Thoughts on Dr. Stacy Sims interview on Huberman!

Dr. Stacy Sims is a renowned exercise physiologist and nutrition scientist who specializes in female physiology and performance. Her work emphasizes that women are not small men and have distinct physiological differences that affect how they should approach training and nutrition.

Here is an overview of her viewpoint and scientific explanations regarding fasted or fed exercise for females at various hormone stages of life:

The interview discusses the impact of intermittent fasting and time-restricted eating on women’s health, particularly focusing on active women.

Here are the key points:

• Intermittent Fasting vs. Time-Restricted Eating: Intermittent fasting involves a 20-hour fasting window, typically delaying the first meal until noon or later. Time-restricted eating aligns with natural circadian rhythms, having meals during the day and avoiding food after dinner.
• Negative Impact on Active Women: For active women, intermittent fasting can be detrimental unless they have conditions like PCOS. Women naturally have more oxidative fibers, making them more metabolically flexible. This means they use more free fatty acids and require less glucose during prolonged exercise.
• Oxidative Fibers and Metabolism: Women’s oxidative fibers, which have high aerobic capacity, allow them to sustain long-duration, low-intensity exercise. They utilize free fatty acids more efficiently but need some glucose to activate these fatty acids. Women typically do not deplete liver and muscle glycogen as much as men during exercise.
• Increased Stress and Cortisol: Fasted workouts and extended fasting periods elevate cortisol levels, increasing overall stress. This can prevent women from reaching high exercise intensities necessary to trigger beneficial hormonal responses like growth hormone and testosterone release, which help lower cortisol.
• Kisspeptin Neurons and Hormonal Disruption: Women have two distinct areas of kisspeptin neurons in the brain, unlike men who have one. These neurons regulate appetite, luteinizing hormone, estrogen, and thyroid function. Prolonged fasting can downregulate these neurons, leading to thyroid dysregulation and altered luteinizing hormone pulses, affecting endocrine function.
• Circadian Rhythm and Eating Timing: Aligning eating patterns with circadian rhythms improves cognitive function and reduces thyroid dysfunction. Population studies indicate that people who eat earlier in the day have better outcomes than those who delay eating until noon.
• Cortisol Fluctuations: Cortisol peaks about 30 minutes after waking. For women, fasting during this peak increases sympathetic drive, causing them to feel tired yet wired. Small meals in the morning can signal the hypothalamus that nutrition is available, helping to balance the day’s hormonal fluctuations.
• Perimenopause and Fasted Training: Women in perimenopause experience more hormone fluctuations and higher baseline cortisol. Fasted training during this time can exacerbate stress and hinder achieving necessary exercise intensities. Fueling before high-intensity workouts is crucial to avoid moderate intensity and ensure effective training.

Overall, the interview emphasizes the importance of considering individual hormonal responses, particularly for active women, and aligning eating patterns with natural circadian rhythms to optimize health and performance.

Here are the main points:

• Women and Oxidative Fibers:
  • Women have more oxidative fibers, which are muscle fibers with higher aerobic capacity, allowing for long-duration, low-intensity exercise using free fatty acids.
  • Women are naturally more metabolically flexible due to these oxidative fibers.
  • During exercise, women initially use blood glucose, then shift to free fatty acids, and don’t deplete liver and muscle glycogen as much.
• Fasting and Metabolic Flexibility:
  • Fasting can increase overall stress and cortisol levels in women.
  • Fasted workouts may prevent women from reaching high enough intensity to stimulate growth hormone and testosterone, which are important for reducing cortisol post-exercise.
  • Chronic fasting can negatively impact thyroid function and luteinizing hormone pulses.
• Brain and Hormonal Effects:
  • The female brain has two areas of neurons related to appetite, hormones, estrogen, and thyroid, making women more sensitive to stress and fasting.
  • Extended fasting can downregulate these neurons, leading to thyroid dysregulation and other hormonal imbalances.
• Circadian Rhythm and Eating Windows:
  • Aligning eating windows with circadian rhythms can reduce stress and improve overall health.
  • Breaking a fast earlier in the day (e.g., 8 AM) and finishing the eating window by 4-5 PM has better metabolic outcomes than eating later.
  • For women, cortisol peaks about 30 minutes after waking, so delaying food intake can increase sympathetic drive and stress, leading to negative effects on cognitive function and thyroid health.
• Population Research and Obesity:
  • Research shows that people who delay eating until noon and then eat until 6 PM or later have worse metabolic outcomes compared to those who start eating earlier.
  • Strategic fasting might be useful for specific conditions like obesity, inactivity, or PCOS.
• Recommendations:
  • It’s better for women to eat according to their circadian rhythm and hormonal fluctuations rather than following strict fasting protocols.
  • Small amounts of food upon waking can help regulate cortisol and support better parasympathetic responses throughout the day.

