When and how we eat is largely determined by our metabolism (the rate at which are body uses energy) and this is regulated by several physiological mechanisms: Set Point theory – biologically determined standard which our body weight is regulated. If we over/under eat our homeostatic mechanisms alter our metabolism and appetite (Keeley, 1986). If we persistently over/under eat, it is difficult for homeostatic mechanisms to work so we settle at a new weight (Passer et al, 2009) Role of hypothalamus –main area of appetite regulation. Lateral hypothalamus (LH) – when stimulated it produces hunger and when damaged results in dramatic reduction in food intake Ventromedial (VMH) – triggers a sense of fullness thereby reducing appetite.
Role of stomach – hunger was largely determined by hunger pangs (muscle contractions of an empty stomach. Contractions were measured and were found at height of hunger (Conner and Washburn, 1912) Other mechanisms must play a role in triggering hunger (Passer et al, 2009) Role of Ghrelin (hormone) – secreted from the walls of an empty stomach. This stimulates appetite and the secretion of Ghrelin stops when food is eaten (Berthoud and Morrison, 2008)
Ghrelin can have an effect on our mood. Starved mice had increased stress and anxiety (Lutter, 2008) Thinking about food – influence neural activity in parts of brain involved in the control of appetite. This leads to physiological responses such as saliva (Berthoud and Morrison, 2008). nticipation of eating leads to dopamine being released therefore pleasure. Genetic predispositions; Born to prefer sweet/salty foods and reject bitter/sour foods – in evolutionary past this would have aided survival – unlikely to eat something that will make us ill.
Food Neophobia is being afraid of the new. This means that animals have a powerful tendency to avoid food that they have not yet encountered. An aspect of neophobia is that we tend to show a greater liking of foods once they become familiar (Frost, 2006). We can see this in young children. We also have a built preference for meat (protein). E.g. hunter gatherers Humans have a genetic predisposition to learn preferences for food by associating them (classical conditioning) with the context and consequences (Birth, 1999). E.g. taste aversion.
Supporting research; Preference for sweet foods by: Grill and Norgen (1973) found lab rats accept sweet foods in almost reflex like way that required no decision making. Bell et al (1973) Inuit Indians that do not have sugar in their diet, very quickly choose to eat it when it became available. Preference for meat is supported by Milton (2008) – it is unlikely that early humans could have secured enough nutrition from a vegetarian diet to evolve into the active and intelligent creatures they have become. Taste aversion is supported by Garcia et al (1955) – rats that had been made ill through radiation shortly after eating saccharin, developed an aversion to it very quickly.