Effects of Fasting & Time Restricted Eating on Fat Loss & Health | Huberman Lab Podcast #41
Introduction, Blood Glucose & Mortality, Mice Vs. Humans (00:00:00)
- The podcast explores the relationship between fasting, or time-restricted eating, and health.
- The focus is on how fasting schedules can influence aspects of health such as weight loss, fat loss, muscle maintenance, organ health, inflammation, recovery, cognition, mood, lifespan, and others.
- The discussion probes the workings of intermittent fasting and time-restricted feeding.
- The presenter touches on tools that can aid in scheduling and mitigating potential negative impacts of unregulated eating periods.
- A study exploring the relationship between fasting blood glucose and mortality is highlighted, revealing that in humans, increased blood glucose is associated with increased mortality.
- In this context, the distinction is made between studies conducted on mice and those on humans, and this difference will be carried through the rest of the discussion.
Neuroplasticity Protocols & Online Lecture (00:09:42)
- The presenter references a free online event held by Logitech where he gave a talk about how modern principles of neuroplasticity can be effectively used for learning and teaching.
- He covered how various tools in and out of the classroom can facilitate better and longer-lasting learning, based on current neuroscience research.
- The discussion also included the introduction of a 'plasticity super protocol' outlining these tools.
Feeding, Fasting, Performance (00:11:20)
- In discussing the relationship between feeding, fasting, and performance, the presenter instances the term 'time-restricted feeding' to encapsulate intermittent fasting and eating within specific time frames.
- The focus is on biological mechanisms, arguing that understanding these mechanisms allows for more control and flexibility over mental and physical health.
- Strategies and tools for implementation are provided within the discussion of these mechanisms.
- The presenter emphasizes that the goal is to equip listeners with the understanding they need to navigate life effectively.
Calories-In, Calories-Out (CICO); Perfect Diets (00:13:50)
- The topic of diet and nutrition is often controversial and largely dependent on individual biology.
- A study published in JAMA by Chris Gardner and his team in 2018 found that there wasn't a significant difference in weight loss between individuals following a healthy low-fat diet and those on a healthy low-carb, high-fat diet.
- These results generated a lot of discussion in the nutrition science community and among the general population.
- The study emphasized that if the main goal is to lose weight, what one eats doesn't matter as long as the number of calories burned is higher than the number consumed.
- However, factors including the amount/type of exercise, basal metabolic rate, non-exercise induced thermogenesis, and hormones can impact the calories burned part of the equation.
- The ideal diet or feeding schedule will depend on individual factors and conditions, such as hormone levels.
- The perfect diet for an individual is contextual and depends on factors such as what one did yesterday and what one is planning to do tomorrow.
Feeding-Induced Health Conditions (00:19:48)
- What and when one eats sets conditions in the body which can be beneficial or detrimental to health.
- When you eat is as important as what you eat in regards to health parameters, particularly liver and mental health.
- Typically, when you eat, your blood sugar levels and insulin go up. The extent of this increase depends on what and how much you've eaten.
- Blood sugar and insulin levels go down when you don't eat, and the longer since your last meal, the lower your blood glucose and insulin will likely be.
- When you don't eat, other hormones associated with the fasted state, like glucagon-like peptide 1 (GLP1), go up.
- Insulin and glucose levels take some time to decrease even after you've stopped eating.
- The health benefits from time-restricted feeding come about because certain conditions are met in the brain and body over a certain amount of time.
- In the field of nutrition, there are a few landmark studies that provide a cornerstone for building our understanding of what and when to eat, like the Gardner study mentioned previously.
Time Restricted Eating: When We Eat Is Vital (00:25:33)
- Satchin Panda, a professor at the Salk Institute of Biological Studies, is a major contributor to the literature on time restricted feeding and intermittent fasting.
