The aim of this study was to investigate the possibility that different personality traits are differentially related to different weight loss diets so that individuals might in future be matched to treatments to maximize weight loss. In particular, we hypothesized that there would be a significant positive correlation between the personality trait, Self Control, and weight loss on a program that required participants to follow a healthy diet and restrict their food intake without the aid of satiety enhancing supplementation (HEWLD). No specific predictions were made about which personality trait(s) would correlate most strongly with weight loss on the other program that initially removed food choices but reduced feelings of hunger with satiety enhancing meal replacements (VLED).
Using 2 different weight loss strategies, we found there was a significant difference in weight change from baseline in the VLED group, but the change in weight loss from baseline was not significantly different for the HEWLD group. A lack of willpower or self-discipline is often blamed for the inability to lose and manage weight but controlling hunger is not easy. Participants in the HEWLD were required to reduce their food intake and to eat healthy foods. This reduction in food intake would have been associated with increased feelings of hunger requiring considerable self control to resist the immediate temptation to assuage the pangs of hunger for the delayed reward of weight loss. The mean scores for self control were similar for HEWLD and the VLED, 118.5 and 117.3 respectively. For both trials, the correlations between self control and weight change or BMI change are negative and not significant. In particular, the treatment outcome in the HEWLD, that is low weight loss, was not associated with our Self Control measure. A study by Carels (2003) investigating failure to lose weight during treatment with 44 obese, postmenopausal women found that one of the significant influences on poor treatment outcome was diminished self control [9
], but they attributed the poor treatment outcomes to a number of other causes as well. A study which examined the control of eating (restraint, measured using the TFEQ [29
]) and a possible association with general self control (measured using the SCS [21
]) found that, among the obese participants and dieters, restraint was related to more successful weight control [22
]. They found that overweight and obese participants had higher restraint scores compared to those of normal weight; however, normal weight participants had higher self control scores. Also, current and past dieters had higher restraint scores compared to never-dieters; however never-dieters had higher self control scores. We did not measure eating restraint in our study, but the findings of the study by Konttinen (2009) appear to indicate that self control is not associated with the control of food intake among overweight and obese individuals and current and past dieters. It has been suggested that, overall, self control is unrelated to decision making [30
]. The study found that, in their daily lives, individuals who were high in self control made less frequent references to positive and negative affect and physiological states, for example feeling tired and hungry, and were seen as being less spontaneous compared to individuals with low self control [30
]. They suggest that self control may inhibit affective experiences in general. Tangney (2004) suggests that individuals that are high in self control favor long-term goals in the guidance of their behavior [21
], so it is possible that these individuals are not concerned with the immediate issues of their weight and are focused on other aspects of their lives. While the HEWLD was underpowered to determine significant correlations, there was no association between weight loss and self control in the VLED group either.
It is possible that an alternative measure for self control is the trait Conscientiousness. In the current study Conscientiousness and Tangney Self Control were highly correlated (r = .769 for HEWLD and r = .701 for VLED, p < .001 for both). Previous research using the FFM has reported significant negative correlations between Conscientiousness and adiposity in males and females; that is, high Conscientiousness was associated with a low BMI [18
]. In particular, the facets "order" and "self discipline" were strongly associated with weight [20
]. Sutin (2011) suggests that people with high scores in these facets are thinner because they are organized and follow their diet and meal plans [19
]. However, it should be noted that these studies were about personality profiles and weight/BMI, not about weight loss [18
]. In the current study the correlations between Conscientiousness and weight loss were negative and modest for both groups apart from the 2 facets "dutifulness" and "self discipline" that were significantly and negatively correlated with weight loss in the VLED group. If, as Sutin suggests, those that are high in Conscientiousness are thinner, then there is less need for them to follow a weight loss regime. Thus, in the current sample, high Conscientiousness could be comparatively lower in this group wanting to lose weight, and that may also explain the conflicting results compared to previous studies that did not focus on weight loss. It is also possible that people high in Conscientious do not respond well to the weight loss regimes followed in this study.
Despite prior research reporting that high Extraversion was associated with a high BMI [19
] and a high BMI in males but not in females [18
] our study found no significant relationship between Extraversion and weight loss or BMI in this group.
The VLED participants consumed satiety enhancing meal replacements and, with hunger initially controlled, the small bars and shakes enabled the stomach to reduce in size so that when healthy meals were phased in to the diet, participants were satisfied with less food. The satiating effect of the Optifast® bars and shakes appear to have facilitated dietary compliance in the VLED group, as evidenced by > 5% weight loss in all but 2 of the participants over 4 weeks. In this group there was a significant positive correlation between weight loss and Neuroticism and its facets "anxiety, anger, depression, self consciousness and vulnerability" but not "immoderation".
Previous studies on personality and adiposity have reported that high Neuroticism is significantly associated with a high BMI in females [18
] and a high BMI in both males and females [19
]. Elfhag (2005) suggests that disinhibited eating is related to the factor Neuroticism [31
]. It has also been suggested that unrestrained eaters, who eat as a natural response to hunger and appetite, appear to reduce their food intake more radically with enhanced satiety, resulting in greater weight loss [32
]. A study by Elfhag (2008), using the NEO Personality Inventory-Revised which is based on the FFM of personality [33
], reported that weight loss supplemented with Sibutramine, which enhances satiety, was significantly and positively correlated with the factor Neuroticism, and 2 of its facets, 'anxiety' and 'depression' [34
There is also the suggestion that Sibutramine appears to be more effective with people who eat as a natural response to hunger and not as a response to cognition and conscious control [34
provides a similar satiating effect to Sibutramine and weight loss with both showing a significant correlation with Neuroticism. It is possible that the VLED group was also people who responded to hunger and appetite rather than control for weight loss but our study did not measure eating behavior so this cannot be confirmed.
The VLED continued to maintenance after the 4 weeks of weight loss to determine whether the participants could continue to manage their weight, and for this phase participants continued consuming a diet based on the AGHE. This extended their trial to match the time span of the HEWLD. Although weight loss for the 2 phases, that is weight loss and maintenance, was only moderately correlated, the correlations with personality are very similar.
Some studies have found no link between personality and weight loss. The Dutch Personality Questionnaire which includes 7 scales; Neuroticism, Social anxiety, Rigidity, Hostility, Egoism, Dominance and Self-esteem was used with gastric banding for weight loss and the findings showed that none of the personality variables was associated with weight outcomes [14
]. The 10-item Life Orientation Test was used to determine whether dispositional optimism had a predictive value for weight loss with no significant results [35
]. A study by Poston [15
] used the Karolinska Scales of Personality to predict weight loss and found that the personality traits identified by the Karolinska Scales of Personality did not predict weight loss. We hypothesized that self control would be associated with being able to limit food intake and restrict food choices so it was interesting to observe that, in our study, there was no link between weight loss and self control in the Tangney SCS. However there do not appear to be any studies which positively associate the personality attribute self control with weight loss.
Schwartz (1995) surveyed a group of obesity experts to determine whether or not they agreed about factors important for matching individuals to weight loss treatment [36
]. She refers to previous research that suggests that people with different personality styles, levels of obesity and disturbed eating practices will respond differently to the various treatments. The position of the American Dietetic Association on weight management is that it is important to find ways to optimize individualized treatments appropriately [37
]. Using measures of personality traits to identify appropriate weight loss and weight management strategies remains an intriguing possibility, but so far none of the relationships that have been found are reliable enough to base treatment regimes on them.