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NCT Number: NCT07499167

BRAHMS: Bed Rest And HypoMetabolism Study

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.

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Key information

Conditions

Microgravity Caloric Restriction

Age range

20 year–40 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

Medes - Imps

Toulouse, Medes-imps, 31400, France

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

head down bedrest and caloric restriction

Other

the intervention is 10 days of head down bedrest (-6°) and controlled and progressive caloric restriction, then controlled and progressive refeeding

Primary outcomes

  1. Lean Body Mass

    Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention

    Lean Body Mass assessed by dual energy x-ray absorptiometry (DEXA)

Secondary outcomes

  1. Change in body fluid compartments by bioelectrical impedance analysis

    Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention

    Extracellular, intracellular and total body water (L) will be estimated by bioimpedance

  2. Change in whole-body Magnetic Resonance Imaging (MRI)

    Time frame: At baseline and at day 9 of intervention period

    Change in MRI-measured whole-body Lean mass (kg) and Fat mass (kg) will be estimated

  3. Change in mood

    Time frame: At baseline, during the ten days of intervention and until 4 days after the end of the intervention

    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).

  4. Assessment of movements by volunteers

    Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention

    Actigraphs attached to wristbands placed on the non-dominant wrist and ankle of each volunteer

  5. Change in cardiovascular deconditioning and orthostatic tolerance (stand test)

    Time frame: At baseline and 1 day after the end of intervention period

    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

  6. Changes in orthostatic tolerance

    Time frame: At baseline and 1 day after the end of intervention period

    Orthostatic tolerance will be assessed during a tilt test combined with Lower Body Negative Pressure test (LBNP test)

  7. Changes in peak aerobic power (VO2max test)

    Time frame: At baseline and 4 days after the end of intervention period

    Exercise capacity wil be assessed by graded cycling on sitting ergometer until exhaustion

  8. Changes in plasma volume

    Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention

    Plasma volume (L) will be assessed by the Dill & Costill method

  9. Change in long term blood pressure

    Time frame: At baseline, during the 10 days of the intervention, and 4 days after the end of the intervention

    This test continuously measures Blood Pressure during 24 hours with the SOMNOTouch device.

  10. Change in macrocirculation

    Time frame: At baseline, during the 10 days of the intervention, and at 3 days after the end of the intervention

    Macrocirculation will be assessed using standard ultrasound measurements at the carotid and femoral levels (arteries and veins).

  11. Change in endothelial function

    Time frame: At baseline, during the 10 days of the intervention, and 3 days after the end of the intervention

    The tests consists in the measurement of the variations of the brachial artery diameter as a response to shear stress.

  12. Myofiber atrophy evaluation

    Time frame: At baseline and at day 9 of intervention

    Biopsy sampling from m. vastus lateralis will be performed to measure structure and function of muscle fibers.

  13. Changes in jump performance

    Time frame: At baseline and 1 day after the end of the intervention

    Jump performance will be assessed on a platform and height of the jump will be evaluated

  14. Change in protein metabolism

    Time frame: At baseline and at day 9 of the intervention

    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.

  15. Change in muscle strength

    Time frame: At baseline and 2 days after the end of the intervention

    Muscle strength will be assessed via dynamometry

  16. Change in bone biological marker

    Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention

    Measuring bone-specific Alkaline Phosphatase (bAP) in blood

  17. Changes in bone density (by High Resolution Peripheral Computed Tomography (HR-pQCT))

    Time frame: At baseline and until 90 days after the end of the intervention

    Bone density (g/cm2) is measured at tibia and radius level with HR-pQCT.

  18. Changes in Resting Metabolic Rate (RMR)

    Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention

    RMR will be measured by indirect calorimetry technique

  19. Change in nitrogen balance

    Time frame: At baseline, during the ten days of intervention and at 90 days after the end of the intervention

    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.

  20. Change in metabolic flexibility (Oral Glucose Tolerance Test (OGTT))

    Time frame: At baseline and 4 days after the end of the intervention.

    Metabolic flexibility will be measured during OGTT to assess the ability of the body to adjust energy substates' availability.

  21. Change in glucose homeostasis

    Time frame: From baseline to day 5 after the end of the intervention

    Continuous measurement of interstitial glucose concentration by Dexcom sensor

  22. Change in energy expenditure of tissues and organs (by PET-scan)

    Time frame: At baseline and at day 7 of the intervention period

    Regional mapping of metabolic activity by dynamic PET-scan with ¹⁸F-fluorodeoxyglucose

  23. Metabolic change in adipose tissue

    Time frame: At baseline and at day 9 of the intervention

    Histology, cell culture, adipocyte size distribution and whole adipose tissue transcriptome, proteome, lipidome and metabolome on adipose tissue biopsy

  24. Change in gut microbiota

    Time frame: At baseline, during the ten days of the intervention and 4 days after the end of the intervention period

    Gut microbiome, metabolome and proteome will be measured in stool samples

  25. Modification of self perceived hunger

    Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention period

    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')

  26. Change in energy requirements

    Time frame: At baseline and at day 9 of the intervention period

    Change in energy requirements using water labeled with a stable oxygen isotope (H218O)

  27. Change in motor function (Sit-to-stand test)

    Time frame: At baseline and 1 day after the end of the intervention period

    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.

  28. Change in standing balance

    Time frame: At baseline and 1 day after the end of the intervention period

    This test assesses standing balance on a platform covered with 12-cm thick medium density foam.

  29. Change in vestibular health

    Time frame: At baseline and 1 day after the end of the intervention period

    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

  30. Change in cognitive state

    Time frame: At baseline, during the ten days of the intervention period and at day 5 after the end of the intervention

    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).

  31. Salivary cortisol evolution

    Time frame: At baseline, at day 1, 3 & 10 of intervention period, and day 4 after the end of the intervention

    To characterize stress level, morning and evening salivary cortisol (ng/ml) will be assessed

  32. Change in memory performance

    Time frame: At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention

    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

  33. Change in the internal representation of 3D space

    Time frame: At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention

    This tests consist in a rhythmic point-to-point hand movements in virtual reality.

  34. Change in gastro-brain interaction

    Time frame: At baseline, during the ten days of the intervention period, and until 4 days after the end of the intervention

    Assessment of the correlation between gastric electrical activity (measured via Electrogastrography) and neural oscillatory responses (measured via Electroencephalography) during a cognitive task

  35. Change in motor function (Walk and turn test)

    Time frame: At baseline and 1 day after the end of the intervention period

    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.

  36. Change in motor function (Tandem Walk)

    Time frame: At baseline and 1 day after the end of the intervention period

    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.

Sponsors and collaborators

Lead sponsor

Centre National d'Etudes Spatiales

Other Gov

Collaborators

  • MEDES Institut de Médecine et de Physiologie Spatiales, Toulouse

Registry information

Official study title

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.

Acronym: BRAHMS

Important dates

Study start
2026
Primary completion
2026
Study completion
2027
First posted
Mar 30, 2026
Registry last updated
Jul 10, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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