Introduction:
Breastfeeding is the best way to nourish infants and young children. It also has many benefits for the mother and society. It has a positive effect on the mother's metabolism, insulin sensitivity, increased release of fats used in milk production and faster postpartum weight loss^1-3. This protects breastfeeding mothers from obesity and metabolic diseases, and lowers healthcare spending considerably^4,5.

Aim:
The aim of this study was to evaluate the effect of breastfeeding on the women’s body mass composition, the levels of selected hormones (leptin, ghrelin, adiponectin, resistin, and insulin), and weight loss during the 6-8 week postpartum period and 1 year after childbirth.

Materials and methods:
The study group included 60 women with a singleton pregnancy. The study was carried out 7-8 weeks after childbirth. The women were subjected to body weight measurement, and body composition analysis performed using a professional body composition analyzer TANITA DC-430 S MA. Waist circumference and subcutaneous fat was measured. Blood for laboratory tests was taken in the morning, on an empty stomach. The same tests were performed 1 year after childbirth. The research was conducted from January 2017 to December 2019. The Shapiro-Wilk test was used to assess the normality of the distribution. The evaluation of data in two groups was performed using the Mann-Whitney U test. A comparison of the variables six weeks postpartum and one year postpartum was performed using the Wilcoxon test. The analysis assumed a significance level of 0.05. Thus, all p-values below 0.05 were interpreted as indicating significant relationships.

Results:
Exclusive breastfeeding had a more significant impact on postpartum weight loss 6-8 weeks after childbirth, but not one year after childbirth (partial breastfeeding). One year after delivery, all women had significantly lower lean body mass (breastfeeding p=0.026; non-breastfeeding p=0.027) and smaller waist circumference (breastfeeding and non-breastfeeding p<0.001), but only breastfeeding women had lower BMI (p=0.0014), lower subcutaneous adipose tissue thickness (p<0.001) and lower obesity risk (p=0.016). Higher insulin and ghrelin levels were also observed in both breastfeeding and non-breastfeeding women (p<0.001), but lower resistin levels were observed in non-breastfeeding women (p=0.004).

Conclusions:
Breastfeeding affected women's weight loss 6-7 weeks postpartum, but not one year postpartum, compared to non-breastfeeding women. However, it was observed that women who breastfed one year postpartum had a statistically significant lower BMI, less subcutaneous fat, and lower obesity risk and resistin levels. Further research is needed to determine effect of breastfeeding on women’s weight loss after childbirth and body mass composition.