Written by Stephen Anton PhD on November 29th, 2022

Intermittent fasting has become one of the most popular topics in recent health conversations.

It is also becoming more widely accepted by the general medical community as a lifestyle approach to assist with weight management and potentially reduce the risk of some chronic disease conditions, such as type 2 diabetes.

There are many different types of fasts that one can consider, which can range from several hours to several days on end.

Today we will cover the 18/6 intermittent fasting plan which involves daily fasting for 18 hours, and a 6-hour eating window.

In contrast to starvation, intermittent fasting is the voluntary withholding of food for health, spiritual, or other reasons. Food is easily available, but you choose not to eat it.

If done correctly, fasting allows the body to use its stored fat for energy. But if done incorrectly, it can feel very unpleasant and result in uncomfortable symptoms, such as headaches, fatigue, and extreme hunger.

Fasting has no standard duration, as it is merely the absence of eating or drinking any beverage that contains calories. Anytime that you are not eating, you are technically “fasting.”

However, it typically takes 4-6 hours to metabolize food consumed during a meal. Thus, most people do not enter the “fasted state” until 6-8 hours after their last meal.

The term intermittent fasting, however, can mean many different things. So, when someone says they are practicing intermittent fasting, it’s good to clarify the type of intermittent fasting they are doing.

Depending on the type of fasts used, the effects on the body will be different, similar to how different types of exercise routines have different effects on the body. Thus, it’s important to understand the potential pros and cons of different types of intermittent fasting approaches.

Before we get into the potential pros and cons of this particular approach to intermittent fasting, it’s important to explore how fasting works and why it could have such dramatic results in shifting the body’s metabolism to burn fat for energy instead of sugar/glucose.

If done correctly, fasting results in the body flipping its metabolic switch.

Flipping the metabolic switch refers to the very natural process in which the body shifts its energy source from glucose to ketones, which are high energy molecules derived from your own body fat while fasting.

And this is where the extended fast can come in. The longer the fast, the more likely it is that the metabolic switch will be activated and lead to higher levels of ketones in the blood.

So, there are definitely benefits to longer fasts but there are also potential downsides that should be considered.

Of course, what someone does while fasting in terms of energy expenditure can also influence whether or not the metabolic switch is activated.

In general, the longer the fast, the more likely you are to tap into your body’s fat stores and to lose unhealthy weight. This is why one common approach, called alternate day fasting, is so effective for fat and weight loss.

For this reason, an alternative approach, called the 5/2 plan, has become more popular recently. With this approach, an individual fasts for two non-consecutive days of the week.

For the reasons mentioned above, a particular type of intermittent fasting, called time restricted eating, in which the fasting is limited to portions of the day, rather than the entire day, has become popular.

This is typically what most people mean when they say they practice intermittent fasting.

A common type of time-restricted plan is the 16/8 approach where an individual will fast by not eating from the period of time after dinner (generally 8 pm on) until lunch time (12 pm) the next day.

With the 18/6 plan, the daily fasting period is extended to be approximately 18 hours, instead of the commonly recommended 16 hours.

The reason one may consider 18/6 plan over the 16/8 plan is that it has the potential to produce even greater health and metabolic benefits. It also increases the likelihood that the metabolic switch will be activated.

For many people, this switch may not be activated from a 14-16 hour fast alone and thus they may not experience the many potential benefits associated with intermittent fasting.

Before trying this plan, it’s important to recognize that this is an advanced type of intermittent fasting and it is not recommended until one has mastered easier approaches to time restricted eating, such as the 14/10 plan and/or 16/8 plan.

Just as you would not try to run five miles if you are only capable of running one mile before getting winded, you should not attempt the 18/6 plan until you are able to comfortably do a 16 or 17 hour daily fast.

As with any extended fasting program, there needs to be a balance between the fat burning period and the eating/recovery period.

The eating/recovery period is when the body is provided with the fuel it needs to function, as well as tissue repair and growth. By shortening the eating period, it naturally shifts this balance away from muscle growth and onto fat burning.

This is not to say that you cannot gain muscle or lean tissue while following the 18/6 plan but rather that it would likely be more challenging to do so than when following the 14/10 or 16/8 plans.

In general, you want to align the fasting and eating periods with your body’s natural circadian rhythms. This means not eating during the night time, when the cellular process of autophagy is most active, and focusing on consuming all calories during the day time.

For the 18/6 plan, a common eating windows that many people find sustainable is from 12 to 6 pm but this can be adjusted depending on individual preferences. This means that the fasting period would be from 6 pm to 12 pm the next day.

When adapting to a new lifestyle involving extended fasting periods, it can be helpful to have guidelines to determine whether or not you should continue fasting or should break the fast.

Below is a list of key signs that I believe indicate you are in a healthy fasted state and can continue with the fast.

This is not an exhaustive list, but I think it is enough to help you evaluate if you are in a healthy fasting state or not.

If you are experiencing one or more of the above signs while fasting, you have most likely activated your metabolic switch and can feel comfortable continuing with the fast.

On the other hand, there are some key symptoms that would suggest you are not in a healthy fasted state and should consider breaking the fast.

Unfortunately, many people experience these symptoms when they try to fast for an extended period of time.

As mentioned above, the key factor that I believe determines whether you enter the healthy fasted state is whether or not the body can flip its metabolic switch.

The beauty of fasting is that there are many types to choose from.

The 18/6 intermittent fasting plan is a more advanced type but can deliver amazing results once your body adapts.

Begin with a shorter fast like a 14/10 fast or a 16/8 fast, and if you notice you can complete those comfortably, start increasing your fasting window by 30 or 60 minutes until you get to 18 hours.

As with most things, it’s best to take it one step at a time.