- Satchin's landmark study published in 2012 showed that mice who ate a high-fat diet only during a restricted feeding window of eight hours each day maintained or lost weight over time. In contrast, mice that consumed the same diet and amount of calories unrestrictedly gained weight and became sick.
- Furthermore, mice that restricted their feeding to an eight-hour window showed improvements in health markers and reversal of some prior negative health effects.
The Eight Hour Feeding Window (00:29:45)
- The eight-hour feeding window used in Satchin's study was mainly due to logistical reasons and the graduate student’s schedule, not because there was anything inherently significant about this specific time frame.
- Different time restricted windows may impact health parameters and weight loss differently, but the eight-hour feeding window holds no special status.
Feeding Deep Into the Night Is Bad (In Humans) (00:31:26)
- The timing of the feeding window within the 24-hour cycle is crucial, with the best effects typically seen when feeding is restricted to the more active parts of the day.
- Night-time eating has been shown to be detrimental to health with many studies pointing to this fact.
- This study found that restricting food intake to a particular phase of the 24-hour cycle benefited factors like lean body mass, fat loss, and brought about regular and stable circadian rhythms.
- The study also showed that when mice limited their eating to an eight-hour period within the most active phase of their 24-hour cycle, many of the genes associated with the body's circadian clocks had regular, healthy patterns.
- Similarly, for optimal health, humans should aim to eat during their more active phase (typically daylight hours), accompanying light exposure, which acts as the primary way our bodily systems get entrained or synced with the external light-dark cycle.
Liver Health (00:36:33)
- Constant feeding throughout the day may lead to liver disease in mice due to the generation of fatty deposits in the liver.
- Time-restricted feeding can reverse these harmful effects, maintaining and even improving liver health in both mice and humans.
- The benefit comes from limiting the body's constant active process of digestion, which can become problematic when it extends over too large a part of the 24-hour cycle.
- Continuous eating patterns trigger increased expression of certain proteins and genes such as TNF alpha, IL-6, and IL-1, which are pro-inflammatory markers.
- These markers are not inherently harmful but become troublesome when overproduced due to constant eating patterns.
- Time-restricted eating schedules may contribute positively to weight maintenance or loss, liver health, energy expenditure, inflammation regulation, and other aspects of health.
Time Restricted Feeding Protocol: Rules (00:39:45)
- Metabolic and health benefits, including weight maintenance, can be achieved by not consuming food within the first hour of waking up and for at least 2-3 hours before bedtime.
- Ingesting any type of calorie, liquid or food during these specified periods can lead to poorer health outcomes regarding weight and liver health, among others.
When to Start & Stop Eating (00:41:35)
- The eating window's ideal timing and duration are often questioned in relation to intermittent fasting.
- While there isn't a single answer, general frameworks suggest that it's best to extend the sleep-related fasting period either into the morning or to start it in the evening.
- During sleep, the body undergoes processes like autophagy (cleaning up dead or injured cells) governed by circadian genes.
- By avoiding food for the first few waking hours or starting the fast earlier in the day, the body can maintain a 'deep fast' which could potentially have more significant health benefits.
Gastric Clearance, Linking Fasting to Sleep (00:45:38)
- Digestion and energy utilization from food takes about five to six hours after a meal.
- Optimal fasting and eating schedules should be synchronized with sleep patterns to maximize the health benefits.
- A midday feeding window (eating from noon to 6 PM) can maximize the benefits of intermittent fasting and time-restricted feeding, but may not be practical for many due to social and work commitments.
- Consuming the last meal of the day a few hours before bedtime can ensure the body enters a fasted state during sleep.
- Fasting during sleep is associated with a number of healthy cellular processes, including the clearing of metabolic debris and potential offsetting of dementia.
- Best eating schedules for both health benefits and social considerations include starting to eat each day around 10:00 AM or noon, with the last meal occurring by 8:00 PM, allowing the body to transition from feeding to fasting before sleep.
Effects of Specific Categories of Food (00:52:35)
- The type and volume of food consumed have a significant influence on the transition from fed state to fasted state.
