The PKU-FeeD trial is a cluster-randomized controlled trial conducted in Jinan, Shandong Province, China. This study aims to: 1) Develop and evaluate a digital health-assisted, multidisciplinary intervention for preschool children with obesity, assessing its effectiveness and cost-effectiveness. 2) Investigate how lifestyle-based interventions influence the composition and function of the gut microbiota in obese preschoolers, and elucidate the mechanisms by which these interventions may modulate gut microbiota to affect obesity-related metabolic phenotypes.

Childhood obesity has become a global public health challenge, and early prevention and management are crucial to curbing its epidemic. However, compared to school-aged children, evidence on effective obesity interventions for preschoolers remains limited and inconsistent. While preventive approaches may have broader population-level implications, targeted management interventions may be more cost-effective in settings with lower obesity prevalence but rising trends, providing foundational evidence for future preventive strategies.

The gut microbiota plays a key role in host energy metabolism and metabolic homeostasis, and its dysbiosis is strongly linked to obesity. Diet and physical activity, as core components of lifestyle interventions, may significantly shape gut microbial ecology, potentially influencing host metabolism and obesity-related outcomes. However, due to challenges in sample collection, existing studies on gut microbiota in children are scarce, with small sample sizes, and few intervention studies have established causal relationships. The interplay between healthy lifestyle interventions, gut microbiota, and childhood obesity remains understudied, and the underlying mechanisms require further exploration. Thus, this trial seeks to: 1) determine effectiveness of a digital health-supported, comprehensive intervention for preschool obesity management. 2) Elucidate causal relationships between dietary behaviors, gut microbiota, and obesity in preschoolers.

Inclusion Criteria:

• The child's primary caregivers can proficiently use smart phones.
• Child is expected to remain in the same kindergarten for at least one year.
• No use of antibiotics or probiotic supplements, no acute stress events (e.g., trauma or severe infection), gastrointestinal symptoms (e.g., abdominal pain, constipation, diarrhea), or vaccinations within the 3 months prior to stool sample collection.
• Parents voluntarily agree to participate in the study and provide written informed consent.

Exclusion Criteria:

• Obesity caused by genetic factors, diseases (e.g., endocrine disorders, central nervous system damage), or medication use.
• History of major organ diseases, including cardiovascular, pulmonary, hepatic, or renal conditions (e.g., heart disease, hypertension, asthma).
• Children following special diets (e.g., vegetarians).
• Children with pathological eating disorders or medical conditions that limit physical activity.

Individual participant data (IPD) will not be shared publicly due to ethical considerations. In accordance with the study's ethical approval and informed consent procedures, the data contain potentially sensitive personal health information and are protected to ensure participant confidentiality and privacy. Data access is therefore restricted to authorized research personnel only and cannot be made publicly available.

Randomization will be performed after the baseline survey. The assessors measuring childrens' health indicators will be blinded at follow-up phases.