Reasons for the success and failure of dieting

- There are two main reasons as to why diets can fail, one of these being explained by the restraint theory. This theory suggests that attempting to eat increases the chances of overeating, leading to weight gain and the failure of the diet (Herman and Mack). Restrained eating is seen as restricting the amount of food consumed, not consuming certain foods or not eating at certain times.

- In attempt to explain why dieting may lead to overeating Herman and Polivy devised the boundary model. This model suggests that hunger keeps intake of food above a certain minimum, and satiety works to keep intake below a maximum level. However dieters tend to have a larger range between hunger and satiety levels as it takes them longer to feel hungry and more food to satisfy them.

- Diets then tend to fail due to restrained eaters going over their desired intake (diet boundary), as when they go over this boundary they continue to eat until they reach satiety which in many cases tends to go beyond maximum level imposed not only by their diet but also the satiety level of a normal eater.

- A further explanation for the failure of dieting is denial, which involves attempting to suppress or deny a thought frequently and this can sometimes have an opposite effect making it even more prominent in the mind. Wegner (1987) refers to this as the theory of ironic processes of mental control, as it represents a paradoxical effect of thought control. This therefore can lead to the indulgence of forbidden food as they cannot stop thinking about it, hence increasing the chance of diet failure.

+ Herman and Mack's restraint theory has strengths in the form of supporting evidence. Wardle and Beales conducted a study whereby they randomly assigned 27 obese women to a diet group (focusing on restrained eating patterns), an exercise group, or a non-treatment group for 7 weeks. At weeks 4 intake and appetite were assessed before and after a 'preload', and at 6 weeks food intake was assessed under stressful conditions.

+ Results showed that in both assessment sessions, women in the diet condition ate more than the other test groups. This supports the restraint theory as it suggests that attempting not to eat does in fact increase the probability of overeating.

+ Due to the fact that there is empirical evidence which supports the restraint theory the validity of it increases and therefore it can be argued that this is one of the main factors as to why dieters fail. This can then be used by dieticians and weight loss services as they will be able to give more effective advice on how to lose weight and emphasise what will result in the failure of a diet.

- However there are flaws to this theory, due to the fact that it does not explain why people with eating disorders such as anorexia manage to starve themselves to lose weight. The restraint theory proposes that those who restrict food intake will eventually succumb to overeating past what would normally reach satiety levels, which therefore does not explain how people with anorexia who severely restrict their food intake/diet do succeed in losing large amounts of weight.

- Due to this the internal validity is reduced as we cannot accurately conclude that this is always the reason as to why dieting can fail. This in turn reduces the usefulness of this theory as it is not applicable to all situations.

- On the other hand there are explanations as to why dieting can be successful suggested by Redden. Redden believes that the key to a successful diet is to pay attention to the details of what is being eaten. This is because it is suggested that people are less inclined to become bored of the food that they are eating if they think of it in a more imaginative way.

- For example instead of thinking 'not another salad' the dieter should focus on the details of the meal and its contents. This should then result in them becoming bored less easily and so they are better able to maintain their diet making it more likely for their diet to become a success.

+ A strength of this explanation is that Redden conducted a study to provide evidence in support of this theory. Redden gave 135 participants 22 jelly beans each, one at a time. As each bean was dispensed, information about it was flashed onto a computer screen. One group saw general information such as 'bean number 7' whereas the other group saw specific flavour details such as 'cherry flavour number 7'.

+ Results showed that participants got bored with eating beans faster if they saw the general information, and enjoyed the task more if they saw the specific flavour details. This therefore supports the theory as it shows that focusing on the details of a food makes the meal appear more appetising, which in turn would encourage a person to stick to their diet and therefore succeed.

+ Due to the fact there is consistent evidence which upholds the assumptions of this theory it can be argued that it is high in external reliability. This high reliability means that this evidence can confidently be used to develop treatments that are suitable for eating related illnesses such as obesity.

- However there are methodological flaws with the supporting evidence, thus weakening the explanation. Due to the fact that Reddens study was a laboratory experiment the situation in which the participants were put in was not representative of a real life situation.

- Due to this the ecological validity is reduced meaning it would not be accurate to generalise the research findings beyond that particular setting in which Redden subjected his participants to.

- This reduced ecological validity means that we cannot be sure that this particular explanation is applicable to all situations and therefore a strong scientific cause and effect relationship cannot be established between focusing on food detail and a successful diet.

- However though, these explanations for the success and failure of dieting are reductionist due to the fact they only consider the cognitive approach, and ignore biological, psychological and behaviour perspectives. This means our behaviour is looked at only in terms of thoughts, beliefs and attitudes.

- This reductionist outlook can be a problem because it means we may not get a valid, in-depth understanding of all the contributing facts which may influence the success or failure of dieting. As a result the explanations are less scientific because the internal validity is reduced, subsequently the accuracy of the explanation has been compromised. This means we cannot establish a paradigm when considering reasons for the success and failure of dieting as other approaches have been excluded.

- However, being reductionist can also have its strengths as it allows us to analyse the explanations for the success or failure of dieting in greater depth and get a full valid understanding of that one factor alone.

- Overall a holistic approach would be more appropriate as it would consider how these differing factors interact with one another to cause diet failure or success.