Nutrition and pregnancy: Scientists challenge ‘eat for two’ myth

28 Jul 2015

A new study, published today in eLife, has shown that women may not need to ‘eat for two’ during pregnancy because the body could adapt to absorb more energy from the same amount of food.

The findings may also help to explain why some women struggle to lose weight after giving birth.

Previous studies have shown that the intestines of many mammals grow during pregnancy, but until now it has not been clear exactly why this happens. Researchers at the Medical Research Council’s Clinical Sciences Centre, based at Imperial College London, are the first to show that a hormone released after fertilisation in fruit flies, which have similar metabolic responses to humans, causes the intestine to grow dramatically and stimulate the mother’s body to store more fat.

This latest study has shown that a fly hormone, called ‘juvenile hormone’, triggers the changes to the intestine and fat metabolism. Juvenile hormone acts in a similar way to human thyroid hormones, which regulate the body’s energy demands.

Scientists had previously thought that a woman’s appetite changed in response to the baby’s increasing demands for energy. However, MRC researchers found that levels of juvenile hormone begin to rise in female flies surprisingly early, in fact immediately after mating. This tells the intestine to rapidly adapt so that it is prepared to meet the energy needs of the fertilised eggs.

The changes in metabolism also appear to have a role in determining fertility. If the juvenile hormone is prevented from changing the intestine, the flies produce fewer eggs. It is this hormone that is key to the fly producing as many healthy eggs as possible.

The study also suggests that, in people, if hormone levels fail return to normal after birth, a mother’s intestine may remain abnormally large, so she will continue to extract extra energy from her food.

Dr Irene Miguel-Aliaga, head of the Gut Signalling and Metabolism Group at the MRC Clinical Sciences Centre, and lead author of the study, said: “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.”

Dr Jake Jacobson, co-author of the study, and also based at the MRC Clinical Sciences Centre, added: “Many of the fly genes that we studied exist in humans. Flies also utilise and store fat like we do, and their metabolism is controlled by similar hormones.

“Some women find it difficult to lose weight after pregnancy, and we may now have found a biological reason for this.”

Dr Joe McNamara, Head of Population and Systems Medicine at the MRC, added: “Studies in fruit flies have been very valuable in providing insights into human physiology. 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.

“The important next step will be to reproduce these findings in humans.”