Exercise & Fat Loss: The Science Explained: Andy Galpin
How We Lose Fat Through Respiration: Carbon Cycle of Life
Huberman initially assumed that weight loss was primarily governed by the “calories in, calories out” principle, where ingesting fewer calories than burned leads to weight loss.
However, Galpin challenged this notion, asking how the body physically loses weight.
The conversation then turned to the various fuel sources in the body, such as glycogen, body fat, and protein.
Huberman suggested that fat cells (adipocytes) liberate fat as a fuel source when other sources are depleted or when the body’s metabolic systems signal that body fat is the optimal fuel for a given activity.
Galpin then steered the discussion towards the process of losing fat through respiration. He explained that when we inhale, we primarily take in oxygen, and when we exhale, we release carbon dioxide (CO2).
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The key difference between these two gases is the carbon molecule.
Carbohydrates and fats are essentially chains of carbon atoms. Metabolism, in terms of energy production, revolves around breaking these carbon bonds to release energy, which is then used to create ATP (adenosine triphosphate), the primary energy currency for living organisms. The leftover carbon must be expelled from the body to maintain balance.
Galpin emphasized that oxygen is not a fuel source but rather a necessary component for the metabolic process to occur. He likened it to the role of oxygen in a fire, where its presence is essential for the fire to burn, but it is not the fuel itself.
The discussion then delved into the carbon cycle of life, comparing the respiration processes of plants and humans.
Plants take in CO2 and release oxygen, while humans do the opposite. This symbiotic relationship maintains the balance of oxygen and CO2 in the atmosphere.
Galpin further explained the structure of triglycerides (fats), which consist of a three-carbon backbone called glycerol, with fatty acid chains attached to each carbon.
The number of carbons in these chains determines the type of fatty acid (e.g., stearic acid, linoleic acid) and whether it is saturated, monounsaturated, or polyunsaturated.
Plants utilize the energy from the sun (photosynthesis) to form bonds between the carbon atoms they inhale, storing them as starches in roots or converting them into sugars like sucrose, glucose, and fructose in fruits.
Similarly, the human body stores glucose as glycogen in the liver, blood, and muscles, while fat is primarily stored in adipose tissue.
To lose weight, the body must break down these stored carbon compounds, releasing the carbon into the bloodstream. Oxygen is then brought in to bind with the carbon, forming CO2, which is exhaled, returning the carbon to the atmosphere.
Science Behind Carbon Exchange: Exhalation Rates, Exercise & Fat Loss; Calories
Dr. Galpin explained that there are two ways to approach fat loss: ingesting less carbon or expelling more carbon.
While the percentage of intake from fats or carbohydrates doesn’t significantly impact fat loss, the total calorie intake does.
A calorie is a measure of the energy released when breaking a carbon bond, so ultimately, it’s about the total carbon intake.
The question then arises: Can increasing the duration or intensity of exhales accelerate fat loss? The answer is yes, but with some caveats.
While hyperventilation training can technically lead to fat loss by increasing the rate of exhalation, it comes with side effects such as tingling, sweating, and anxiety due to rapid changes in adrenaline levels and other factors.
So, what’s the best way to increase the rate of exhalation without these negative effects? The answer lies in exercise.
Steady-state exercise, lifting weights, intervals, and moderate training all work equally well for fat loss because they increase the demand for energy and, consequently, the respiration rate.
Dr. Galpin emphasized that the type of exercise doesn’t matter as much as maintaining consistent adherence over time.
Whether you’re burning fat or carbohydrates during the exercise session is irrelevant to your net fat loss over time. This explains why various diets and training protocols can be effective for different people.
Cardiovascular Adaptations, Cardiac Output & Maximum Heart Rate
Dr. Andy Galpin and Andrew Huberman discuss the intricacies of cardiovascular adaptations, cardiac output, and maximum heart rate.
When asked about the potential of increasing lung capacity to enhance fat loss, Dr. Galpin explained that exhaling more carbon dioxide than needed would lead to inefficiency, as the body would be burning more energy than necessary for a given activity. He emphasized that the heart’s cardiac output, which is the product of heart rate and stroke volume, is specific to energy needs and automatically adjusts to maintain efficiency.