What about those oxidative fibers?

Chronic fasting can negatively impact thyroid function and luteinizing hormone (LH) pulses through several mechanisms related to hormonal regulation and metabolic stress:

Thyroid Function

1. Thyroid Hormone Production:
   • Energy Balance: The thyroid gland produces hormones (T3 and T4) that regulate metabolism. Chronic fasting can signal to the body that energy intake is low, leading to a reduction in thyroid hormone production to conserve energy.
   • Conversion of T4 to T3: T4 is converted to the more active T3 in various tissues. Fasting and caloric restriction can decrease this conversion, leading to lower levels of T3, slowing metabolism, and conserving energy.
2. Stress Response:
   • Cortisol: Chronic fasting increases cortisol levels, a stress hormone that can interfere with the hypothalamic-pituitary-thyroid (HPT) axis. Elevated cortisol can inhibit the release of thyroid-stimulating hormone (TSH) from the pituitary gland, which is necessary for thyroid hormone production.
   • Sympathetic Nervous System Activation: Prolonged fasting keeps the body in a state of sympathetic activation (fight or flight response), which can further disrupt thyroid function and hormone balance.

Luteinizing Hormone (LH) Pulses

1. Hypothalamic-Pituitary-Gonadal (HPG) Axis:
   • Gonadotropin-Releasing Hormone (GnRH): The hypothalamus releases GnRH in pulses to stimulate the pituitary gland to release LH. Chronic fasting can disrupt the frequency and amplitude of these pulses.
   • Energy Availability: Adequate energy is crucial for regular GnRH pulses.
   • Low energy availability due to chronic fasting can lead to irregular or diminished GnRH pulses, affecting LH secretion.
2. Impact on Reproductive Health:
   • Menstrual Irregularities: LH is essential for ovulation and maintaining regular menstrual cycles.
   • Disrupted LH pulses can lead to irregular menstrual cycles, anovulation (lack of ovulation), and other reproductive issues.
   • Hormonal Balance: LH is also important for maintaining levels of other reproductive hormones such as estrogen and progesterone. Disrupted LH pulses can lead to hormonal imbalances, affecting overall reproductive health and well-being.

Summary – Chronic fasting can lead to a cascade of hormonal disruptions:

• Thyroid Function: Reduced thyroid hormone production and conversion, primarily due to energy conservation and elevated cortisol.
• LH Pulses: Disrupted GnRH and LH pulses due to low energy availability, leading to irregular menstrual cycles and hormonal imbalances.

Overall, the stress and energy deficits associated with chronic fasting can significantly impact both thyroid and reproductive health, particularly in women.

The mechanism of action for females regarding the timing of cortisol peaks and its relationship with food intake involves several physiological processes:

Cortisol and Circadian Rhythm

1. Cortisol Awakening Response (CAR):
   • Morning Peak: Cortisol levels naturally rise in the early morning and peak about 30 minutes after waking. This is part of the circadian rhythm, helping to wake the body and prepare it for the day’s activities.
   • Role of Cortisol: Cortisol helps regulate metabolism, immune responses, and stress. It increases blood sugar levels to provide immediate energy, supports alertness, and helps manage physical and psychological stress.

Impact of Delaying Food Intake

1. Sympathetic Nervous System Activation:

   • Increased Sympathetic Drive: Delaying food intake can prolong the body’s sympathetic (fight-or-flight) response, which is naturally high in the morning due to elevated cortisol levels.
   • This can keep the body in a heightened state of stress.
   • Stress Hormone Cascade: Without food, the body may perceive a continued lack of energy availability, maintaining high cortisol levels and further activating the sympathetic nervous system.

