Consuming more energy than is expended may reflect a failure of control over eatingbehaviour in obesity. Behavioural control arises from a balance between two dissociablestrategies of reinforcement learning: model-free and model-based. We hypothesized thatweight status relates to an imbalance in reliance on model-based and model-free control,and that it may do so in a linear or quadratic manner. To test this, 90 healthy participants in awide BMI range (normal-weight (n=31), overweight (n=29), obese (n=30)) performed asequential decision-making task. The primary analysis indicated that obese participantsrelied less on model-based control than overweight and normal-weight participants, with nodifference between overweight and normal-weight participants. In line, secondary continuousanalyses revealed a negative linear, but not quadratic, relationship between BMI and model-based control. Computational modelling of choice behaviour suggested that a mixture of bothstrategies was shifted towards less model-based control in obese participants. Furthermore,exploratory analyses of separate weights for model-free and model-based control showedstronger reliance on model-free control with increased BMI. Our findings suggest that obesity may indeed be related to an imbalance in behavioural control as expressed in a phenotype of less model-based control potentially resulting from enhanced reliance on model-free computations.
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