 diet makes more sense. 

Does an Intermittent 12 Hour Fast Actually Work?

The 12/12 intermittent fasting plan allows you to have a more flexible eating method and still gain the highly desired weight loss benefit. This is achieved by your metabolism being effectively ramped up by the calorie deficit of the plan. The 12/12 fast enables you to burn those pesky and hard to lose fat cells, converting them into energy at a high rate.

The 12/12 intermittent fast is one of the easiest fasting plans and is an ideal choice for many beginners that have busy schedules. The major advantage of the 12 hour fast is that much of your fasting time is spent on the hours when you are sleeping. Thus, those pesky food cravings and hunger pains are not felt and not a problem. 

The 12 hour fast is a great way to start your fasting journey. Just stick to your guns and follow the rules and you will achieve the results you desire and gain the benefits that come with a healthier lifestyle.

Guidelines for Successfully Completing a 12 Hour Fast

An obvious rule of the 12/12 fast is that all meals and snacks must be finished before the 12 hour fasting window begins. Breakfast, lunch, dinner, and any snacks between are all allowed but only during your 12 hour eating window. Initial hunger pains and cravings are to be expected in the beginning but eventually should subside with time as your body gets used to its new eating regime. 

The 12 hour fasting window is best scheduled for the night. This allows you to have a full meal before 8 p.m., go to sleep, and wake up able to have a satisfying and energizing breakfast at 8 a.m. 

Losing Weight By Fasting

It is possible for you to shed unwanted weight with any fasting plan. However, it will also depend on your level of physical activity and your diet. Simply fasting will not guarantee very consistent or satisfying results. You must include healthy foods and enough physical activity to keep you motivated and achieve the goals you have set for your weight and health. 

Weight loss will also occur when you have entered a calorie deficit state. This is a metabolic state which allows you to burn more calories than were consumed on that day. The result is your body will begin to burn stored fat in order to meet its energy demands. With a 12/12 intermittent fast, you must achieve a calorie deficit to achieve weight loss. 

Initially, the weight you lose will be water weight. However, once you continue to push forward past the first few weeks, you will begin to notice inches disappear from your waistline. 

Additional Health Benefits From Fasting

Aside from weight loss, burning through your body’s fat reserves is also a good way to boost mental clarity and battle mental health issues. Fasting has been reported as helping to enhance brain health and reduce cognitive decline. 

A 12 hour fast is also beneficial in its ability to reduce inflammation. Inflammation can lead to cardiovascular disease, diabetes, and cancer, so any help with reducing those risks is a big help. Research has shown that by incorporating fasting and the introduction of healthy foods into your lifestyle can battle inflammation in your body.

Intermittent fasting has also been shown to significantly reduce risk factors associated with heart disease, including: 

  • high blood sugar
  • insulin resistance
  • LDL cholesterol
  • High blood triglycerides
  • And inflammation

Is It Possible to Fast While Following a Keto Diet?

Those who keep up with health trends will already know how big of a boom both intermittent fasting and keto diets have made in recent years. Now, many people are wondering if you should combine the two to get optimized results. The main idea behind the keto diet is to help your body reach ketosis, the process in which your body breaks down fats to form substances called ketones that serve as an alternate fuel source. This diet can be an incredibly effective way to lose weight. 

Believe it or not, researchers believe that intermittent fasting may help your body reach ketosis quicker than the keto diet alone. This is because your body, when fasting, maintains its energy balance by shifting its fuel source from carbs to fats which is the exact premise of the keto diet. While it’s safe to combine the two if you’re healthy, it’s unnecessary to combine both. 

Does the 16 Hour Intermittent Fasting Diet Really Work?

There is research that points to the idea that there’s virtually no difference between those who partake in intermittent fasting versus those who simply cut back their calorie intake. Some believe the better strategy is optimizing the nutritional quality of what you already eat. Also, science suggests any potential benefit from fasting is quickly undone during the eating part of the cycle, in which appetite-suppressing hormones switch gears to make you feel even hungrier than you felt at baseline.

However, an intermittent fasting diet plan 16/8 can be very beneficial for those who have trouble sticking to prescribed meal plans or restrictive diets. It should be noted that fasting provides benefits that extend beyond losing weight. Fasting can give your vital organs, digestive and absorptive hormones, and metabolic functions a break. It can also induce autophagy, which is the body’s way of replacing old, dying cells with newer, healthier cells. This can help improve your longevity, leading to a longer, healthier life. 

