That the present is understood much better if we understand the past is a dogma that is usually repeated in the humanities and social sciences. However, fortunately the need to investigate more and more interdisciplinary has made this dogma also apply to other scientific branches. Un buen ejemplo lo encontramos en estudios que, tratando de conocer mejor la fisiología deportiva y la salud actual, 1,2 evalúan adaptaciones que pudieron ocurrir en poblaciones del pasado 3 y que podrían estar detrás de por qué enfermamos hoy en día. 4.5 After all, we are the product of millions of years of evolution, and disciplines such as human evolution and biological anthropology can contribute greatly to the current study of nutrition, physiology and health in general .
Recently I have had the privilege of attending a seminar taught by Professor Herman Pontzer (renowned researcher in Human Metabolism and Evolution) at the Polytechnic Institute and State University of Virginia (Virginia Tech, USA), where I work as a postdoctoral researcher. In this seminar, to the astonishment of an audience mostly without training in evolutionary biology, Professor Pontzer commented that " life is summarized in obtaining energy and transforming it into babies, and that natural selection rewards those who do so in the most efficient way . " I could not help smiling when I saw the reaction of my colleagues, most of them with a long career as researchers in physiology and metabolism. The concepts behind this statement are the basis of my research career, but for the rest of my colleagues, an issue that many wonder: what have to do with human evolution and current metabolism? Although Professor Pontzer's phrase can be simplistic, it is an excellent example that, to understand metabolism in current populations, we must seek the origin and evolutionary sense of certain adaptations .
Using an evolutionary perspective helps us, therefore, to better understand what makes us unique as humans . And if we highlight, it is in our ability to multiply , regardless of difficulties, famines, wars and pandemics through which we have historically passed.
Video . Human population through times. Credit: American Museum of Natural History.
Therefore, under this evolutionary look, can we understand the reasons for our population growth rate if we study the changes that occur during pregnancy? It is time to talk about kilocalories, weight and body composition.
Metabolism during pregnancy
It has been assumed that , because the mother can need a total of 80,000 kcal to take pregnancy, 6 during pregnancy you have to "eat for two ." However, beyond this popular belief, scientific literature is not agreed when defining the costs of pregnancy. It is normally a great variability among the mothers studied. 7.8 There are women who do not see their basal energy expenditure increased , 9,10 despite the fact that their body is generating new tissues necessary to create the fetus, placenta and accumulation of fat. 11 In the same way, others do not increase the cost of physical activity as expected (given the same physical activity, the cost of it seems not to increase), even having a greater body weight. 12 This would be related to physiological adaptations that are not known completely, but that could suppose greater energy efficiency when performing physical activity. 13,14 On the other hand, sometimes some women become more sedentary at this stage more or less unconsciously. 15,16 This would end up resulting in less burn calories per day. Everything seems to indicate that there are no universal truths with respect to the cost of pregnancy.
In 2021, we published in the American Journal of Human Biology a study conducted with 77 women, 17 of which 35 were in the last quarter of their gestation. This work focused on measuring metabolic spending at rest and the cost of walking . The first is one of the largest components of an individual's daily energy expenditure, 18 and the second is a basic action that is usually implicit in numerous daily activities. In our article, 17 the comparison between resting and walking spending determined that, for a similar body weight, pregnant women needed less energy than non -pregnant women . Al comparar a las mujeres embarazadas en dos puntos diferentes de su tercer trimestre (la semana 28 versus la semana 32), las mujeres embarazadas consumían menos energía caminando en la semana 32 que durante la semana 28 .
Figure 1. Comparison of the relationship between body weight and energy expenditure between pregnant and not pregnant women. A) Body weight against restless energy expenditure. B) Body weight against the cost of locomotion. Adapted figure of Prado-Navoa et al., 2021.
Thanks to this study we proposed that these differences would be determined by the body composition of one and the other participants, 17 since pregnant women have a significantly higher percentage of fat mass than non -pregnant. This fat mass is considered metabolically less active than the rest of body tissues, 19 so it could make "weigh the same, the same does not cost." In addition, the fat dough accumulates naturally during pregnancy, even under conditions of famine or without mothers varying their diet . 20
It has been proposed that estrogens play an important role in the accumulation of this tissue during pregnancy. 21 However, it seems that other adaptations also occur during pregnancy. These other adaptations, related to changes in the microbiome of the digestive system, 22,23 could improve efficiency during pregnancy in obtaining certain diet macronutrients, such as fat. It can, therefore, that women have a whole series of mechanisms that allow us to accumulate fat more easily during pregnancy . This, in turn, could be reducing the cost of our gestation.
