In the animal kingdom, one of the most important energy investments is reproduction. Some animals, such as octopuses and cicadas, even forget their own needs to ensure the survival of the next generation. In the case of mammals, knowing the energy expenditure involved in the gestation process allows doctors to evaluate strategies that ensure a risk-free process for both the offspring and the mother.
There are mathematical models that allow estimating the energetic costs of reproduction. However, the figures from these first attempts could be very far from reality. A new study from Monash University in Australia has evaluated the amount of energy required to produce a calf. According to the results presented in the magazine Sciencethe real energy expenditure could be up to twenty times greater than previously thought.
The key to this misunderstanding, scientists admit, is simple: until now, the amount of energy used to produce a new being is determined only by the energy demand that changes after gestation begins. In other words, the estimate was calculated by how much additional energy the mother consumed each day since the start of pregnancy. This factor is known as “direct cost”. The Monash University study also takes into account the metabolic burden of carrying the fetus, identified as “indirect cost”.
Mammals pay the highest reproductive costs, and of these, 90% are indirect costs. Scientists compare this difference in energy expenditure with the preparation of a dish. It is not possible to calculate the energy investment only by the calories that a food will provide. It is necessary to take into account the fuel needed to cook it.
The energy needed to produce a baby
In humans, having a baby could be up to 24 times more costly, metabolically speaking, than the most widely accepted mathematical models had estimated. According to the authors of the research, the accepted energy expenditure was measured by calculating the metabolic rate during and after pregnancy. The 2004 baseline study said energy needs increased by only 340 kilocalories per day (kcal/d) for the second trimester, and 500 kcal/d for the third.
The research added up the indirect costs in humans. In total, almost 50,000 kilocalories are required for reproduction, and 96% of these pay for the costs of sustaining the baby for nine months.
Researchers are intrigued by the disparity in the cost of reproduction. Dustin Marshall, lead author of the study, infers that it may have been because the field did not initially have metrics that accounted for indirect expenses. “Most people have said that, in retrospect, it seems obvious that these costs should have existed, although no one realized they would be so high,” he said for Nature.
There are more and more scientific studies on the biological effects of pregnancy. In March 2024, for example, researchers found that the gestation period can increase a woman’s biological age by up to 2.5 years.
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