- Larger meals and meals with a high fat content take longer to digest, delaying the onset of a fasted state.
- Consuming calories in a liquid form accelerates digestive processes, leading to faster gastric emptying and a quicker start to the fasted state.
- Foods high in sugar lead to steeper and quicker rises in glucose and insulin, while foods high in fiber and fats result in a more sustained glucose release.
- Calculating the optimal feeding window should factor in the types of food consumed and individual lifestyles, ensuring the chosen meal schedule is maintainable long term.
Precision In Fasting: Protocol Build (00:55:40)
- Satchin and colleagues have created a free-cost website, My Circadian Clock, to examine the feeding behaviors of thousands of individuals over extended periods of time.
- Findings from tracking eating habits reveal that almost everyone underestimates their feeding window. In most cases, individuals' eating windows are longer than they anticipated.
- If aiming for a 10-hour feeding window, one should aim for an 8-hour feeding window as most people generally eat a bit outside their intended eating window.
- Several rules for a fasting/time-restricted eating schedule are listed: no food for at least an hour after waking up; no food intake for two to three hours before bedtime; shorten your preferred eating window by two hours to account for extended eating windows in reality.
4-6 Hour Feeding Windows (00:59:30)
- Studies indicate that very short feeding windows of about 4-6 hours result in a number of positive health effects such as increased insulin sensitivity, improved pancreatic function, reduced blood pressure, and decrease in evening appetite.
- However, such short feeding windows do not result in weight loss and may instead lead to weight gain, likely due to overconsumption of food within the feeding window.
- Adherence to the diet regimen appears to be higher with an 8-hour feeding window and has shown benefits across several parameters including inflammation, weight loss, and fat loss.
- One meal a day schedule has been shown to result in either weight maintenance or loss.
Protein Consumption & Timing for Muscle (01:03:08)
- Recent studies indicate that muscle tissue responds better to protein synthesis early in the day, a beneficial consideration if your main interest is maintaining or building muscle.
- As such, protein intake should ideally occur before 10 a.m. which supports muscle tissue maintenance and/or growth.
- This improved capacity for muscle growth and maintenance seems to occur regardless of when weight-bearing exercise occurs during the day.
- While ingesting protein later in the day isn't detrimental, prioritizing protein intake early in the day can enhance muscle maintenance and hypertrophy efforts.
- As such, individuals interested in muscle maintenance and hypertrophy might benefit from shifting their feeding window to earlier in the day.
How to Shift Your Eating Window (01:08:13)
- It's recommended to transition your eating window over a period of one week to 10 days. Each day should see your feeding window shift by about an hour.
- Once a comfortable feeding schedule is established, it should be maintained for at least 30 days, but ideally indefinitely.
- People generally think they're eating in an eight-hour window, but most often, the window is broader.
- The feeding window often fluctuates significantly over a 24-hour period. For instance, on the weekends, people tend to eat according to a different "time zone". This can disrupt the circadian clock mechanisms and cause metabolic disturbances, requiring two to three days for recovery.
- It's vital to have a regular feeding window. If the window keeps shifting, it offsets some of the health benefits of intermittent fasting.
- People should consider what feeding schedule they can adhere to on a regular basis. It's also crucial to realize that they often underestimate their actual feeding window. They should strive to place their eating window consistently within the 24-hour cycle.
- Individuals do not have a rigid feeding window unlike lab mice. They have access to food almost 24 hours a day. Hence, they can take measures to offset the potential "drift" in their feeding window.
Glucose Clearing, Exercise & Compounds (01:13:20)
- The transition from a fed state to a fasted state is not limited to the time of eating but also includes the period of metabolic and digestive processes that follow. This can be referred to as being in a 'fed state'.
- The transition from a fed to a fasted state can be accelerated by 'glucose clearing', which can be achieved through various means including light movement or exercises like walking.
