Context: Energy balance and physical activity potentially influence systemic inflammation.
Objective: Our objective was to test the hypothesis that moderate energy restriction may prevent activation of inactivity-induced inflammatory response.
Design: Participants were studied four times at the end of 14-d periods of experimental bed rest or controlled ambulation, after receiving eucaloric or hypocaloric diets.
Setting: The study was conducted at the clinical research center of the German Space Agency.
Subjects: Nine healthy young volunteers participated.
Interventions: Energy intake was calibrated to physical activity and decreased by about 20% in hypocaloric conditions.
Main outcome measures: Changes in body fat by dual-energy x-ray absorptiometry as well as plasma inflammatory markers and cytokine mRNA levels in blood cells were measured.
Results: Fat mass did not change significantly in eucaloric conditions and decreased in hypocaloric periods (-1.0 +/- 0.3 and -1.0 +/- 0.3 kg in ambulatory and bed rest, respectively). Bed rest in eucaloric conditions increased plasma C-reactive protein (CRP) (+143 +/- 53%) and both the ratios between plasma IL-6 and IL-10 (4+/-1 times) and white blood cell IL-6 and IL-10 mRNAs (5 +/- 1 times). Energy restriction prevented bed-rest-mediated increases in CRP and the IL-6 to IL-10 ratio. Bed rest increased (P = 0.03) long pentraxin-3 (PTX3) plasma concentration, without significant activity-by-diet interaction. In all conditions (n = 36), CRP and PTX3 were inversely correlated (r = -0.61; P < 0.001). Changes in fat mass, leptin, and IL-6 directly correlated with CRP and inversely correlated with PTX3. IL-10 inversely correlated with CRP and directly correlated with PTX3 (r = 0.52; P < 0.01).
Conclusions: Calorie restriction prevents the inflammatory response induced by 14 d of bed rest. We suggest an inverse regulation of CRP and PTX3 in response to changes in energy balance.