The following is a summary by Dr. Rhonda Patrick, renowned expert in nutrition, metabolism and aging. She has a Ph.D. in Biomedical science and answers the questions about time-restricted eating and fasting and it’s benefits. Her transcripts were posted on a podcast in May 2017 after being interviewed by Tim Ferriss.

. Some people prefer a more extreme type of restricted eating which is a 16:8 intermittent fasting. This means fasting for 16 hours and only eating within a specific 8 hour window. A common example is eating from noon-8 PM, so you skip breakfast.

The duration of the time windows are important because they have to do with our circadian rhythm. There are metabolic changes throughout the day. In other words, when healthy adults eat meals that have the same macronutrient and calorie content at breakfast, lunch and dinner, the postprandial glucose (the amount of glucose in the blood after a meal) is lowest after breakfast and highest after dinner even though the meals are 100% identical. Besides these metabolic changes, we know that metabolic genes are more active during the day and less active at night. The reason is because humans are diurnal beings which means most of our activities are during the day, including feeding, exercising and working, while resting at night.

Our circadian rhythm is regulated by light (by the presence of an internal clock in the brain) as well as timing of our food intake which is influenced by peripheral tissues such as the liver that influence metabolism. These clocks regulate thousands of genes which are expressed based on what time it is. Even the bacteria in our gut (microbiome) has its own circadian rhythm with the species of bacteria changing according to the time of day. Unfortunately due to changing work schedules and artificial lighting, peoples’ eating times have occurred later in the day which can have negative consequences. Eating late “resets” our internal clocks and causes an imbalance of metabolism.

Research has shown some amazing results if you limit your eating between 9-12 hours per day, which means fasting for 12-15 hours.  These benefits include:

1. Decreased breast cancer risk and reduction in recurrence by as much as 36%

2. Decreased fat mass and increase in lean muscle mass

3. Improved glucose intolerance and lipid levels

4. Reduced inflammation, especially if fasting after 5 PM with a reduction in the inflammatory marker C-reactive protein (CRP).

5. Increased weight loss and prevention of obesity

6. Improved sleep

7. Favorable improvements in gene expression and reduced cancer risk

Dr. Rhonda Patrick feels that the most important thing is to mitigate chronic systemic inflammation. And I couldn’t agree more. It is one of the most important predictors of successful longevity that increases in importance with age.

So if you decide to eat within a 9-hour window and fast for 15 hours, you may also find that it enhances your endurance and athletic performance. This is because it takes 10-12 hours for glycogen stores to be depleted. Fatty acids are then pulled from adipose tissue (fat) which are transported to the liver and converted into ketone bodies. These ketones are transported to a variety of tissues such as muscle and used for energy.

As you can see, there are many benefits in time-restricted eating. Many people also prefer to do a 24-hour fast to “reset” their metabolism. That can also be helpful even one or two times per week. Drinking water, tea or broth for 24 hours is easy to do without setting a timer of when to eat and not to eat. Any prolonged fasting more than 3 days should be supervised or approved by a physician.