Eating Behaviour

Why we like some foods

Evolutionary explanations: our ancestors survived better if they liked foods with energy and nutrients.

• Sweet = energy (ripe fruit). Salty = minerals the body needs. Fatty foods = lots of energy.
• Bitter or sour may mean poison or rotten food, so babies dislike them.
• Food neophobia: fear of new foods, strongest in early childhood. It kept young children safe.
• Taste aversion: if a food makes us sick once, we may avoid it for a long time. This is learned in one trial.

Learning explanations:

• Classical conditioning: foods paired with good feelings (parties, comfort) become liked. Mere exposure: tasting a food many times (often 10–15) increases liking.
• Social learning: children copy parents and friends, and are influenced by TV and adverts.
• Culture: spicy food, insects, or meat-free diets are normal in some cultures and not in others.

Evaluation: evolution explains common patterns but not why people now prefer different foods; learning explains this variety.

Hunger and fullness: the brain and hormones

Eating is kept in balance (homeostasis) like a thermostat.

• Ghrelin is a hormone made by the empty stomach. It rises before meals and tells the brain we are hungry.
• Leptin is made by fat cells. More fat = more leptin, which tells the brain energy is stored and lowers appetite.
• Low blood glucose also signals hunger.
• The lateral hypothalamus (LH) is the 'start eating' area. Damage in rats stopped eating.
• The ventromedial hypothalamus (VMH) is the 'stop eating' area. Damage in rats caused overeating.

Evaluation: the system is more complex: other brain areas (like the arcuate nucleus) and habits, time of day and social eating also matter. Much evidence comes from animal studies, which may not fully apply to people.

Explanations of anorexia nervosa

Anorexia nervosa is a serious mental illness. A person keeps their weight very low, has an intense fear of gaining weight, and may not see how thin they are. It is most common in teenage girls, but affects boys and adults too.

Biological:

• Genes: twin studies suggest genes explain roughly half the risk.
• Serotonin: changes may link to anxiety and obsessive thoughts; low food intake may lower anxiety for a while.
• Dopamine: changes may make food feel less rewarding and push for control.

Psychological:

• Family systems theory: in enmeshed families (very close, over-protective, little privacy), a teen may control food as a way to gain autonomy.
• Social learning: modelling of thin celebrities, media images and praise (reinforcement) for losing weight.
• Cognitive: distorted body image (seeing oneself as larger) and irrational beliefs such as perfectionism.

Eating disorders can be treated. If you are worried about yourself or a friend, talk to a parent, teacher or doctor.

Obesity and dieting

Obesity means body fat high enough to harm health (often a BMI of 30 kg/m² or more for adults).

Biological: many genes each add a small risk; twin and adoption studies show a strong genetic part. Leptin resistance: the brain stops responding to leptin, so fullness is not felt. Some neurotransmitters like serotonin and dopamine affect reward from food.

Psychological:

• Restraint theory: trying hard to restrict eating can backfire. After a small 'slip', dieters may overeat ('what the hell' effect).
• Disinhibition: stress, alcohol or seeing tasty food can remove control.
• Boundary model: we eat between a hunger boundary and a fullness boundary. Dieters have a wider gap and set their own lower 'diet boundary'; once it is crossed, they eat until full.

Why diets fail: denying a food makes it more tempting (theory of ironic processes: trying not to think of a food makes you think of it more). Diets often focus on short-term loss. Why diets succeed: small, realistic goals, focusing on healthy foods rather than banning foods, and support from others.

Try it

In step 5, press 0, 2, 4 and 6 hours. Predict before each press: will LH or VMH light up? Then at home, for one day, rate your hunger from 1 to 10 every two hours. Does your hunger rise before your usual meal times? That is ghrelin learning your routine.

Key formulas and definitions

• Key term: Food neophobia = fear of new foods; Taste aversion = avoiding a food after one bad experience
• Key term: Ghrelin = hunger hormone from the stomach
• Key term: Leptin = hormone from fat cells that lowers appetite
• Key term: LH (lateral hypothalamus) = start eating; VMH (ventromedial hypothalamus) = stop eating
• Key term: Enmeshment = family members too involved; Autonomy = independence
• Key term: Restraint = deliberate limiting of food; Disinhibition = loss of control over eating
• Formula: BMI = mass (kg) ÷ height² (m²)

Worked examples

Common mistakes

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