ROTTERDAM, Netherlands — A major review published Nov. 19 in Obesity Reviews found that higher maternal weight before pregnancy, maternal smoking during pregnancy and not breastfeeding rank among seven early-life factors most consistently linked to childhood obesity. The authors say the evidence points to the first 1,000 days—from preconception through infancy—as a critical window for prevention before growth patterns become harder to change, Dec. 28, 2025.
The systematic review assessed 177 publications tracking nearly 1.88 million children across 37 countries and weighed the strength and practical “actionability” of dozens of candidate risk factors. While the evidence was generally rated moderate—reflecting common limits such as imperfect measurement and confounding—the review’s top signals were strikingly consistent across studies.
Early-life risks for childhood obesity
Across the evidence base, the strongest early-life risk factors for childhood obesity clustered around pregnancy, birth size and infant growth:
Higher maternal prepregnancy weight
Higher gestational weight gain
Maternal smoking during pregnancy
Higher birth weight
Being large for gestational age at birth (larger than expected for the pregnancy’s length)
No breastfeeding
Higher infant weight gain
Several of these factors can be influenced by clinical support and public health policy, but the authors stress they are not a guarantee of outcomes for any one child. Experts who study childhood obesity also caution against placing the burden solely on families: access to prenatal care, smoking-cessation support, paid leave, lactation counseling and affordable healthy food can shape these risks long before a child reaches school age.
Why the first 1,000 days has become a focal point
The review lands amid rising concern about the scale of childhood obesity globally. The World Health Organization estimates 35 million children younger than 5 were overweight in 2024, and the share of children and teens with overweight (including obesity) has climbed sharply over recent decades, according to its latest obesity and overweight fact sheet.
In the United States, the Centers for Disease Control and Prevention reports that obesity affected 19.7% of people ages 2-19 in data collected from 2017 through March 2020, as outlined in its childhood obesity facts page. Researchers say earlier prevention could reduce the need for more intensive interventions later in childhood, when unhealthy patterns can be more entrenched.
A long-running signal, now consolidated
Many of the review’s “top seven” are not new. A large U.K. cohort study published in 2005 found childhood obesity at age 7 was associated with higher birth weight and maternal smoking during pregnancy, among other factors, in a BMJ cohort analysis. A 2010 synthesis of systematic reviews also highlighted maternal smoking, rapid infant growth and short or no breastfeeding as recurring early-life predictors in a review-of-reviews. And a 2012 systematic review concluded there was strong evidence linking rapid infant weight gain, high birth weight, maternal prepregnancy overweight and smoking in pregnancy to higher later risk in a meta-analysis of infancy-identifiable risks.
For clinicians, the new review’s value is less about naming a single culprit than about prioritizing where help is most likely to matter early—especially around healthy prepregnancy weight, appropriate pregnancy weight gain, smoke-free pregnancies and close attention to infant growth patterns. For families, health agencies continue to emphasize support for feeding and bonding early in life; WHO guidance notes that breastfeeding should begin within the first hour after birth and be exclusive for the first six months, with continued breastfeeding alongside complementary foods thereafter.
