Dietary Carbohydrate Restriction, Energy DeficitMetaFlexNCT07429058
Metabolic Flexibility and Ketone Production During Energy Deficit
A study testing Low-Carbohydrate Diet and Standard Diet With Caloric Restriction in people with Dietary Carbohydrate Restriction, Energy Deficit, run by Technical University of Munich at 1 site in Germany.
Trial summary
This randomized, interventional study examines the effects of short-term carbohydrate restriction, with and without caloric restriction, on indices of metabolic flexibility in healthy adults. Read more about this study
- Who is it for?
- Ages 18 to 40 yearsHealthy volunteers can take part
- Conditions the study is for
- Dietary Carbohydrate Restriction, Energy Deficit
- What is being tested?
- Low-Carbohydrate Diet and Standard Diet With Caloric Restriction
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 30 participants
- Where
- 1 siteGermany
- Study dates
- 24 Nov 2023to 26 Apr 2024
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 40 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Age 18-40 years
- Body mass index (BMI) 18.5-27 kg/m²
- Regular exercise or vigorous physical activity at least once per week
- Willing and able to comply with the dietary intervention and study procedures
- For female participants: non-pregnant and using hormonal contraception
Who cannot join
- Acute or chronic illness
- Metabolic disorders or conditions associated with altered glucose or lipid metabolism (exclusion of pre-diabetes and diabetes via HbA1c measurement)
- Use of medications known to interfere with study outcomes
- Intolerance or allergy to components of the study diets
- Pregnancy or breastfeeding
Trial locations and contacts
1 site in 1 country.
About this study
Official title: Indices of Metabolic Flexibility and Ketone Production During Short-Term Energy Deficit With and Without Dietary Carbohydrate Restriction
This randomized, interventional study examines the effects of short-term carbohydrate restriction, with and without caloric restriction, on indices of metabolic flexibility in healthy adults. Participants are randomly assigned to either a low-carbohydrate diet or a standard diet under energy balance, followed by the same diet under controlled caloric restriction. Primary outcomes include measures of carbon dioxide production, breath ketones and interstitial glucose. Secondary outcomes include blood and urinary ketones, body weight, body composition, and selected metabolic biomarkers.
Read the detailed description
This is a monocentric, randomized, open-label nutrition intervention conducted in healthy adults aged 18 to 40 years. The study investigates the effects of short-term carbohydrate and caloric restriction on indices of metabolic flexibility.
After screening and baseline assessments, participants undergo an initial period of energy balance with a standardized diet, followed by a 2-week intervention phase. Participants are randomly assigned in a 1:1 ratio to either a low-carbohydrate diet or a standard mixed diet. Participants are instructed to maintain their habitual physical activity throughout the study. During the first week of the intervention period, energy intake is equivalent to estimated energy requirements. During the second week, energy intake is reduced by ~500 kcal/d.
Metabolic outcomes are assessed using repeated laboratory and remote measurements. Primary outcomes include breath-based measures of carbon dioxide and acetone production, as well as continuous glucose monitoring. Secondary outcomes include urinary and capillary blood ketones, body weight, body composition, resting metabolic rate, plasma glucose and selected biomarkers (leptin, insulin, triiodothyronine, GLP-1, HbA1c).
Data are collected at baseline, during the intervention, and post-intervention. The total participation time per participant is approximately three weeks. The study aims to characterize short-term metabolic responses to dietary carbohydrate manipulation and energy deficit under controlled conditions.
- Being tested
- Low-Carbohydrate Diet, Standard Diet With Caloric Restriction
- Keywords
- Metabolic Flexibility, Ketone Production, Caloric Restriction, Low Carbohydrate Diet, Continuous Glucose Monitoring
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Low-Carbohydrate DietOther
Participants receive a low-carbohydrate diet. All meals are provided and individually tailored based on estimated energy requirements. Carbohydrate intake is restricted to 75-125 g per day, with the remaining energy intake derived from fat and protein. The intervention is administered for 14 days.
Standard Diet With Caloric RestrictionOther
Participants receive a standard mixed diet. All meals are provided and individually tailored based on estimated energy requirements. The macronutrient distribution consists of approximately 50-55% carbohydrates, 25-35% fat, and 15% protein. The intervention is administered for 14 days.
| Study group | Role | What they receive |
|---|---|---|
| Low-Carbohydrate Diet | Experimental | Participants assigned to this arm follow a low-carbohydrate diet. Daily carbohydrate intake is reduced to approximately 75-125 g per day (about 15% of total energy intake), with remaining energy derived primarily from fat (~70%) and protein (~15%). Diets are individually tailored to meet estimated energy and micronutrient requirements. Participants are instructed to maintain their habitual physical activity throughout the study. Receives: Other: Low-Carbohydrate Diet |
| Standard Diet | Active comparator | Participants assigned to this arm follow a standard mixed diet combined. The diet consists of approximately 50-55% carbohydrates, 25-35% fat, and 15% protein. Diets are individually tailored to meet estimated energy and micronutrient requirements. Participants are instructed to maintain their habitual physical activity throughout the study. Receives: Other: Standard Diet With Caloric Restriction |
What is being measured
The primary outcome is the main question the study is designed to answer.
