Identifying predictors of success and valid measures of eating behavior and diet satisfaction in a portion-control weight loss trial
Open Access
- Author:
- James, Brittany L
- Graduate Program:
- Nutritional Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 07, 2017
- Committee Members:
- Barbara Jean Rolls, Dissertation Advisor/Co-Advisor
Barbara Jean Rolls, Committee Chair/Co-Chair
Penny Margaret Kris-Etherton, Committee Member
Kathleen Loralee Keller, Committee Member
Eric Loken, Outside Member
Rena Wing, Special Member - Keywords:
- weight loss
obesity treatment
adults
eating behavior
diet - Abstract:
- Controlling portion size has been shown to have a significant impact on energy intake in experimental work and on weight management in longer-term studies. However, there is little evidence directly comparing different portion-control strategies in the context of a behavioral weight loss trial. Identifying the factors that can have a long-term impact on weight management could have a beneficial role in improving long-term outcomes. Study 1 focused on identifying early predictors of weight loss as a key part of developing personalized treatment to promote long-term success. Few individual factors/characteristics have been identified that predict weight loss during intervention, other than early weight loss itself. Women with overweight or obesity (n=186, mean±SD age 50.0±10.6 y, BMI 34.0±4.2 kg/m2) participated in a one-year randomized controlled trial examining the effect of portion-control strategies on weight loss. Repeated assessment allowed evaluation of early change in eating behaviors and psychological factors in the first month of intervention as predictors of weight-loss trajectory from baseline to Month 3 and Month 12. Across all participants, greater increases in dietary restraint and healthy lifestyle ratings after one month, as well as greater decreases in disinhibition, predicted more rapid weight loss from baseline to Month 3. Greater increases in restraint and healthy lifestyle ratings predicted more rapid weight loss and slower regain from baseline to Month 12. Restraint remained a significant predictor after controlling for early weight loss. Initial improvement in psychological and behavioral measures predicted 3-month and 12-month weight loss. For individuals with less improvement, early additional support or tailored treatment could promote long-term success. Study 2 honed in on eating behavior measurement, an area that is often associated with weight loss. Using data from the same one-year weight loss trial, the Three-Factor Eating Questionnaire (TFEQ), a valid 51-item measure of restraint, disinhibition, and hunger subscales, was compared to the newer 16-item Weight-Related Eating Questionnaire (WREQ), which measures routine and compensatory restraint and external and emotional eating. In the trial, both questionnaires were administered five times to 186 women (mean±SEM, age 50±0.35 y, BMI 34±0.14 kg/m2). Confirmatory factor analysis was conducted on baseline WREQ data and correlations were calculated between TFEQ and WREQ subscales. Multilevel models evaluated the relationship between each subscale and weight change over time. Factor analysis revealed a WREQ structure consistent with previous research, and corresponding subscales on the TFEQ and WREQ were correlated. Lower baseline TFEQ restraint predicted greater weight loss. Across five administrations, TFEQ and WREQ restraint scores were positively related to weight loss (p<0.01) and TFEQ disinhibition and WREQ external and emotional eating scores were negatively related (p<0.001). Thus, with one baseline administration, only TFEQ restraint was significantly related to weight change, but multiple administrations showed relationships between all TFEQ and WREQ subscales and weight change. The WREQ offers a shorter alternative to the TFEQ when repeatedly assessing eating behaviors related to weight change. Study 3 focused on validating a new tool for measuring diet satisfaction. Satisfaction with the prescribed diet likely affects adherence to weight loss treatment, one of the strongest correlates of weight outcomes. However, currently there are no validated measures to directly assess diet satisfaction. The 45-item, seven-scale Diet Satisfaction Questionnaire (D-Sat) was developed in previous work to fill this need and was further validated in this study. It measures seven scales identified from the literature that likely affect satisfaction with the current diet: healthy lifestyle, convenience, cost, family dynamics, preoccupation with food, negative aspects, and planning and preparation. It was administered five times during the same one-year weight loss trial and one time as part of an online survey in a separate sample (n=510 women and men). Questionnaire structure was determined using confirmatory factor analysis, and reliability and internal consistency estimates were compared for the two samples. Associations between D-Sat scales and weight loss over one year were examined. The healthy lifestyle, preoccupation with food, and planning and preparation scales were associated with weight loss across time (p<0.05). Confirmatory factor analysis revealed a five-scale structure provided a better fit, and this revised questionnaire showed strong internal consistency (⍺ range 0.73-0.91) and reliability in both samples. The new structure retained the healthy lifestyle, cost, preoccupation with food, and planning and preparation scales as they were and shortened the convenience scale to the restaurant-specific items. The D-Sat is a reliable, valid questionnaire of diet satisfaction that can consistently identify correlates of weight loss. The revised five-scale structure should be used in future work. These studies combine to offer guidance for future work in identifying predictors of weight loss success and for measuring key factors before, during, and after treatment that impact that success.