Episode 81: Dr. Charles Zuker – The Biology Of Taste Perception & Sugar Craving | Huberman Lab

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Key Takeaways

  • The inherent goal of the taste system is to get nutrients to survive – attracted to the ones we need, aversion to the ones that may kill us
  • Taste is predetermined: parts of the brain will experience the full behavioral stimulus, even if activated when only ingesting water
  • “I don’t believe obesity is a disease of metabolism, I believe obesity is a disease of brain circuits.” – Dr. Charles Zuker
  • Sugar molecules activate the “gut-brain axis” which drives the preference for sugar
  • Artificial sweeteners fail to curb the appetite for sugar because they work on the tongue to recognize sweetsness but do not activate sensors in the gut which satisfy the craving
  • Diseases of malnutrition today are linked to overnutrition (of processed foods), not the actual absence of food
  • Highly processed foods highjack the gut-brain axis, continuously reinforcing “wanting”

Introduction

Dr. Charles Zuker, Ph.D., is a Professor of Biochemistry, Molecular Biophysics, and Neuroscience at Columbia University and an Investigator with the Howard Hughes Medical Institute. Dr. Zuker is the world’s leading expert in the biology of taste, thirst, and craving.

Andrew Huberman and Dr. Charles Zuker discuss the neural circuits of taste, the “gut-brain axis,” the basis of food cravings, and the key difference between wanting (craving) and liking (perceiving) sugar.

They break down taste, food satiety, the damage down by highly processed foods, and more.

Host: Andrew Huberman (@hubermanlab)

Where to find Dr. Zuker: Columbia Zuckerman Institute, Lab website, Howard Hughes Medical Institute (HHMI) profile

Defining Perception

  • The brain weights 2% of body mass but consumes 25-30% of the body’s energy
  • Perception: neurons only understand electrical signals so there needs to be a reconciliation of understanding the world
  • Individuals perceive the world differently depending on how we transform these signals, even given the same sensory cues
  • Perception divides our responses into seeking, avoiding, or tolerating
  • Detection: cells interacting with the brain directly, think of something touching the tongue

Taste

  • The brain has to compute, encode, and decode taste
  • The five basic tastes detectable by humans: sweet, sour, salty, bitter, umami (e.g., seaweed, tomatoes, cheese)
  • Dietary practicality of the five basic tastes:
    • Sweet: energy
    • Umami: protein and essential nutrients
    • Salt: electrolyte balance
    • Bitter: prevent ingestion of toxic chemicals
    • Sour: prevent ingestion of spoiled foods
  • Taste is a hardwired system, but you can train to like something
  • Detectors in the tongue activate entire programs depending on the taste stimulated and lead us to either recoil or seek more
  • Myth: taste receptors are relegated to specific parts of the tongue
  • Every taste bud in the oral cavity has receptors for all of the five basic tastes
  • The flavor does not equal taste – flavor is the experience of tastes coming together with smell, texture, temperature, vision  
  • It’s possible there are additional tastes, such as fat (but this is really more of a textural stimulation), metallic (we don’t like to eat it but we know what it tastes like)
  • When you burn your tongue on hot food or beverage, taste receptors and somatosensory cells are disrupted but will be renewed
  • Sweet vs. bitter: diametrically opposed flavors which evoke different behaviors
    • Sweet has a positive valence independent of flavor and quality – sweet activates the amygdala         
    • Bitter has a negative valence and evokes aversive behaviors
  • Conditioned taste aversion: you can train animals to change the nature, quality, and meaning of a stimulus as a function of its state

The Addictive Nature Of Sugar & “Gut-Brain Axis”

  • Perception and craving for sugar happen at multiple stages: (1) receptors in tongue sensing sugar which seek more as they become desensitized; (2) loss of signaling by continuous activating of circuit
  • Sugar activates reward-pleasure centers in ways that dramatically change our internal state
  • The body tells the brain what you need
  • The brain monitors & modulates the state of all organs and systems in the body to ensure everything works together to achieve healthy physiology
  • The brain creates associations that food is coming & signals to the pancreas to release insulin in anticipation
  • The vagus nerve innervates the majority of organs in the body, monitors function, sends signals to the brain, and responds accordingly
  • The vagus nerve carries thousands of fibers with different meanings associated with their specific task
  • The brain is the conductor of the physiology of orchestra and metabolism
  • Like versus want: “liking” sugar is a function of the taste system (sweet); “wanting” sugar is a function of the gut-brain axis
  • Gut-brain axis drives sugar preference: mice will drink exponentially more from sugar versus water if given the choice; once sweet receptors are removed, it will still drink sugar because mouse learned behavior and detects it via smell, location, etc.
  • Sugar is recognized on its own then cells in the intestine cell signal to the brain via vagal ganglia which reinforce desire and pursuit

Brain Sensors & Processed Foods

  • Sugar, fat, and amino acids are essential nutrients for all animals
  • The taste system gives us immediate recognition, but the gut-brain axis reinforces it only when the brain doubles down
  • Highly processed foods highjack the gut-brain axis, continuously reinforcing “wanting”
  • We have a destructive reliance on foods that are not healthy
  • Processed foods are already broken down so your system doesn’t have to work in the same ways it would if the food were natural
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Notes By Maryann

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