Is it true that breastfeeding helps loose weight which one has gained during pregnancy?

I breastfed both of my kids until they were 2.5 years old. I think breastfeeding really helped me to loose my weight very fast, I was able to get back my pre-pregnancy weight 3-4 months post delivery. However, I did see some of my friends who were breastfeeding fully gained weight instead as they tend to eat more during breastfeeding. Thus, I think it depends on individual's diets also.