Hunger and the Chemical Senses

Anthropocene

• Significant human impact on earth, new era in Earth history defined by geologists

What are the two food reinforcers?

• 1º food reinforcer: Pleasure

• 2º food reinforcer: Social facilitation

What are the benefits of cooking?

• Δ food molecular composition

  • ↓ digestive E → E fuels larger brain, other processes

  • Kill harmful bacteria

  • Decompose polymers → monomers (more digestible)

  • Shrink jaws/intestines, grow skulls

blood glucose levels

Regulate feelings of hunger and satiety

Low = hungry

liver and pancreas

Liver store glycogen and converts glycogen into glucose when blood glucose levels are low

Pancreas secretes insulin for immediate uptake for respiration or converts excess glucose into glycogen

Both help buffer extreme swings in blood glucose levels and regulate ingestive behaviours

NPY (Neuropeptide Y)

neurotransmitter from NPYergic neurons that drives activity in hypothalamus and increase hunger and food-seeking behaviours

Ghrelin

hunger hormone from stomach cells that motivates eating behaviour (hunger pangs - uncomfortable contractions) and increase gastric motility (involuntary stomach muscle contractions to prepare for digestion)

function of CCK

Secreted from small intestine to promote short-term satiety (signifies need to end a meal)

why is fat the ideal form of long term energy storage not glycogen?

fat is more energy dense and can last for up to 2 months

Leptin

Secreted by adipose tissue

long term energy balance and correlate with fat mass

• long term satiety

• high level inhibit NPY, appetite

• low levels promote feeding, energy conservation

OB gene Controls leptin secretion

what happens when leptin level rise? decrease?

• when rise, act on receptors and hypothalamus to reduce appetite and lower food consumption

• when decrease, show increase in foraging effort or minimize activity

leptin and NPY interact together to _ and how

regulate weight to optimal levels

• when glycogen reserve decrease, increase release of NPY to stimulate hunger. adipose tissue start releasing leptin to balance that out. the battle continues until the drive to eat wins leptin

what inhibits NPY release

• high levels of insulin and glycogen

• high levels of leptin

NPY increase intake of which macronutrient

Carbs

functions of endogenous opioids

contribute to palatability and reward-driven feeding

naturally occuring chemical substances that have morphine-like actions in the body

naloxone

blocking opioid receptors to reduce intake of saccharin, sucrose and saline

Injecting NPY in rats

NPY injected into rat brains satiated by prior food consumption

• ↑ sucrose consumption

• Work harder for sucrose associated cue

• ↑ saccharin consumption (similar taste to sucrose without calories)

• Prefer carbohydrate diet (over protein or fat)

Higher genetic carbohydrate preference → greatest carbohydrate preference after NPY injection

Inject NPY → rat brain trained to press button for food: Press button more for little food (control gives up earlier)

Inject NPY → rat brain: More willing to eat quinine-laced (bitter) foods

Similar in all animals

Injecting CCK in humans and rats

Inject CCK in humans - feeling full sooner

Inject CCK → rats: Shorter meal durations, more meals per day (same total daily food intake)

Leptin injections in mice and humans

Inject leptin → Ob-KO obese mice: ↓ eating → normal mass

Inject leptin → WT obese mice: no effect, remain obese

Human clinical trials: Defective leptin signalling != obesity

Most obese individuals have functional leptin signalling systems

Naloxone in mice

Opioid receptor knock-out mice show lower preference to saccharin

Gherlin in rats/humans

Ghrelin spikes in rat/human anticipating scheduled daily meal → immediate, intense hunger from skipping meal

(+) learning: Binds to hippocampus neurons to facilitate making new synapse

how can endogenous opioids explain overeating

Overeating people might have maladaptive opiod-mediated reward-driven feeding mechanism

Fiber

more satiating

• Cannot digested into calories

• Forms sludge in sI: slow absorption → increase high t [CCK]

Vagus nerve

gut to brainstem connection

Portal vein

Connects small intestine to the liver

Satiety

Inhibit NPYergic activity

• All monomers pass after absorption, before assimilatioN

• More sensitive to AA → proteins more satiating

How is high glucose harmful?

• Stick to blood vessel epithelium to make stiff, narrow

• Directly kill certain cell types

What has more energy density fat or carbs?

Fat (9 kcal/g) vs. Carbohydrates (4 kcal/g)

Does high fat or low fat cause satiety to a lesser extent?

