Lecture 5: Hunger, Eating and Health

mouth and salivary glands (human digestive system)

-mastication and saliva (alkaline)

-breaks up food and mixes it with salvia

-lubricates food and begins its digestion

oesophagus (human digestive system)

-transporting food to stomach

-set up for alkaline conditions, so acid from the stomach can damage it

stomach (human digestive system)

-churning food and breaking it down 

-acid digestive enzymes breaks down food 

liver/gall bladder (human digestive system)

-additional digestive enzymes added into the small intestine

pancreas (human digestive system)

0produces insulin and glucagon to store and release energy

small intestine (human digestive system)

-absorbs most nutrients from the food we eat

large intestine (human digestive system)

-removes water and packages waste

liver and kidneys (human digestive system)

-filter out toxins for excretion

rectum/anus and bladder (human digestive system)

-store and expel waste

insulin (key pancreatic hormone)

-shifts carbohydrates from the blood to storage

glucagon (key pancreatic hormone)

-shifts fuel from storage to where it is needed to fuel the body 

-converts glycogen and proteins to carbohydrate 

-frees fat stores to use as fuel when the glucose stores are low 

energy storage in the body

-three core products

• lipids/fats → fats, largest and most efficient energy store

• amino acids → proteins, mostly in the form of muscle tissue

• glucose → simple sugar, stored in muscles and liver, fast release

-minerals and vitamins are also stored in body structure

mechanisms for eating

-body has developed to be able to balance our intake and output

-homeostasis kicks in when our body’s set point is violated

-going over or below the set point → fat metabolism will change to push it up or down

-body tries to stay in a particular zone - not always successful

detectors (mechanisms for eating)

-detectors tell us when we are running low on nutrients/fuel and trigger our biology and behaviour

-brain is sensitive to shortages of glucose (hypothalamic regulatory nuclei)

-liver is sensitive to shortages of glucose and lipids

-stomach sends signals to the brain to signal need for food if it is unstimulated

satiety cascade

-sensory → cognitive → post-ingestive → post-absorptive

set-point theory (homeostasis)

-after eating energy resources assumed to be near set point and to decline after

→ body using energy to fuel physiological processes

-when energy resources fall far below set point, become motivated by hunger to initiate another meal →

• craving - automatic behavioural state

• hunger - motivational state

-negative feedback system

satiety (why we stop eating)

-body generates a range of short-term satiety signals 

-adequate glucose and lipid activity levels → detected in brain and liver 

-stomach distension 

-buccal activity 

-high levels of sensory information 

-appetite suppression chemicals 

leptin (satiety)

-long-term feedback mechanism to attend to

-hormone secreted by fat tissues

• increases metabolic intake

• decreases food intake by:

1. desensitizes the brain to hunger signals

2. inhibits the effect of other hormones that drive eating

Minnesota starvation experiment (health implications of poor eating)

-men appeared gaunt and extremities filled with extra fluid, lost hair, loss of coordination, ringing in ears, no sex drive

-obsession surrounding food, creating rituals

-increasingly irritable and moody

-struggled with weight gain and loss even after starvation effects finished

health implications of poor eating 

-obesity affects multiple systems 

-strong link to premature mortality 

-specific problems in children: bullying, school absence, stigma, self-esteem 

factors that take us away from homeostasis

• genetics

• learning

• social learning

• social pressures

• food industry

• toxic environment

genetic/evolutionary factors (homeostasis)

-genetic factors can make us more likely to eat particular foods

-predisposed to high-energy, high-taste foods: sweet, fatty, salty → more likely to contain nutrients

-less likely to enjoy bitter foods → associated with toxicity

learned taste preferences and aversions (homeostasis)

-influenced by: 

• culture → foods can be common in one culture but rare in another 

• upbringing → foods experienced early tend to be more readily approached 

• satiety to specific foods → keeps diet varied 

sensory-specific satiety (homeostasis)

-the decrease in pleasantness and consumption of a specific food after eating it to satiety 

-sensory properties of food influence intake and ratings of pleasantness 

-e.g., if have three flavours of sandwich found to eat more than those given one flavour 

social learning (homeostasis)

-we eat in a number of ways that are influenced by what we see going on around us

-imitation of what and how others eat

-cultural influence → tend to eat what they see as normal/local/customary

environmental factors (homeostasis)

• lighting → eat more in dim lighting

• temperature → eat more when cold

• portion sizes

• smells → of the food and the environment

• location and proximity of foods

agriculture and food industry (homeostasis)

-food industry goes through stages in its level of positive/toxic influence 

-currently in more toxic place → cheap processed food in large quantities ensures profit margins, fatty and sugary foods are more addictive 

-premium prices on more healthy foods → often out of season 

Malthusian hypothesis (agriculture and food industry)

-population growth is potentially exponential 

-but growth of food supply and other resources is linear 

-this reduces living standards to the point of triggering a population decline → so that we are not starved 

high fructose corn syrup (agriculture and food industry)

-famers subsidised to grow corn → but government needed something to do with excess corn

-created a market for HFCS

-supplied cheap for use in products (sugar in everything)

-related to obesity levels

-has unwanted side effects such as fatty liver, decreased insulin sensitivity and gout precursors

toxic environment

-term to describe the way in which human evolution and the environment that we are now in are completely at odds

-evolutionary we would stock up on food due to scarcity and eat as much as possible → in modern world can have as much food as we want and food industry forces sugary, fatty and addictive foods onto us

-food scarce cultures view obesity as a status symbol

-food plentiful cultures view obesity as a sign of weakness

evolution (toxic environment)

-evolved to grab food where we can 

-high-energy food was only seasonally available 

-high fat, high salt and high sugar foods are preferred 

-genes mean we are going to eat as much as we can - so we can live on our fat in the leaner times 

-but our environment has changes and the foods we were genetically programmed to eat are now abundant and easier to eat 

-so food industry gets as much sugar, fat and salt into foods as possible → makes them cheaper to produce and more palatable 

-healthier foods become more expensive and harder to get 

modern day (toxic environment)

-culture has changes from exercising to screen time → adverts for food and drink

• has dissociative effects which reduce our self-control

-social events centre around fast food joints

-seeing intergenerational effects