Comparison of the Health Belief Model and the Theory of Planned Behavior in the Prediction of Dieting and Fasting Behavior

The Theory of Planned Behavior (TPB), the Health Belief Model (HBM), and a modified HBM including intention were compared in their ability to predict dieting and fasting. Female university students (n = 373) completed a survey assessing variables from the TPB and the HBM. Three months later, a subsample reported subsequent weight loss behaviors. The TPB predictor model explained 35% of the variance in follow-up dieting and 67% in intention. The HBM model explained 29% of the variance in follow-up dieting and the modified HBM model explained 38% of the variance in follow-up dieting and 57% in intention.. The TPB model for fasting explained 14.5% of the variance in follow-up fasting and 58% in intention. The modified HBM model explained 19% of the variance in follow-up fasting and 41% in intention. Results show all models were able to predict a significant portion in the variance of dieting and fasting follow-up behavior; however the variance explained in follow-up fasting increased when intention was added to the HBM model. Attitude measures were the strongest predictors of behavioural intention and intention was the strongest predictor of follow-up dieting and fasting in the TPB and modified HBM models. Theoretical and clinical implications are discussed.