Dr. Andrew Huberman, Ph.D. is a Professor of Neurobiology and Ophthalmology at Stanford University School of Medicine. His lab focuses on neural regeneration, neuroplasticity, and brain states such as stress, focus, fear, and optimal performance.
In this episode of Huberman Lab, Dr. Huberman reviews the science and practice of time-restricted eating and fasting. He discusses data, tips for best practice, and its impact on weight loss, focus, muscle, and longevity.
Host: Andrew Huberman (@hubermanlab)
Time-restricted eating or intermittent fasting means restricting one’s eating to a specific period during a 24-hours day – or going without food for a fixed number of days
There is a biological difference between fasting and time-restricted feeding
Because we don’t eat during sleep, everyone deploys some sort of time-restricted eating or fasting
Time-restricted eating have a powerful impact from weight loss and fat loss to longevity
When you eat is just as important as what you eat – it’s important that the feeding window take place during the most active parts of the day
The 8-hour feeding window was really born out of time constraints of the lab, not necessarily because it’s the holy grail of feeding times (though it has been repeatedly tested and is a good rule of thumb)
Resources for time-restricted eating: myCircadianClock, Zero app
Read more: Comprehensive Review On Fasting In Humans
Blood glucose and insulin go up when you eat and down when you don’t eat (barring type 1 or 2 diabetes)
What you eat has a differential impact on the rise in blood glucose (e.g., simple carbs and sugars will raise it the most, grains will raise it more than fibrous carbs like lettuce, etc.)
High blood glucose is correlated with mortality
Almost everyone has an increasing, resting blood glucose level as we age
In endurance athletes, time-restricted eating led to a significant decrease in free testosterone (not to the extent that it should be avoided unless you have low testosterone at baseline)
Studies in athletes have shown significant reductions in cortisol as a result of time-restricted eating
Shortening the feeding window to less than 8-hours can increase stress hormones and pro-inflammatory hormones and decrease some sex hormones
Effects on fertility: reducing food intake or food calories too much can have negative effects on the ovulation cycle in women and sperm count in men because signals in the brain are looking for good reproductive conditions without stress  
Alternate day fasting (eating one day, fasting the other) can lead to weight loss and have positive effects on glucose control – but it’s less likely to sustain over time
Using time-restricted eating + caloric restriction creates the best hormonal environment for fat loss
If the main goal is to lose weight (i.e., weight loss not health), it doesn’t matter what you eat as long as the calories burned exceed the calories consumed
Many factors impact calories burned (e.g., resting metabolic rate, hormones, exercise, non-exercise activity thermogenesis, etc.)
Time-restricted eating anchors gene systems of the body and provides a more stable circadian rhythm
Benefits you can’t see: regulation of liver health, inflammation, decreased blood pressure, reduced oxidative stress, enhance healthy microbiota, clarity of mind
Fasting that takes place during sleep is critical for longevity: during sleep we’re undergoing cellular processes related to reducing inflammation, clearing out debris from the brain that clear dementia
1. Don’t ingest any food first hour after waking up
Extend natural deep fast (from sleep) into the morning as long as possible
2. Don’t ingest any calories 2-3 hours before bed
Take advantage of a deep fast during sleep: if you eat late in the night, you will not enter fasting for several hours into sleep because your body is still digesting
Schedule to maximizes health & social eating: consume calories from 12pm-8pm (meaning no calories after 8pm)
  • Caveat: large meals will take longer to digest than smaller meals
3. Tip: if you want to have an 8-hour feeding window, you should probably think about it as a 6 or 7-hour window because people tend to eat a little past feeding window
When people restrict the feeding window too much (i.e., 4-6 hour window), they tend to eat more than metabolic need demands
One meal per day: people tend to maintain or lose weight (but there are very few studies on this)
Muscle tissue is better able to undergo protein synthesis early in the day – before 10am ideally which can be tricky to balance when considering 8-hour window
If your main interest is in building or maintaining muscle, it’s good to consume protein early in the day regardless of when exercise takes place
To start intermittent fasting or shift eating window: allow yourself a transition period of 7-10 days where you shift window one hour until you get to the desired schedule
Drifts in the feeding window (e.g., weekends versus weekdays, special occasions) can cause disruptions in circadian clock rhythms that can take several days to recover from
Consumption that will not breakfasted state: water, tea (no sugar or milk), coffee (black; data is mixed on plant-based sweeteners)
The best way to know what’s going on during feeding and fasting is to wear a continuous glucose monitor (though understandably it’s not desirable for everyone)
Time-restricted eating is really more about accessing fasted state than it is about eating states Glucose clearing through light movement (i.e., 20-minute walk) or light exercise
High-intensity interval training later in the day (afternoon) can lower blood glucose and help transition to a fasted state
Berberine is over the counter and has effects almost identical to metformin which can mimic fasting; it can be used when consuming high carbohydrate meals but is a little difficult to titrate
Feeding and fasting is about setting conditions in the body: you are either promoting cellular growth or cellular repair