The old wives tale that "eating for two" is important during pregnancy has been disproven by a team of scientists.

Before the experiment, experts thought that a pregnant woman's appetite increases due to the energy requirements demanded by the baby in her womb. But researchers from the Clinical Sciences Centre at the Imperial College in London said that this is apparently not the case, for during pregnancy, a woman's hormones develop to absorb more energy from the same amount of food she eats.

The scientists conducted their experiment on fruit flies to study the biology of a pregnant woman. "Many of the fly genes that we studied exist in humans. Flies also utilize and store fat like we do, and their metabolism is controlled by similar hormones," said Jake Jacobson of the research team, via a press release.

They found out that a fly's "juvenile hormone," released instantly after fertilization, causes a growth in the intestines that also triggers the body to expand its ability to store more fat.  This same biological event also happens in a pregnant woman's body.

"We normally think of our internal organs as being a fixed size, but the fact is that they are not. They can grow and change, and we show that this is important for making babies," said Irene Miguel-Aliaga, the head of the study, in the same press release.

"Previous studies have shown that eating for two during early pregnancy is unnecessary. Our research suggests that this is because the digestive system is already anticipating the demands that the growing baby will place upon our body," she further added.

The researchers believe that their findings also explain why a pregnant woman often have problems with weight long after giving birth, as her intestines continue to be enlarged. Thus, her body could continue to take in more calories from the food she eats.

Meanwhile, eating a healthy and balanced diet is more important than eating for two, according to nutritionist Alison Tedstone. "You don't need to eat for two, even if you are expecting twins or triplets. Evidence shows that expectant mothers may need to eat more in the last few months of the pregnancy, around 200 extra calories a day," she said via Independent

The researchers are hoping to do more studies on this findings in humans next.

The findings were published in the journal eLife.