Breastfeeding and healthy infant diets may help lower obesity risk by age nine

By Tarun Sai LomteReviewed by Susha Cheriyedath, M.Sc.Feb 11 2026

Early feeding choices may shape long-term weight outcomes, but new research shows the relationship is complex and influenced by multiple factors beyond infancy.

Study: Infant Diet Is Associated With BMI Later in Childhood: A Nation-Wide Mother-Child Cohort Study in Iceland (ICE-MCH). Image Credit: MNStudio / Shutterstock

In a recent study published in the journal Maternal & Child Nutrition, researchers investigated the associations between infant nutrition and the risk of childhood obesity and overweight.

Obesity and overweight are increasing worldwide; obesity prevalence has quadrupled in adolescents and children and doubled in adults between 1990 and 2022. Childhood obesity has been associated with impaired glucose tolerance, insulin resistance, and higher cardiometabolic risk. Obesity in childhood can also elevate the risk of noncommunicable diseases later in life.

Infant nutrition undergoes significant changes during the first year of life as infants transition from breast milk to family foods. As such, adequate nutrition during this period is critical for both short- and long-term health. Composite indices that evaluate the alignment of infant diets with nutritional guidelines help assess the relationship between early-life nutrition and subsequent health and growth outcomes.

However, few studies have developed composite indices that integrate breastfeeding and complementary feeding practices during the first year and investigated their associations with the risk of obesity or overweight. Previously, the authors developed the infant diet score (IDS), a comprehensive metric to assess alignment with infant nutrition guidelines.

Study Design and Infant Diet Score Assessment

In the present study, researchers examined the association between IDS and the risk of childhood obesity or overweight. They used data on all children born in Iceland between 2009 and 2015 from three sources: the Saga Maternal and Child Health Database, the Ískrá School Health Care Registry, and the Icelandic Medical Birth Registry.

Nutritional data were collected at healthcare screenings at multiple time points during the first year of life. The IDS was calculated based on these dietary records, which comprised six components: duration of 1) exclusive breastfeeding or 2) any breastfeeding, age of introduction of 3) cow’s milk or 4) semi-solid foods, 5) food group variety, and 6) vitamin D supplementation.

Children were stratified into quintiles based on their IDS. Body mass index (BMI) z-scores were computed and used to classify weight status. Children aged six and nine years were deemed overweight if their BMI z-scores were +1 to +2 and obese if > +2. Children aged 2.5 and 4 years were considered obese/overweight if the z-score was > +2.

Group differences were examined using the chi-squared test and the two-sample t-test. Logistic regression was performed to assess the association between IDS quintiles and the odds of obesity and overweight at ages 2.5, 4, 6, and 9 years. One model was unadjusted, whereas the other was adjusted for residency and birth weight. Model 3 was additionally adjusted for parental cohabitation and for maternal pre-pregnancy age, BMI, and employment status.

Associations Between IDS Quintiles and Weight Outcomes

The study included 12,848 children, with a mean birth length of 51.2 cm and birth weight of 3.64 kg. About 51% were boys, and 93% were born at term. On average, maternal age was 29.5 years, and pre-pregnancy BMI was 26.2 kg/m². About 7% and 4% of children were classified as obese/overweight at 2.5 and 4 years, respectively. At age six years, 19.1% were overweight, and 8% were obese. At nine years, 23% were overweight, and 14.6% were obese.

Children in the two lowest IDS quintiles, corresponding to lower-quintile thresholds of approximately 2.52 to 3.23, had a higher risk of obesity at ages six and nine years than those in the highest quintile (IDS > 4.08). Children in quintile 3 (IDS 3.24 to 3.67) also had a higher risk, although this association was not observed in the fully adjusted model 3. Low IDS quintiles showed no consistent associations with obesity/overweight at ages 2.5 or 4 years, except for quintile 2, which exhibited increased odds at age 2.5 years, highlighting age-specific variability and inconsistency in observed associations.

Interpretation and Public Health Implications

Overall, poorer alignment with infant nutrition guidelines was associated with a higher likelihood of obesity at ages 6 and 9 years. Specifically, children in the two lowest quintiles had 37% to 58% greater odds of obesity compared to those in higher quintiles. At age 2.5 years, children in quintile 2 had higher odds of obesity/overweight.

There were no associations between IDS quintiles and overweight at ages 6 and 9 years, or obesity/overweight at age 4 years. Aligning with nutrition guidelines in infancy may therefore be linked with healthier later weight patterns, although causal effects cannot be inferred from this observational cohort study. Additional influences later in childhood, including environmental, behavioral, and socioeconomic factors, likely contribute to obesity risk and may partly explain observed associations. Because this was a registry-based observational study, residual confounding, missing dietary data, and unmeasured childhood factors may also influence the risk of obesity. Public health initiatives may aim to improve diet quality in infancy through targeted education and support.