High fat causes satiety to lesser extent as low fat causes hunger

• High fat not evolutionary harmful

• Leptin only inhibits NPY to threshold

How is energy usage prioritized before increasing hunger

1. Glycogen reserves deplete → ↑[NPY] → requires food

2. Adipose tissue secretes leptin → inhibit requirement for food (physiological antagonism)

3. Eventually hormones cannot inhibit appetite

4. Meal consumed, CCK prompts short-term satiety

why does body defend weight loss stronger than weight gain

Make evolutionary sense because calories and nutrition used to be less certain, so better consume more than less

glucose

primary fuel for brain

Memories and food

Innate behavioural responses are correlated to emotional processing

Taste is an indication of

Nutritional quality

why are bitter and sour taste not normally preferred

Evolutionarily thought to be toxic

why are sweet, salty and savory always preferred

Because evolutionarily more food that taste like this were/are safe, nutritious and rich in energy

Is taste response universal in infants? what does this indicate?

• yes

• indicate taste response is controlled by adaptive mechanisms, in older and lower regions of the brain

  • Certain taste preferences universal, basic to human behaviour

    • Specific tastes elicit same facial reactions from infants from different birthplaces

    • Healthy, brain-damaged infants have same responses

Taste sensitivity depends on

The number of taste buds on tongue, more sensitive = more taste buds

Are female or male more sensitive to sweet and bitter taste? why?

female, especially during early pregnancy, corresponding to the period when fetus is most sensitive to toxins and otehr harmful substances

wwhat are the 5 different types of taste? what do they each indicate for nutritional values

• sweet = energy rich food (fruits, sugars)

• salty = essential electrolytes/NaCl

• sour and bitter = potentially harmful, spoiled or poisonous foods

• umami = AA glutamate and aspartate

How do artificial sweeteners work?

Activate sweet cells without being digested into E

Evolution of sweet receptors

Meat-eaters have non-functioning sweet receptors

Why are salty food important?

Salt essential for AP

Evolutionarily rare, explains enjoyment

Na+ diffuses through Na+ channels to depolarize cell → AP

Homeostasis

Low [NaCl] → (+) salt receptors

High [NaCl] → (+) sour/bitter receptors

Sour taste

Innate unpleasant perception

Avoid acids damaging mouth, esophagus soft tissues

Vitamin C high in sugar, acidity

• Enjoy right proportion of sweetness/sourness

Acquire sour taste with experience

Bitter taste

Nutritious foods contain small amounts of bitter substances

• Tolerate bitterness if ingestion does not cause (-) effects

• Enjoy bitterness if paired with (+) effects

Genes dependent on the toxic chemicals avoided in evolutionary history

• Very bitter tastes produce automatic gagging, nausea

Individual variation of bitter receptor expression

PTC (phenylthiocarbamide)

• receptor detecting bitterness

• Less toxin exposure → less selective pressure to maintain bitter receptors → 11x non-functional bitter receptors

Denatonium

Most bitter chemical, added to toxic flavourless products for child safety

Umami

Increased in cooked foods

• Chimpanzees willing to postpone eating for cooked foods

• Cooked food preference precedes invention of cooking

• Common in meat-eating diets

  Absent in Pandas (eat bamboos high in sugars, low in protein)

Are different tastes detected in different areas of the tongues

no, all areas of tongues can detect all types of taste

Cultural influences on universal taste preferences rooted in local food availability

• Foods enjoyed as adult learned by experience

• Individual differences in taste sensitivity

  • Culture's preferred foods α local food availability

Where are taste receptors located

2/3 are located on tongue, 1/3 on soft palate and throat

Texture and Taste neuro pathways

Primary Taste Pathway

Food dissolves in saliva, molecules bind to taste receptor cells - Taste receptor cells send AP to brainstem through main gustatory nerve - medulla-thalamus - primary somatosensory cortex or gustatory cortex (primary taste area) then orbital cortex

Which brain area combine taste with its feel and texture

primary somatosensory cortex

Which brain area combine taste with smell (producing flavor)

orbital cortex

neuropathway for emotional and hormonal responses of taste

Secondary taste pathway

Food is dissolved in saliva - molecules bind to taste receptor cells - taste receptor cells send AP to brainstem through main gustatory nerve - brainstem - pons - hypothalamus + amygdala

how is spice produced as a "taste"

contain capsaicin heat and pain receptor agonist

• Cause pain, inflammation

• Prevent mammals from eating capsaicin-producing plants

• Enjoyable in moderate amounts

Sensation of taste-smell begins at

nasal pharynx (retronasal smell interaction at back of throat)

gustatory and olfactory info first interact in ____ both integrated in ____

nasal pharynx, both integrated in orbital cortex

smell identity is distinguished by

Specific patterns of firing of AP by olfactory cells

how are chemical signal (odor) translated into neural signal

1. odourants enter nasopharnyx from external environment and dissolve in mucous membrane in nasal cavity

2. odourants interact with olfactory cilia and bind to olfatory receptors in olfactory epithelium (single odourant binds to many receptors)

3. olfactory receptor cells are activated and send electrical signals passing cribriform plate (thin skill area)