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In this sense, some of the mechanisms that we have just discussed and of which we have today, were selected throughout our evolution as a species, allowing us to survive and reproduce more easily in the past . An already extinct human population had the ability to accumulate more fat and reproduce more and better. This adaptation comes to stay. Thus, today we know that pregnancy is the physiological state with the greatest flexibility of the life cycle, 6 which makes women successful in very diverse conditions . 9.24
The relevance of fat mass throughout evolution
Having fat mass as a energy tank to throw in moments of energy need is a well -known adaptation in the Homo sapiens . It is also proposed that this feature had great relevance in the evolution of the genus Homo . 25 The accumulation of fat mass is considered a derived trait , since it is not a characteristic that we share with other primates. 26 That is, the last common ancestor among the other great apes and we did not have this capacity. Thus, it may increase fat levels compared to other primates is the reason we could increase our cranial capacity . 26
In addition, the fat not only allows us to survive in moments of shortage . 27 An adequate level is also essential for us to mature sexually and have our first rule. 28 Our ovarian function and the probability of conception, also respond to the availability we have of energy, 29 among other things, related to an adequate percentage of body fat deposits. 30 During the last months of pregnancy, although we eat as many calories as we need, the body of some mothers begins to use this body tissue to sustain their daily energy needs. 31
During breastfeeding , the mother is able to feed the baby and maintain her own energy demands for months, in part, catabolizing the fat that her body accumulated during pregnancy. 32 De hecho, es habitual que el período de lactancia se acompañe con una fase de amenorrea ( ausencia de regla ). 33 This period of ovarian suppression prevents the mother from getting pregnant again. Thus, the body ensures that the energy available is used exclusively to survive, generate milk and keep the baby. 34 However, it is interesting to note that the duration of breastfeeding and the recovery of ovarian function are highly variable and may depend on the maternal energy condition. 10 Therefore, recovering the menstrual cycle after childbirth, is also related to body fat levels . Adequate levels of body fat allow us to reduce the time between births and reproduce at a greater pace compared to other great apes. 35
Conclusions
There is no doubt that pregnancy is one of the most challenging and changing moments at the physiological level. This has led some researchers to compare pregnancy at the metabolic level with extreme physical activity and resistance events. 36 However, we begin to have evidence that points to the opposite. 8
Although in our study 17 we do not measure the daily energy expenditure of the participants, the results allow hypothesizing that, perhaps, the cost of human pregnancy is not as high as expected . Under an evolutionary point of view, it is reasonable to think that in the past those with multiple strategies survive to ensure a lower cost of reproduction. A very interesting study published in the journal Science 37 also shows us that the greatest costs of reproduction are indirect: the most expensive is not to create the breeding, if not to raise it and ensure its survival. In relation to breastfeeding demands, mammals assume an indirect cost much greater than other kinds of the animal kingdom. The extraordinary thing is to be aware of how skilled it is our species by cutting these costs.
In addition to the accumulation of fat and the reduction of energy expenditure, they deserve the amount of behavioral strategies that humans have to deal with day -to -day difficulties, especially when we talk about reproduction and keep our young. Our high reproduction rates do not depend solely on our physiological adaptations. The collaboration between individuals and the livelihood and help of other members of our family or social group are essential to shorten the time between births, to be able to move forward several children at the same time and, ultimately, to share the energy burden of reproduction. 38
Our ability to adapt and modulate metabolism in the face of changes in the life cycle, either through physiology or behavior, fits within the lines of work of the aforementioned Herman Pontzer 39 on the “limited energy expenditure”, or Vincent Careau and collaborators 40 on the “compensatory models of energy expenditure”. These research suggests that our daily energy expenditure usually maintains in a specific range , regardless of whether we have a more or less active lifestyle, thanks to adaptations that occur in our metabolism. If the different components of our metabolism tend to always stay in a certain balance, we would spend less energy up to date than it would be expected. All these mechanisms can also be acting during different phases of our reproduction, causing us to reproduce exorbitant rates compared to other primates and, most importantly, at a lower cost.
