Eating2

Eating2 - Eating Hunger & Satiety IS FEEDING BEHAVIOR...

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IS FEEDING BEHAVIOR HOMEOSTATICALLY CONTROLLED? Consider the following diagram. It shows that as hours go by, an organism's energy reserves are used and thus its internal resources or reserves are diminished. As the energy reserves fall, hunger sets in (shown in blue), which is followed by the eating of a meal (shown in green). The energy reserves are restored as the meal is digested and the nutrients are absorbed. Then the process cycles again, and again, etc. Do you think this is how your eating is controlled? This seems to correlate largely with what our cognitive experience is, and is what many people's intuitions are for how feeding is regulated. But as we take a closer look at it, you may see that this type of set point theory – in which the animal monitors and attempts to maintain the level of some internal energy reserve –doesn't quite explain why we eat, how much we eat, or why we stop eating. It may not even do a very good job of explaining how our body weight is maintained -- or not maintained in other cases. ;-)
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2 GENERAL APPROACHES TO THE STUDY OF FEEDING 1. Control of Body Weight Is there homeostatic regulation of our body weight ? Do we defend a body weight " set point" ? It seems like there should be. Animals (except humans and other critters in captivity) don’t get fat. They seem to regulate pretty well. In fact, it seems that most animals (including humans) don’t regulate calories or nutrients within a meal but do so over a several week period. Energy expenditure and food intake are NOT strongly correlated within a 24-hour period , but there IS a strong correlation if weekly intake and energy expenditure are examined. The figure on the right contains data showing that energy expenditure and caloric intake are not correlated within a single day (top panel), but are linearly correlated over a week-long period (bottom panel). This means that control of a meal is not particularly homeostatic . 2. Control of a Meal
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• What makes us start eating? (hunger) • What makes us stop ? (satiety) • Why can’t we eat just one M and M? (reward) Consider the following diagram for a bit. .. This diagram shows the behavioral sequence of eating and the potential feedback controls via the brain. The two arrows at the top of the diagram pointing to the brain indicate that external influences (smells, time of day, social stimulation, stress) can trigger food search without information from an empty stomach or from nutrient absorption. So we can “need” to eat because we are getting signals that we need food, or we can “desire” to eat because of signals that stimulate desire. Similarly, we may stop eating because a signal tells us that our tummy is full , or because a signal tells us that we have ingested enough nutrients to meet our immediate needs. Finally, there may be sensory feedback systems
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This note was uploaded on 09/17/2008 for the course PSY 91 taught by Professor Williams during the Spring '08 term at Duke.

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Eating2 - Eating Hunger & Satiety IS FEEDING BEHAVIOR...

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