Abstract
Aims: Post-prandial increases in inflammatory markers IL-6 and C-reactive protein (CRP) have been observed following high fat and high carbohydrate meals. Inflammation is associated with increased risk of chronic diseases such as cancer. In addition, sedentary behaviour is also associated with negative health outcomes. Meanwhile, elevated IL-6 and CRP have been associated with a negative mood. The study aim was to compare the effects of continuous physical activity to breaks in sedentary behaviour on post-prandial IL-6 and CRP. The secondary aim was to compare the impact of these patterns (as detailed above) on measures of mood states.
Methods: Twenty four healthy sedentary participants (15 female, nine male, mean ± SD, age 25.8 ± 5.8 yr, BMI, 23.6 ± 5.0 kg/m2) completed three, 9 h testing days. These were: sedentary (SE), participants remained seated for 9 h; physical activity (PA), participants performed 30 min of exercise at a speed and incline to elicit 60% VO2max prior to the first meal replacement beverage and were then seated for the remainder of the 9 h; active living (AL), participants walked for 1 min 40s every 30 min throughout the day (this equals 30 min of physical activity spread out over 9 h) at the same speed and incline as the PA condition. For each condition participants received three meal replacement beverages at 1, 4 and 7 h. Each meal provided 0.46 g fat/kg BW, 0.54 g protein/kg BW and 1.12 g CHO/kg BW. Venous blood samples were collected at baseline, 4 and 8 h to measure IL-6 and CRP. Mood was assessed using the Brunel University Mood Scale at 0 and 9 h.
Results: In the SE and PA conditions there was a post-prandial increase in IL-6 at 4 and 8 h compared to baseline (SE p<0.0001, 4 and 8 h; PA p<0.001 and p<0.0001, 4 and 8 h respectively. In the AL condition, IL-6 increased at 8 h compared to baseline (p<0.05). The IL-6 concentration at 8 h in AL was significantly lower than the 8 h concentration in the SE and PA conditions (p<0.05). There was no change in CRP from baseline, nor was there a difference between conditions. No correlation existed between mood and CRP. Increases in IL-6 correlated with a more depressed mood. Both PA and SE conditions decreased tension. There was no effect of AL on mood.
Conclusions: Interleukin-6 increased 4 and 8 h post-prandially when sedentary. Thirty min of moderate continuous physical activity following an overnight fast and prior to a meal does not decrease the post-prandial IL-6 response. Breaking sedentary behaviour by as little as 1 min 40 s every 30 min attenuates the post-prandial IL-6 response and thereby, may reduce the risk of chronic diseases. Practical applications from these findings include the use of computer prompts or television advertising to promote standing and walking in individuals with desk jobs or when watching television for long periods of time.