BRAHMS: Bed Rest And HypoMetabolism Study (BRAHMS)

BRAHMS: Bed Rest And HypoMetabolism Study Integrative Physiological Responses to 10 Days of Bedrest and Caloric Restriction: An Exploratory Pilot Study In 10 Healthy Men.

The goal of this single arm, interventional monocentric clinical trial is to investigate the physiological effects of a combination of head-down bedrest and caloric restriction on the human body. A set of measurements will assess the changes in the musculoskeletal, cardiovascular, hematological, immune, neurological, cognitive and metabolic systems, in 10 healthy male volunteers.

The main question it aims to answer is: what are the physiological responses to fasting in a microgravity environment?

In an exploratory study such as this one, where many physiological systems are explored, it is difficult to select a single important endpoint. However, given the known effect of both caloric restriction and head-down bedrest on muscle loss, and its critical importance for the success of space missions, lean body mass, as assessed by DEXA, was chosen as the primary endpoint.

The secondary endpoints are:

• Cardiovascular, muscular, neuro-vestibular and neuropsychological functional performance
• The onset of clinical symptoms and biological changes

Participants will be exposed to a microgravity analog model (head down bed rest) and controled caloric restriction environment for 10 days, multiple physiological assessments will be performed during this period. Followed by a rehab period before leaving the study.

Study Overview

• Status: Recruiting
• Conditions: Caloric Restriction; Microgravity
• Intervention / Treatment: Other: head down bedrest and caloric restriction

• Study Type: Interventional
• Enrollment (Estimated): 10
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Marie-Pierre Bareille; Phone Number: +33562174950; Email: marie-pierre.bareille@medes.fr

Study Locations

• France
  • Medes-imps
    • Toulouse, Medes-imps, France, 31400
      • Recruiting
      • Medes - Imps
      • Contact: Rebecca Billette de Villemeur; Phone Number: +33562174950; Email: rebecca.billette@medes.fr

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Healthy male volunteers (see below the description of medical tests and laboratory analysis performed at the selection visit)
• Certified as healthy by a comprehensive clinical assessment (detailed medical history and complete physical examination): in particular, free from any known chronic disease or any acute mood or eating disorder, infectious disease or cardiovascular, metabolic, neurological, ENT (especially orthostatic hypotension and vestibular disorders), orthopedic or musculoskeletal disorders.
• 20 to 40 years old
• 165 to 185 cm
• Body Mass Index between 20 and 26 kg.m-2
• Stable body weight in the past 3 months (less than 4% change)
• Fat Mass Index (FMI), defined as (bodyfat weigh in kg)/(height in m)2: between 3 and 6 kg.m-2, measured by whole-body DEXA
• Triglyceride level under 1.7 mmol.L-1
• Normal bone mass density at left hip and lumbar spine: T-score>-1.5, measured by DEXA
• VO2peak/VO2max between 35 and 55 mL.min-1.kg-1
• Non-smokers
• No alcohol or drug dependence, no medical treatment on a regular basis
• Affiliated to a Social Security system and, for non-French resident, holding a European Health Insurance Card (EHIC) or a Global Health Insurance Card (GHIC).
• Free of any engagement during the study
• Who agreed to take part in the study and signed the informed consent

Exclusion Criteria:

• Any history or presence of clinically relevant chronic disease; any acute infectious disease. Particularly (but not limited to):
• Symptomatic orthostatic hypotension whatever the decrease in blood pressure, or asymptomatic postural hypotension defined by a decrease in SBP equal to or greater than 20 mmHg within 3 minutes when changing from the supine to the standing position
• Personal or family history of thrombosis, genetic mutation for factor V or prothrombin gene
• Cardiac arrhythmia
• Hypertension
• Auto-immune diseases or Raynaud's syndrome
• History or symptoms of sleep apnea
• Chronic back pains,
• Vertebral fracture, scoliosis, or herniated disc,
• Color-blindness,
• Self-reported hearing problems or binocular visual acuity under 6/10 after correction
• Vestibular disorders
• Drug addiction
• History of migraines,
• History of hiatus hernia or gastro-esophageal reflux,
• History of thyroid dysfunction or diabetes
• History of head trauma,
• History of neurological diseases (e.g. epilepsy)
• History of genetic muscle and bone diseases of any kind
• Significant history of allergies
• Significant abnormality in blood tests
• Positive serology for hepatitis A, hepatitis B, hepatitis C or AIDS (HIV) virus
• Mood and Eating disorder (current or past), screened with the Hospital Anxiety Depression Scale (HADS), SCOFF (Sick, Control, One, Fat, Food) and the Eating Disorder Examination Questionnaire (EDE-Q)
• Antibiotics exposure 2 months prior to the study
• Major lifestyle changes (e.g. significant weight/body changes, diet or exercises regimen) 6 months prior to the study
• Specific diet (e.g vegan, carnivore, intermittent fasting, dietary supplements consumption)
• History of hypocaloric diet, judged as significant by the investigator
• Subject who, in the judgment of the investigator, is likely to be non-compliant during the study, or unable to cooperate because of a language problem or poor mental development,
• Subject in the exclusion period of another clinical research,
• Subject who received 6000 Euros or more within 12 months for being a research subject,
• Poor tolerance to blood sampling,
• Subject who cannot be contacted in case of emergency,
• Contraindications for MRI: claustrophobia, presence of osteosynthesis material or metal implants,
• Blood donation of more than 7 ml/kg in the 8 weeks prior to the start of the study,
• Vulnerable people according to law "Code de la Santé Publique" (L1121-5 to L1121-8):
• Pregnant or nursing women (urine pregnancy test for women of childbearing potential)
• People deprived of their liberty by an administrative or judicial decision
• People under involuntary psychiatric care
• People admitted in a health or social establishment for purposes other than research
• Minors
• Adults subject to legal protection (subject under guardianship or trusteeship) or unable to express their consent

