Lec 6 -Learning Flashcards
how long does it take to typically consume a meal? and how long does it take to empty the stomach?
20 minutes
Food is emptied from the stomach at 2-3 kcal per min (for mainly solid meal)
So… 600 kcal meal will take 3.5-5 h to empty from the stomach.
what is sham feeding? and how does it effect intake?
Sham feeding mimics normal food consumption but where food and drink are not actually digested or absorbed, they are instead drained from the stomach.
The early sham feeding studies in the rat showed that meal size was larger during sham feeding than real feeding.
what does Orosensory stimulation do?
Orosensory stimulation can both inhibit and
stimulate intake
what did Davis 2009 find (sham feeding)
argue that sham feeding actually tells us that two things happen; 1) the animal consumes more food 2) over successive days the amount of food increases quite dramatically. So it is a dynamic and not immediate effect. They argue that if you look at what happens after first day, although food is being drained from stomach they don’t consume as much as they do in day 5. So the act of consuming the food itself is inhibiting intake. After five days, food intake suddenly increases, so relative to this there is inhibition of intake.
=The progressive increase may reflect the extinction of a control signal that normally modulates the rate of fluid ingestion.
=Conditioned orosensory satiating effect extinguishes when sham feeding occurs repeatedly without intervening real feeding tests
who first investigated learned satiety? and how was it demonstrated?
Booth - rats were exposed repeatedly to two different-tasting odours (10% or 50%). One liquid was presented with a high-energy density and the other was presented with a low-energy density. After this training, Booth observed that when the same flavours are presented with an identical energy density (30%), rats tend to consume more of the liquid that had been presented previously with a low-energy density, and less of the 50% high energy density.
Booth argued that the acquisition of this learned satiety is critical, because it demonstrates that dietary control is achieved by incorporating information that has been gleaned from previous exposure to the consequences of ingesting a particular food (the US).
Animals learn to drink diff amounts..
Booth concluded that an association is formed between the sensory characteristics of the odour and the somatic cues that are present towards the end of a meal.
Zandstra study - yogurt
2 Yoghurts: low-energy = 67 kcal (280 kJ)
high-energy = 273 kcal (1142 kJ)
Each yoghurt (high/low) was presented in a different and novel ‘tropical’ flavour
Participants consumed a low- and high-energy yoghurt on alternate days. Each yoghurt was presented 20 times (40 days).
=they conclude that adults do not readily acquire accurate conditioned adjustments for energy content in food after repeated experience…”
how many meals has average 21 year old consumed?
23,000
what determines meal size?
expected satiety vs expected satiation
meal size is determined by psychological and physiological ‘events’ during and towards the end of a meal
Expected satiety: The extent to which foods differ in the satiety they are expected to confer when compared on a calorie-for-calorie basis (absence of hunger from outset).
Expected satiation: The extent to which foods differ in the fullness they are expected to confer when compared on a calorie-for-calorie basis.
Wilkinson, Brunstrom et al study - expectations
investigated whether flavour–nutrient learning modifies expectations by manipulating energy content (calories).
On day 1, participants tasted a novel dessert and then completed a measure of expected satiation. Participants then consumed either a low or high energy-dense dessert (sensory characteristics matched).
On day 2, expected satiation was assessed and then intake was measured using an intermediate energy-dense dessert.
=Although in the high energy condition, the day 1 expected satiety was lower, this then increased in day 2, whereas low energy decreased.
Expected satiation did increase but only in the high energy-dense condition.
This is evidence that some conditioning takes place before the meal begins and may govern the amount of food that we put on our plate.
what happens as familiarity with a novel food increases?
who demonstrated this?
if exposed to novel food, you don’t expect it to give you satiety. As exposure increases, as does expectation of satiety.
Brunstrom - sushi study
Brunstrom sushi study
looked at sushi consumption. 40% had never consumed it. 29% they had it monthly or weekly, and measured expectations relative to commonly consumed foods.
=Those who never consumed it before had lower expectations of satiation than those who had consumed it before.
Swithers 2011 study
and follow up study
rats exposed to plain yogurt for three days, then another three days they receive sweetened yogurt (governed in calories so slightly more energy dense). They are fed these combinations over period of 5 weeks.
=Over time, body weight is getting heavier (as they get older), but this is greater in those fed in non-predictive sweet condition relative to sweet predictive.
=weight gain increases in weeks 2, 3 and 5
=this is because sweet predictive response have increased cephalic phase response but you have blunted cephalic phase response in non-predictive
CHANGES IN BODY WEIGHT ARE ALSO ASSOCIATED WITH CHANGES IN BODY TEMPERATURE IN NON PREDICTIVE BUT NOT PREDICTIVE GROUP - they experience a greater depature from baseline
follow up study was done on fat and found similar findings
Rogers - low energy sweetners..
that use of low energy sweetners in place of sugar, in children and adults, leads to reduced energy intake (EI) and body weight (BW), and possibly also when compared with water.
Hardman et al .. pizza study
took measure of energy content of energy in pepperoni pizza and found there is great variety. Those people who had sampled a wide range showed relatively less energy responsiveness (more compensation) compared to those who tend to stick to one variety of pizza.
what is Sensory-specific satiety
the process whereby the pleasantness of a food
declines as it is eaten