Dr. Galpin further elaborated on the cardiovascular adaptations that occur with endurance training.
As fitness improves, resting heart rate typically decreases, with a target of below 60 beats per minute being ideal for most individuals.
This decrease in resting heart rate is accompanied by an increase in stroke volume, allowing the heart to pump the same amount of blood with fewer beats per minute. However, cardiac output remains the same at rest, as energy demands have not changed.
During submaximal exercise, cardiac output remains identical in both unfit and fit individuals. The difference lies in the lower heart rate and higher stroke volume observed in fitter individuals, indicating improved efficiency.
Dr. Galpin noted that maximum heart rate does not significantly change with fitness and is not a reliable proxy for fitness level.
While stroke volume increases with training, it is limited by the filling capacity of the heart, particularly at high heart rates.
Dr. Galpin emphasized that increasing maximum heart rate is not necessarily a good goal, and individuals should focus on improving cardiac output through increased stroke volume.
When asked if training at near-maximal heart rates should be avoided, Dr. Galpin firmly stated that individuals should absolutely engage in such training.
Relationship Between Exercise Intensity and Fat Loss
One of the key points discussed was the concept of excess post-exercise oxygen consumption (EPOC).
This phenomenon occurs when the body continues to breathe heavily after exercise to repay the oxygen debt accumulated during intense activity.
The ratio between oxygen intake and carbon dioxide output, known as the respiratory exchange ratio (RER) or respiratory quotient (RQ), increases as exercise intensity rises.
A common misconception addressed in the podcast was the idea that training fasted or at a lower intensity burns more fat.
Dr. Galpin clarified that while a greater percentage of fuel comes from fat during low-intensity exercise, the total fuel expenditure is low, making it less effective for fat loss. In fact, the highest percentage of fuel from fat occurs during sleep, which doesn’t necessarily lead to significant fat loss.
As exercise intensity increases, the body starts to rely more on carbohydrates for fuel and less on fat. However, this doesn’t mean that high-intensity exercise is ineffective for fat loss.
Dr. Galpin explained that the body regulates its net energy expenditure, and after depleting carbohydrate stores through intense exercise, it will prioritize using fat as a fuel source.
The key takeaway from the discussion is that the source of fuel during exercise, whether it’s fat or carbohydrates, is less important than the overall energy balance.
To achieve fat loss, it’s crucial to create a caloric deficit through a combination of diet and exercise, regardless of the specific fuel source utilized during the activity.
Complexities of Fat Loss, Carbohydrate Stores, and Fatigue
Dr. Galpin emphasized that burning fat does not necessarily equate to losing fat from the body. It is crucial to differentiate between the burning of body fat stores and the burning of dietary fat that is consumed.
The discussion also touched upon the role of carbohydrate stores in the body, such as muscle glycogen and liver glycogen.
High-intensity exercise is an efficient way to tap into these stores, leading to the question of whether a specific exercise protocol could enhance body fat loss.
Dr. Galpin suggested that a combination of hypertrophy or muscular endurance strength training, followed by short bouts of high-intensity cardiovascular exercise, could be effective in depleting muscle glycogen and potentially even liver glycogen.
However, Dr. Galpin noted that the body prioritizes the use of energy from the local exercising muscle first, primarily from phosphocreatine and carbohydrate stores (glycogen).
If additional glucose is needed, it is pulled from the blood. The body tightly regulates blood pH, blood glucose, blood pressure, and electrolyte concentrations, and will make adjustments to maintain these levels.
Interestingly, blood glucose concentrations actually rise during exercise as an anticipatory response. The liver kicks in to break down its glycogen and release glucose into the blood to maintain stable levels.
This process can continue until the liver’s glycogen stores are depleted, which is known as “bonking” in long-duration endurance activities.
Dr. Galpin also discussed the concept of glycogen depletion in muscles, stating that it is generally a misnomer.
Individuals typically experience significant fatigue when muscle glycogen levels drop below 75%, leading most people to quit around 50% depletion. True depletion is rare and has only been observed in highly trained athletes.
The conversation also touched on the fascinating idea of the liver sending a neural signal to the brain when it is depleted, prompting a “stop” response to preserve the body.