2. Glucose and Energy Regulation:

   • Gluconeogenesis: Without food intake, the body may increase gluconeogenesis (production of glucose from non-carbohydrate sources) to maintain blood sugar levels. This process is cortisol-dependent and can increase cortisol levels further.
   • Blood Sugar Fluctuations: Stable blood sugar levels are crucial for cognitive function. Prolonged fasting can lead to blood sugar fluctuations, impairing cognitive performance and mood.

Negative Effects on Cognitive Function

1. Cognitive Impairment:
   • Energy Deficit: The brain relies heavily on glucose for energy. Delaying food intake can lead to an energy deficit, impairing cognitive functions such as memory, attention, and decision-making.
   • Mood and Anxiety: Prolonged fasting and high cortisol levels can increase feelings of anxiety and stress, negatively affecting mood and overall mental health.

Negative Effects on Thyroid Health

1. Hypothalamic-Pituitary-Thyroid (HPT) Axis Disruption:
   • Thyroid-Stimulating Hormone (TSH) Inhibition: Chronic stress and high cortisol levels can inhibit the release of TSH from the pituitary gland, reducing thyroid hormone production.
   • Conversion of T4 to T3: Elevated cortisol can impair the conversion of T4 (inactive thyroid hormone) to T3 (active thyroid hormone), leading to lower levels of T3 and a slowed metabolism.
2. Energy Conservation:
   • Metabolic Slowdown: The body may slow down metabolic processes to conserve energy when food intake is delayed, affecting overall metabolic rate and thyroid function.
   • Hormonal Imbalance: Prolonged fasting and high cortisol can disrupt the balance of other hormones, further impacting thyroid health and overall metabolic function.

Delaying food intake after waking can exacerbate the natural morning peak of cortisol, keeping the body in a state of heightened stress and sympathetic activation.

This can lead to:

• Increased Sympathetic Drive: Prolonged stress response and energy deficit.
• Cognitive Impairment: Decreased mental performance, mood disturbances, and increased anxiety.
• Thyroid Dysfunction: Inhibited TSH release, impaired T4 to T3 conversion, and overall metabolic slowdown.

For women, who are particularly sensitive to hormonal fluctuations and stress responses, aligning eating habits with the body’s natural circadian rhythm and cortisol peaks can help maintain hormonal balance, cognitive function, and overall health.

 

Fueling pre workout suggestions:

Overall, Dr. Stacy Sims emphasizes the importance of considering hormonal fluctuations and individual responses when deciding between fasted or fed exercise. Women at different hormonal stages of life will have varying needs, and a personalized approach is key to achieving optimal performance and health.

Summary in Bullet Points Time stamp 32:41 – 34:12

• Fasted Training and Fat Loss:

  • Training fasted may increase the percentage of fat used as fuel.

  • Overall body fat loss is not significantly different between fasted and fed training.

At some point, there was a lot of discussion about training fasted burns more body fat. I think now most people accept that that’s not the case, that perhaps the percentage of fat as fuel is increased when one trains fasted, but that overall, in terms of loss of body fat, it doesn’t matter if you train fasted or you train fed. Okay. I think that can’t be stated enough by experts like you.

That doesn’t mean that one prefers to train fasted or with a minimum of food in their gut that they can’t do that.

I like to train fasted, but what I’m hearing is that women should probably ingest at least some protein, high quality protein, and maybe drink the protein in a protein shake form if they don’t want to ingest solid food.– Huberman

• Recommendations for Women:

  • Women should ingest at least some high-quality protein before training, possibly in the form of a protein shake.

• Endocrine Dysfunction Tipping Point:

  • Men: Tipping point at 15 calories per kilogram of fat-free mass.

  • Women: Tipping point at 30 calories per kilogram of fat-free mass.

• Baseline Calorie Needs:

  • Women have higher baseline calorie and carbohydrate needs due to greater reliance on kisspeptin regulation.

  • Adequate calorie intake is crucial to avoid endocrine dysfunction and maintain hormone balance.

• Biological and Evolutionary Aspects:

  • Historically, men sought calories while women conserved energy to support reproductive functions.

  • Modern-day hormone regulation across the circadian rhythm still requires more calories for women than for men.