Carbon dioxide production and breath acetone concentration
Carbon dioxide production and breath acetone concentration are assessed using portable breath analysis devices during standardized daily measurements and timepoints.
Measured: Baseline, during the energy-deficit intervention period, and post-intervention (over approximately 3 weeks)
Interstitial glucose concentration assessed by continuous glucose monitoring
Continuous glucose monitoring is used to assess interstitial glucose concentration, including average glucose levels, glucose variability, and time in glycemic ranges.
Measured: Continuously assessed throughout the study period (approximately 3 weeks)
Secondary outcomes (12)
Urinary ketone concentration
Urinary ketone concentration is assessed once daily using reagent test strips and self-reported by participants.
Measured: Daily during the study period (approximately 3 weeks)
Capillary blood ketone concentration
Capillary blood ketone concentration is measured once daily in the fasting state using a handheld ketone meter.
Measured: Daily during the study period (approximately 3 weeks)
Fasting capillary blood glucose concentration
Fasting blood glucose concentration is measured once daily using a capillary blood glucose meter.
Measured: Daily during the study period (approximately 3 weeks)
Body weight
Body weight is measured daily using a Bluetooth-enabled electronic scale.
Measured: Daily during the study period (approximately 3 weeks)
Fat Mass
Fat mass is assessed using bioelectrical impedance analysis and air displacement plethysmography.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Fat-Free Mass
Fat-free mass is assessed using bioelectrical impedance analysis and air displacement plethysmography.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Body Fat Percentage
Body fat percentage is assessed using bioelectrical impedance analysis and air displacement plethysmography.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Resting metabolic rate
Resting metabolic rate is assessed by indirect calorimetry during laboratory visits.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Leptin Concentration
Blood samples are collected to assess plasma leptin concentration.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Insulin Concentration
Blood samples are collected to assess plasma insulin concentration.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Triiodothyronine (T3) Concentration
Blood samples are collected to assess plasma triiodothyronine (T3) concentration.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Glucagon-Like Peptide-1 (GLP-1) Concentration
Blood samples are collected to assess plasma glucagon-like peptide-1 (GLP-1) concentration.
Measured: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted24 Feb 2026
- Study start24 Nov 2023
- Primary completion11 Mar 2024
- Study completion26 Apr 2024
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Dietary Carbohydrate Restriction, Energy DeficitStudies of the same condition, open and under way.
- More trials run by Technical University of MunichThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 30 participants (actual)
Sponsor and investigators
- Lead sponsor
- Technical University of Munich
- Sponsor type
- University, hospital or other
- Collaborators
- Metaflow Ltd.
- Responsible party
- Principal investigator, Karsten Koehler, Technical University of Munich
- Investigators
- Karsten Köhler, Prof. Dr., Principal investigator, Professorship for Exercise, Nutrition and Health, Technical University of Munich
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07429058
- Sponsor's protocol ID
- MetaFlex
- Acronym
- MetaFlex
- Status last verified
- Feb 2026
- First submitted
- 10 Feb 2026
- Last updated
- 24 Feb 2026
- Results posted
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided: Individual participant data will be shared upon reasonable request in accordance with the Technical University of Munich's data sharing policy and applicable data protection regulations
Study at a glance
From the registry record, last updated by the sponsor on 24 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Indices of Metabolic Flexibility and Ketone Production During Short-Term Energy Deficit With and Without Dietary Carbohydrate Restriction
- ClinicalTrials.gov ID
- NCT07429058
- Acronym / sponsor ID
- MetaFlex / MetaFlex
- Keywords
- Metabolic Flexibility, Ketone Production, Caloric Restriction, Low Carbohydrate Diet, Continuous Glucose Monitoring
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 30 participants (actual)
- Lead sponsor
- Technical University of MunichUniversity, hospital or other
- Collaborators
- Metaflow Ltd.
- Study start
- 24 Nov 2023 (actual)
- Primary completion
- 11 Mar 2024 (actual)
- Study completion
- 26 Apr 2024 (actual)
- First posted
- 24 Feb 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This randomized, interventional study examines the effects of short-term carbohydrate restriction, with and without caloric restriction, on indices of metabolic flexibility in healthy adults. Participants are randomly assigned to either a low-carbohydrate diet or a standard diet under energy balance, followed by the same diet under controlled caloric restriction. Primary outcomes include measures of carbon dioxide production, breath ketones and interstitial glucose. Secondary outcomes include blood and urinary ketones, body weight, body composition, and selected metabolic biomarkers.
Detailed description
This is a monocentric, randomized, open-label nutrition intervention conducted in healthy adults aged 18 to 40 years. The study investigates the effects of short-term carbohydrate and caloric restriction on indices of metabolic flexibility.