- A simple 20-30 minute walk after dinner can significantly reduce the time it takes to transition from a fed to a fasted state.
- High-intensity interval training (HIIT) late in the day can lower blood glucose levels and aid the transition into a fasted state. However, it can have an opposing effect if performed early in the day, causing blood glucose levels to increase. Regardless of these effects, the optimal time for high-intensity interval training should align with one's individual biology and psychology.
- The aim of intermittent fasting or time-restricted feeding is to extend the duration of the fasting period in a manner that is compatible with eating. The overarching goal is to optimise the body's biological rhythms to support repair, reduce inflammation and clear out waste.
- Supplements or prescription drugs, such as Metformin or berberine, can act as glucose disposal agents and help to reduce blood glucose levels radically, promoting transition from a fed to a fasted state.
- Caution is advised when using glucose disposal agents like berberine or Metformin as they can cause hypoglycemia and induce effects such as headaches. The effects vary between individuals and depend on the time of day they are taken.
Blood Glucose: Monitoring, mTOR & Related Pathways (01:22:37)
- Continuous glucose monitors are commercially available devices that provide information on blood glucose fluctuations.
- By using one of these devices, individuals can learn how different foods, exercises, and substances like berberine or Metformin impact their blood glucose levels.
- Fasted states can induce changes in the expression of various proteins in our cells, such as a reduction in the activity of mTOR (mammalian target of rapamycin), which is associated with cell growth and can be active in cancers.
- Fasting can reduce the activity of certain proteins involved in cell growth, and instead promote mechanisms associated with cell repair and breakdown.
- Consumption of any type of food can spur cell growth, while fasting or having low blood glucose can spark cellular repair.
Gut Health: Fasting, Clock Genes and Microbiota (01:27:40)
- Intermittent fasting and time-restricted feeding have been shown to provide health benefits, including improvements in gut health and treatment of irritable bowel syndrome and colitis.
- The benefits are attributed to impacting expression of various 'clock' genes, thereby affecting the gut's mucosal lining.
- Intermittent fasting can reduce lactobacillus levels, which when high, is associated with various metabolic disorders.
- Time-restricted feeding can promote the proliferation of gut microbiota that are beneficial for intestinal function.
Non-Alcoholic Fatty Liver (01:29:15)
- Non-alcoholic fatty liver disease, characterized by fatty deposits in the liver, is becoming increasingly common in both adults and children.
- A recent study indicates that there is no clear link between this disease and the gut microbiome, which contradicts popular belief.
- However, the study found a direct correlation between the disease and brown fat levels in the body; reduced levels of brown fat were associated with increased instances of non-alcoholic fatty liver disease.
- Thankfully, brown fat stores can be increased through measures such as cold exposure and time-restricted feeding, which could potentially be helpful in preventing or reversing non-alcoholic fatty liver disease.
Effects of Fasting on Hormones: Testosterone, Cortisol (01:32:00)
- Time-restricted feeding has positive effects on overall insulin profiles.
- A study on elite cyclists using time-restricted eating tracked hormonal parameters, including things like glucose, thyroid hormone, and testosterone.
- The study found that time-restricted feeding leads to significant decreases in free testosterone, but also significantly reduces cortisol levels, a stress hormone.
- The interplay of these hormones indicates time-restricted feeding may still maintain hormonal balance.
- Time-restricted feeding showed reductions in stress hormones and inflammatory markers.
- An eight-hour feeding window is recommended, taking into account both the metabolic benefits of intermittent fasting and the need to maintain hormone health.
- The relationship between feeding, body fat, and fertility hormones is established; leptin, a hormone from body fat, triggers puberty and maintains menstrual cycles.
- Over-restricting food intake can lead to a drop in fertility.
- Data suggests intermittent fasting may have different effects on males and females, but this is still being studied in humans.
- Decisions around time-restricted feeding should be individual and considers lifestyle as well as physical and psychological stress levels.
