PsychExchange.co.uk Shared Resource

Eating Behaviour

PYA 3

Outline of topic

• Biological explanations of eating behaviour - neural mechanisms for control;evolutionary explanations of food preference

• Eating Behaviour - factors influencing attitudes to food and success/failure of dieting

• Eating Disorders - psychological and biological explanations of one eating disorder from anorexia nervosa, bulimia nervosa, obesity.

Learning Objectives

• To be able to describe the neural mechanisms involved in controlling eating and satiation

• To form a glossary of the key terms in the neural mechanisms and other relevant terms.

• To be able to explain the evolutionary explanations of food preference.

• To be able to apply previous knowledge to each area that is covered.

Biological Explanations of Eating Behaviour

Answer the following -

• Why did you eat the food ?

• How did you feel once you ate it?

• Did you have breakfast this morning?

• Why did you stop eating the food?

• What are your favourite foods? Why?

• How do you feel after a large meal?

Outline how it feels when you are hungry.

• Is it biological or psychological?

What does satiation mean?

• How does it feel?

• Is it biological or psychological?

Task

• Label the digestive tract on the worksheet.

• Can you also outline the functions of the parts?

• NB - Adipocytes are fat cells and the number of these in your body are determined in the first year of life. The amount of fat that they hold can vary throughout life.

Homeostasis

• We keep our bodies in equilibrium.

• Insulin and glucagon are two hormones that help to regulate our blood sugar. They are both released from the pancreas.

• If the body is unable to produce enough insulin it can lead to diabetes.

Blood Sugar regulation

• Look at the diagram on the info sheet.

• Put what you see into words.

INSULIN

Neural Mechanisms

• This is quite complex - ensure you choose your level carefully. Study the following topic with your glossary (filled in!!) to hand.

• It is important to realise that the neural mechanisms do not take into account cultural differences, emotions and other motivations. It is purely biological.

Key points

• The hypothalamus plays a huge part in controlling eating behaviour (VMH and LH are key)

• It was also once thought that the stomach had a key role in controlling short-term food intake (may be through stretch receptors??) but we now know that people who have lost part or all of their stomach due to cancer can still control their food intake.

The Hypothalamus

• 2 areas of the hypothalamus are believed to control eating behaviour -

VMH - Ventromedial hypothalamus (damage can cause over-eating and obesity in rats - Hetherington and Ranson, 1942)

LH - Lateral hypothalamus ( Damage causes lack of appetite - Anand and Brobeck,1951)

Research study

• Cannon and Washburn (1912) - Cannon persuaded Washburn to swallow a deflated balloon. He then inflated the balloon to measure the stomach contractions in relation to Washburn’s feelings of hunger.

• This showed that the presence of absence of food in the stomach is an important signal for the brain.

What do you notice about these studies ?

• They are old studies but still have very high reliability.

• Still very influential in this area of research.• Good clinical empirical evidence• Good lab techniques with goods controls.• But can we generalise for rats to humans?• Is it ethical to carry out this type of research?

Task

• Put the given phrases into the diagram

• Diagram (max size 4 lines depth)

Phrases

VMH satietycentre activated

Lateralhypothalamusfeeding centreactivated

Feelings ofhunger – feedingstarts

Signals ofdecliningnutrient levels,eg decrease inblood glucose,increase inghrelin release

Signals of foodintake, eg risein blood glucoselevel,decreasein ghrelinrelease.

Satiety –feelings offullness, feedingstops.

What is Ghrelin ?• This is another hormone which is released from

the empty stomach in order to stimulate feeding. Ghrelin levels were studied by Cummings et al in 2004.

• Find out what he did and his findings and conclusions

• The amount of ghrelin is directly proportional to the emptiness of the stomach.Injections of Ghrelin will increase food intake in humans and animals(Cummings 2004)

• Ghrelin is thought to act directly on the brain mechanisms of feeding behaviour including the hypothalamus. (Cummings 2006)

• Gastric bands will reduce the amount of Ghrelin released.

Homework

• Due next Monday 1st March 2010.

• ‘Discuss the importance of the hypothalamus in controlling eating and satiation.’

• 25 marks.

Why do we start a meal?• In the West - we eat following certain

schedules. The digestive system will know when a meal is coming up and prepare itself by releasing saliva and enzymes before food is eaten (Pinel 2007). This is a learned response.

• Taste and smell are important in preparing the digestive system.

• Ghrelin release.