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NCT Number: NCT06684834

Intermittent Carbohydrate Restriction in Cardiometabolic Health

Metabolic conditions, such as heart disease, type 2 diabetes, and metabolic syndrome, are among the leading causes of disability and mortality worldwide. Identifying innovative lifestyle strategies to reduce metabolic risk remains a public health priority. Further research is essential to understand how low carbohydrate intake influences human metabolism and how intermittent carbohydrate restriction impacts weight loss and metabolic health markers.

This study will investigate two interventions that restrict dietary carbohydrate intake on different schedules, examining their effects on metabolic health and energy balance in adults with abdominal overweight or obesity. The physiological mechanisms potentially underlying these effects will be explored by measuring a range of lifestyle and metabolic health parameters in both free-living and laboratory settings. A digital behaviour-change intervention will be incorporated after the dietary intervention to assess whether any metabolic effects can be sustained over time.

The study employs a three-arm parallel-group design consisting of a two-week lifestyle monitoring phase, a four-week dietary intervention, and a four-week digital intervention, with four laboratory visits throughout each phase. During the dietary intervention, participants will be allocated to one of three groups: (i) carbohydrate restriction (<8% of energy intake) on two consecutive days per week, (ii) carbohydrate restriction after 4 pm each day, or (iii) no dietary changes.

Dietary intake, physical activity, and glucose levels will be monitored through wearable devices in free-living conditions. The digital intervention will use a mobile health application that provides individualised lifestyle recommendations and education based on data collected in free-living conditions. Laboratory-based measures will include anthropometry, body composition scans, indirect calorimetry, blood pressure monitoring, fat biopsies, and postprandial sampling of blood and expired air.

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Key information

Conditions

Obesity and Overweight Body Weight Nutrition Disorders Nutritional and Metabolic Diseases Obesity Overnutrition Overweight Pathological Conditions, Signs and Symptoms Signs and Symptoms

Age range

18 year–65 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Who can participate

Healthy volunteers accepted: Yes

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

Inclusion criteria

  • Waist circumference of ≥94 cm (37 inches) if male and ≥80 cm (31.5 inches) if female, or BMI above 25 kg/m2
  • Fat mass index (FMI) of >6 kg/m2 for males, and >9 kg/m2 for females
  • Aged between 18-65 years
  • Has maintained a stable weight in the last three months (<3% change in body mass)
  • Keeps track of menstrual cycle regularity or oral contraceptive use (females only)

Exclusion criteria

  • Has a body weight of ≥120kg
  • Plans to undertake other lifestyle modifications during the study to manage weight (e.g. changes in dietary intake or activity levels)
  • Current or previous eating disorder
  • Diagnosed with major chronic conditions (e.g. type 2 diabetes, coronary heart disease, cancer, chronic kidney disease, etc.)
  • Use of medication that may interfere with study outcomes (e.g. glucose or lipid lowering medications)
  • Currently or recently pregnant (within last 6 months), planning to get pregnant or currently lactating
  • Has donated more than 500ml of blood in the last 3 months prior to the initial laboratory visit
  • Insufficient mental capacity or language skills to independently understand and follow the study protocol
  • Dietary restrictions to ingredients in test meals (e.g. gluten and lactose)
  • Has an irregular sleeping pattern (e.g. due to undertaking night-shift work)
  • Any condition, concurrent intervention or behaviour deemed either to pose undue personal risk to the participant or to introduce bias into the experiment

Treatment and study plan

5:2 carbohydrate restriction

Other

Carbohydrate ingestion restricted to <8% of energy intake on 2 self-selected consecutive days each week over 28-30 days. Ad libitum dietary amount, type and pattern followed on the remaining 5 days each week.

Early time-restricted carbohydrate intake

Other

Carbohydrate intake restricted to <8% of energy intake after 4pm each day for 28 days. Ad libitum dietary amount, type and pattern followed before 4pm.

