It has been unclear whether lactation facilitates postpartum weight loss, as the research findings have been mixed. There seem to be several factors associated with changes in postpartum BMI, such as race, income, education, and pre-pregnancy BMI.
The researchers for this study hypothesized that lactating mothers would have a different trajectory of postpartum BMI changes as compared to mothers who never lactated, and that it might depend on the individual’s pre-pregnancy BMI status and their eating behaviors.
The researchers evaluated BMI gain or loss during the first year postpartum among 208 women by evaluating their lactation history, pre-pregnancy BMI, various demographic factors, and their eating behavior (e.g. dietary restraint, disinhibition, and susceptibility to hunger). Among the 208 subjects, 96 lactated for at least 4.5 months, with 62% having lactated for 1 year, and 112 exclusively formula fed. All subjects were categorized into pre-pregnancy BMI categories as follows: Healthy (≤ 24.9 kg/m2), Overweight (25-29.9 kg/m2), and Obese (≥ 30.0 kg/m2).
They obtained BMI measurements from each subject 8-13 times during the first year postpartum.
They found that the effect of lactation on postpartum BMI depended on psychological eating behavior traits, with greater BMI loss among those with higher dietary restraint, higher disinhibition, and lower susceptibility to hunger.
The effect of lactation on change in postpartum BMI also depended on the pre-pregnancy BMI. For more information, see the question!