Mechanism of Action

• Fasted Training and Fuel Usage:
  • Training fasted can increase the percentage of fat used as fuel due to lower insulin levels and increased reliance on fat oxidation.
  • However, the overall impact on body fat loss is minimal when compared to fed training, as total calorie expenditure and intake are more critical factors.
• Kisspeptin Regulation:
  • Kisspeptin is a key hormone involved in regulating reproductive hormones and energy balance.
  • Adequate calorie intake, especially carbohydrates, supports kisspeptin upregulation, which is essential for maintaining endocrine function in women.
• Endocrine Dysfunction Tipping Point:
  • The tipping point for endocrine dysfunction is reached when calorie intake falls below a certain threshold, disrupting hormone balance.
  • Women have a higher tipping point (30 calories/kg fat-free mass) compared to men (15 calories/kg fat-free mass) due to their complex hormonal regulation and reproductive needs.
• Evolutionary Context:
  • Historically, women’s bodies were adapted to conserve energy to support pregnancy and lactation, making them more sensitive to low calorie intake.
  • Modern-day hormone regulation still reflects these evolutionary adaptations, requiring women to have higher calorie and carbohydrate intake to maintain optimal health and hormonal balance.

Mechanism of Action: Endocrine Dysfunction Tipping Point??

Men: Tipping Point at 15 Calories per Kilogram of Fat-Free Mass

• Hormonal Stability:
  • Men have a simpler hormonal landscape primarily dominated by testosterone.
  • Lower calorie requirements can still support the basic metabolic and hormonal needs without significant disruption.
• Energy Utilization:
  • Men’s bodies are more adapted to short-term calorie deficits, enabling them to maintain metabolic and hormonal stability even with lower energy intake.
  • They utilize stored glycogen and fat more efficiently to maintain energy balance and support physical activities.
• Kisspeptin and Reproductive Hormones:
  • Kisspeptin neurons regulate testosterone and other reproductive hormones.
  • Men have a higher threshold for calorie-induced hormonal disruption, allowing them to maintain kisspeptin activity and reproductive hormone balance even at lower calorie intakes.

Women: Tipping Point at 30 Calories per Kilogram of Fat-Free Mass

• Complex Hormonal Regulation:
  • Women’s hormonal landscape is more complex, involving estrogen, progesterone, and other reproductive hormones that are sensitive to energy availability.
  • Adequate calorie intake is crucial to maintain this delicate hormonal balance.
• Energy Requirements:
  • Women require higher calorie intake to support multiple physiological processes, including menstrual cycle regulation, ovulation, and potential pregnancy.
  • A higher tipping point ensures that energy needs for these functions are met, preventing hormonal disruption.
• Kisspeptin Regulation:
  • Kisspeptin neurons in women play a crucial role in regulating both reproductive hormones (estrogen, progesterone) and metabolic functions.
  • Adequate energy intake supports kisspeptin activity, ensuring proper signaling for hormone release and metabolic balance.
• Evolutionary Adaptations:
  • Historically, women’s bodies have adapted to conserve energy to support reproductive functions, making them more sensitive to low energy availability.
  • A higher calorie threshold ensures that these adaptations do not lead to endocrine dysfunction, preserving reproductive health and overall metabolic stability.

Impact of Calorie Intake on Hormonal Balance

• Low Energy Availability:
  • When calorie intake falls below the tipping point, the body perceives a state of energy deficiency.
  • For men, this occurs at 15 calories/kg fat-free mass, while for women, it occurs at 30 calories/kg fat-free mass.
• Hormonal Disruption:
  • In men, calorie intake below the tipping point can lead to reduced testosterone levels and impaired metabolic functions.
  • In women, insufficient calorie intake disrupts kisspeptin signaling, leading to irregular menstrual cycles, reduced fertility, and impaired metabolic functions.
• Metabolic and Reproductive Health:
  • Maintaining calorie intake above the tipping point supports metabolic functions, hormone balance, and overall health.
  • For women, this includes maintaining regular menstrual cycles, adequate reproductive hormone levels, and stable energy metabolism.

Understanding the differences in calorie requirements and the impact on hormonal balance helps tailor nutritional and exercise strategies to maintain optimal health and performance for both men and women.