What Type Of Health Benefits Does Intermittent Fasting Offer?

As we mentioned previously, the benefits of intermittent fasting extend beyond weight loss. There is a mound of evidence that points to intermittent fasting providing full-body benefits as well as brain benefits. Here are some of the benefits of intermittent fasting, whether it be 16/8 or 12/12:

  • Lowered risk of type 2 diabetes - Fasting can reduce your insulin resistance, which can help lower blood sugar levels, protecting against type 2 diabetes
  • Reduce oxidative stress and inflammation - Oxidative stress can oftentimes lead to chronic diseases. Fasting can help enhance your body’s resistance to oxidative stress, fighting off inflammation
  • Improved heart health - Intermittent fasting has been shown to improve numerous different risk factors, including blood pressure, total and LDL cholesterol, blood triglycerides, inflammatory markers, and blood sugar levels
  • Prevent cancer - While more research is needed, current research does show that fasting can help prevent cancer
  • Brain health - Fasting can induce bodily functions, such as autophagy, which help reduce oxidative stress, reduce inflammation, and reduce blood sugar levels

When considering starting a fasting diet, you should consider all of these benefits, on top of the weight loss aspect of the diet. 

What You Can Expect From An Intermittent Fasting Diet Plan

So what exactly does an intermittent fasting diet plan look like? Keep in mind, these diets do not dictate what foods you should or shouldn’t eat. These diets dictate how many hours during the day you can eat. Here are some common types of intermittent fasting (1):

  • The 16/8 method - As mentioned earlier, this method involves a 16-hour fasting window. While this may sound extreme, it can be as simple as not eating anything after dinner and skipping out on breakfast
  • 12-hour intermittent fasting - This plan has a 12-hour fasting window. This can be as simple as skipping out on breakfast
  • 5:2 diet - This diet involved eating normally five days of the week and restricting your calorie intake to 500-600 for two days of the week. It is highly recommended that you space these days out
  • OMAD Intermittent Fasting - OMAD (one meal a day) involves fasting for 23 hours and then consuming your calories in a one-hour feeding window.
  • Eat Stop Eat - The Eat Stop Eat diet is a more extreme version of the 5:2 diet. This diet requires you to eat normally five days a week, and fast for 24-hours for two days. You can accomplish this by eating dinner one night and waiting a full 24-hours to eat dinner again. You don’t necessarily have to go the entire day without eating
  • The Warrior Diet - This diet is essentially an all-day fast with a small eating window. The idea is that you only eat small amounts of vegetables and fruits throughout the day, then a large meal at night

As you can tell, some of these diets are more extreme than others. Before starting a diet that requires 24-hour fasting windows, you should consult with your doctor to ensure it’s safe. These diets are not intended for pregnant women or those with diabetes. 

How Often Can You Safely Repeat A 16 Hour Intermittent Fast?

Since 16:8 fasting diet plans aren’t as extreme as diets that require full 24-hour fasting windows, you can repeat this cycle as much as you want. Some practice the diet once or twice a week while others practice it every day. How often you do it can be personal preference. You can also ease your way into the diet as you see fit. 

It can’t be stressed enough that you should consult with your doctor before beginning any diet, especially a diet that involves fasting. If at any point during the fast you begin to feel nauseous, light-headed, or dizzy, you should stop the fast and eat something, preferably something nutritious, as soon as possible. These are signs from your body that you are in desperate need of nutrients for energy. 

What is Allowed During An Intermittent Fast?

As you may imagine, there is no food allowed during the fasting period. However, you can drink water, coffee, tea, and other non-caloric beverages during the fast. Depending on the diet, you may be allowed to eat low-calorie foods, but on diets such as the 16:8 and 12:12 diet, there are no snacks during the fasting period. 

You can take supplements during fasting as long as there are no calories inside of the supplements. In fact, many doctors may recommend taking supplements in order to get your body the nutrients it needs during the fasting period. Supplements allow you to get the benefits of a fast while still getting the nutrients, vitamins, and minerals you need to stay healthy. 

