5. Appetite Flashcards
Digestion
Food is broken down by our gut microbiome (bacteria and other organisms in our intestines) and we absorb nutrients from it
Forms of Energy
Lipids - fats
Amino acids - proteins
Glucose - sugar from carbs
Energy storage
Fat (main, more energy per gram)
Glycogen
Proteins
3 Stages of Metabolism
Cephalic phase
Absorptive phase
Fasting phase
Cephalic phase
Sight/smell of food
Ends with absorption of nutrients into bloodstream
A lot of insulin, small amounts of glucagon
Absorptive phase
Energy is absorbed, body’s immediate needs are met
A lot of insulin, small amounts of glucagon
Fasting phase
The body withdraws energy from its reserves
Energy from the previous meal has been used up
Ends at the beginning of the next cephalic phase
High glucagon levels
Skipping of fasting phase
Fast weight gain occurs
Metabolic Phases/Cycle (hormones)
- Insulin is released
Enabling glucose to enter cells
Fuel conversion for storage is promoted - Blood glucose levels decline, insulin stays the same
- Rapid return of hunger
Insulin levels are low, so glucagon cannot enter cells
Glucagon goes to the brain instead, stopping it from being the body’s main energy source
Free fatty acids are used as the main source
Hunger related hormone
Galanin - triggers hunger for fats
Ghrelin
Ghrelin
Neurotransmitter, binds to the same receptors as growth hormones
Increases hunger
Galanin
Hunger related hormone
Triggers hunger for fats
Satiety Related Hormones
CCK
Leptin
CCK - satiety related hormone
In the short-term
- Constricts the sphincter muscle, leading to the stomach being constricted and filling more quickly
- Stimulates the vagus nerve, sending signals to the hypothalamus, signals satiety
Leptin - satiety related hormone
Satiety related hormone
Function is to decrease appetite and increase fat metabolism
Released after meals
Orexin/Hypocretin - hunger related hormone
Released in the hypothalamus
Two roles in feeding
Increase in seeking food
Reward response
Sensory specific satiety
The number of different tastes influences meal size
More tastes = eating more
Cafeteria diet
Positive incentive value
Satisfied with one food but still crave other tastes
Set-point theory
The motivation to eat comes from energy deficits, eating is a method of returning to our normal levels of energy
We eat until this ‘set-point’ is obtained/we reach homeostasis
Lots of evidence against
Criticism of set-point theory
Inconsistent with basic related evolutionary theories
That we eat as much as possible to survive
Obesity
Unaccounted for:
Tastes
Social influences
Appetizer Effect
Hunger is increased after eating appetizers as the cephalic phase responses are increased
Lateral Hypothalamus
Releases orexin, making you seek food
Controls insulin secretion
Alters taste responsiveness, enhancing the taste of food
Paraventricular Hypothalamus
Gathers all information and provides it to the lateral nucleus
Inhibitory effect
Sham eating experiments
Food is chewed and swallowed but not taken to the stomach, redirected by a tube inserted into the body
If set-point was true, the rats would’ve eaten huge meals as the energy threshold was not being met but this was not the case
Rats ate a relatively normal amount of food
After several meals, rats ate more
Showed that people enjoy physical eating
Causes of Obesity
Related to taste preferences, cephalic responses, culture, genetic factors (predisposition) etc.
Drugs
Surgeries
Differences in energy expenditure
Not everyone exercises the same amount
Differences in the basal metabolic rate in each person
Diet induced thermogenesis
Social influences
Diet induced thermogenesis
Mechanism by which the body adjusts the efficiency of energy utilization in response to body fat
Less body fat - more efficient energy usage
Leaky Barrel Model
There has to be balance between all factors
(food intake, energy expenditure, satiety signals etc.)
Remember the image with the hole in the barrel & the barrel on the hose
Glucostatic set-point theory
The set-point involves glucose intake
Short-term (energy)?
Lipostatic set-point theory
Lipid set-point
Long-term (energy?)
Evidence: adults body weight is relatively consistent
Conditioning
Conditioned taste aversion, can determine what we do and don’t eat
Preferences
High calorie foods like sweets (reminiscent of Mother’s milk)
Foods high in minerals and vitamins (usual choice but with so many options our bodies find it hard to differentiate and choose the best one)
Arcuate Nucleus
One set of hunger neurons and one set of satiety neurons that affect the paraventricular nucleus
Paraventricular Nucleus
Output stimulates satiety
Lateral Nucleus
Output stimulates feeding
Ventromedial hypothalamus
Output inhibits feeding
