class iii , or severe ( extreme ) , obesity ( bmi  40  kg / m ) occurs in approximately 7% of the u.s .
female population ( with some subgroups as high as 14% ) , and appears to be increasing .
it is associated with a high incidence of diabetes , high blood pressure , high cholesterol , and asthma .
weight loss treatments focused primarily on caloric restriction have been ineffective , and bariatric surgery is now commonly considered for severe obesity .
there is an incomplete understanding of the psychosocial correlates of successful behavioral treatment for weight loss , in general , and specifically for those with class iii obesity .
exercise is associated with weight loss , and is the strongest predictor of sustaining loss of weight , but it is not always an integral part of treatments . because of the low amounts of physical exertion typically possible for deconditioned persons , it has been suggested that an exercise program may be associated with weight reduction mostly due to improvements in psychological factors that may moderate overeating such as mood , self - efficacy , and self - concept , rather than the associated energy expenditure itself .
thus , it is not known whether the amount of exercise completed , or simply participation in a program , may be associated with weight loss through proposed psychological pathways .
change in psychological constructs postulated in behavioral theories may provide alternate explanations for weight loss to that achieved by energy expenditure .
for example , social cognitive theory   proposes reciprocal relationships between person , environment , and behavior ; and suggests that individuals receive reinforcement value from connecting behaviors ( e.g. , physical activity , appropriate eating ) to valued outcomes ( e.g. , improved health , a more attractive body ) .
self - efficacy theory , which is embedded in social cognitive theory , posits that confidence in completing behaviors of interest will lead to accomplishing those behaviors ( e.g. , completing regular exercise ; controlling intake of food ) .
considering social cognitive and self - efficacy theories , baker and brownell suggested a model of the relationship of exercise and improvements in mood , perceptions of the body , and self - efficacy ; and relations of improvements in those psychological factors with weight loss . in a recent investigation limited to the possible mediation effects of psychological changes ( based on baker and brownell 's model ) on the relationship between a treatment and adherence to exercise , the specific constructs measured were self - efficacy to overcome barriers to exercise , physical self - concept , body satisfaction , and overall mood .
although preliminary investigation suggested the usefulness of the baker and brownell model , testing did not include women with extreme obesity  who might have the most severe health risks but react differently to physical exertion compared to those of a lower weight .  
thus , the present research assessed women with class iii obesity on changes over 6 months in psychological factors consistent with the baker and brownell model . the model 's ability to predict weight loss , both with and without accounting for compliance with the assigned exercise frequency , was evaluated .
participants were 51 women ( mean age = 43.9  9.8 years ) with class iii obesity ( mean bmi = 43.8  2.8  kg / m ) who initiated a 6-month exercise and nutrition information program administered through ymcas in the atlanta , georgia area .
racial make - up was 53% white , 39% african american , and 8% other races / ethnicities .
institutional review board approval , written physician approval to participate , and informed consent from participants were obtained .
the scale aggregates scores from the profile of mood states subscales of depression , tension , fatigue , vigor , confusion , and anger .
internal consistency of the 30-item scale ( range = 20100 ) for females averaged 0.90 , and test - retest reliability averaged 0.74 .
the exercise self - efficacy scale   measured perceived psychological resources ( e.g. , self - regulatory skills ) to overcome barriers to exercise . internal consistencies of the 5-item measure ( range = 535 ) were 0.82 and 0.76 , and test - retest reliability was 0.90 .
the physical self - concept subscale of the tennessee self - concept scale   measured perceptions of physical abilities
. internal consistency of the 14-item measure ( range =    1470 ) was 0.83 , and test - retest reliability was 0.79 .
the body areas satisfaction subscale of the multidimensional body - self relations questionnaire   measured satisfaction with areas of one 's body . internal consistency of the 9-item measure ( range = 945 ) for women was 0.73 , and test - retest reliability was 0.74 .   a recently calibrated scale and stadiometer were used to measure bmi ( kg / m ) .
exercise session attendance was the ratio of sessions attended divided by the assigned number of sessions , or 72 ( 3 sessions assigned per week  24 weeks ) .
attendance at exercise sessions was recorded electronically through a computer system suggested to be valid through strong correlations with cardiorespiratory fitness measures such as vo2max  , blood pressure , and resting heart rate .  
participants were given access to ymca wellness facilities that included cardiovascular exercise apparatus and areas for walking and running .
