An interventional study of Buchinger Wilhelmi prolonged fasting and Online exercise program in Fasting Conditions and Metabolic Health, sponsored by Universidad de Almeria. Not yet recruiting at 1 site in Spain. Open to participants aged 18 Years to 80 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-29.
Sponsored by Universidad de Almeria · Not applicable, Interventional, and Other
Type of Study: Clinical Trial
Goal: The goal of this clinical trial is to investigate whether combining the Buchinger Wilhelmi prolonged fasting program with a structured exercise program can improve physical fitness, body composition, cardiometabolic health, sleep quality, and health-related quality of life. The study will also investigate metabolic responses to prolonged fasting and whether these responses are influenced by exercise.
Participant Population/Health Conditions: The study will involve adults attending the Buchinger Wilhelmi Clinic who undergo the prolonged fasting program and meet the study eligibility criteria.
Main Questions:
Participants Will:
Comparison Groups: Researchers will compare the four study conditions to determine whether structured exercise performed before and/or during prolonged fasting enhances the physiological, metabolic, and functional effects of the Buchinger Wilhelmi fasting program.
Prolonged fasting induces substantial metabolic adaptations, including increased ketone body production and changes in glucose and lipid metabolism, and has been associated with improvements in cardiometabolic health and body composition. However, fasting may also be accompanied by fatigue, sleep disturbances, and changes in well-being that can affect physical function and quality of life during the intervention.
Exercise is a potent non-pharmacological strategy for improving physical fitness, body composition, cardiometabolic health, sleep, and quality of life. Combining exercise with prolonged fasting may provide complementary benefits by enhancing fasting-induced metabolic adaptations while helping to maintain physical function and well-being. The timing of exercise may also be relevant, as exercise performed before the fasting period may influence the physiological response to fasting, while exercise performed during fasting may directly interact with fasting-induced changes in substrate utilization and energy metabolism.
Based on this rationale, the main hypothesis is that structured exercise performed before and/or during prolonged fasting enhances the physiological and metabolic effects of fasting while improving physical fitness, sleep, and quality of life. The main objective is to determine the independent and combined effects of exercise performed before and during the Buchinger Wilhelmi prolonged fasting program on physical fitness, body composition, cardiometabolic health, sleep, and health-related quality of life.
The study will involve adults undergoing the Buchinger Wilhelmi prolonged fasting program as part of their clinical stay. Participants will choose whether to complete an online exercise program before attending the clinic and whether to participate in a supervised exercise program specifically designed for the fasting period during their clinical stay. These choices will result in four study conditions: (1) online exercise followed by prolonged fasting alone; (2) online exercise followed by prolonged fasting combined with supervised exercise; (3) prolonged fasting alone; and (4) prolonged fasting combined with supervised exercise. Allocation to these conditions will not be randomized. During fasting, participants will receive approximately 200-250 kcal/day and may participate in the activities routinely available at the clinic.
Before and after the intervention, participants will undergo physiological and physical fitness assessments. Blood samples will be collected to assess cardiometabolic and metabolic responses, including glucose and lipid metabolism and ketone production. Body composition will be assessed using bioelectrical impedance analysis, and physical fitness will include handgrip and lower-limb strength assessments. Sleep will be evaluated objectively using accelerometry and subjectively using the Pittsburgh Sleep Quality Index, while health-related quality of life will be assessed using the SF-36 questionnaire. These assessments are consistent with those specified in the study protocol.
By comparing the four study conditions, the study aims to determine whether structured exercise performed before and/or during prolonged fasting enhances fasting-induced metabolic adaptations and improves physical fitness, body composition, sleep, and health-related quality of life.
Exclusion Criteria:
Participants will undergo the Buchinger Wilhelmi prolonged fasting program for at least 4 consecutive days without completing the study-specific online exercise program before the clinical stay or the supervised exercise program during fasting.
Behavioral: Buchinger Wilhelmi prolonged fasting
Participants will undergo the Buchinger Wilhelmi prolonged fasting program for at least 4 consecutive days and participate in the study-specific supervised exercise program during the fasting period. Participants will not complete the online exercise program before the clinical stay.
Behavioral: Buchinger Wilhelmi prolonged fasting · Behavioral: Supervised exercise program during prolonged fasting
Participants will complete a 21-day study-specific online exercise program before the clinical stay and subsequently undergo the Buchinger Wilhelmi prolonged fasting program for at least 4 consecutive days without participating in the supervised exercise program during fasting.