While individuals can learn to override this signal to some extent through training, pushing past this point can lead to rapid breakdown and potential problems.
Secrets of Metabolic Flexibility, Carbohydrates, and Fat
One of the key points addressed was the myth that fat can be turned into muscle or vice versa.
Dr. Galpin emphasized that these are distinct structures and cannot be interchanged. The discussion then shifted to the concept of losing stored fat while engaging in glycogen-burning exercises.
Dr. Galpin explained that the key to fat loss lies in maintaining a hypocaloric state, where the total caloric intake is below the body’s total energy needs.
When an individual burns muscle glycogen through exercise and remains in a hypocaloric state, the body must find an alternative energy source to replenish the depleted glycogen stores. This is where stored fat comes into play.
The body’s energy systems work in tandem, with carbohydrates providing flexibility and fat offering an unlimited capacity.
Carbohydrates are the primary fuel source, allowing for quick energy bursts and enhanced cognitive function. On the other hand, fat serves as a slow-release energy source, ideal for sustained activities and maintaining steady energy levels throughout the day.
Dr. Galpin clarified that the term “metabolic flexibility” has been misinterpreted by some to mean maximizing fat burning.
However, true metabolic flexibility refers to the body’s ability to utilize the optimal fuel source at the appropriate time, not just focusing on fat utilization.
When an individual engages in glycogen-depleting exercise and remains in a hypocaloric state, the body prioritizes the replenishment of muscle glycogen stores.
Any carbohydrates consumed are directed towards storage, while fat is utilized for fuel. This shift in fuel utilization is reflected in changes in the respiratory quotient and the ratio of carbohydrate to fat oxidation.
The Role of Muscle in Basal Metabolic Rate and Fat Loss
Dr. Galpin explained that while muscle is indeed more metabolically active than fat at rest, the difference is not as substantial as previously believed.
In the past, it was estimated that adding one pound of muscle could increase BMR by around 50 calories per day. However, more recent estimates suggest that the actual number is closer to 6-10 calories per day.
While this may seem insignificant, Dr. Galpin pointed out that the impact of muscle mass on BMR can add up over time. For example, if an individual were to gain five pounds of muscle, their BMR could increase by 30-40 calories per day.
Over the course of 1,000 days, this could result in a notable difference in energy expenditure.
Despite the potential long-term benefits, Dr. Galpin emphasized that having sufficient muscle mass is crucial for successful fat loss, regardless of the additional caloric expenditure it may provide. He explained that individuals with inadequate muscle mass may face challenges in their fat loss journey due to other consequences not directly related to BMR.
Furthermore, Dr. Galpin stressed that the impact of muscle mass on BMR should not be the primary focus when it comes to fat loss. He noted that a single poor food choice per day can easily negate the caloric benefits gained from increased muscle mass.
Instead, he suggested that regulating caloric intake should be the main priority for individuals seeking to lose fat.
Assessing Metabolic Flexibility: Blood Glucose, Carbohydrates, and Energy Regulation
Dr. Galpin emphasized that there is no specific standard for optimal metabolic flexibility, as it varies based on an individual’s goals and needs.
For example, athletes performing in glycolytically dominated sports may not want to be “fat adapted” and instead should focus on optimizing their ability to utilize carbohydrates as fuel.
To assess metabolic flexibility, Dr. Galpin suggests looking at a combination of biological markers and practical tests, rather than relying on a single diagnostic measure.
One key marker is blood glucose levels, with a recommended range of 80-90 milligrams per deciliter. However, Dr. Galpin personally prefers levels at 85 or lower, as research has shown that every single point increase above 85 increases the likelihood of developing type 2 diabetes by about 6%.
In addition to blood glucose levels, other factors to consider include overall energy regulation throughout the day, the ratio of liver enzymes AST and ALT, and performance in standard workouts.
If an individual experiences significant drops in performance or prolonged heart rate recovery when exercising in a fasted state, it may indicate poor utilization of fat as a fuel source.
Conversely, if consuming a moderate amount of carbohydrates (around 50 grams) leads to a sudden energy crash or the need for caffeine, it may signify poor carbohydrate utilization.
