Toddlerhood (ages 2-3) is a critical window when the gut microbiome is still developing and eating habits are being established. Yet, many Canadian toddlers eat diets high in sugar and salt, which may affect long-term health. This study will test whether a MED diet can improve dietary inflammation, gut health, and body composition in toddlers and whether a tailored nutrition education program for parents can help families maintain healthy eating patterns.

In this study, toddlers will be randomly assigned to a 3-week MED diet or their usual diet. Families in the MED diet group will receive free meal boxes for the 3 weeks, plus guidance from a nutrition researcher through a structured education program. The standard diet group will continue their regular diet with general nutrition advice. Researchers will collect dietary information, body composition assessments, and stool samples to measure gut microbiome composition and metabolites.

This first study of a controlled diet intervention in toddlers, combining behavioral support, high-quality food provision, and advanced gut microbiome analysis, will help understand how early diet shapes lifelong eating habits and health, guiding public health strategies and precision nutrition approaches to prevent chronic disease from early life.

The gut microbiome, central to immune and metabolic regulation, is highly responsive to dietary inputs. In adults, interventions like the Mediterranean (MED) diet rapidly increase beneficial microbial taxa and anti-inflammatory metabolites. Toddlerhood (24-36 months) represents a critical window when the gut microbiome continues to stabilize and dietary patterns become established. Yet, the diets of Canadian toddlers remain suboptimal, often dominated by high-sodium, high-sugar foods.

The aims of this study are to determine the effects of a (i) MED diet food-provision intervention on dietary inflammation, the gut microbiome and metabolites, and body composition of toddlers aged 2-3 years at 3 weeks and (ii) comprehensive, tailored nutrition education program, with or without food provision, in promoting adherence to the prescribed diets at 3 weeks and 3 months post-baseline.

This parallel randomized controlled trial at the University of New Brunswick will randomized parent-toddler dyads to either a 3-week MED diet or a Standard diet. Families in the MED diet group will receive free food provision and a tailored, theory-driven parental nutrition program. They will be provided with packaged food boxes including three meals (breakfast/lunch/dinner) and two snacks for each day of the week. Meals will be developed and prepared by a registered dietitian in UNB's metabolic kitchen under sterile conditions and delivered to parents in coolers. Families in the Standard diet group will continue to consume their regular diet and receive general nutrition education. Both groups will be initially screened using the KIDMED 2.0 to ensure they do not already adopt a MED diet. The nutrition education programs will be delivered over a 3-month period from baseline.

The primary outcome is the between-group difference in Children's Dietary Inflammatory Index scores at 3 weeks, diet adherence, and program satisfaction. Secondary outcomes include microbial diversity, taxa, metabolite profiles, body composition, blood pressure, and additional feeding metrics. Assessments will occur at baseline, 3 weeks, and 3 months. Stool samples will be analyzed using shallow shotgun metagenomics and metabolomics to assess microbial taxa, SCFAs, and other metabolites. Statistical analyses, conducted in R, will include t-tests, PERMANOVA, and mediation models.

The toddler years are a pivotal time for shaping lifelong eating habits and health outcomes, persisting into adolescence and adulthood. This is the first trial to test a controlled dietary intervention in toddlers, integrating behavioural theory and patient-oriented research. It will bring together a multifaceted team, combining expertise in nutrition and dietetics with cutting-edge knowledge in genomics for gut microbiome analysis. Findings will inform public health strategies and advance precision nutrition to reduce chronic disease risk from early life.

Inclusion Criteria:

• Parent is ≥19 years of age.
• Carried a singleton pregnancy.
• Delivered at term (≥37 weeks gestation).
• Delivered vaginally or by cesarean section.
• Infant was born with a birth weight between 2,500 g and 4,500 g.
• Toddler is between 24 and 36 months of age at enrollment.
• Parent is able to communicate in English.
• Parent is willing to adhere to the Mediterranean diet for their toddler for 3 weeks.
• Parent is willing to participate in a nutrition education program for 3 months.
• Parent is willing to complete all measurements and provide a stool sample from their toddler.

Exclusion Criteria:

• Toddler has food allergies or dietary restrictions (e.g., gluten-free) that make it difficult to follow a Mediterranean diet.
• Toddler is at high risk for food allergies (e.g., strong family history of multiple food allergies common to the Mediterranean diet).
• Toddler is already following a Mediterranean diet.
• Toddler has had recent or active consumption of antibiotics, probiotics, or prebiotic drops.
• Toddler has an active acute illness, such as fever, diarrhea, or constipation.
• Toddler was born with a congenital illness or malformation that could affect diet, inflammation, gut health, or body composition.
• Toddler is currently breastfeeding, formula-feeding, or combination feeding.