Eating behaviors - why diets fail

Herman and Mack (1975) suggest that restraints have negative effects, such as lower moods and the attempt to not eating can lead to over eating. 

Herman and Polivy (1984) developed the boundary model to try and explain why restraint eating leads to over eating. We have a homeostasis, to limit eating, which is controlled by the hypothalamus. This is known as the hunger to satiation 'set point'. A diet will permanently stretch the hunger and sateity boundaries further apart. Restraint eaters set cognitive limits on themselves, to limit how much they will eat. If they pass the self set limit they will become disinhibited and will eat until they are satisfied . This is known as the 'what the hell effect'. (e.g. if they intend to eat half a sandwich, but eat the whole thing they will think what the hell and eat until they're full)

Wardle and Beales (1988) tested this theory, they used a lab experiment, the experiment lasted 4-6 weeks and involved 27 obese women. They were split into 3 groups, a diet, exercise and control group. It was found that those in the diet group did tend to eat more, supporting this theory.

Wardle and Beales (1988)'s experiment shows that restraint eating doesn't work, but other methods such as exercise do work. The experiment also allows a casual link to be developed. The random allocation also shows that the experiment had the same conditions, except for the group type. 

However, the sample size is very small, which makes it hard to generalise.

There is also a question to about if the participants were happy with the condition they were in, as they were randomly allocated to a condition.

The experiment was done in a lab, so it also raises questions of demand characteristics. 

The theory is also attacked, as if starving yourself leads to over eating, how do anorexics success in starving themselves? 

If trying to not eat something causes you to eat it, then how do vegetarians avoid eating meat?

Restraint eaters tend to try to not think about food. Research by cognitive psychologists have have found the more you try to not think about something to more you're likely to think about it. 

Wegner (1994) refers to the theory of ironic process of mental control, basically denial often backfires. 

Wenzlaff and Wegner (2000) suggests that as the dieter make certain foods forbidden, they immediately seem more attractive to the dieter. 

Soetens et al (2006) divided participants into 2 groups, a restraint and non restraint eaters, both groups were then divided further into high or low in disinhibition. The  disinhibition restraint group used more suppression thoughts than the other and were found to have a rebound effect, after the suppressible thought. So those who restrained eaters who overeat tended to try to suppress the thought of food more. , which leads to thoughts a bout food more.

It can be successful however, one study looked at 50 women, who used self monitoring forms of dieting for 4 days. They found those on restraint diets had less calories than the non restraint dieters. It is believed there are psychological variables that help

• Wanting to boost self esteem and feel good about themselves
• Motivated to lose weight (e.g. health scare/worries) 
• Motivational style
• Individual belief about the cause of obesity - if weight loss is unsuccessful it is blamed on biology

Ogden (2000) found evidence that psychological factors influenced the success of weight-loss. It was found that weight loss maintainers (those who had gone from being obese to the average weight for at least 3 years) were more likely to have had feelings like depression and low self esteem, before losing the weight. They were also less likely to medical models of the cause of obesity (e.g. genetics and hormone imbalance). 

Ogden and Hills (2008) Found that those who had successfully reduced their weight and maintained the weight loss were most likely have started after a key life event. These included things like divorce, illness, a significant birthday, etc. 

Therefore it is not just what the person does to lose weight, but what they believe. They need 

• a focus on the behavior as a control of their weight problem
• avoid denial, so they don't crave food
• find something to replace food as a reward
• establish a new identity as a thinner person

Gender bias

Most of the research has been done on females, not on males. This is because it is mainly women who try to lose weight. This causes a inherent gender bias. However, obese men have a more serious health problem, as the excess weight is mainly on the abdominal, whereas women have their excess weight on their bottom and thighs

Freewill and determinism

There has been evidence of genetics that influences weight. One is the Lipoprotein Lipase (LPL), this enzyme produces fat cells to store calories. When there are high levels of LPL, the body is more effective in storing calories.

LPL activities also increase weight loss and stays elevated for a few months. Weight loss is not normal, the body wants to preserve and store energy (as a evolutionary advantage). When the body senses weight loss it automatically stores more energy.

Kern et al (1990) found that LPL levels rose after weight loss, the more obese person was to start with, the more LPL there was.  

Therefore, success of dieting may be different for different people.