Warm Ambient Temperature Decreases Food Intake in a Simulated Office Setting: A Pilot Randomized Controlled Trial

Abstract

Background: We hypothesized that exposure to temperatures above the thermoneutral zone (TNZ) would decrease food intake in young adults in a sedentary office environment over a 2-h period.

Methods: Participants wearing standardized clothing were randomized to perform routine office work in the TNZ, considered control (19-20°C), or above the TNZ considered warmer (26-27°C) using a parallel-group design (n = 11 and 9, respectively). Thermal images of the inner canthus of their eye and middle finger nail bed, representing proxies of core and peripheral temperatures, respectively, were taken at baseline, first, and second hour during this lunchtime study. Heat dissipation was estimated using peripheral temperature. General linear models were built to examine the effects of thermal treatment on caloric intake and potential mediation by heat dissipation. Researchers conducted the trial registered as NCT02386891 at Clinicaltrials.gov during April to May 2014.

Results: During the 2-h stay in different ambient temperatures, the participants in the control conditions ate 99.5 kcal more than those in the warmer conditions; however, the difference was not statistically significant. Female participants ate about 350 kcal less than the male participants (p = 0.024) in both groups and there was no significant association between caloric intake and participant's body mass index (BMI). After controlling for thermal treatment, gender and BMI, the participant's peripheral temperature was significantly associated with caloric intake (p = 0.002), suggesting a mediating effect. Specifically, for every 1°C increase in peripheral temperature suggesting increased heat dissipation, participants ate 85.9 kcal less food.

Conclusion: This pilot study provided preliminary evidence of effects of thermal environment on food intake. It suggests that decreased food intake in the experimental (warmer) environment is potentially mediated through thermoregulatory mechanisms.

Keywords: food intake; heat dissipation; obesity; thermal environment; thermoneutral zone.

Figures

Figure 1

Boxplot indicating differences in estimated heat dissipation at midpoint by thermal environment. The central mark is the median and the edges are the 25th and 75th percentiles. The whiskers are the most extreme data points. After 1 h (at midpoint prior to food intake), peripheral temperature in the control group was significantly lower than in the warmer group (24.8 vs. 32.2, p < 0.0001). This suggests reduced heat dissipation in the control group.

Figure 2

Scatterplot of the kcal consumed by participants peripheral temperature °C with dots as individual participants and lines as best fit by treatment; coded by color (red = warm treatment, blue = control treatment). There is a negative correlation between food intake and the estimate of peripheral temperature (Control R2 = 0.37, p = 0.046, Warm R2 = 0.037, p = 0.62).