THE SUCCESS/FAILURE OF DIETING EATING BEHAVIOUR – Question one

DIETS USUALLY FAIL

Restrained eating (dieting)  Research (laboratory studies) has shown that restrained eaters often overeat.

 One to two thirds of dieters end up gaining weight!

Bennett & Gurin’s Weight set point theory (1982)  Some people are genetically predisposed to be bigger than others.

 Weight settles at a particular point and it is difficult to over ride this system. Dieting tries to do this and is often unsuccessful.

 The set point is good at supervising fat storage but bad at telling the difference between dieting and starvation.

 It tries to rescue the body when it detects restricted eating and so weight loss is slowed down in various ways:

1  Increased hunger

2  Reduced metabolism so that less calories are burned

3  Less calories are needed to maintain the weight set point.

Evidence  Statistically dieting is unsuccessful.

 Reviews of controlled studies of dieting in real life situations conclude that reducing calorie input through dieting is not an effective method of losing weight (Mann et al. 2007).

 but some people are successful in maintaining weight loss.  Is this because they over ride their weight set point?  It is not clear how they do this.

Is there any hope?  Research suggests that successful weight loss is possible when combined with lifestyle changes (Powell, Calvin and Calvin, 2007).

 Wilmore et al (1999) suggest that a sustained increase in physical activity may be the way to change the body’s set point.

 This theory focuses on biological explanations for the success and failure of dieting.  There are psychological factors that should be considered as well.

 Group and individual support  Self-monitoring: diary and records – encourage a sense of being in control

Herman & Polivy’s BOUNDARY MODEL (1984)  We all have a biological/physiological boundary for food intake.

 Restrained eaters (dieters) have a cognitive boundary as well.  This is much less than the biological one.

Restrained Eaters  Restrained = restricted, holding back  A ‘restrained eater’ is someone who is trying to eat less (i.e. Dieting)

Two potential boundaries for food intake  Set by the body weight set-point  The body’s fat stores act as a ‘body-weight set- point’.  Under normal circumstances mechanisms controlling food intake do not allow for much weight fluctuation.  Set by the individual  In restrained eaters this is less than the physiological boundary. PhysiologicalCognitive

Food intake boundaries  Eats until satiety (fullness).  The physiological boundary determined by their body weight set-point.  Eats until they reach their cognitive boundary (set by themselves). Unrestrained eaterRestrained eater

 Once the cognitive boundary has been crossed there is a disinhibition effect  ‘What the hell’.

 This can result in the person carrying on eating and even crossing the biological boundary.

Early research  Herman and Mack (1975)  One of the earliest studies using the preload/test method.  Participants = 45 female students]told it was a study on taste experiences  Independent design  3 conditions – 15 participants in each

3 conditions  1 = no preload  2 = preload = one milkshake – asked to rate the taste quality  3 = preload = two milkshakes –asked to rate the taste quality

 All 3 groups then given three tubs of ice cream of different flavours  Given 10 minutes to rate their taste qualities  Told they could eat as much of the ice cream as they wanted

 All participants were given a questionnaire to assess their degree of dietary restraint.

 Each of the 3 groups were divided into high restraint or low restraint depending on their answers given on the questionnaire.

 LOW RESTRAINT GROUP  Ate less ice cream in the 2 milk shake condition than in the one or none group.  AS EXPECTED  Fuller after 2 milk shakes and can’t eat as much ice-cream.

 HIGH RESTRAINT GROUP  Ate significantly more ice cream in the one and two milk shake conditions than in the zero milk shake condition.

 Herman and Mack found a significant positive correlation across all participants between the eating restraint questionnaire and amount eaten after two preloads (milk shakes).  The higher the restraint score, the more they ate after 2 milkshakes.

 The results support a boundary model of dietary restraint.  Restrained eaters have a ‘cognitive’ dieting boundary for food intake.

What the hell-effect?  Eating is disinhibited because the restrained eater feels they’ve already ‘blown it’ so they might as well carry on.

The Boundary model  Introduced by Herman and Polivy (1984)  Explains why restrained eaters sometimes eat more after preloads (milk shakes) than with no preload.

Restrained eater in Herman and Mack’s study  Is still within the diet boundary  In the ‘taste test’ eats enough to reach this boundary (not much)  Pushed beyond the cognitive boundary before the taste test (ice cream).  This disinhibits their feeding behaviour and they simply eat until they reach the physiological boundary (more than in the preload condition). Low calorie preload (one or zero milk shake) High calorie preload (2 milk shakes)

Evaluation of methodology  The restraint questionnaire was given after the feeding tests so the division of each group into high and low-restraint groups was post-hoc (done after the study had been carried out).  Ideally this should be done before but Herman and Mack felt that this would have led to demand characteristics.

 This meant that there were unequal numbers in the high- and low-restraint groups (e.g. 9 high-restraint and 6 low-restraint in the 2 nd condition).  This uneven pattern reduces the reliability of the findings.

 Group sizes were quite small especially after the division into high- and low-restraint participants.  Some participants may have liked ice cream more or less than others. Three varieties were provided to try to deal with this, but it is still possible that dislike of ice cream (or particular liking) may have biased the findings.

 The correlation between restraint scores and food intake after two preloads shows a relationship but not a cause. Some other variable may have produced the association, e.g. High restraint may be linked to depressed mood and it may be the depressed mood which leads to increased eating.

Science at work  The study of the psychology and physiology of dieters and non-dieters has helped us understand why dieting is often difficult and unsuccessful.  However, it has also helped develop psychological and medical interventions that can help people lose weight successfully.