Dietary Carbohydrate Restriction, Energy Deficit
Conditions
Keywords
Metabolic Flexibility, Ketone Production, Caloric Restriction, Low Carbohydrate Diet, Continuous Glucose Monitoring
Brief 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. 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.
Interventions
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.
OTHERStandard Diet With Caloric Restriction
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.
Sponsors
Technical University of Munich
Metaflow Ltd.
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
OTHER
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
* 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
Exclusion criteria
* 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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Carbon dioxide production and breath acetone concentration | 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 | 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. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Urinary ketone concentration | Daily during the study period (approximately 3 weeks) | Urinary ketone concentration is assessed once daily using reagent test strips and self-reported by participants. |
| Capillary blood ketone concentration | Daily during the study period (approximately 3 weeks) | Capillary blood ketone concentration is measured once daily in the fasting state using a handheld ketone meter. |
| Fasting capillary blood glucose concentration | Daily during the study period (approximately 3 weeks) | Fasting blood glucose concentration is measured once daily using a capillary blood glucose meter. |
| Body weight | Daily during the study period (approximately 3 weeks) | Body weight is measured daily using a Bluetooth-enabled electronic scale. |
| Fat Mass | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Fat mass is assessed using bioelectrical impedance analysis and air displacement plethysmography. |
| Fat-Free Mass | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Fat-free mass is assessed using bioelectrical impedance analysis and air displacement plethysmography. |
| Body Fat Percentage | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Body fat percentage is assessed using bioelectrical impedance analysis and air displacement plethysmography. |
| Resting metabolic rate | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Resting metabolic rate is assessed by indirect calorimetry during laboratory visits. |
| Plasma Leptin Concentration | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Blood samples are collected to assess plasma leptin concentration. |
| Plasma Insulin Concentration | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Blood samples are collected to assess plasma insulin concentration. |
| Plasma Triiodothyronine (T3) Concentration | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Blood samples are collected to assess plasma triiodothyronine (T3) concentration. |
| Plasma Glucagon-Like Peptide-1 (GLP-1) Concentration | Baseline (Day 1), mid-intervention (approximately Day 14), and post-intervention (approximately Day 21) | Blood samples are collected to assess plasma glucagon-like peptide-1 (GLP-1) concentration. |
Countries
Germany
Contacts
PRINCIPAL_INVESTIGATORKarsten Köhler, Prof. Dr.
Professorship for Exercise, Nutrition and Health, Technical University of Munich
Outcome results
None listed