an exercise support protocol emphasizing goal setting and progress tracking , exercise that induced improvements in mood , and self - regulatory skills ( e.g. , cognitive restructuring , dissociation from discomfort ) , was administered by trained wellness specialists monthly during six 60-minute one - on - one sessions over 24 weeks .
thus , goals of the exercise support protocol were to improve participants ' ( 1 ) self - efficacy to overcome barriers to exercise ( e.g. , boredom , self - consciousness ) , ( 2 ) perceptions of physical ability to complete exercise , ( 3 ) perception of their bodies , and ( 4 ) moods ( e.g. , depression , fatigue ) .
for each participant , three sessions per week of moderate intensity cardiovascular exercise ( progressing to 30 minutes per session ) were assigned .  
six nutrition information sessions , based on guidelines from the american college of sports medicine and the american dietetic association , were provided in groups .
an intention - to - treat design with baseline - carried - forward imputation for missing data was used .
multiple regression equations assessed the variance in bmi change accounted for by simultaneous entry of changes in exercise self - efficacy , physical self - concept , body areas satisfaction , and total mood disturbance ; both without ( table 1 , model 1 ) , and with ( table 1 , model 2 ) , entry of exercise session attendance .
change in bmi ( 1.62  2.87  kg / m ; range = 8.051.91 kg / m ) was significant , t(50 ) = 4.02 , p < .001 .
each regression model accounted for a significant portion ( p < .01 ) of the variance in bmi change ( table 1 ) . after adjusting the number of predictors in the models , entry of exercise attendance improved the radj - value modestly ( .232 to .274 ) . in both regression models ,
only changes in total mood disturbance demonstrated significant unique contributions to the explained variance in bmi change .   
a post hoc test was conducted where each participant 's kcal expenditure from exercise ( adjusted for body weight ) was first derived , then divided by 7700  kcal , which was estimated to predict 1  kg of weight loss for persons of this weight .
based on this formula , only 19% of the mean loss in weight could be directly attributed to caloric expenditure from exercise .         
findings suggest the usefulness of baker and brownell 's adaptation of self - efficacy and social - cognitive theories for the prediction of weight loss in women with severe obesity initiating supported exercise .
the psychological changes in exercise barriers self - efficacy , physical self - concept , body satisfaction , and mood , associated with moderate exercise supported by cognitive - behavioral means were , together , significant predictors of bmi change , explaining an adjusted 23% of the variance .
inspection of beta values indicated that mood change made the only significant , independent contribution to the explained variance in weight change in the regression equations .
although this preliminary investigation was not powered for further analyses , other research suggests that mood changes may strongly covary with changes in the other psychological factors tested .  
given the finding that exercise session attendance had only a minor effect on weight loss directly through associated caloric expenditure , it is likely that it 's small improvement in the explanatory power was due simply to heightened engagement with the present exercise support treatment .
this premise is further supported because the direct effect exercise volume had on weight loss was small .
thus , further research is required to increase the precision of explanatory models of relations between exercise - induced psychological changes and weight loss .
replication will also be required with larger samples and across participant types , as it is possible that sex , initial weight , and possibly , race / ethnicity , will affect results .
although this study was preliminary , a theoretical rationale was made for an appropriately supported program of moderate exercise early in the treatment of severe obesity in women .
as the present research is extended , better confidence in precisely what exercise - induced psychological factors will induce weight loss may help to improve effect and reliability .      
 
 background . psychological factors ' effect on weight loss is poorly understood , in general , and specifically in the severely obese . objective . to examine whether a behavioral model based on tenets of social cognitive and self - efficacy theory will increase understanding of the relationship between exercise and weight loss . 
 methods . 
 fifty - one women with severe obesity participated in a 24-week exercise and nutrition information treatment and were measured on changes in psychological factors and exercise attendance . 
 results . 
 a significant portion of the variance in bmi change ( adjusted for number of predictors ) was accounted for by the behavioral model ( r2adj = 0.23 ) . 
 entry of exercise session attendance only marginally improved the prediction to 0.27 . 
 only 19% of the weight lost was directly attributable to caloric expenditure from exercise . 
 conclusions . 
 findings suggest that participation in an exercise program affects weight loss through psychological pathways and , thus , may be important in the behavioral treatment of severe obesity . 
1. Introduction
2. Methods
3. Results
4. Discussion
5. Conclusion