Unhealthy diets and a lack of physical activity (PA) often concur in the same individuals and jointly contribute to overweight and related diseases. Limited self-regulation abilities commonly result in a gap between intentions to eat better and move more and respective behavior enactment (‘intention-behavior gap’, IBG). What is less clear is whether the two health behavioral domains eating and physical activity facilitate or inhibit each other. While cybernetic and resource depletion models would predict that engaging in one behavior leads to reduced effort in the other behavior (compensation), motivational accounts predict the opposite: more PA should increase healthy eating and vice versa (transfer). Elucidating such relationships across time requires multiple assessments from the same individuals and sufficient incidences of both behaviors, and hence, relatively long assessment periods. This study aimed to investigate cross-behavior relations in participants for whom both behaviors contribute to a higher-order health goal by using data obtained through ecological momentary assessment. 25 participants (20 women, 5 men, mean age = 56) of a health-insurance organized health promotion course provided daily data on intentions, self-efficacy, and behavior enactment for PA and healthy eating for eight weeks, with the average participant submitting data on 42 days. We found that cross-behavior associations on all assessed variables as well as IBGs (computed as the difference between intentions and behavior) were positive. This positive relation between IBGs was independent of day-level variables typically implicated in self-regulation (stress, mood, tiredness, and hours of sleep during the preceding night). Results contradict cybernetic and resource depletion models of self-regulation and speak more to effects of positive transfer between behaviors in this sample. Providing feedback on such positive associations might be a beneficial intervention component to encourage parallel engagement in PA and healthy eating. Future research should aim to further identify other within- and between-person factors (e.g., willpower beliefs) contributing to the PA-healthy eating association.
Aulbach et al. (Sat,) studied this question.