The Effects of Caloric Restriction Plus Time Restriction on Glycemia, Circadian Rhythms and Cardiometabolic Health

Brief Summary

Detailed Description

In a parallel groups design, a total of 114 individuals will be recruited. After a two-week lead in and collection of data from activity monitors and continuous glucose monitors, plus a 28 hour (h) metabolic ward in-patient stay, participants will be randomised into one of three groups (eCR, 8-hour early time restriction + calorie restriction (e.g. 8:00-16:00); dCR, 8-hour delayed time restriction + calorie restriction (e.g. 12:00-20:00); CR, caloric restriction (\>12 hour eating window (e.g. 8:00-20:00). All participants will receive individualised menus and foods that will be delivered to their homes by a supermarket delivery service at energy balance for 1 week (baseline) and at 70% of energy balance for a further 8 weeks. Repeat assessment occurs from 6-8 weeks with the final metabolic ward stay at 8-weeks to assess changes in primary and secondary outcomes. There are three preplanned sub-studies from the parent trial: A. OMIT-Immune sub-study All participants will have blood samples collected at six timepoints over 24 hours and stool samples will be collected at two timepoints in a subset. The aims of this sub-study are to 1) characterize the changes in 24 h rhythm (mesor, amplitude and acrophase) of immune cells by flow cytometry over 24 hours, 2) describe the changes in the diversity of bacterial in response to intervention and 3) compare the effects of 8 weeks of CR versus eCR and dCR on immune profiles and gut microbiome. B. OMIT-BP sub-study All participants will have blood and urine samples collected at six timepoints over 24 hours. A subset of participants will wear 24 h ambulatory blood pressure monitors. The aims of this sub-study are to compare the effects of CR versus eCR and dCR on 1) the 24-hour profile of blood pressure assessed by ambulatory blood pressure monitoring, 2) Plasma markers of blood pressure regulation and 3) markers of renal function. We hypothesise that both eCR and dCR will alter and enhance these parameters and markers in comparison to CR. Changes in the circadian mesor, amplitude and acrophase in: systolic blood pressure, diastolic blood pressure, heart rate, pulse pressure, mean arterial pressure, nocturnal blood pressure dipping, morning blood pressure surge, plasma renin, aldosterone, creatinine, Urinary potassium, sodium, cortisol, creatinine. C. OMIT- Six month follow up. All participants will be instructed to continue their respective diet intervention and return to the clinic after an additional 16 weeks for a fasting blood sample and assessment of body composition. The aims of this sub-study are to 1) compare the 6 months effects of CR versus eCR and dCR on body composition and fasting blood samples metabolic health from baseline; 2) explore the factors that drive the intention-behaviour gap (describing the failure to translate intentions into action) relation to diet adherence. We hypothesize that participants will maintain the intervention-induced improvements in behavioural and metabolic health outcomes. Additionally, changes in body weight, waist and hip circumference, lean mass, fat mass, blood pressure, glycated hemoglobin, fasting plasma glucose, insulin, total cholesterol, LDL, HDL, triglycerides are assessed.

Primary Outcomes

Secondary Outcomes

• Insulin area under the curve (AUC)(8 weeks)
• Fasting insulin(8 weeks)
• Change in glycated hemoglobin (HbA1c)(8 weeks)
• Fasting glucose(8 weeks)