Breastfeeding duration was independently associated with lower weight, weight retention, body fat, visceral adipose tissue, lean mass, CRP, insulin resistance (Homeostatic Model Assessment for Insulin Resistance), and insulin secretion (Homeostatic Model Assessment of β-cell index) at 1 year postpartum (all p≤0.04) after adjusting for confounders. This evidence concerns the gene INS and Insulin resistance.