Drinks You Can Have Without Breaking Your Fast

Staying hydrated is important, no matter if you are fasting or not. However, while on a fast and attempting to achieve ketosis, you are not allowed to consume calorie-laden drinks or foods. Fortunately, there are more than a few beverages that are calorie-free and can be enjoyed during a fast. Let's discuss a few simple, quick, and beneficial beverages for a fasting period. 


Water is not only essential for digestion, and it will also help you to feel full during a fasting window. Dehydration is a common side-effect of fasting, so it is vital that you drink plenty of water throughout the fasting period. And with zero calories, water is perfect for you to enjoy as much of it as you can possibly hold. 

Lemon Water

Lemon water is another refreshing way to stay hydrated and gain that feeling of fullness while fasting. Without the addition of any sugar, lemon water doesn’t have enough calories to break your fast. You will want to stay away from packaged lemon drinks, though, as many have added calories and sugars that will break your fast and get you kicked out of ketosis. 

Unsweetened and Green Tea

Unsweetened tea is another acceptable beverage during intermittent fasting. In addition, there are several green teas that contain antioxidants beneficial in helping to burn calories. Just be sure to avoid adding any sugar or cream to your tea. 

Unsweetened Black Coffee

Coffee is a great beverage to have during a fast since it acts as an appetite suppressant and supplies the body with energy. Unfortunately, you can only drink your coffee black and unsweetened – not a popular way to drink coffee for many people. But, if you can drink it black and without sweeteners, then this is a great choice for you during your fasting window.

What Does The Body Do After Going Without Food For 12 Hours?

The main benefit of fasting is that your body is forced to look inside for energy rather than using carbohydrates and other nutrients from foods for energy. During the first 12 hours of a fast, your body begins to use stored fats for energy. This is why fasting is such a popular dietary method for those who are looking to lose weight quickly. 

Another reason why fasting helps you lose weight quickly is that it reduces your calorie intake, simply because you’re not eating. By partaking in fasting you may find it easier to cut back on calories every day. The energy restriction from a 12-hour fast may also benefit your metabolism, helping in weight loss.

What Takes Place In Your Body During A 16 Hour Fast?

The 16/8 intermittent diet is one of the most popular intermittent diets because it’s easy to follow, flexible, and is sustainable for the long term. The fasting window isn’t extreme and there are no strict calorie restrictions. It can also help you count down the amount of money you spend on food, so think of that as an added benefit. Here are some of the health benefits of fasting for 16-hours:

  • Weight loss - Fasting for 16-hours can boost your metabolism, quickly increasing weight loss
  • Improved blood sugar control - Fasting for 16-hours has been shown to reduce insulin levels by up to 31% and lower blood sugar by 3-6% (2)
  • Enhanced longevity - Fasting can help you live a longer, healthier life

The benefits of a 16:8 diet are essentially the same as a 12/12 diet. What diet works best for you will largely depend on what you’re hoping to get out of your diet. 

14 Hour Fast vs 16 Hour Fast

Once you have become accustomed to intermittent fasting, you will begin to explore the option of increasing your time spent fasting to boost the benefits it achieves. After all, the more time you spend fasting, the more time your body spends in autophagy and benefits from cellular health and repair. 

When choosing the right fasting plan for you, time spent fasting can be a crucial factor. A popular starting point for beginner fasters is the 12/12 intermittent fast. The 12/12 fast is when you fast for 12 hours and then eat for the next 12. The 14/10 fast involves fasting for 14 hours and then eating for 10. 

The 14/10 can be quite beneficial for anyone looking to step up their fasting game but not sure yet about the 16/8. A 14/10 fast can be beneficial for the transition, allowing your body to condition itself for a longer than 12-hour fast but not yet at a 16-hour one. Let’s explore some benefits and differences of each one so that you can pick the right one for your lifestyle and fasting journey. 

Key Benefits Of 14/10 Intermittent Fasting

With a 14/10 intermittent fasting plan, your body will begin to work through its stored calories and convert that fat into energy. This will not only assist you with losing weight but may also help in reducing bad cholesterol levels and help with lowering your blood pressure. Some individuals have also reported an increase in energy levels and receiving a better quality of sleep as a result. 

The results you experience from your fast will depend largely on your current level of health when beginning. Individuals who begin the fast overweight are more likely to see greater gains in weight loss, lowering blood sugar levels, and other up-front benefits. Those who start the fast at a healthier level may experience results that differ. It all really depends on your body and its ability to process the available fat. 