Dr. Galpin stresses that this is equally problematic, as individuals should be able to consume reasonable amounts of carbohydrates without experiencing significant energy fluctuations.
Optimizing Carbohydrate Utilization and Managing Daily Energy
Huberman shared his personal experience of consuming complex carbohydrates and fruit post-resistance training when he’s hungriest for them. He keeps his daytime meals relatively low in carbohydrates, while preferring slightly less protein and more carbohydrates in the evening.
This approach helps him sleep well and wake up with replenished glycogen stores, enabling him to train fasted in the morning.
Dr. Galpin pointed out that relying on caffeine for fasted training could be a sign of suboptimal fuel utilization. However, he clarified that using caffeine as an ergogenic aid to enhance performance is a different matter. He also debunked the outdated notion that eating carbohydrates late at night leads to increased fat storage, citing ample scientific evidence to the contrary.
To improve fat utilization, Dr. Galpin suggested performing exercise in a pre-fat ingested state, as the body tends to preferentially target the nutrient consumed prior to training. However, he cautioned that this strategy might hinder performance, especially for high-level athletes, as fat is a slower fuel source compared to carbohydrates.
Conversely, to enhance carbohydrate utilization, consuming carbohydrates before exercise can bias the body towards using them as fuel.
Dr. Galpin emphasized the importance of appropriate eating strategies, such as combining carbohydrates with fiber or protein to blunt the glycemic index and stabilize blood glucose levels.
When addressing energy management throughout the day, Dr. Galpin recommended stabilizing protein intake, consuming food in the right combinations, and training at high intensity with pre-exercise carbohydrate meals. He also mentioned that slow starting performance could indicate poor carbohydrate utilization, which can be improved through targeted training and nutrition strategies.
Cellular Energy Production: Carbs, Lactate, and the Interplay of Anaerobic and Aerobic Metabolism
Anaerobic metabolism, which occurs in the cytoplasm of the cell, is the fastest way to produce energy but is limited by the amount of phosphocreatine and glycogen stored within the cell.
On the other hand, aerobic metabolism, which takes place in the mitochondria, yields a much higher energetic output but requires the presence of oxygen.
Dr. Galpin walked listeners through the process of carbohydrate metabolism, starting with the breakdown of glucose, a six-carbon chain, into two separate three-carbon chains called pyruvate. This process, known as glycolysis, releases a small amount of energy.
The remaining two-carbon chains, called acetyl CoA, are then transported into the mitochondria, where they undergo the Krebs cycle, releasing the remaining carbons as CO2 and generating a significant amount of ATP, the cellular energy currency.
The discussion also touched on the role of lactate, often misunderstood as the cause of fatigue during exercise. In reality, lactate is formed when hydrogen ions, a byproduct of ATP hydrolysis, bond with pyruvate.
This process helps to buffer the acidity in the cell, preventing fatigue. Lactate can then be transported to other muscles or organs, such as the heart, where it can be converted back into pyruvate and used as fuel.
Dr. Galpin emphasized the interdependence of anaerobic and aerobic metabolism, likening them to gears on a bicycle.
If either system is compromised, the entire energy production process is affected. He stressed the importance of having a well-functioning mitochondrial network, as it is essential for both anaerobic and aerobic performance.
Science of Energy Production and Waste Management in Endurance Exercise
At the core of this conversation lies the concept of aerobic glycolysis, a process that kicks in when exercise extends beyond the 90-second mark and can sustain an individual for up to 20-30 minutes or even longer.
Highly competitive marathon runners, for instance, rely heavily on carbohydrates as their primary fuel source, with fat metabolism being too slow to meet the demands of their intense pace.
While some endurance athletes may ingest carbohydrates during their races, the specifics of their fueling strategies often remain closely guarded secrets.
However, Dr. Galpin cautions against consuming too many fast carbohydrates prior to exercise, as it can lead to a phenomenon known as the “insulin glucose double whammy.”
This occurs when the sudden influx of carbohydrates causes a spike in blood glucose levels, followed by a rapid crash as both insulin and muscle cells work to remove glucose from the bloodstream.