- A gradual transition into time-restricted feeding over several days is recommended to allow the body's systems to adjust.
8-Hour Feeding Window: Weight Loss Without Calorie Counting (01:41:50)
- An eight-hour feeding window is a recommended time-restricted feeding period and is based on numerous studies.
- A study showed that an eight-hour time-restricted feeding could produce weight loss and reduced blood pressure without calorie counting.
- The eight-hour feeding window has been tested in both obese and non-obese adults and a few studies in children, making it a good rule of thumb for time-restricted feeding.
Eating Every-Other-Day (01:43:20)
- People have experimented with alternate day fasting wherein they eat one day and fast the next or consume very few calories.
- There are online communities exploring longer fasts to offset or reverse dementia but there are no quality clinical peer-reviewed studies on the topic yet.
- Alternate day fasting has been deemed safe with no reported instances of major detrimental effects.
- It has proven beneficial in promoting weight loss and reducing resting blood glucose levels, particularly for obese individuals.
- However, for most people, adhering to an every other day fasting regime is challenging and unsustainable over a long period.
- Questions remain about the potential of rebound weight gain or increase in blood glucose levels after stopping with the regime.
- For now, an eight-hour feeding window and time restricted feeding seem to be the most extensively tested methods, with results supporting their effectiveness in animals and humans.
- Adherence is a major consideration in any diet or eating plan and can differ significantly between controlled study environments and real-world situations.
- Neurologically, some individuals find it easier to refrain from eating for certain periods within each 24-hour cycle (time-restricted feeding), while others find portion control manageable.
- Factors such as work schedule, exercise regime and personal habits can influence the ease and success of adherence.
Mental Focus & Clarity (01:47:15)
- Time restricted feeding and fasting can enhance mental clarity as individuals don't have to constantly make decisions about when and how much to eat.
- Time-restricted feeding involves less decision-making in the brain when compared to calorie or portion restriction.
- This reduction in constant decision-making is likely why many people choose time-restricted feeding.
Enhancing Weight Loss from Body Fat: Hepatic Lipase (01:49:12)
- There is ongoing debate regarding whether time-restricted feeding can help in losing more fat compared to other tissues when in a state of caloric restriction.
- Time-restricted feeding over extended periods can lead to metabolic changes that shift the system towards more fat loss relative to burning of other tissues.
- Time-restricted feeding increases hepatic lipase, an enzyme that metabolizes fat for lipolysis and energy production, whereas it reduces CIDEC, a lipid droplet-associated lipolysis inhibitor.
- Therefore, combining time-restricted feeding with a sub caloric intake could be the most scientifically supported way to ensure that a significant portion of weight lost is from body fat stores.
What Breaks a Fast? Rules & Context (01:53:15)
- Whether something breaks a fast depends on factors such as when you last ate, how much you consumed, and where you are in your circadian cycle.
- Blood glucose is the primary indicator of whether your system is in a fed or fasted state.
- Drinking water, tea, black coffee, and ingesting caffeine in pill form will not break your fast.
- Minor food intake during a fasted state, such as eating one peanut, might not break your fast, but this has much to do with the individual's current glucose state. For example, if you just finished a carbohydrate-rich meal, eating the same peanut may break your fast.
- Sugars, particularly simple sugars, can potentially break your fast.
- The type of food consumed matters during fasting. Consuming purely fats during a fast might not break the fast, especially after strictly fasting for five hours or more. But consuming items like soda or pizza will break your fast.
- In order to establish what breaks a fast for you, it is best to maintain a consistent and strict feeding window, while experimenting with different types of food that work best for you.
- It's also important to note that different diets work for different people, so the same principles apply within intermittent fasting or time-restricted feeding.
Artificial Sweeteners, Plant-Based Sweeteners (01:58:50)
- Opinions differ on whether artificial or non-artificial plant-based sweeteners, like Stevia, break a fast as the data on this subject are mixed.
