Intermittent Carbohydrate Restriction in Cardiometabolic Health

Official title

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

Overview

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.

Interventions

• Other 5:2 carbohydrate restriction
  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.
• Other Early time-restricted carbohydrate intake
  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 outcome measures

• Post Prandial Triglyceride Area Under the Curve (AUC) [Time frame: Pre and post intervention (4 weeks)]

Secondary outcome measures (12)

• Fat Mass [Time frame: Pre and post intervention (4 weeks)]
• Lean Body Mass [Time frame: Pre and post intervention (4 weeks)]
• Fasting and Post Prandial Glucose Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting and Post Prandial Insulin Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting and Post Prandial NEFA Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting Triglyceride Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting Total Cholesterol Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting LDL-C Concentration [Time frame: Pre and post intervention (4 weeks)]
• Fasting HDL-C Concentration [Time frame: Pre and post intervention (4 weeks)]
• Substrate Oxidation [Time frame: Pre and post intervention (4 weeks)]
• Adipose Tissue Gene Expression [Time frame: Pre and post intervention (4 weeks)]
• Adipose Tissue Protein Expression [Time frame: Pre and post intervention (4 weeks)]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Open label

Primary purpose

Basic science

Study locations

United Kingdom · 1 center

• University of Bath — Bath

Identifiers

NCT: NCT06684834 · 323721

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