As we discuss in this 90 grams podcast , the extraordinary of the human being may not be the energy it spends, but how much it is able to save.
References:
1. Longman, DP, Wells, Jck & Stock, JT Human Athletic Paleobiology; Using Sport as Model To investigate human evolutionary adaptation. AM J Phys Anthropol 171 , 42–59 (2020).
2. Longman, DP, Dolan, E., Wells, Jck & Stock, Jt Patterns of Energy Allocation During Energetic Scarcity; Evolutionary Insights from Ultra-Endurance Events. Comp Biochem Physiol A Mol Integra Physiol 111422 (2023) DOI: 10.1016/J.CBPA.2023.111422.
3. Lieberman, of Is Exercise Really Medicine? An evolutionary perspective. Curr Sports Med Rep 14 , 313–319 (2015).
4. Speakman, Jr & Elmquist, JK Obesity: An evolutionary context. Life Metabolism (2022) DOI: 10.1093/Lifemeta/Loac002.
5. Pontzer, H. Hotter and Sicker: External Energy Expenditure and the Tangled Evolutionary Roots of Anthropogenic Climate Change and Chronic Disease. American Journal of Human Biology E23579 (2021) DOI: 10.1002/AJHB.23579.
6. Prentice, Am & Goldberg, Gr Energy Adaptations in Human Pregnancy: Limits and Long-Term Concenences. AM J Clin NUT 71 , 1226S-1232S (2000).
7. Goldberg, GR et al. Longitudinal Assessment of the Components of Energy Balance in Well-Nourished Lactating Women. American Journal of Clinical Nutrition 54 , 788–798 (1991).
8. CORDY, C., Webb, NM & Haeusler, M. Take it to the limit. The Limitations of Energetic Explanations for Birth Timing in Humans. Evol Med public Health 11 , 415–428 (2023).
9. Butte, NF & King, JC Energy requirements during pregnancy and lactation. Public Health Nut 8 , 1010–1027 (2005).
10. DUFOUR, DL & SAUTHER, ML Comparative and Evolutionary Dimensions of the Energetics of Human Pregnancy and Lactation. American Journal of Human Biology 14 , 584–602 (2002).
11. Emery Thompson, M. Comparative Reproductive Energetics of Human and Nonhuman Primates. Annu Rev Anthropol 42 , 287–304 (2013).
12. Melzer, K., Schutz, Y., Boulvain, M. & Kayser, B. Pregnancy-Related Changes in Activity Energy Expenditure and Resting Metabolic Rate in Switzerland. EUR J CLIN NUT 63 , 1185–1191 (2009).
13. Rucha, SM et al. Walking Program of Low Or Vigorous Intelling During Pregnancy Confers An Aerobic Benefit. Int J Sports Med 33 , 661–666 (2012).
14. Lawrence, M., Singh, J., Lawrence, F. & Witehead, RG the Energy Cost of Common Daily Activities in African Women: Increased Expenditure in Pregnancy? American Journal of Clinical Nutrition 42 , 753–763 (1985).
15. Heini, A. et al. Free-Living Energy Expenditure Measured By Two Independent Techniques in Pregnant and Nonpregnant Gambian Women. Am J Physiol Endocrinol Metab 261 , E9 - E17 (1991).
16. Vitzthum, Vj Why not so great is Still Good Aough. Flexible Responsiveness in Human Reproductive Functioning. In Reproductive Ecology and Human Evolution (Ed. Ellison, PT) 179–202 (Routledge, New York, 2001).
17. Prado - Navoa, O., Rodríguez, J., Martín García, A. & Mateos, A. Body Composition Helps: Differences in Energy Expenditure Between Pregnant and Nonpregnant femals. American Journal of Human Biology 33 , E23518-Endefined (2021).
18. Speakman, Jr & Selman, C. Physical Activity and Resting Metabolic Rate. Proceedings of the Nutrition Society 62 , 621–634 (2003).
