Expanded gut (blue) and stored fat (orange) to meet energy demands of eggs in the fruit fly.
Image credit: MRC - Clinical Sciences Centre
The findings explain why it is not necessary to "eat for two" in early pregnancy, says the international team of researchers, including members from Imperial College London in the UK.
They note that the digestive system enlarges and adapts so it can absorb more energy from the same amount of food.
The study may also explain why some women find it hard to lose weight after giving birth.
Previous research has already shown that in mammals, a pregnant female's intestines grow during pregnancy. But until the new findings - published in the journal eLife - it was not clear why this happens.
The study is the first to show that a hormone released after fertilization in fruit flies causes dramatic growth of the intestines and stimulates increased fat storage.
Fruit flies are a useful lab model for exploring human biology, as co-author Dr. Jake Jacobson, from the Medical Research Council's (MRC's) Clinical Sciences Centre in London, explains:
"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."
Hormone instructs gut to prepare for increased energy demand
At first, scientists thought that a pregnant woman's appetite changed as her baby's demand for energy increased.
But the new study finds that a hormone called "juvenile hormone" tells the intestine to adapt and prepare to meet the anticipated energy demands of fertilized eggs.
The hormone - which behaves in a similar way to the human thyroid hormones that regulate the body's energy demands - also changes fat metabolism.
In fruit flies, the levels of the hormone begin to rise soon after mating, and also appear to influence fertility. If the hormone is prevented from changing the gut, the flies produce fewer eggs.
The researchers believe their findings may also explain why a woman may struggle to regain her normal weight after giving birth. Her intestines may remain enlarged, and her body may continue to extract more calories from her food.
While the findings have yet to be reproduced in humans, they do provide valuable insights into human physiology, says Dr. Joe McNamara, head of population and systems medicine at the MRC, who concludes:
"This research points to a new scientific explanation why eating for two during pregnancy is not necessary, and may even be harmful, as a growing body of evidence indicates that a mother's diet can impact a child's propensity to be obese in later life."
Meanwhile, Medical News Today recently reported a study that followed 10,000 men for 20 years and found new dads put on weight, while childless counterparts lose weight.
Writing in the American Journal of Men's Health, researchers from Northwestern University Feinberg School of Medicine in Chicago, IL, explain how they found this to be true even of men who did not live with their children.