Importance of Strength Training Across Ages

• Focus on Strength Training:
  • As people age, maintaining and building lean muscle mass becomes more challenging.
  • Strength training is crucial for enhancing longevity and mitigating age-related muscle loss.
• Benefits of Strength Training:
  • Central Nervous System: Improved proprioception, cognitive function, and neural growth.
  • Cognitive Health: Research indicates strength training can help attenuate cognitive decline, reduce risks associated with dementia and Alzheimer’s disease.

Sex Differences and Timing

• For Women:
  • Perimenopause: Significant hormonal changes occur, including reduced sex hormones (estrogen and progesterone) and more anovulatory cycles.
  • Impact on Body:
    • Increased risk of soft tissue injuries such as frozen shoulder and plantar fasciitis.
    • More pronounced need for strength training and heavy lifting to manage these changes and prevent injuries.
  • Training Recommendations:
    • Early Implementation: Begin focusing on strength training and polarized training (emphasizing strength over endurance) in the mid-40s to early 50s.
    • Conditioning: Prepare the body to handle the stresses of perimenopause and menopause by establishing strong strength training patterns early.
• For Men:
  • Age-Related Changes: Soft tissue injuries and changes in body composition typically become more noticeable in late 50s to early 60s.
  • Training Recommendations:
    • Later Implementation: Strength training remains important but can be started later compared to women.
    • Broader Flexibility: Men generally have more flexibility regarding when to start focused strength training.

Key Takeaways

• Strength Training: Essential for maintaining muscle mass, cognitive function, and overall health with aging.
• Sex-Specific Timing:
  • Women should prioritize strength training and adaptation strategies earlier due to hormonal changes in perimenopause.
  • Men should focus on strength training as they age but typically start later.

Understanding these differences helps tailor strength training programs to better meet the specific needs of individuals as they age, supporting overall health and longevity.

Summary and Key Points:  Training Intensity for Women (40s and Up):

Moderate Intensity:

• • • Not Ideal: Moderate intensity workouts can increase cortisol levels without sufficiently triggering growth hormone and testosterone responses needed to manage cortisol.
    • Result: Women may feel exhausted but not see the desired benefits in body composition, health, or cognitive function.

Optimal Training:

• • • High Intensity:
      • Effective: Engage in true high-intensity workouts, such as 1 to 4 minutes of effort at 80% or more, or full-effort sprints lasting 30 seconds or less.
      • Frequency: Perform high-intensity training a few times a week, allowing for adequate recovery between sessions.
      • Benefits: Promotes hormonal responses to lower cortisol, improves body composition, metabolic control, and brain health.

Endurance Activities:

• • • Mental Health: Long, low-intensity endurance activities (e.g., long bike rides) can be beneficial for mental health and enjoyment.
    • Limitations: For optimal health, longevity, and body composition changes, focus on resistance training and high-intensity work rather than prolonged endurance sessions.

Training Recommendations:

• • Focus on Resistance Training: Establish resistance training as a fundamental part of the exercise routine.
  • Incorporate High-Intensity Intervals: Use high-intensity intervals to enhance metabolic control and hormonal balance.
  • Balance Enjoyment and Effectiveness: While longer endurance activities are fine for enjoyment and mental health, prioritize effective training methods for physical health and longevity.

Summary and Key Points on Polarized Training

• Polarizing Training Approach:

  • High Intensity:
    • Strength Training: Involves heavy, intense strength workouts that challenge the central nervous system.
    • Cardiovascular: Includes true sprint interval training, such as 30-second all-out efforts on the assault bike, followed by adequate recovery.
    • Example: A typical session might involve a 20-minute lower body strength workout followed by intense 30-second sprints on the assault bike.
  • Low Intensity:
    • Recovery: Activities like walking should be very easy, serving as recovery from more intense sessions.
    • Balance: Ensure a clear distinction between very low-intensity recovery and very high-intensity work for optimal results.

• Menstrual Cycle and Performance:

  • Tracking: Women should track their menstrual cycle to identify personal patterns of performance and fatigue.
  • Cycle Phases:
    • Low Hormone Phase (Day 1 to Ovulation):
      • Optimal for Intensity: This phase allows for better handling of physical and mental stress, making it ideal for high-intensity workouts and achieving personal records.
      • Physiological Adaptation: The body is better at accommodating stress, with improved immune response, muscle performance, and core temperature regulation.