The discussion then delved into the intricate process of carbohydrate metabolism, starting with a six-carbon glucose molecule in the cytoplasm. Through a series of steps involving anaerobic glycolysis, the Krebs cycle, and the electron transport chain, the glucose molecule is gradually broken down, releasing energy in the form of ATP while producing water and carbon dioxide as byproducts.
Dr1. Galpin emphasizes that endurance is primarily a game of waste management and fatigue resistance, rather than a concern over running out of fuel.
For most endurance events lasting less than 90 minutes, the focus lies on managing the buildup of carbon through efficient oxygen utilization and developing better acid buffering systems.
Protein & Fat Utilization for Energy; Exercise & Fat Loss
When it comes to fat as a fuel source, the majority is pulled from the body systemically, unlike carbohydrates which are primarily stored and utilized in the exercising muscle tissue.
This is why fat loss occurs throughout the entire body, even if only certain parts are being exercised. The process of breaking down and utilizing fat for energy involves several steps, including lipolysis, transportation through the bloodstream, uptake into the muscle, and finally, entry into the mitochondria for oxidation.
The oxidation pathway and final endpoints of metabolism are the same for both carbohydrates and fats, resulting in the production of water, ATP, and CO2.
Dr. Galpin emphasized that for maximizing fat loss, the type of training is less important than consistency and adherence. Whether one prefers longer steady-state exercise, high-intensity intervals, or a combination, the key is to find a challenging yet enjoyable approach that can be sustained over time.
Understanding Protein, Carbohydrates, and Fat as Fuel Sources
According to Dr. Galpin, if you were in the wilderness and needed to start a fire, you would likely begin with a match. The match represents phosphocreatine, which burns quickly and is depleted rapidly.
Next, you would use the match to light a piece of newspaper on fire. The newspaper represents carbohydrates, which provide more energy than the match but still burn relatively quickly.
Finally, if you were smart, you would use the burning newspaper to ignite a piece of wood. The wood represents fat, which can provide energy for an extended period.
Dr. Galpin explained that the average person with around 15% body fat has enough stored fat to survive for more than 30 days without ingesting any calories.
Dr. Galpin emphasized that fat will never be a limiting factor in endurance performance because the human body has such a large store of it. However, fat is slow to mobilize and utilize, which is why it is always used in combination with carbohydrates for energy.
Protein, on the other hand, is not an ideal fuel source for exercise or metabolism.
Dr. Galpin compared protein to a piece of metal in the fire analogy. While it is technically possible to melt metal, it requires a lot of energy and depletes a valuable resource.
Similarly, the body can convert protein into glucose through gluconeogenesis, but it is an inefficient process that depletes the body’s protein stores, which are not as readily available as fat and carbohydrate stores.
Low-Carbohydrate Diets on Performance and Weight Management
Dr. Galpin explained that when an individual reaches a certain level of adaptation to a low-carbohydrate diet, their body becomes extremely efficient at generating glucose from alternative sources, such as fat.
However, this adaptation comes with a downside – a decrease in performance, particularly in activities that require maximal effort for a few minutes.
The enzymes responsible for anaerobic glycolysis, a key process in high-intensity exercise, become downregulated in low-carbohydrate diets.
This means that the body becomes less efficient at using carbohydrates as a fuel source, leading to slower performance in anaerobic-based sports or activities.
However, Dr. Galpin noted that for individuals who engage in little to no physical activity, a high-fat, low-carbohydrate nutrition strategy can be very effective for weight management and energy stabilization throughout the day.
The research supports this approach for those who do not prioritize exercise performance.
Andrew Huberman shared his personal experience with low-carbohydrate diets, noting that he tends to feel lousy after two or three days of severely limiting or eliminating carbohydrates.
This is primarily because he enjoys training intensely in the gym and engaging in longer runs throughout the week.
Huberman also observed that several people he knows who love very low-carbohydrate or ketogenic-type diets tend to engage in limited exercise or focus on long, low-intensity endurance activities like walking.
These individuals often find success in managing their weight with this dietary approach.
Dr. Galpin emphasized that the discussion should not be viewed as a judgment of better or worse, but rather as an acknowledgment of the numerous options available to individuals.
The choice of diet and exercise should be based on personal preferences, goals, and a balance of performance, aesthetics, and health.
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