Top Advantages Of a 16/8 Intermittent Fast

A 16/8 intermittent fasting plan is when you can expect to see greater positive side effects. In 16/8, you will keep all of the benefits achieved in a 14/10, plus some. A major benefit of the 16/8 is that it can trigger autophagy. Autophagy is when your body begins to heal itself on a cellular level, feeding on the build-up of junk and renewing cells to a healthier level. 

Autophagy is very beneficial in that it is a great tool for preventing disease. Some people who have fasted have reported a reduced risk of diabetes, heart disease, cancer, and more. A 16/8 intermittent fasting plan allows your body to achieve optimal overall health. This can be boosted further through simple improvements in diet and exercise. 

Differences In Fasting Periods

The fasting time is the most apparent difference between the 14/10 and 16/8 intermittent fasting plans. On the 14/10 intermittent fast, if you time it correctly, you will spend a good chunk of your 14 hour fast asleep. If you have a meal at 8 p.m., go to sleep and wake up the next day ready to eat again at 10 a.m. Fasting becomes much more manageable when it is effectively planned for.

To a lesser extent, the same can be said about the 16/8 fast. Plan it right and you can sleep for half of your fasting time and only be awake for the other half of it. By eating your last meal at 6 p.m. you can then sleep away a good portion of the fasting time and wake the next day ready to eat again by 10 a.m. It may be a challenge to not get up in the morning and eat right away, but with time your body will adjust. The 16/8 fast is also great for those who don’t like to eat breakfast, aren’t big on snacking, and prefer larger meals. 

Successfully Reaching Autophagy

On a 14/10 intermittent fast, you may achieve the beginning stages of ketosis. However, autophagy won’t be achieved until you have fasted for at least a full 16 hours. The minimum for autophagy is 16 hours which is why the 16/8 intermittent fast is so popular. You get a lot of the long-term fasting benefits and you are still able to eat every day. 

Ideally, autophagy is where you want your fasting plan and body to be. Once you have succeeded at reaching autophagy, your body will look and feel noticeably better. This is because those damaged and dead cells will be purged and new ones can then be regenerated. 

Choosing The Ideal Intermittent Fast For You And Your Health Goals

Intermittent fasting is a generally safe way to lose weight and improve your overall health, but may not be a good plan for everyone. This is why it is important to talk with your healthcare provider before beginning any new diets or plans. Your doctor will know what your health and body are capable of handling at the moment and will provide you with valuable insight on what may be the best plan of action for you at that time.  

The following individuals should take care to speak with their doctor before attempting an intermittent fasting plan:

  • If you are underweight
  • Have nutritional deficiencies
  • Have been diagnosed with diabetes
  • If you take multiple medications throughout the day
  • Have, in the past or present, struggled with eating disorders
  • Women who are pregnant or are trying to conceive
  • Women with fertility issues
  • Women who have a history of missed periods
  • Anyone under the age of 18

Ultimately, you want to ensure that you reap the rewards of whichever intermittent fast plan you choose while also staying healthy and safe. Your lifestyle and goals surrounding the fast may also be good indicators as to which fasting plan would be best for you. The best approach is one that can be easily adapted to your lifestyle. 

Remember just because you begin with a 14/10 fast doesn't mean that you can’t later switch it up and start a 16/8 once you have grown accustomed to the fasting process. It is important, no matter what you choose that you choose the one that benefits you most and that you can be successful in right now.

Spermidine Supplements May Be Able To Help

One supplement that can help you get the most out of your fasting diet is spermidine supplements. This is because spermidine helps induce something called autophagy. This is the body’s process of replacing old and potentially damaged cell parts with healthier new ones. Autophagy literally means ‘self-eat.’

This process helps keep you feeling and looking young while also lowering your chances of developing aging diseases such as Parkinson’s and Alzheimer’s. While it is possible to get your recommended daily intake of spermidine through your diet, it’s recommended to take supplements so you ensure you get the right dose. Simply taking your supplements with your dinner is a great way to remember to take spermidine supplements every night. 




  • Don Moxley - Director of Applied Science

    Don Moxley is the Director of Applied Science at Longevity Labs. Moxley draws upon his career as an athlete, a sports scientist, and an instructor to lead and educate on the science of autophagy and longevity.