- Artificial sweeteners may cause a transient increase in blood glucose, which can increase hunger.
- There is a lack of research on how plant-based non-sugar sweeteners impact fasting states.
- The best way to understand your personal reaction to sweeteners while fasting is to wear a continuous glucose monitor and ingest these substances during a fasted state.
- In moderation, plant-based non-sugar sweeteners like Stevia seem to have a minimal impact on overall blood glucose.
- However, consuming sweeteners excessively might affect the gut microbiome negatively.
- The effect of sweeteners on fasting is also impacted by individual variations such as discipline in adhering to the feeding window and individual response to sweet tastes.
- Therefore, it can not be definitively stated that artificial sweeteners break a fast, but consumption should be moderated during fasting periods.
Glucose Clearing II, Cinnamon, Acidity, Salt (02:01:42)
- Some behaviors and compounds like Metformin, berberine, and to a lesser extent, cinnamon, lemon, and lime juice, can act as glucose disposal agents, helping reduce blood glucose levels.
- Sodium assists in chemical and electrical signaling in neurons, and taking a small amount of sea salt with water can help to stabilize the body during fasts, reducing feelings of lightheadedness and shakiness.
- Ingesting sodium, providing one does not have chronic hypertension or high blood pressure, can be beneficial in managing mental and physical states during fasting.
- Drinking water with a pinch of sea salt or lime juice can significantly help to stabilize one's body and mind during fasting, making it easier to reach the end of the fasting window.
My Circadian Clock, Zero-App (02:06:42)
- My Circadian Clock and the Zero app are useful resources for people interested in or practicing time-restricted feeding.
- My Circadian Clock allows users to log food intake and get information about time-restricted feeding.
- The Zero app helps track the user's feeding and fasting windows and offers averages and progress logs.
Odd (But Common) Questions (02:08:20)
- Brushing teeth with toothpaste will not break your fast unless swallowed.
- Consuming wine a few hours after dinner will break your fast due to its sugar content.
Effects of Sauna & Dehydration on Blood Glucose (02:09:23)
- Going into a sauna can increase blood glucose levels due to dehydration, which increases the concentration of sugar in the blood.
- This glucose spike wouldn't deter those valuing the psychological and physical health effects of the sauna, although others concerned about glucose spikes may want to consider this information.
The Ideal Fasting Protocol (02:11:12)
- The ideal intermittent fasting or time-restricted eating schedule will depend on individual circumstances and what can be maintained consistently.
- It is recommended to avoid food for at least 60 minutes after waking up and two to three hours before bedtime.
- Sleep-related fasting is important for health benefits, particularly for cell repair processes in the liver, gut, microbiome, and brain.
- An eight-hour feeding window is recommended; shorter windows can lead to overeating and weight gain.
- People tend to not strictly adhere to an eight-hour feeding window; setting your goal to a slightly shorter window can ensure better adherence.
- Regular timing for your feeding window every 24 hours is important; adjusting it during weekends disrupts the health benefits of time-restricted feeding.
- The most beneficial feeding window placement is in the middle of the day, for instance, from 10:00 AM to 6:00 PM, but this can be impractical for some schedules.
- Feeding windows can be adjusted depending on individual experiences with hunger and exercise routines.
- Consuming protein early in the day can be beneficial for those focusing on muscle maintenance or hypertrophy.
- In situations where a meal is taken too close to a fasting period, activities like a brisk walk or agents like lemon juice or Metformin can help lower blood glucose levels.
- Keeping hydrated and maintaining sodium levels, especially when consuming caffeine, can help avoid feelings of hunger.
- Artificial or plant-based non-sugar, non-caloric sweeteners do not seem to significantly impact blood glucose levels and fasting states.
- Constantly monitoring feelings and reactions associated with eating, fasting, sunlight exposure, and exercise can help individuals to establish their ideal nutrition schedule.
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