Now scientists have foundÂ it can help them to stay slimÂ for decades.
They discovered that women who breastfed their babies even for a few months after the birth were less likely to be obese 30 years later.
The Oxford University researchers worked out that for every six months a woman gives her baby breast milk, she loses around 2lb â€“ depending on her initial weight and height.
Although this may not sound much, the academics claim that it could help prevent thousands of deaths from cancer, heart problems and other illnesses related to obesity.
Doctors and midwives are growing increasingly concerned that many women are becoming obese by gaining weight during pregnancy, which they never manage to shift after the birth.
If they go on to have several children, they will become progressively fatter with every pregnancy.