Lec 2 - Short term influences on eating Flashcards
What is our rate of energy intake between meals? When is it highest?
When is the rate of energy expenditure lowest?
(according to Frayn)
Rate of energy intake is zero except when eating and drinking. Highest during lunch
Rate of energy expenditure is lowest during sleep, increases on waking, and increases more with physical exertion
Excess energy intake is mainly stored as..
Fat
What are meal initiation, eating episode, satiation and satiety
Meal initiation= when you start a meal
Eating episode=start eating
Satiation=fullness, no longer interested in food and stop the eating episode. Satiationsignals the brain the meal is over. occurs DURING meals
Satiety=absence of hunger BETWEEN meals. It is a physical feeling of fullness that allows us to stop eating for a while
who created the Glucostatic hypothesis/depletion-repeation and what year and what is it
Jean Mayer 1955
In the hypothalamus there are receptors that monitor blood glucose in ventromedial nucleus, when this glucose level reduces there is a drive to consume food to restore blood glucose levels and cycle repeats.
Reduced glucose utilisation in the brain leads to hunger
Problems with Glucostatic hypothesis
- Very large change in blood glucose are required
- Liver tends to mobilise energy reserves – glucose levels remain fairly constant
Eg if you look at glucose over 24 hour period, eating isn’t well predicted by decreases in blood glucose. There isn’t a clear correspondence. There is often increase in glucose after meal has been consumed.
How and why do we maintain blood glucose levels?
Glucagon increases blood glucose, insulin reduces glucose levels
Insulin is released from pancreas. We draw on immediate fuels from liver and for muscle tissue.
more on bath analogy.. appetite is governed by..
Appetite is governed primarily by
recent eating (strong negative feedback)
Feedback from energy stores is generally weak
(1) water in a bathtub represents body energy content, (2) water in a saucepan represents food in the gut, and (3) the bathtub is filled via the saucepan. Furthermore, (4) it takes hours to process and pass the full energy (macronutrient) content of the saucepan to the bathtub, and (5) both the saucepan and bathtub resist filling, representing negative feedbacks on appetite (desire to eat
This model is consistent with the observations that appetite is reduced greatly by energy intake (a meal added to the limited capacity of the saucepan/ gut), but not increased by a large increase in energy expenditure (energy removed from the large store of energy in the bathtub/body).
Despite this, hunger is often attributed to an acute energy depletion
Assand et al - beliefs
measured beliefs of undergraduates and nurses, dietitians etc
=Both undergraduates and health professionals were as likely to maintain set-point beliefs. It was found that almost all believed that deviations from energy set points were the primary source of their motivation to eat.
=The findings from this study suggest that misconceptions about hunger and eating may have adverse implications for health that are common among both lay people and health professionals.
Cultural norms of french spanish italians hunter-gatherers
French cultural norm to eat at prescribed times of day compared with Americans who eat at any time of day
Spanish eat late in the evening (around 9pm)
Italians eat a main meal at lunchtime
Hunter-gatherers eat opportunistically
Blundell (1999) - after exercise…intake..
After periods of exercise, 19% report increase in intake after exercise. The majority (65%) show no change- this is good for weight loss but not good if you become sedentary, when people become sedentary after a period of high activity, food intake is not “down-regulated” to balance a reduced energy expenditure. 16% show a decrease in appetite
Collier and Johnson - rat
rat study looking at consumption based on cost to get food
=When cost to get food increases they eat more food at that meal
=When there is low procurement price (no cost associated with access to food) they eat little and often (because they are rats)
Animals are strategic in way in which they pattern their meals with respect to meal size throughout the day.
describe Cephalic insulin release (Powley)
Insulin permits glucose to leave the blood and enter cells in muscle tissue and the liver at a higher rate.
This limits perturbations in blood-glucose levels.
When we eat food, there is an increase in blood glucose. This is perturbation and is disruptive.
Insulin protects against post-meal increase in glucose (hyperglycemic).
anticipated cephalic phase in animals
If animals are provided with food-associated stimuli (but don’t give it food), the animal will become hypoglycemic – they experience reduction in glucose- it has secreted insulin for a meal that never came.
The converse occurs when food is injected into the stomach – you infuse food into the stomach and humans and animals become hyperglycemic – increase in blood glucose because less insulin has been secreted.
hypoglyemic vs hyperglyemic
hypoglyemic = reduction in glucose because of secreted insulin
hyperglyemic = increase in glucose because of less insulin secretion
insulin therefore protects against hyperglyemic and limits perbutation
stephen woods eating paradox
Uses word insult - argues that we are learning to anticipate or to tolerate the food that we are about to consume. We adjust our physiology
Draws parallel to drug addiction - learned tolerance of dangerous drugs. heroin is a pain killer and so in the absence of ingesting the drug, users experience increased sensitivity to pain (hyperalgesia). this is a conditioned response. Hunger becomes assoicated with preparedness to consume food (associated with insulin, salivation etc).
Key point is that hunger isnt in response in change to energy stores, but occurs as an anticipatory learned conditioned response.