19. Berggren, Ek et al. Variations in Resting Energy Expenditure: Impact on Gestational Weight Gain. Am J Obstet Gynecol 217 , 445.E1-445.E6 (2017).
20. Abeysekera, MV, Morris, Ja, Davis, GK & O'Sullivan, Aj Alterations in Energy Homeostasis To Favour Adipose Tissue Gain: A longitudinal Study in Healthy Pregnant Women. Australian and New Zealand Journal of Obstetrics and Gynaecology 56 , 42–48 (2016).
21. A BIOLOGICAL ADVANTAGE FOR FERTILITY AND GESTATION. Obesity Reviews 10 , 168–177 (2009).
22. JOST, T., Lacroix, C., Bragger, C. & Chassard, C. Stability of the Maternal Gut Microbiota During Late Pregnancy and Early Lactation. Curr Microbiol 68 , 419–427 (2014).
23. Koren, O. et al. Host Remodeling of the Gut Microbiome and Metabolic Changes During Pregnancy. Cell 150 , 470–80 (2012).
24. Ellison, PT Energetics, Reproductive Ecology and Human Evolution. Paleoanthropology 2008 , 172–200 (2008).
25. Navarrete, A., Van Schaik, CP & isler, K. Energetics and the Evolution of Human Brain Size. Nature 480 , 91–93 (2011).
26. Pontzer, H. et al. Metabolic Acceleration and the Evolution of Human Brain Size and Life History. Nature 533 , 390–392 (2016).
27. Wells, JCK Ecological Volatility and Human Evolution: A Novel Perspective on Life History and Reproductive Strategy. Evol Anthropol 21 , 277–288 (2012).
28. Scheffler, C. & Hermanussen, M. Growth in Childhood and Teennce. In the International Encyclopedia of Biological Anthropology 1–11 (John Wiley & Sons, Inc., Hoboken, NJ, USA, 2018). DOI: 10.1002/9781118584538.IBA0537.
29. Ellison, PT Energetics and Reproductive Effort. American Journal of Human Biology 15 , 342–351 (2003).
30. Jasienska, G. Why Energy Expenditure Causes Reproductive SUPPRESSION IN WOMEN. In Reproductive Ecology and Human Evolution (Ed. Ellison, PT) 59–84 (Transaction Publishers, New Jersey, 2001).
31. Heldstab, SA, Van Schaik, CP & isler, K. Getting Fat or Getting Help? How Female Mammals Cope with Energetic Constraints on Reproduction. Front Zool 14 , 1–11 (2017).
32. McFarland, R. Female Primates: Fat or Fit? In the evolving female: A Life History Perspective (Eds. Morbeck, Me, Galloway, A. & Zihlman, Al) 163–176 (Princeton University Press, Princeton, 1997).
33. Ellison, PT Breastfeeding, Fertility, and Maternal Condition. In Breastfeeding: Biocultural Perspectives. (Eds. Dettwyler, Ka & Stuart-Macadam, P.) 305–345 (Aldine de Gruyter, Hawthrone, NY, 1995).
34. Valenggia, C. & Ellison, P. Interactions Between Metabolic and Reproductive Functions in the Summation of Postpartum Fertum. American Journal of Human Biology 21 , 559–566 (2009).
35. Zafon, C. Oscillaments in Total Body Fat Content Through Life: An evolutionary perspective. Obesity Reviews 8 , 525–530 (2007).
36. Thurber, C. et al. Extreme Events Reveal An Food Limit on Sustaned Maximal Human Energy Expenditure. SCI ADV 5 , EAW0341 (2019).
37. Ginther, SC, Cameron, H., White, Cr & Marshall, DJ Metabolic Loads and the Costs of Metazoan Reproduction. Science (1979) 384 , 763–767 (2024).
38. HRDY, SB Postpartum Variable Responsiveness Among Humans and Other Primates With “Cooperative Breeding”: In comparative and evolutionary perspective. CONC BEHAV 77 , 272–283 (2016).
39. Pontzer, H. Constrained Total Energy Expenditure and the Evolutionary Biology of Energy Balance. Excer Sport Sci Rev 43 , 110–116 (2015).
40. Careau, V. et al. Energy Compensation and Adiposity in Humans. Current Biology (2021) DOI: 10.1016/J.Cub.2021.08.016.