Obesity and Overweight
Conditions
Keywords
carbohydrate restriction, carbohydrate timing, intermittent carbohydrate restriction, intermittent energy restriction, evening carbohydrate restriction, carbohydrate periodisation
Brief summary
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
OTHER5:2 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.
OTHEREarly 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.
Sponsors
University of Bath
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE
Masking
NONE
Intervention model description
A randomised, three-arm parallel-group study
Eligibility
Sex/Gender
ALL
Age
18 Years to 65 Years
Healthy volunteers
Yes
Inclusion criteria
1. Waist circumference of ≥94 cm (37 inches) if male and ≥80 cm (31.5 inches) if female, or BMI above 25 kg/m2 2. Fat mass index (FMI) of \>6 kg/m2 for males, and \>9 kg/m2 for females 3. Aged between 18-65 years 4. Has maintained a stable weight in the last three months (\<3% change in body mass) 5. Keeps track of menstrual cycle regularity or oral contraceptive use (females only)
Exclusion criteria
1. Has a body weight of ≥120kg 2. Plans to undertake other lifestyle modifications during the study to manage weight (e.g. changes in dietary intake or activity levels) 3. Current or previous eating disorder 4. Diagnosed with major chronic conditions (e.g. type 2 diabetes, coronary heart disease, cancer, chronic kidney disease, etc.) 5. Use of medication that may interfere with study outcomes (e.g. glucose or lipid lowering medications) 6. Currently or recently pregnant (within last 6 months), planning to get pregnant or currently lactating 7. Has donated more than 500ml of blood in the last 3 months prior to the initial laboratory visit 8. Insufficient mental capacity or language skills to independently understand and follow the study protocol 9. Dietary restrictions to ingredients in test meals (e.g. gluten and lactose) 10. Has an irregular sleeping pattern (e.g. due to undertaking night-shift work) 11. Any condition, concurrent intervention or behaviour deemed either to pose undue personal risk to the participant or to introduce bias into the experiment
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Post Prandial Triglyceride Area Under the Curve (AUC) | Pre and post intervention (4 weeks) | Plasma triglyceride concentrations assessed postprandially for 5 hours after a mixed meal test |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Fat Mass | Pre and post intervention (4 weeks) | Measured in kilogrammes using Dual Energy X-ray Absorptiometry |
| Lean Body Mass | Pre and post intervention (4 weeks) | Measured in kilogrammes using Dual Energy X-ray Absorptiometry |
| Fasting and Post Prandial Glucose Concentration | Pre and post intervention (4 weeks) | Plasma glucose concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test |
| Fasting and Post Prandial Insulin Concentration | Pre and post intervention (4 weeks) | Plasma insulin concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test |
| Fasting and Post Prandial NEFA Concentration | Pre and post intervention (4 weeks) | Plasma NEFA concentrations assessed after an overnight fast, postprandially for 5 hours after a mixed meal test |
| Fasting Triglyceride Concentration | Pre and post intervention (4 weeks) | Plasma triglyceride concentrations assessed after an overnight fast |
| Fasting Total Cholesterol Concentration | Pre and post intervention (4 weeks) | Assessed after an overnight fast |
| Fasting LDL-C Concentration | Pre and post intervention (4 weeks) | Assessed after an overnight fast |
| Fasting HDL-C Concentration | Pre and post intervention (4 weeks) | Assessed after an overnight fast |
| Substrate Oxidation | Pre and post intervention (4 weeks) | Carbohydrate and fat oxidation rates will be measured using indirect calorimetry at rest and every hour postprandially |
| Adipose Tissue Gene Expression | 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) |
| Adipose Tissue Protein Expression | Pre and post intervention (4 weeks) | Expression of several proteins related to energy metabolism in adipose biopsies using Western blot |
Countries
United Kingdom
Outcome results
None listed