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The Metabolic Balancing Act: Insulin, Cortisol, and Thyroid Hormones in a Modern Overfed, Stressed-Out World

Throughout human history, survival depended on our body’s ability to adapt to feast and famine cycles. Our ancestors thrived because their metabolic systems could seamlessly shift between storing energy in times of plenty and mobilizing it during scarcity. Insulin, cortisol, and thyroid hormones played central roles in this finely tuned system, orchestrating energy balance, stress adaptation, and metabolism regulation. However, in today’s world of constant stress and overabundance of food, this once-helpful system is now working against us, contributing to obesity, metabolic disease, and hormonal imbalances.

The Ancestral Feast-or-Famine Balance

In the past, our ancestors experienced natural cycles of eating and fasting, stress and recovery, and activity and rest. The interplay of insulin, cortisol, and thyroid hormones was essential for survival in these conditions:

  1. Feasting State (High Insulin, Low Cortisol)
    • When food was plentiful, insulin was released to store energy in the form of glycogen (in muscles and liver) and fat (in adipose tissue).
    • Thyroid hormones (T3 and T4) remained active, ensuring metabolism stayed efficient and energy levels were optimized.
    • Cortisol levels were low, allowing for muscle growth, repair, and reproductive health.
  2. Fasting or Famine State (High Cortisol, Low Insulin)
    • When food was scarce, cortisol increased to mobilize stored energy, breaking down fat and muscle for fuel.
    • Insulin levels dropped, allowing fat burning and ketone production to sustain brain function.
    • Thyroid function slowed down slightly to conserve energy, reducing metabolic rate until food was available again.

This delicate dance between anabolism (growth/storage) and catabolism (breakdown/mobilization) ensured that early humans could withstand harsh conditions and still reproduce, hunt, and survive.

The Modern Disruption: A World of Chronic Stress and Overeating

Unlike our ancestors, we now live in an environment of constant food availability and unrelenting stress. This has disrupted the natural balance of insulin, cortisol, and thyroid hormones, leading to chronic metabolic dysfunction:

1. Chronic High Cortisol (Stress Overload)

  • Modern life exposes us to chronic psychological stress, poor sleep, stimulants, and overtraining, leading to persistently high cortisol levels.
  • High cortisol promotes insulin resistance, making it harder for cells to absorb glucose and leading to high blood sugar.
  • Cortisol increases belly fat storage, driving inflammation and metabolic dysfunction.
  • Thyroid function is suppressed, slowing metabolism, reducing energy levels, and worsening weight gain.

2. Constantly High Insulin (Overfed State)

  • Unlike our ancestors who cycled between fasting and feasting, we are in a constant fed state, consuming processed carbs, sugar, and frequent meals.
  • Excess insulin leads to insulin resistance, meaning cells become unresponsive, forcing the body to produce even more insulin to compensate.
  • This disrupts thyroid function, reducing T4-to-T3 conversion and increasing reverse T3 (rT3), which slows metabolism.
  • Chronic high insulin blocks fat burning, leading to obesity and metabolic inflexibility.

3. Thyroid Suppression & Metabolic Slowdown

  • With chronically high cortisol and insulin resistance, the thyroid senses stress and lowers metabolism to protect energy stores.
  • This leads to fatigue, brain fog, sluggish metabolism, weight gain, and poor energy utilization.
  • Many people develop functional hypothyroidism, where thyroid hormone levels appear “normal” on lab tests, but they still experience symptoms due to poor hormone conversion and receptor sensitivity.

Breaking the Cycle: How to Restore Metabolic Balance

To reset the natural insulin-cortisol-thyroid balance, we need to mimic ancestral metabolic rhythms by incorporating fasting periods, stress management, and nutrient-dense eating.

1. Lower Chronic Cortisol

  • Prioritize sleep (7-9 hours of deep sleep enhances insulin sensitivity and lowers stress hormones).
  • Reduce stimulants (limit caffeine, avoid late-night screen exposure, and manage work-life balance).
  • Incorporate stress management (meditation, deep breathing, time in nature, and social connection lower cortisol levels naturally).
  • Use adaptogens (ashwagandha, rhodiola, and phosphatidylserine help modulate cortisol response).

2. Improve Insulin Sensitivity

  • Intermittent fasting or time-restricted eating allows insulin levels to drop, promoting fat burning.
  • Strength training + Zone 2 cardio (improves insulin sensitivity, enhances mitochondrial function, and reduces visceral fat).
  • Low-glycemic, whole-food diet (avoid processed carbs and sugars, increase protein and healthy fats).

3. Optimize Thyroid Function

  • Support T4-to-T3 conversion with adequate selenium, zinc, magnesium, and iodine.
  • Check reverse T3 levels (if high, address stress and inflammation to improve thyroid function).
  • Ensure sufficient protein intake (essential for hormone production and metabolic health).
  • Consider thyroid hormone support if necessary, particularly in cases of subclinical hypothyroidism.

Conclusion: Thriving in a Modern World with an Ancestral Blueprint

Our bodies were designed to cycle between anabolic (storage) and catabolic (mobilization) states, just as our ancestors did. The constant stress and overfeeding of modern life disrupt this balance, leading to insulin resistance, thyroid dysfunction, and metabolic disease. By reintroducing ancestral habits—fasting, movement, stress resilience, and mindful eating—we can restore this metabolic harmony, enhancing energy, longevity, and overall health.

By working with, not against, our natural metabolic rhythms, we can reclaim the resilience and vitality that allowed our ancestors to thrive for thousands of years.