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Caloric restriction; head down bedrest and caloric restriction (250 kcal/day)	Other: head down bedrest and caloric restriction; the intervention is 10 days of head down bedrest (-6°) and controlled and progressive caloric restriction, then controlled and progressive refeeding

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Lean Body Mass	Lean Body Mass assessed by dual energy x-ray absorptiometry (DEXA)	At baseline, during the ten days of intervention and until 90 days after the end of the intervention

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in body fluid compartments by bioelectrical impedance analysis	Extracellular, intracellular and total body water (L) will be estimated by bioimpedance	At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Change in whole-body Magnetic Resonance Imaging (MRI)	Change in MRI-measured whole-body Lean mass (kg) and Fat mass (kg) will be estimated	At baseline and at day 9 of intervention period
Change in mood	Change in mood is assessed using the Profile of Mood States (POMS) questionnaire. POMS questionnaire gives 6 measures of mood: Tension/anxiety, Depression, Anger/hostility Dynamism, Fatigue, Confusion A Total Mood Disturbance (TMD) score is calculated by summing the totals for the negative subscales (tension, depression, fatigue, confusion, anger) and then subtracting the totals for the positive subscale (vigor /esteem-related affect).	At baseline, during the ten days of intervention and until 4 days after the end of the intervention
Assessment of movements by volunteers	Actigraphs attached to wristbands placed on the non-dominant wrist and ankle of each volunteer	At baseline, during the ten days of the intervention and until 4 days after the end of the intervention
Change in cardiovascular deconditioning and orthostatic tolerance (stand test)	This test continuously measures heart rate (bpm) via a Finapres device while subjects sit for 5 minutes, then stand for 10 minutes and then sit again for 5 minutes	At baseline and 1 day after the end of intervention period
Changes in orthostatic tolerance	Orthostatic tolerance will be assessed during a tilt test combined with Lower Body Negative Pressure test (LBNP test)	At baseline and 1 day after the end of intervention period
Changes in peak aerobic power (VO2max test)	Exercise capacity wil be assessed by graded cycling on sitting ergometer until exhaustion	At baseline and 4 days after the end of intervention period
Changes in plasma volume	Plasma volume (L) will be assessed by the Dill & Costill method	At baseline, during the ten days of the intervention and until 4 days after the end of the intervention
Change in long term blood pressure	This test continuously measures Blood Pressure during 24 hours with the SOMNOTouch device.	At baseline, during the 10 days of the intervention, and 4 days after the end of the intervention
Change in macrocirculation	Macrocirculation will be assessed using standard ultrasound measurements at the carotid and femoral levels (arteries and veins).	At baseline, during the 10 days of the intervention, and at 3 days after the end of the intervention
Change in endothelial function	The tests consists in the measurement of the variations of the brachial artery diameter as a response to shear stress.	At baseline, during the 10 days of the intervention, and 3 days after the end of the intervention
Myofiber atrophy evaluation	Biopsy sampling from m. vastus lateralis will be performed to measure structure and function of muscle fibers.	At baseline and at day 9 of intervention
Changes in jump performance	Jump performance will be assessed on a platform and height of the jump will be evaluated	At baseline and 1 day after the end of the intervention
Change in protein metabolism	Labeled tracers (¹³C leucine for oxidation, ¹⁵N-phenylalanine for degradation, ²H₅-phenylalanine for synthesis monitoring and NaH13CO3 for quantification of amin acid oxidation) will be infused to the volunteers, and blood, urine, muscle and breath samples will be collected.	At baseline and at day 9 of the intervention
Change in muscle strength	Muscle strength will be assessed via dynamometry	At baseline and 2 days after the end of the intervention
Change in bone biological marker	Measuring bone-specific Alkaline Phosphatase (bAP) in blood	At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Changes in bone density (by High Resolution Peripheral Computed Tomography (HR-pQCT))	Bone density (g/cm2) is measured at tibia and radius level with HR-pQCT.	At baseline and until 90 days after the end of the intervention
Changes in Resting Metabolic Rate (RMR)	RMR will be measured by indirect calorimetry technique	At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Change in nitrogen balance	Nitrogen balance is a measure of nitrogen input minus nitrogen output. Nitrogen intake is calculated with a nutrition software. Protein oxidation measured in the 24-Hour urine collection estimates nitrogen output.	At baseline, during the ten days of intervention and at 90 days after the end of the intervention
Change in metabolic flexibility (Oral Glucose Tolerance Test (OGTT))	Metabolic flexibility will be measured during OGTT to assess the ability of the body to adjust energy substates' availability.	At baseline and 4 days after the end of the intervention.
