Pregnancy puts a lot of extra stress on the body, requiring you to eat more than usual over the course of nine months to support the pregnancy and the growing fetus.
According to studies, the number of calories a baby needs for growth ranges widely, from about 50,000 to about 85,000 additional calories over the entire pregnancy.
These are additional calories in addition to what a woman's body needs without pregnancy.
“I would say that for most women, 50,000 calories would be a significant underestimate,” said Herman Pontzer, a professor of evolutionary anthropology and global health at Duke University. “I think for the majority, it would be about 70,000, or even more.”
Scientists have arrived at these numbers using a variety of methods. For example, a 2024 study devised a formula to calculate the caloric cost of pregnancy for many species across the animal kingdom.
Researchers from Monash University have calculated the cost of reproduction for 81 species, ranging from microscopic and aquatic animals to large mammals, including humans.
“We calculated that a pregnant woman would need 50,000 more calories over a 9-month period than a comparable non-pregnant female over the same time period,” said Samuel Ginther, who led the study.
Of the additional 50,000 calories required during pregnancy, the team estimated that only 4% go directly to the growth of fetal cells.
Pontzer noted that the majority are instead used to support a pregnant woman's body as it changes throughout pregnancy.
Energy requirements during pregnancy change over the course of the nine months. The first three months consume the least amount of added energy, according to a 2005 article. During this time, the average weight gain for a healthy pregnant woman is about 18 grams per day.
This rises to 60 grams per day during the second trimester and then decreases slightly to 54 grams per day in the last trimester.
The calories needed to support this extra tissue and grow a full-term baby are likely to be higher than Genther and colleagues' study suggests, Pontzer said.
After reviewing several studies that calculated the total energy cost during pregnancy, Nancy Pott, professor of pediatrics and nutrition at Baylor College of Medicine, and her colleagues came up with an estimate of 77,675 calories — that's 90 extra calories per day in the first trimester, 287 extra calories per day in the second trimester, and 466 extra calories per day in the third trimester.
A review by a different group of researchers, published in 2019 in the journal Nutrients, that looked at Bott et al.'s study, concluded that pregnancy needs ranged from 50 to 150 additional calories per day in the first trimester, 340 calories per day in the second trimester, and 452 calories per day. Daily in the third and final trimester of pregnancy. This amounts to about 78,400 to 84,700 additional calories over the nine months.
Pontzer revealed that the differences in the number of calories calculated in the studies are difficult to consider given several factors, including the age and size of each woman as well as the extent of the pregnant woman's physical activity and other physiological characteristics, such as metabolism.
But, at least based on previous research, Pontzer said, most pregnancies probably require more than 70,000 extra calories.