Behavioral: Buchinger Wilhelmi prolonged fasting · Behavioral: Online exercise program
Participants will complete a 21-day study-specific online exercise program before the clinical stay and subsequently undergo the Buchinger Wilhelmi prolonged fasting program for at least 4 consecutive days combined with the study-specific supervised exercise program during fasting.
Behavioral: Buchinger Wilhelmi prolonged fasting · Behavioral: Online exercise program · Behavioral: Supervised exercise program during prolonged fasting
Participants will undergo the medically supervised Buchinger Wilhelmi prolonged fasting program for at least 4 consecutive days. During fasting, participants will receive approximately 200-250 kcal/day, primarily from vegetable juices and vegetable broth, together with non-caloric fluids.
Participants will complete a 21-day study-specific remotely delivered exercise program before admission to the Buchinger Wilhelmi Clinic. The program provides structured exercise training before the prolonged fasting period.
Participants will complete a study-specific supervised exercise program during the prolonged fasting period at the Buchinger Wilhelmi Clinic. Exercise sessions will be conducted under professional supervision and adapted to participants' individual physical capacity.
Handgrip Strength
Change from baseline in mean bilateral handgrip strength (kg) to the end of the fasting period, assessed using a handgrip dynamometer. For each hand, three trials will be performed and averaged. The mean values obtained for the right and left hands will then be averaged to obtain one bilateral handgrip strength value per participant.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Fasting Blood Glucose
Change in fasting blood glucose concentration (mg/dL) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Fasting Insulin
Change in fasting insulin concentration (µIU/mL) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
LDL Cholesterol
Change in low-density lipoprotein cholesterol concentration (mg/dL) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
HDL Cholesterol
Change in high-density lipoprotein cholesterol concentration (mg/dL) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Triglycerides
Change in triglyceride concentration (mg/dL) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
C-Reactive Protein
Change in C-reactive protein concentration (mg/L) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Five-Times Sit-to-Stand Test
Change in the time required to complete five consecutive sit-to-stand repetitions (seconds) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
30-Second Sit-to-Stand Test
Change in the number of complete sit-to-stand repetitions performed within 30 seconds (repetitions) from baseline to the end of the fasting period.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Blood Lactate Response to the 30-Second Sit-to-Stand Test
Change from baseline to the end of the fasting period in the blood lactate response to the 30-second sit-to-stand test, calculated as post-exercise blood lactate minus pre-exercise blood lactate (Δ lactate; mmol/L) at each assessment.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Total Body Fat Mass
Change in total body fat mass (kg) from baseline to the end of the fasting period, assessed by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Body Fat Percentage
Change in total body fat percentage (%) from baseline to the end of the fasting period, assessed by DXA.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Total Lean Mass
Change in total lean mass (kg) from baseline to the end of the fasting period, assessed by DXA.
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Visceral Adipose Tissue Fat Mass
Change in visceral adipose tissue (VAT) fat mass (g) from baseline to the end of the fasting period, assessed by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Subcutaneous Adipose Tissue Fat Mass
Change in subcutaneous adipose tissue (SAT) fat mass (g) from baseline to the end of the fasting period, assessed by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline and Day 4 to Day 28 (final fasting day, depending on participant)
Physical Activity - International Physical Activity Questionnaire (IPAQ)
Change in self-reported physical activity (MET-min/week) from baseline to the end of the fasting period, assessed using the International Physical Activity Questionnaire (IPAQ). Higher MET-min/week values indicate greater physical activity.
Time frame: Baseline; Day 4 to Day 28 (final fasting day, depending on participant); and 30 days after the final fasting day
Pittsburgh Sleep Quality Index (PSQI)
Change from baseline in subjective sleep quality assessed using the Pittsburgh Sleep Quality Index (PSQI) global score (0-21 points). Higher scores indicate poorer subjective sleep quality.
Time frame: Baseline; Day 4 to Day 28 (final fasting day, depending on participant); and 30 days after the final fasting day
Health-Related Quality of Life - SF-36
Change in health-related quality of life assessed using the 36-Item Short Form Health Survey (SF-36). The eight domains assessed are physical functioning, role limitations due to physical health, bodily pain, general health, vitality, social functioning, role limitations due to emotional problems, and mental health (each scored from 0 to 100 points). Higher scores indicate better health status.
Time frame: Baseline; Day 4 to Day 28 (final fasting day, depending on participant); and 30 days after the final fasting day
Plan to share: Yes
Supporting information: Study protocol, Icf, Csr
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Universidad de Almeria