Summary and Key Points:  Cycle Tracking and Ovulation:

• • Variability: Not all women ovulate consistently; many have 4-5 anovulatory cycles per year.
  • Importance: Tracking menstrual cycles and personal patterns helps in understanding individual responses.
• Luteal Phase:
  • Characteristics:
    • Pro-inflammatory Response: Immune system shows increased inflammation.
    • Carbohydrate Access: Difficulty accessing carbohydrates.
    • Sympathetic Drive: Higher baseline stress levels.
  • Nutritional Needs:
    • Increase Carbohydrates and Protein: Necessary to support tissue building and manage stress.
    • Tracking Ovulation: If ovulation is uncertain, focus on increasing carbohydrate and protein intake a week before the next period.
• Training Adjustments:
  • 10-Minute Rule:
    • Assessment: If feeling unwell or unable to perform after 10 minutes, modify the workout to lower intensity or recovery-focused.
    • Consistency: Adjust training based on how the body feels, especially during challenging phases of the cycle.
• Mental and Physical Resistance:
  • Listening to the Body: If training feels overly taxing, it’s better to adjust rather than push through, which helps in long-term recovery and performance.
  • Psychological Aspect: Avoid external pressures; focus on internal cues and self-permission to modify training for better outcomes.

• :00 Dr. Stacy Sims
• 00:02:24 Sponsors: Maui Nui, Eight Sleep & Waking Up
• 00:07:03 Intermittent Fasting, Exercise & Women
• 00:12:50 Cortisol & Circadian Rhythm, Caffeine & Training
• 00:17:25 Reps in Reserve, Rate of Perceived Exertion (RPE); Age & Women
• 00:21:06 Pre-Training Meal & Brain, Kisspeptin
• 00:26:45 Post-Training Meal & Recovery Window
• 00:29:59 Sponsor: AG1
• 00:31:48 Hormones, Calories & Women
• 00:34:24 Women, Strength Improvements & Resistance Training
• 00:39:10 Tool: Women & Training Goals by Age Range
• 00:44:16 Women, Perimenopause, Training & Longevity
• 00:47:14 Women & Training for Longevity, Cardio, Zone 2
• 00:51:42 Tools: How to Start Resistance Training, Machines; Polarized Training
• 00:58:23 Perform with Dr. Andy Galpin Podcast
• 00:59:10 Menstrual Cycle & Training, Tool: Tracking & Individual Variability
• 01:04:31 Tool: 10-Minute Rule; High-Intensity Training & Menstrual Cycle
• 01:08:36 “Train Hard & Eat Well”; Appetite, Nutrition & Menstrual Cycle
• 01:12:22 Oral Contraception, Hormones, Athletic Performance; IUD
• 01:20:57 Evaluating Menstrual Blood, PCOS; Hormones & Female Athletes
• 01:26:31 Iron, Fatigue; Blood Testing & Menstrual Cycle
• 01:29:33 Caffeine & Perimenopause; Nicotine, Schisandra
• 01:34:24 Deliberate Cold Exposure & Women, Endometriosis; Tool: Sauna & Hot Flashes
• 01:42:19 Tools: “Sims’ Protocol”: Post-Training Sauna & Performance; “Track Stack”
• 01:49:37 Women, Hormones & Sleep, Perimenopause & Sleep Hygiene
• 01:52:54 Supplements: Creatine, Water Weight, Hair Loss; Vitamin D3
• 01:57:21 Protein Powder; Adaptogens & Timing
• 02:00:11 Pregnancy & Training; Cold & Hot Exposure
• 02:06:19 Tool: Women in 50s & Older, Training & Nutrition for Longevity
• 02:09:38 Tool: Women in 20s-40s & Training, Lactate
• 02:12:18 Tool: What is High-Intensity Training?, Cardiovascular Sets & Recovery
• 02:17:22 Training for Longevity, Cellular & Metabolic Changes
• 02:19:30 Nutrition, 80/20 Rule
• 02:23:30 Listening to Self
• 02:26:00 Zero-Cost Support, YouTube, Spotify & Apple Follow & Reviews, YouTube Feedback, Protocols Book, Social Media, Neural Network Newsletter

https://www.hubermanlab.com/episode/dr-stacy-sims-female-specific-exercise-nutrition-for-health-performance-longevity