According to a new study women should not put themselves under too much pressure straight away.
Now, celebrities have started a new craze among new mums, shedding baby weight immediately after giving birth.
Experts from German Institute for Quality and Efficiency in Health Care (IQWiG) have revealed that overdoing early weight loss attempts could have a negative impact on breastfeeding.
They said that weight gain during pregnancy is not only normal, it is necessary.
The mother's body has to nourish the growing baby. Her body needs to take on more fluid to support the extra circulation the placenta and baby need. Some of this added weight will usually be lost as soon as the baby is born.
"Often, the extra effort women have to make to look after a new baby and breastfeed after giving birth means the kilos just melt away without effort," according to the Institute's Director, Professor Peter Sawicki.
"But for about half of all women, the weight will not go away as quickly," her added.
However, eating for two in pregnancy can cause problems if you are overweight.
Recent studies have revealed that women who have become overweight or more overweight during pregnancy have a higher chance of ongoing weight problems if they are not back to a normal weight within six months or a year after having a baby.
"Avoiding weight problems after birth means already being careful about balanced and healthy eating during pregnancy," said Professor Sawicki.
"It is not a good idea to 'eat for two' in pregnancy and forget about your weight until after the baby is born if you are at all overweight or prone to overweight already.
"Women need to eat well enough for themselves and their baby, but pregnancy is not a time to overeat," he added.
Exercise is important when people are overweight, but after pregnancy, a lot of exercise does not necessarily help a great deal.
The evidence shows that a balanced diet helps "with or without extra exercise".