Pregnancy places a significant amount of extra strain on the body, necessitating an increased intake of food over the nine months to support both the pregnancy and the developing baby. Determining the exact number of additional calories needed to grow a baby reveals a wide range of estimates, varying from approximately 50,000 to nearly 85,000 extra calories throughout the entire duration of pregnancy. These figures represent additional calories beyond what would be required if the person were not pregnant.
For most women, an estimate of 50,000 calories is likely too low, with many requiring closer to 70,000 or more calories to meet the demands of pregnancy.
Scientists have used various methods to arrive at these estimates. A study published in 2024 in the journal Science developed a formula for calculating the calorific cost of pregnancy across different species. This research, led by Samuel Ginther during his doctoral studies at Monash University, calculated the reproductive cost for 81 species, ranging from microscopic aquatic animals to large mammals, including humans.
Research indicates that a pregnant person requires an additional 50,000 calories over a nine-month period compared to a non-pregnant individual. Of these extra calories, only about 4% are used directly for the growth of fetal cells. The majority of the calories support the physiological changes occurring in the pregnant person’s body throughout pregnancy.
The energy expenditure during pregnancy is fundamentally about all the body’s cells performing their functions continuously. During pregnancy, the body gains approximately 12 kilograms (26 pounds), consisting of new tissue and cells that need energy to perform their functions.
The energy requirements of pregnancy vary throughout the nine months. The first trimester requires the least additional energy, with an average healthy pregnant woman gaining about 0.6 ounces (18 grams) per day. This daily weight gain increases to 2.1 ounces (60 grams) during the second trimester and slightly decreases to 1.9 ounces (54 grams) per day in the final trimester. This gradual increase and subsequent slight decrease in weight gain reflect the changing energy demands as the pregnancy progresses.
The calories required to support the development of new tissue and grow a baby are likely higher than some studies suggest.
The significant contribution of this new research lies in its broad examination across various species, including reptiles, amphibians, fish, and mammals. However, earlier groundbreaking work by Nancy Butte has long established that the energy costs of human pregnancy are substantial, often exceeding 70,000 calories.
Nancy Butte, a professor of pediatrics and nutrition at Baylor College of Medicine, conducted a meta-analysis of several studies and found that the total energy cost of pregnancy amounts to approximately 77,675 calories. This includes an additional 90 calories per day during the first trimester, 287 calories per day in the second trimester, and 466 calories per day in the third trimester.
Another review published in 2019 in the journal Nutrients examined Butte’s work and other research, concluding that the calories needed during pregnancy ranged from 50 to 150 extra calories per day in the first trimester, 340 calories per day in the second trimester, and 452 calories per day in the third. This totals approximately 78,400 to 84,700 additional calories over the nine months of pregnancy.
Discrepancies in the estimated number of calories needed to grow a baby arise due to various factors. Energy costs can differ based on the size of the woman, with larger women likely having higher energy requirements than smaller women. Additionally, the amount of energy needed depends on physical activity levels and other physiological traits, such as metabolism. Despite these variations, most pregnancies likely require well over 70,000 extra calories to sustain, based on past research.
- ONLINE NEWS Arthur, A. (2024, June 26). How many extra calories does a person need during pregnancy? livescience.com. [livescience.com]
- JOURNAL Ginther, S. C., Cameron, H., White, C. R., & Marshall, D. J. (2024). Metabolic loads and the costs of metazoan reproduction. Science, 384(6697), 763–767. [Science]
- JOURNAL Butte, N. F., & King, J. C. (2005). Energy requirements during pregnancy and lactation. Public Health Nutrition, 8(7a), 1010–1027. [Public Health Nutrition]
APA 7: TWs Editor. (2024, June 29). Pregnancy’s Energy Needs: Calculation of Extra Calories. PerEXP Teamworks. [Online News Link]
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