Pregnant women already know that carrying and nurturing a baby is hard work, and anyone who has given birth knows that the energy drain is real, and that it’s not just your uterus that’s working, your whole body feels it.
Now, there’s new research showing just how much energy it takes to give birth to a baby, and it’s no wonder the results show that the energy required to give birth to a baby is much greater than previously estimated.
A study published in Science magazine found that over the course of a typical nine-month pregnancy, an average woman would need to eat about 50,000 calories to carry a pregnancy to term. For comparison, that’s the equivalent of eating 18 jars of Jif peanut butter (16-ounce bottles of the creamy kind).
Australian researchers looked at data from thousands of existing studies of the reproductive health of dozens of organisms. Their cumulative work across 81 species found that the energy metabolic rate required to produce offspring is about 10 times higher than previously estimated.
Until now, scientists have only focused on the amount of energy the uterus uses to produce a baby.
“We had a hunch that this wasn’t the whole story, so we started measuring energy expenditure during pregnancy,” said Samuel Ginther, lead author of the study and a postdoctoral researcher in biological sciences at Monash University. “If researchers could measure the energy content of the offspring, they could get an idea of the total energy spent on reproduction.”
Pregnancy research findings
Research includes studying the reproductive energy ratios of tiny insects, reptiles, warm-blooded mammals such as goats and deer, and humans. Researchers have found that an animal’s size directly affects the amount of energy it needs to reproduce.
Naturally, the smaller the animal, the fewer calories it consumes. Again, this varies by species. Species that produce a placenta, like humans, were found to have the highest indirect costs of pregnancy, at around 96%.
“Across mammals, most of the energy invested in reproduction is ‘evaporated’ as metabolic heat, and only 10% of the total reproductive energy is actually invested in the offspring,” explains Dr Ginther. “Mammals expend so much energy on reproduction before the offspring are born that it may explain why they take such good care of their young after they are born; the sunk costs are much higher.”
Humans have a longer gestation period than many other mammals, which means higher costs. Dr. Ginther also points out individual differences, saying, “recommended energy intakes are completely different for each individual pregnant woman,” and may be lower in the first trimester and higher in the second trimester.
Milk production and lactation also affect energy expenditure. “Milk is very energy dense and females expend a lot of energy to produce milk,” he explains. “We found that the energy required to produce milk exceeds the energy content of the milk itself.”
“When you take into account the costs of both pregnancy and lactation, the cost of the child itself is only one-twentieth of the total cost of reproduction, and this is an even smaller portion of the total energy expended during reproduction,” Dr Ginther added.
Should pregnant women eat more?
The study concluded that pregnant women, on average, consume about 183 more calories per day than non-pregnant women.
But that doesn’t mean pregnant women should eat a Snickers bar every day during their pregnancy, says Dr. Melane Chuang, chair of obstetrics and gynecology at NYU Langone Hospital in Brooklyn, who was not involved in the study.
“During pregnancy, aim to eat 1,800 calories a day in the first trimester, then add an additional 340 calories in the second trimester and 450 calories in the third trimester,” she recommends.
When it comes to breastfeeding, the American College of Obstetricians and Gynecologists (ACOG) says breastfeeding requires approximately 450 to 500 extra calories per day. According to the Academy of Nutrition and Dietetics, two-thirds of these calories should come from all five food groups. The remaining calories come from weight gain during pregnancy.
Healthy habits, including sleep, are also important. Getting a good night’s sleep can be difficult for pregnant women, but Dr Chuang says doing some light exercise, like walking before bed, can help.
“Avoiding naps and getting enough sleep can help naturally reset your circadian rhythm to a more predictable schedule,” she adds.
In general, a balanced diet that includes colorful fruits and vegetables, lean meats, and regular exercise are recommended for good health during and after pregnancy. Staying hydrated and taking vitamin supplements are important to get minerals that you cannot get from food.
Most people who have been pregnant probably don’t need comprehensive studies to back up just how exhausting childbirth can be, but some hard statistics would certainly be valuable.