4. Olfactory cell axons synapse with glomeruli dendrites

5. Signal is relayed and then transmitted to higher regions of the brain - limbic system

neuropathway of smell after signals are relayed in the glomeruli

Olfactory bulb - orbital cortex in frontal lobe - primary olfactory cortex in temporal lobe - limbic system (thalamus, hippocampus, hypothalamus, amygdala, pituitary)

OR - secondary olfactory cortex in frontal lobe

Word for describing smell

• Only 3x English words {fragrant, musty, stinky} describing smell

  • Hunter-gatherer societies with more words describing smell are better attuned to smell, describe smell better

  • All other words are synonyms, borrowed from other senses

Food for pleasure

Start with savoury then sweet

Miraculin

Glycoprotein from miracle fruit berry that binds to sweet taste receptor cells and can make them respond to acid (inactive if pH 7)

• make sour food taste sweet

thrifty genes are promoted in environment

feast or famine

thrifty gene theory

people consuming more energy have a better change of survival during famine

• Most efficient with every calorie consumed, efficiently storing excess calories as fat

  • No external calorie storage, only fat/glycogen

• Agriculture stabilized feast/famine environments

  • Consistent access to calories

  • Human role specialization

• Difficult to identify exact genes in thrifty genotype

Amount of food consumes depends on

portion size put in front (ketchup in small containers)

Why is it bad for kids to only eat carbohydrates

Cannot develop learned bitter/sour taste preferences

Rats and Food-Reward Study

• Diet 1: Perfect nutritional balance rat chow

  • Rats eat as much as needed (natural equilibrium)

• Diet 2: 1-hour/day - go down tunnel to super salty/sweet food

• Diet 3: 23-hours/day - go down tunnel to super salty/sweet food

  • Rats overeat → become obese

  • Rats would endure electric shock to access food

• Dopaminergic reward experiences

why are processed food irresistible

They are made to deliver intense, transient (disappearing) flavour

how can perceived enjoyment of chips be manipulated by sound

louder = crunchier (higher pitch) = more fresh = better

how does portion size affect how much we eat

bigger portion = tend to eat more, cuz we tend to finish stuff in the plate/bowl

post eating calm

after we eat a meal, we feel sleepy because our body need to focus energy on digesting, so will slow down HR

• Hypothalamus induces parasympathetic activity throughout body after eating

  • ↓ HR, ↓ ventilation rate, ↑ deep breathing, drowsiness [food coma]

what chemical in mint makes it taste cool? why?

menthol - bind to receptors on tongue that detect cold temperatures

Possible to simultaneously experience hot/cold sensations (Icy hot)

Heat/cold sensing neurons are scattered throughout the body (taste buds are only on tongue

what situation makes people have less appetite and what makes them have increased appetite? (in terms of stress)

• constant stress: continuous activity of their fast-response nerves -> tend to eat less when stressed

• short bursts of stress: intense stress throughout the day, nterspersed with periods of time where their slow, hormonal stress response -> tend to eat more when stressed

Post natal weight regulation factors

• Overweight individuals increasing across all SES countries

  • 15 years ago: More adults overweight than underweight

  • Developed countries: More overweight than underweight (greatest difference)

  • Undeveloped countries: More underweight than overweight

• Scarcity to overabundance

  • Decreased exercise

  • Increased E-dense food consumption

• Specific world areas with have longer life spans

  • Active lifestyles (1º transport = walking)

    • Manual labour {household chores, gardening}

  • Eat unprocessed natural foods

  • Expansive social networks

Pre-natal weight regulaiton Factors (gestation)

• Dutch famine: WWII Holland blockade → pregnant females experience food scarcity

• Metabolic diseases more common for infants born during restricted calorie phase

• Infants born during restricted calorie phase consumed normal amount of food as adults

• H: Permanent shift in thrifty genotype, "even-thriftier genotype" activated to teach infants how to function as efficiently as possible in world with minimal calories

  • Prenatal environment impacts post-natal food interactions

• Processed foods engineered to deliver intense, transient flavour for addiction

  • Exploit evolved sugar taste preferences

  • Sugar added to processed tomato sauce

  • Sugar added to yogurt (0 natural sugar)

• Sound manipulates chip enjoyment: Perceived crispiness α perceived freshness

  • Create maximally tasty chip transiently

  • Attenuate to ↓f sounds

  • Amplify ↑f crunch sound

• Cues to guide when to stop eating

  • Internal: When satisfied, when stomach full

  • External: When plate empty, when TV show over, when others finished eating

  • Social behaviours match rate of eating and consumption pattern

• Bottomless soup experiment: Discuss social issues while eating soup

  • 1x person has soup with tube connecting to refill

  • Normal bowls: 250 mL, 5.7 full

  • Bottomless bowls: 400 mL, 5.1 full

• Popcorn container size influences amount consumed

  • Eat more fresh/stale popcorn in large containers

  • Generates food waste

• Food portion increases from 1960-2011, != caloric needs