Eating for two while you’re pregnant could increase risk of obesity

Pregnancy causes hormone-driven growth of the intestines that allows more energy to be extracted from the same amount of food, new research by the Medical Research Council (MRC) Clinical Sciences Centre in London suggests.

The discovery, made in fruit flies, could explain why some women struggle to lose weight after giving birth, say scientists.

They point out that the same metabolic responses seen in fruit flies should also occur in humans.

A “juvenile hormone” in the flies was found to trigger growth of the intestines soon after mating and also stimulated fat storage. The hormone acted in a similar way to human thyroid hormones, which regulate the body’s energy demands.

Lead scientist Dr Irene Miguel-Aliaga 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.”

Co-author Dr Jake Jacobson, also from 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.”

The metabolic changes appeared to have a role in determining fertility, said the scientists writing in the journal eLife. Female flies produced fewer eggs when the juvenile hormone was prevented from enlarging their intestines.

Human mothers are thought to experience similar intestinal growth after becoming pregnant.

If her hormone levels fail to normalise after birth, a mother’s enlarged intestine might continue to absorb more calories, said the researchers.

Dr Joe McNamara, head of population and systems medicine at the MRC, said: “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.”

Current NHS Choice advice warns that while women may feel hungrier than usual during pregnancy, there is no need to “eat for two”.

Leeds-based registered nutritional therapist Elizabeth Cooper, a specialist in fertility and pregnancy nutrition, works across Yorkshire and has advised midwives on diet during pregnancy.

She told The Yorkshire Post: “It’s not so much about how much you eat, but what you eat, during pregnancy that counts. It’s vital to eat the right amount of protein, the right types of carbohydrate and beneficial fats. While current research recommends eating slightly more calories in the second trimester, and slightly more again in the third, it is important to eat healthily and ensure you get all the right nutrients.

“Pregnancy certainly isn’t an excuse to eat for two.”