Community-Based Time-Restricted Eating and Health Education for Adults With Stage 1-2 Cardiovascular-Kidney-Metabolic Syndrome in Can Tho City

This study uses a controlled community-based intervention design with cluster allocation by drawing lots, with longitudinal follow-up and repeated measurements in the same participants. The unit of allocation is the residential-area cluster within each ward or commune, while study outcomes are assessed at the individual level.

CLUSTER ALLOCATION: The intervention phase is implemented in four administrative study sites that previously participated in the community-based CKM survey, including two urban wards and two rural communes in Can Tho City, Viet Nam. Within each administrative site, two geographically separate residential areas are selected. One area is allocated to the intervention condition and the other to the control condition by drawing lots, without discretionary assignment by the investigators. Cluster allocation is used to reduce contamination between study groups and to facilitate community-level implementation.

The study areas are allocated as follows:

• Phong Dien Commune: the intervention area is Giai Xuan, a former administrative unit now incorporated into Phong Dien Commune; the control area is Phong Dien.
• Truong Long Tay Commune: the intervention area is Truong Long Tay; the control area is Truong Long A, a former administrative unit now incorporated into Truong Long Tay Commune.
• O Mon Ward: the intervention area is Thoi An, a former administrative unit now incorporated into O Mon Ward; the control area is O Mon.
• Phuoc Thoi Ward: the intervention area is Phuoc Thoi; the control area is Truong Lac, a former administrative unit now incorporated into Phuoc Thoi Ward.

The study therefore includes four intervention clusters and four control clusters. Allocation occurs at the residential-area level rather than at the individual level.

PARTICIPANTS: Participants are recruited from individuals who completed the preceding community-based cross-sectional assessment of cardiovascular-kidney-metabolic syndrome and are eligible for the intervention phase. The same participants are followed throughout the study. Data are collected at three time points:

T0: baseline assessment before intervention initiation; T1: interim assessment at three months; T2: final assessment at six months. This design is intended to measure within-participant changes over time and to compare changes between the intervention and control groups.

SIX-MONTH INTERVENTION: The intervention group receives a combined program consisting of 10-hour time-restricted eating, health education, and behavioral support. The intervention is delivered continuously for six months.

• Phase 1 - Initiation and adaptation, weeks 1-2:

Participants select a fixed 10-hour daily eating window, preferably during daytime hours and compatible with their usual routine.

All energy-containing foods and beverages must be consumed within the registered eating window.

Outside the eating window, participants may consume only water or non-caloric beverages according to study instructions.

Participants are trained to identify caloric beverages, record the time of their first and last daily caloric intake, and manage common situations such as early hunger, changes in work schedules, family events, or eating outside the home.

The research team provides support to modify the eating window when necessary, and any modification is documented in the intervention record.

• Phase 2 - Maintenance and behavioral support, week 3 through month 6:

Participants continue the 10-hour daily eating window. Formal calorie counting and mandatory caloric restriction are not required. Participants are encouraged to avoid compensatory overeating and to maintain dietary practices that support cardiovascular, kidney, and metabolic health.

Educational content addresses CKM awareness, healthy diet, physical activity, weight management, tobacco and alcohol risk reduction, adequate sleep, recognition of warning symptoms, and long-term self-management.

Support is delivered through in-person counseling, small-group sessions, telephone calls, printed materials, and Zalo-based communication.

Participants are contacted during weeks 1 and 2, weekly during weeks 3 and 4, every two weeks during month 2, and are assessed in person at months 3 and 6.

During follow-up contacts, the study team records the first and last caloric intake, the number of adherent days, implementation difficulties, changes in health status, and any adverse symptoms.

A day is classified as adherent when all energy-containing foods and beverages are consumed within the participant's registered 10-hour eating window. Good adherence is defined as following the prescribed eating window on at least five days per week or on at least 80% of monitored days.

