October 11, 2021 • 2hr 22min

Effects of Fasting & Time Restricted Eating on Fat Loss & Health

Huberman Lab

In this episode, Dr. Andrew Huberman discusses the science and practice of fasting, also called time-restricted feeding. He reviews the data on how limiting food intake to specific portions of every 24-hour cycle impacts weight loss, fat loss, liver health, mental focus, muscle, longevity and more. Huberman explains how "fasted" is contextual and relates to blood glucose levels and their downstream effects. He also discusses how the depth of fasting can be adjusted with behaviors such as different types of exercise or with glucose disposal agents. The episode covers the optimal fasting protocol, including both the absolute (non-negotiable) and variable (contextual) features of a fasting/time-restricted feeding protocol to get the most benefits. Huberman also discusses what does and does not break a fast, the effects of fasting on hormones like testosterone and cortisol, and on fertility.

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Key Takeaways

Time-restricted feeding (limiting food intake to a specific window each day) can have significant health benefits, including weight loss, improved metabolic health, and better liver function
An 8-hour feeding window seems to be ideal for most people to get the benefits of time-restricted eating while still being socially/practically feasible
When you eat is as important as what you eat - eating late at night is particularly detrimental to health
Fasting helps synchronize circadian rhythms and gene expression throughout the body
Sleep-related fasting (not eating close to bedtime) is especially important for health benefits
Consistency in timing of the feeding window is key - shifting it around on weekends can negate benefits
Glucose disposal through exercise, supplements like berberine, or other means can help transition to a fasted state faster
Salt intake during fasting can help manage hunger and energy levels
Very short feeding windows (4-6 hours) may lead to overeating and weight gain in some people
Time-restricted feeding may help bias weight loss towards fat loss over time by increasing fat-burning enzymes

Introduction

In this episode, Dr. Andrew Huberman discusses the science and practice of fasting, also called time-restricted feeding. He reviews the data on how limiting food intake to specific portions of every 24-hour cycle impacts weight loss, fat loss, liver health, mental focus, muscle, longevity and more.

Huberman explains how "fasted" is contextual and relates to blood glucose levels and their downstream effects. He also discusses how the depth of fasting can be adjusted with behaviors such as different types of exercise or with glucose disposal agents.

The episode covers the optimal fasting protocol, including both the absolute (non-negotiable) and variable (contextual) features of a fasting/time-restricted feeding protocol to get the most benefits. Huberman also discusses what does and does not break a fast, the effects of fasting on hormones like testosterone and cortisol, and on fertility.

Topics Discussed

Basics of Time-Restricted Feeding (11:20)

Huberman explains the foundational concepts of time-restricted feeding:

It involves limiting food intake to a specific window of time each day
This creates periods of feeding and fasting that impact metabolism
When we eat, blood glucose and insulin rise
When we don't eat, glucose and insulin fall and other hormones rise
The transition between fed and fasted states takes time - you're not instantly fasted after your last bite

He emphasizes that "When you eat is as important as what you eat" in terms of health impacts.

Key Research on Time-Restricted Feeding (25:33)

Huberman discusses landmark studies on time-restricted feeding, including:

A 2012 mouse study by Satchin Panda showing an 8-hour feeding window prevented metabolic disease even with a high-fat diet
The origin of the 8-hour window in this study (based on researcher constraints, not biological necessity)
Human studies showing benefits of 8-10 hour feeding windows

He notes that "80% of the genes in your body and brain are on a 24-hour schedule" and time-restricted feeding helps synchronize these circadian rhythms.

Optimal Fasting Protocol (39:45)

Huberman outlines key elements of an optimal fasting protocol:

No food for at least 1 hour after waking
No food for 2-3 hours before bed
Target an 8-hour feeding window
Be consistent with timing of the window
Place the window during active daytime hours

He explains that "sleep-related fasting is vital" for health benefits, so avoiding late night eating is crucial.

Glucose Clearing and Transitioning to Fasted State (1:13:20)

Huberman discusses ways to accelerate the transition from fed to fasted state:

Light exercise like walking after meals
High-intensity exercise (timing matters - better later in day for glucose lowering)
Glucose disposal agents like berberine or metformin (use caution)
Lemon juice or other acidic foods

He notes "glucose clearing is an important aspect of the transition from the fed state to the fasted state."

Effects on Hormones and Fertility (1:32:00)

Huberman reviews research on how time-restricted feeding impacts hormones:

May slightly lower free testosterone levels
Can reduce cortisol levels
Very short feeding windows may negatively impact fertility

He recommends an 8-hour window as a good balance for hormone health for most people.

Fat Loss and Metabolic Effects (1:49:12)

Huberman explains how time-restricted feeding may enhance fat loss over time:

Increases fat-burning enzymes like hepatic lipase
Decreases enzymes that inhibit fat breakdown
May bias more weight loss to come from fat stores vs other tissues

He notes this effect seems to occur after consistent time-restricted feeding for 60+ days.

What Breaks a Fast? (1:53:15)

Huberman discusses what does and doesn't break a fast:

Water, black coffee, and plain tea do not break a fast
Even 1g of sugar can disrupt fasting benefits
Effects are contextual based on recent food intake, exercise, etc.
Artificial sweeteners likely don't break a fast in moderation

He emphasizes "it's all contextual" - there's no universal rule for what breaks a fast.

Salt Intake During Fasting (2:01:42)

Huberman explains how salt intake can help manage energy and hunger during fasting:

A pinch of salt in water can stabilize blood volume and reduce jitters/lightheadedness
Helps offset sodium loss from caffeine intake
Can make it easier to reach your feeding window start time

He notes "sometimes you think you need food, but what you really need is salt."

The Ideal Fasting Protocol (2:11:12)

Huberman summarizes the key elements of an ideal fasting protocol:

No food for 1+ hour after waking
No food 2-3 hours before bed
8 hours of sleep
8-hour feeding window (may need to target shorter to actually achieve this)
Consistent timing of feeding window
Window placed during active daytime hours
Consider exercise timing, protein intake for muscle gain if relevant
Use glucose disposal methods if needed
Salt intake to manage energy/hunger

He emphasizes this is an ideal to work towards, not rigid rules - consistency and sustainability are key.

Conclusion

Time-restricted feeding offers significant potential health benefits by aligning our eating patterns with our circadian rhythms. An 8-hour feeding window placed during active daytime hours and avoiding late night eating appears to be ideal for most people. Consistency in timing is crucial.

While the specifics may vary based on individual goals and lifestyles, the core principles of extending the overnight fast, avoiding late night eating, and maintaining a consistent feeding window can help optimize metabolic health, weight management, and overall wellbeing.

Huberman emphasizes that understanding the mechanisms allows for flexibility in applying these principles. The goal is to find a sustainable approach that works within your lifestyle while maximizing the health benefits of fasting.