There are many methods of fasting, each with their own specifications and reported benefits. Previously we introduced the concept and definition of fasting, as well as a brief description of the types of fasting.  Here we will go into greater depth about these types so you know the pros and cons:

TYPES OF FASTING AND THE BENEFITS OF FASTING

In lay terms, fasting is the omission of food. However, it truly is much more than just that. What are the benefits of fasting? What determines the fasting state is actually a combination and quantity of the specific macro- and micronutrients of the foods we eat. Luckily, there is more than one way to fast, but there is only one that has been shown to induce rejuvenation and regeneration.¹

Time-Restricted Feeding (TRF)

TRF is a form of intake restriction, specifically focused on the when and how long eating occurs rather than macronutrients.^2,3 This type of fasting is based off of the theory that our ancestors likely fed during daylight with limited resources and fasted during the night. Interestingly, this is controlled by what we call the circadian system. The circadian system oscillates every ~24 hours in a rhythm that enables organisms to respond to the light-dark cycle, which coincides with food accessibility. Today, this system has been disrupted due to long work hours, artificial light exposure, and haphazard eating behavior. To get back control of this system, we can mimic the natural circadian pattern by restricting feeding to a certain period of time.

As far as benefits of fasting and TRF specifically, preclinical trials have been positive, but clinical trials are inconsistent.

Preclinical⁴:

• Reduction in body weight, total cholesterol, triglycerides, glucose, insulin, inflammatory markers, insulin resistance

Clinical^4,5:

• Fat mass decrease, muscle mass retention, IGF-1 decrease, adiponectin increase, total leptin decrease (when adjusted for fat mass, this did not change)
• Decreased body weight (inconsistent), triglycerides, glucose, LDL

Intermittent Fasting (IF) – How to Intermittent Fast

Intermittent fasting is a form of fasting where the individual will fast for an interval of time, usually no more than 48hrs, and then eat normally for the remaining period of time per week. The most common example of this is known as the “5:2” diet, where the individual restricts calories for 2 days, consecutive or not, and then eats normally for the remaining 5 days.

For the most part, the preclinical trials have shown positive results, but clinical trials have been mixed.

Preclinical⁶

• Reduction in body weight, glucose, insulin, inflammation, myocardial tissue damage, and leptin; elevation of adiponectin levels

Clinical^7,8

• Maintenance of healthy levels of blood glucose
• Increased metabolism of fatty acids and ketones
• Lower adherence rates compared to daily caloric restriction
• No comparable difference between alternative day fasting versus daily caloric restriction regarding: weight loss, fat mass loss, blood pressure, cholesterol, insulin sensitivity, inflammation

Periodic Fasting

Periodic fasting is simply fasting for a periodic time; usually, this is anywhere from 4 to 7 days. The overarching goal of periodic fasting is to induce the stress of fasting onto the body for a period of time in order to induce the stress-resistant mechanisms in the body to combat future stressors^1,9. An example of a periodic fast would be either a water fast for 5 days or a fasting-mimicking diet for 5 days.

As far as the preclinical trials go, the results are promising. The same can be said for the clinical trials.

Preclinical¹

• Extend lifespan, induce stress resistance, and promote visceral fat loss
• Induce stem cell proliferation
• Promote cellular regeneration and rejuvenation
• Improve cognitive performance

Clinical^1,10

• Maintain healthy levels of glucose, triglycerides, LDL, total cholesterol, diastolic blood pressure, insulin-like growth factor-1, and insulin

Promote weight loss (specifically visceral adiposity) while preventing lean body mass loss

Ultimately, there are multiple ways to fast, but it seems that there are ways to optimize this process. Specifically, if you eat within a certain window of time, it appears that we can gain many benefits from simply eating whenever we want to – which makes sense. Not everything is meant to be function at all times and resting is important! It is almost like a car; imagine if you kept the engine on all day, every day for weeks on end. It is sure to break far sooner than if you were to drive it normally. The same can be said with the body. But not only does the timing of meals seem to be important, but also the duration of the fast. It seems that the body takes a little time to initiate a response and needs to be in the “fasting” state for at least 4 days in order to gain the benefits after the fast is over.