CONTROL GROUP: Participants in the control group continue their usual diet, daily activities, and routine community healthcare. They do not receive structured 10-hour time-restricted eating instructions, time-restricted eating monitoring diaries, or the intervention-specific behavioral support program. Control participants are assessed at T0, T1, and T2 using the same procedures and instruments as the intervention group.

SAFETY MONITORING: Participants are monitored throughout the intervention for tolerability and clinically relevant symptoms. If marked fatigue, dizziness, suspected hypoglycemia, or another concerning symptom occurs, the participant is advised to temporarily discontinue time-restricted eating and contact a healthcare provider. Participants who develop an indication for medication or specialist management are referred to an appropriate healthcare facility. The study intervention is not intended to replace medical evaluation, diagnosis, or physician-directed treatment.

ANALYSIS: The primary analysis follows the intention-to-treat principle, with participants analyzed according to their initially allocated cluster. Intervention effects are estimated using a Difference-in-Differences approach through the interaction between study group and time. The interaction term represents the change in the intervention group beyond the concurrent change observed in the control group.

Models appropriate for binary and continuous outcomes are used and adjusted for relevant baseline characteristics. The analysis accounts for the clustering of participants within residential areas. Additional per-protocol and adherence-based analyses are conducted to assess the consistency of the findings.

Inclusion criteria

• Age and residence Aged 30 to 79 years at enrollment. Has resided in the study area for at least 6 months and intends to remain in the area throughout the study period.
• Cardiovascular-kidney-metabolic status Classified as having stage 1 or stage 2 cardiovascular-kidney-metabolic syndrome according to the 2023 American Heart Association staging framework.

Assessed by a study physician as not currently having an indication for pharmacological treatment of a cardiovascular, kidney, or metabolic condition.

• Criteria indicating no current indication for pharmacological treatment. Participants must meet all of the following conditions:

No history or current diagnosis of clinical cardiovascular disease, diabetes mellitus, chronic kidney disease, or glomerular disease.

Serum albumin concentration of at least 3.5 g/dL, with no clinical or laboratory evidence suggestive of glomerular disease, severe liver disease, malnutrition, or another systemic condition requiring specialist evaluation or treatment.

No use during the previous 3 months of medications for cardiovascular, kidney, or metabolic conditions, including antihypertensive agents, glucose-lowering medications, lipid-lowering agents, anti-obesity medications, sodium-glucose cotransporter-2 inhibitors, glucagon-like peptide-1 receptor agonists, or medications with similar therapeutic purposes. Medication use is assessed through participant interview and review of prescriptions or medical records when available.

Mean blood pressure below 140/90 mmHg, measured using a standardized study protocol. For participants with a mean systolic blood pressure of 130-139 mmHg or a mean diastolic blood pressure of 80-89 mmHg, the estimated 10-year total cardiovascular disease risk calculated using the PREVENT equation must be below 7.5%.

Fasting plasma glucose below 126 mg/dL and glycated hemoglobin below 6.5%. Low-density lipoprotein cholesterol below 190 mg/dL. Estimated glomerular filtration rate of at least 60 mL/min/1.73 m² and urinary albumin-to-creatinine ratio below 30 mg/g.

Body mass index below 30 kg/m². Recruitment will preferentially approach overweight individuals with a body mass index of at least 23 kg/m², but this is not a mandatory eligibility requirement when all other criteria are met.

• Ability to participate in the intervention Has access to a smartphone and is able to use Zalo or an eating-time monitoring application.

Is able to complete an eating-time diary and attend scheduled health education, counseling, and assessment sessions.

• Informed consent and study commitment Voluntarily agrees to participate and provides written informed consent after receiving adequate study information.

Agrees to participate in the intervention and follow-up for 6 months, with assessments at baseline, 3 months, and 6 months

Exclusion criteria

Individuals with cardiovascular-kidney-metabolic syndrome stage 0, stage 3, or stage 4, or those with stage 1 or stage 2 who have a current physician-determined indication for pharmacological treatment according to applicable clinical guidelines, are excluded.