After screening and baseline assessments, participants undergo an initial period of energy balance with a standardized diet, followed by a 2-week intervention phase. Participants are randomly assigned in a 1:1 ratio to either a low-carbohydrate diet or a standard mixed diet. Participants are instructed to maintain their habitual physical activity throughout the study. During the first week of the intervention period, energy intake is equivalent to estimated energy requirements. During the second week, energy intake is reduced by ~500 kcal/d.
Metabolic outcomes are assessed using repeated laboratory and remote measurements. Primary outcomes include breath-based measures of carbon dioxide and acetone production, as well as continuous glucose monitoring. Secondary outcomes include urinary and capillary blood ketones, body weight, body composition, resting metabolic rate, plasma glucose and selected biomarkers (leptin, insulin, triiodothyronine, GLP-1, HbA1c).
Data are collected at baseline, during the intervention, and post-intervention. The total participation time per participant is approximately three weeks. The study aims to characterize short-term metabolic responses to dietary carbohydrate manipulation and energy deficit under controlled conditions.
Study design
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Low-Carbohydrate Diet | Experimental | Other: Low-Carbohydrate DietParticipants assigned to this arm follow a low-carbohydrate diet. Daily carbohydrate intake is reduced to approximately 75-125 g per day (about 15% of total energy intake), with remaining energy derived primarily from fat (~70%) and protein (~15%). Diets are individually tailored to meet estimated energy and micronutrient requirements. Participants are instructed to maintain their habitual physical activity throughout the study. |
| Standard Diet | Active comparator | Other: Standard Diet With Caloric RestrictionParticipants assigned to this arm follow a standard mixed diet combined. The diet consists of approximately 50-55% carbohydrates, 25-35% fat, and 15% protein. Diets are individually tailored to meet estimated energy and micronutrient requirements. Participants are instructed to maintain their habitual physical activity throughout the study. |
Who may qualify
- Ages
- 18 to 40 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (5 listed)
- Age 18-40 years
- Body mass index (BMI) 18.5-27 kg/m²
- Regular exercise or vigorous physical activity at least once per week
- Willing and able to comply with the dietary intervention and study procedures
- For female participants: non-pregnant and using hormonal contraception
Key exclusion criteria (5 listed)
- Acute or chronic illness
- Metabolic disorders or conditions associated with altered glucose or lipid metabolism (exclusion of pre-diabetes and diabetes via HbA1c measurement)
- Use of medications known to interfere with study outcomes
- Intolerance or allergy to components of the study diets
- Pregnancy or breastfeeding
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Low-Carbohydrate DietParticipants receive a low-carbohydrate diet. All meals are provided and individually tailored based on estimated energy requirements. Carbohydrate intake is restricted to 75-125 g per day, with the remaining energy intake derived from fat and protein. The intervention is administered for 14 days. | Other | Low-Carbohydrate Diet |
| Standard Diet With Caloric RestrictionParticipants receive a standard mixed diet. All meals are provided and individually tailored based on estimated energy requirements. The macronutrient distribution consists of approximately 50-55% carbohydrates, 25-35% fat, and 15% protein. The intervention is administered for 14 days. | Other | Standard Diet |
Primary outcome
Carbon dioxide production and breath acetone concentration
Time frame: Baseline, during the energy-deficit intervention period, and post-intervention (over approximately 3 weeks)
Carbon dioxide production and breath acetone concentration are assessed using portable breath analysis devices during standardized daily measurements and timepoints.
Interstitial glucose concentration assessed by continuous glucose monitoring
Time frame: Continuously assessed throughout the study period (approximately 3 weeks)
Continuous glucose monitoring is used to assess interstitial glucose concentration, including average glucose levels, glucose variability, and time in glycemic ranges.
12 secondary outcomes
Urinary ketone concentration
Time frame: Daily during the study period (approximately 3 weeks)
Capillary blood ketone concentration
Time frame: Daily during the study period (approximately 3 weeks)
Fasting capillary blood glucose concentration
Time frame: Daily during the study period (approximately 3 weeks)
Body weight
Time frame: Daily during the study period (approximately 3 weeks)
Fat Mass
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Fat-Free Mass
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Body Fat Percentage
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Resting metabolic rate
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Leptin Concentration
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Insulin Concentration
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Triiodothyronine (T3) Concentration
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Plasma Glucagon-Like Peptide-1 (GLP-1) Concentration
Time frame: Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21)
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 24 Feb 2026.
- Individual participant dataSharing planned: Undecided. Individual participant data will be shared upon reasonable request in accordance with the Technical University of Munich's data sharing policy and applicable data protection regulations
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Karsten Köhler, Prof. Dr. principal investigator
Professorship for Exercise, Nutrition and Health, Technical University of Munich
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Low-Carbohydrate Diet and Standard Diet With Caloric Restriction in people with Dietary Carbohydrate Restriction, Energy Deficit, run by Technical University of Munich at 1 site in Germany.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 24 Feb 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Germany. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Carbon dioxide production and breath acetone concentration (time frame: Baseline, during the energy-deficit intervention period, and post-intervention (over approximately 3 weeks)). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 24 Feb 2026.