Human pregnancy is easy to quantify. Ideally it lasts a good nine months, i.e. around 280 days. There are times at which we now know very precisely when, for example, the fetal heartbeat is most likely to be heard on the ultrasound for the first time. There are guidelines for how much weight a mother will gain before giving birth. What was not known exactly until now was how much energy the human body uses in the period from fertilization to birth. Pregnancy requires two forms of energy investment. Firstly, the energy that goes directly to the offspring. And then the energy that the mother uses for the growing child. The second value in particular has so far been largely unexplored.
In a new study, evolutionary biologists at Monash University in Clayton, Australia, have found surprising results. According to the study now published in the scientific magazine “Science”, a woman consumes around 50,000 calories during pregnancy. According to a calculation by the New York Times, this is equivalent to about 50 cups of Ben and Jerry’s Cherry Carcia ice cream. And above all, it is significantly more than was previously assumed.
The high value surprised everyone. Also because it was previously assumed that most of the energy was stored in the fetus. But this value is almost negligible at just four percent. Dustin Marshall, one of the researchers involved in the study, says: “The baby is basically just the number rounded up, it took us some time to understand that.”
We are currently in a phase in which there are many new discoveries related to human metabolism. The examination methods have become much more precise in recent years. At the same time, interest in the internal processes in the body has also increased significantly. The evolutionary biologist Marshall is one of the leading scientists in this field of research.
As warm-blooded animals, humans face all sorts of challenges. For example, in order to keep the body temperature stable, a constant supply of energy in the form of food is required. It’s like an oven that you have to keep running. Of course, this especially applies to pregnancy. Because in these months women are faced with the big task of also having to care for a growing organism.
The new study that is now available provides reliable figures for the first time. All previous ones were based solely on estimates – and were therefore inaccurate. For a long time, for example, the rule of thumb among scientists was that around 20 percent of energy was stored in the tissue of the fetus. An assumption that has now proven to be completely inflated.
Marshall and his team calculated the metabolic values not only for humans, but for a total of 81 species – from insects to snakes to goats. The body size of an animal has the greatest influence on the number. Microscopically small organisms, for example, only need a millionth of a calorie to reproduce. A white-tailed deer, on the other hand, consumes more than 120,000 calories for a fawn. Snakes that lay eggs and therefore do not carry the offspring in their bodies for a long time also consume less.
Above all, the finding that around 96 percent of human energy is consumed by the mother is considered revolutionary. Why this is the case still needs to be clarified in further studies. It is currently assumed that living beings with a placenta in particular have to do more. In addition, people stay pregnant for longer than average periods compared to everyone else. Marshall raises concerns that the high energy requirements could also be a reason why female mammals put so much effort into their offspring after birth. They want to make sure that their large investment is worth it. He says: “They already had so many hidden costs for the project.”