Caloric restriction decreases orthostatic tolerance independently from 6° head-down bedrest

• Published in: PloS one Vol. 10; no. 4; p. e0118812
• Main Authors: Florian, John P, Baisch, Friedhelm J, Heer, Martina, Pawelczyk, James A
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 27.04.2015; Public Library of Science (PLoS)
• Subjects: Adult; Aerospace medicine; Alcohol; Arterial Pressure; Astronauts; Autonomic nervous system; Bed Rest - adverse effects; Blood pressure; Caloric Restriction - adverse effects; Calories; Cross-Over Studies; Diabetes; Diet; Diet, Reducing - adverse effects; Dietary restrictions; Fatty acids; Gene expression; Heart Rate; Hemodynamics; Humans; Hypertension; Hypocaloric diet; Insulin; Intervention; Intolerance; Kinases; Laboratories; Lower Body Negative Pressure; Male; Metabolism; Muscle, Skeletal - blood supply; Muscle, Skeletal - innervation; Muscles; Nutrition research; Orthostatic Intolerance - etiology; Orthostatic Intolerance - physiopathology; Orthostatic tolerance; Posture; Proteins; Return to Earth space flight; Rodents; Space Flight; Sympathetic Nervous System - blood supply; Variance analysis; Weightlessness Simulation
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0118812

Astronauts consume fewer calories during spaceflight and return to earth with an increased risk of orthostatic intolerance. Whether a caloric deficiency modifies orthostatic responses is not understood. Thus, we determined the effects of a hypocaloric diet (25% caloric restriction) during 6° head down bedrest (an analog of spaceflight) on autonomic neural control during lower body negative pressure (LBNP). Nine healthy young men completed a randomized crossover bedrest study, consisting of four (2 weeks each) interventions (normocaloric bedrest, normocaloric ambulatory, hypocaloric bedrest, hypocaloric ambulatory), each separated by 5 months. Muscle sympathetic nerve activity (MSNA) was recorded at baseline following normocaloric and hypocaloric interventions. Heart rate (HR) and arterial pressure were recorded before, during, and after 3 consecutive stages (7 min each) of LBNP (-15, -30, -45 mmHg). Caloric and posture effects during LBNP were compared using two-way ANOVA with repeated measures. There was a strong trend toward reduced basal MSNA following caloric restriction alone (normcaloric vs. hypocaloric: 22±3 vs. 14±4 burst/min, p = 0.06). Compared to the normocaloric ambulatory, both bedrest and caloric restriction were associated with lower systolic blood pressure during LBNP (p<0.01); however, HR responses were directionally opposite (i.e., increase with bedrest, decrease with caloric restriction). Survival analysis revealed a significant reduction in orthostatic tolerance following caloric restriction (normocaloric finishers: 12/16; hypocaloric finishers: 6/16; χ2, p = 0.03). Caloric restriction modifies autonomic responses to LBNP, which may decrease orthostatic tolerance after spaceflight.