Primary outcomes

  1. Post Prandial Triglyceride Area Under the Curve (AUC)

    Time frame: Pre and post intervention (4 weeks)

    Plasma triglyceride concentrations assessed postprandially for 5 hours after a mixed meal test

Secondary outcomes

  1. Fat Mass

    Time frame: Pre and post intervention (4 weeks)

    Measured in kilogrammes using Dual Energy X-ray Absorptiometry

  2. Lean Body Mass

    Time frame: Pre and post intervention (4 weeks)

    Measured in kilogrammes using Dual Energy X-ray Absorptiometry

  3. Fasting and Post Prandial Glucose Concentration

    Time frame: Pre and post intervention (4 weeks)

    Plasma glucose concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test

  4. Fasting and Post Prandial Insulin Concentration

    Time frame: Pre and post intervention (4 weeks)

    Plasma insulin concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test

  5. Fasting and Post Prandial NEFA Concentration

    Time frame: Pre and post intervention (4 weeks)

    Plasma NEFA concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test

  6. Fasting Triglyceride Concentration

    Time frame: Pre and post intervention (4 weeks)

    Plasma triglyceride concentrations assessed after an overnight fast

  7. Fasting Total Cholesterol Concentration

    Time frame: Pre and post intervention (4 weeks)

    Assessed after an overnight fast

  8. Fasting LDL-C Concentration

    Time frame: Pre and post intervention (4 weeks)

    Assessed after an overnight fast

  9. Fasting HDL-C Concentration

    Time frame: Pre and post intervention (4 weeks)

    Assessed after an overnight fast

  10. Substrate Oxidation

    Time frame: Pre and post intervention (4 weeks)

    Carbohydrate and fat oxidation rates will be measured using indirect calorimetry at rest and every hour postprandially

  11. Adipose Tissue Gene Expression

    Time frame: Pre and post intervention (4 weeks)

    Expression of several genes related to energy metabolism in adipose biopsies using real-time polymerase chain reaction (RT-PCR)

  12. Adipose Tissue Protein Expression

    Time frame: Pre and post intervention (4 weeks)

    Expression of several proteins related to energy metabolism in adipose biopsies using Western blot

Other outcomes

  1. Physical Activity Energy Expenditure (kJ or kcal)

    Time frame: 1 week during baseline monitoring, and weeks 1 and 4 of the intervention

    Assessed using combined heart rate and accelerometery wearable monitor (Actiheart™) in free-living conditions.

  2. Time Spent in Different Physical Activity Intensities (minutes)

    Time frame: 1 week during baseline monitoring, and weeks 1 and 4 of the intervention

    Assessed using combined heart rate and accelerometery wearable monitor (Actiheart™) in free-living conditions

  3. Dietary Intake

    Time frame: 1 week during baseline monitoring, and weeks 1 and 4 of intervention

    Dietary records manually kept by study participants

  4. Interstitial Glucose

    Time frame: 2 weeks during baseline monitoring, 2 weeks during weeks 3-4 of intervention

    Continuous glucose records will be used to capture interstitial glucose before and during the intervention

  5. Sleep Quality

    Time frame: Pre and post intervention (10 weeks)

    Self-reported sleep quality will be assessed via the Pittsburgh Sleep Quality Index (PSQI) questionnaire, consisting of 9 questions. Seven component scores are derived, scored from 0 (no difficulty) to 3 (severe difficulty)

  6. Diet Satisfaction

    Time frame: Pre and post intervention (10 weeks)

    Diet satisfaction will be assessed via the 28-item Diet Satisfaction Questionnaire (28-DSQ), scored on a five-point Likert scale with 1 being 'Disagree Strongly' and 5 being 'Agree Strongly'

  7. Engagement with Mobile Application

    Time frame: 4 weeks post intervention

    Data on number of sessions, session length, session interval and session frequency will be obtained through the Salus Metabolism mobile health application

  8. Usability of Mobile Application

    Time frame: 4 weeks post intervention

    Assessed via the mHealth App Usability Questionnaire, consisting of 16 statements scored on a seven-point Likert scale with 1 being 'Disagree' and 7 being 'Agree'

  9. Subjective App Usability and Engagement

    Time frame: 4 weeks post intervention

    Participants will be asked to provide feedback on the Salus Metabolism mHealth application through a semi-structured interview. Thematic analysis will be used to analyse interview data.

Study contacts

Contact information is provided by the study sponsor or research team.

Guoda Karoblyte

CONTACT

[email protected]

+44 (0) 1225 386478

Sponsors and collaborators

Lead sponsor

University of Bath

Other

Registry information

Official study title

The Effects of Intermittent Carbohydrate Restriction on Metabolic Health and Energy Balance in Adults with Abdominal Overweight and Obesity

Important dates

Study start
2023
Primary completion
2025
Study completion
2036
First posted
Nov 12, 2024
Registry last updated
Nov 12, 2024

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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