Change in glucose homeostasis	Continuous measurement of interstitial glucose concentration by Dexcom sensor	From baseline to day 5 after the end of the intervention
Change in energy expenditure of tissues and organs (by PET-scan)	Regional mapping of metabolic activity by dynamic PET-scan with ¹⁸F-fluorodeoxyglucose	At baseline and at day 7 of the intervention period
Metabolic change in adipose tissue	Histology, cell culture, adipocyte size distribution and whole adipose tissue transcriptome, proteome, lipidome and metabolome on adipose tissue biopsy	At baseline and at day 9 of the intervention
Change in gut microbiota	Gut microbiome, metabolome and proteome will be measured in stool samples	At baseline, during the ten days of the intervention and 4 days after the end of the intervention period
Modification of self perceived hunger	Questionnaires about self-perceived hunger will be delivered before and after breakfast, lunch, snack, and dinner, or at the equivalent times on the fasting days. The questionnaire consists of a Visual Analogue Scale on which the volunteer must indicate their level of hunger (from 'not at all' to 'extremely')	At baseline, during the ten days of the intervention and until 4 days after the end of the intervention period
Change in energy requirements	Change in energy requirements using water labeled with a stable oxygen isotope (H218O)	At baseline and at day 9 of the intervention period
Change in motor function (Sit-to-stand test)	Sit-to-stand test : volunteer will be requested to rise as fast as possible from a chair without using hands and stand for 10s. The following parameter will be measured : Settling time after standing.	At baseline and 1 day after the end of the intervention period
Change in standing balance	This test assesses standing balance on a platform covered with 12-cm thick medium density foam.	At baseline and 1 day after the end of the intervention period
Change in vestibular health	Battery of tests will be used to asses vestibular health: recovery from fall, path integration, distance perception, perception of self-rotation, how long 1', Posner task, antisaccade task	At baseline and 1 day after the end of the intervention period
Change in cognitive state	This test monitor changes in the subject's emotional state and executive function by evaluatingpsychotechnical tasks on a laptop (the neurosensorybox) with physiological sensors (SOMNO HD system).	At baseline, during the ten days of the intervention period and at day 5 after the end of the intervention
Salivary cortisol evolution	To characterize stress level, morning and evening salivary cortisol (ng/ml) will be assessed	At baseline, at day 1, 3 & 10 of intervention period, and day 4 after the end of the intervention
Change in memory performance	Subjects are exposed to a series of images that will have to be remembered. After a delay of 1 hour or 24 hours they will be questioned on a series of images presented under the same conditions and they will have to indicate in a grid whether these images are known or new	At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention
Change in the internal representation of 3D space	This tests consist in a rhythmic point-to-point hand movements in virtual reality.	At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention
Change in gastro-brain interaction	Assessment of the correlation between gastric electrical activity (measured via Electrogastrography) and neural oscillatory responses (measured via Electroencephalography) during a cognitive task	At baseline, during the ten days of the intervention period, and until 4 days after the end of the intervention
Change in motor function (Walk and turn test)	Walk and turn test : volunteer will be instructed to walk as quickly as possible straight ahead toward a cone walk around it and return to the chair. Completion time per walk-and-turn trial will be measured.	At baseline and 1 day after the end of the intervention period
Change in motor function (Tandem Walk)	Tandem walk : Volunteer will walk 10 heel-to-toe steps with their arms folded across their chests and their eyes closed (3 trials) followed by one trial with their eyes open. Percentage of correct steps will be measured.	At baseline and 1 day after the end of the intervention period

Collaborators and Investigators

• Sponsor: Centre National d'Etudes Spatiales
• Collaborators: MEDES Institut de Médecine et de Physiologie Spatiales, Toulouse

Study record dates

Study Major Dates

• Study Start (Actual): March 10, 2026
• Primary Completion (Estimated): September 21, 2026
• Study Completion (Estimated): September 21, 2027

Study Registration Dates

• First Submitted: February 27, 2026
• First Submitted That Met QC Criteria: March 23, 2026
• First Posted (Actual): March 30, 2026

Study Record Updates

• Last Update Posted (Actual): March 30, 2026
• Last Update Submitted That Met QC Criteria: March 23, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Caloric restriction; Microgravity
• Additional Relevant MeSH Terms: Therapeutics; Diet, Food, and Nutrition; Physiological Phenomena; Nutritional Physiological Phenomena; Diet Therapy; Nutrition Therapy; Diet; Energy Intake; Caloric Restriction
• Other Study ID Numbers: 25-369

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No