Exercise following Mental Work Prevented Overeating

Abstract

Mental work may promote caloric intake, whereas exercise may offset positive energy balance by decreasing energy intake and increasing energy expenditure.

Purpose: This study aimed to replicate previous findings that mental work increases caloric intake compared with a rest condition and assess whether exercise after mental work can offset this effect.

Methods: Thirty-eight male and female university students were randomly assigned to mental work + rest (MW + R) or mental work + exercise (MW + E). Participants also completed a baseline rest (BR) visit consisting of no mental work or exercise. Visit order was counterbalanced. During the MW + R or MW + E visit, participants completed a 20-min mental task and either a 15-min rest (MW + R) or a 15-min interval exercise (MW + E). Each visit ended with an ad libitum pizza lunch. A two-way repeated-measures ANOVA was used to compare eating behavior between groups.

Results: Participants in the MW + R condition consumed an average of 100 more kilocalories compared with BR (633.3 ± 72.9 and 533.9 ± 67.7, respectively, P = 0.02), and participants in MW + E consumed an average of 25 kcal less compared with BR (432.3 ± 69.2 and 456.5 ± 64.2, respectively, P > 0.05). When including the estimated energy expenditure of exercise in the MW + E conditions, participants were in negative energy balance by an average of 98.5 ± 41.5 kcal, resulting in a significant difference in energy balance between the two groups (P = 0.001).

Conclusion: An acute bout of interval exercise after mental work resulted in significantly decreased food consumption compared with a nonexercise condition. These results suggest that an acute bout of exercise may be used to offset positive energy balance induced by mental tasks.

Figure 1

Estimated caloric intake between the Baseline Rest visit (Rest Visit) and the Mental Work + Rest (MW+R) or Mental Work + Exercise (MW+E) visit. Repeated measures ANOVA indicated a significant time by group interaction for caloric intake, F(1,36) = 4.84, p = .034. Participants in the MW+R group significantly increased intake between Baseline Rest and MW+R. Participants in the MW+E group slightly decreased intake following the MW+E visit.

Figure 2

Estimated energy balance differences from Baseline Rest condition for participants in the Mental Work + Rest (MW+R) group and the Mental Work + Exercise group (MW+E), p = .001. The MW+E group includes estimation of energy expended during the exercise bout based only on work intervals and not the entire 15 minutes of exercise. The MW+E group also includes an estimation of energy that would have been expended during the 15 minute rest period; this calculation was based on a revised Harris-Benedict equation. This figure serves as an illustration of estimated mean energy balance differences between groups.

Figure 3

Mean values for blood glucose and lactate measured in the MW+E condition. Measurements were taken upon arrival to the lab (time 1), after the mental work task (time 2), and 4 minutes after exercise (time 3). n = 18 due to a change in study protocol. Bars are standard error bars.