Author Biography: James Josh Snodgrass
Dr. J. Snodgrass’ research interest cover almost every topic related to human biology: adaptations and evolution, nutrition, epidemiology, and the social/behavioral patterns that emerge from them. Specifically, he focuses on elucidating the effect of economic and cultural change plus chronic psychosocial stress on human health patterns, human adaptations to environmental extremes, and energetics and the role of evolution in shaping the human diet. His ongoing work includes the Indigenous Siberian Health and Adaptation Project, The Shuar Health and Life History Project in Ecuador, and his collaborative efforts in studying stress, discrimination, and health among Latin American immigrants in Oregon. His publication topics range from the metabolic correlates to hominid brain expansion to the immergence of obesity in indigenous Siberian populations to muscle mass scaling in primates. He has even published work in the Journal of Forensic Science concerning sex related differences in the aging of the vertebral column and parity assessment utilizing the dorsal pits and pubic tubercle height. He is the membership chair on the executive committee for the American Association of Physical Anthropologists, an advisor for the multi-country studies unit for the World Health Organization, and the director of the Human Biology Research Laboratory at the University of Oregon. He recently received the Michael A. Little Early Career award for his outstanding contributions to the field of human biology, and has been distinguished multiple times for his excellent work as an educator and scientist. Currently, he works at the University of Oregon teaching classes on human growth and development, human biological variation, and evolutionary medicine.
What is energetics and how does it fit into anthropology?
Energetics is the study of the use and transfer of energy. Anthropologists use energetics in order to examine issues within human biology such as the origins of bipedalism and encephalization, prevalence of obesity, growth patterns, human adaption to climate change, influence of diet and physical activity on the reproductive system. The anthropological approach to energetics focuses on how energy is extracted form the environment and affects human’s health, survival, and reproduction.
Basic Principles of Energetics
The foundation of energetics is based on energy transfer. This is how chemical energy is extracted from food and turned into energy for the function of day-to-day activities.
Three purposes that food energy is obtained:
1) Biosynthesis- synthesis of cells, tissues, and organic materials
2) Somatic maintenance- repertory, circulatory, and nervous system activity (internal work)
3) Muscular work for physical activity (external work)
Due to the need for the internal and external needs, mammals and homeotherms must eat regularly in order to produce the chemical energy necessary for these functions.
Metabolism and Dietary Sources of Energy
- The metabolic rate is the rate of energy turnover expressed in calories or joules per unit time. An animal’s metabolic rate is shaped by size, age, sex, activity level, and environment temperature. An animal’s body size has been recognized to correlate with its metabolic rate. An animal’s resting metabolic rate (RMR) as well a their total daily energy expenditure (TDEE) also correlate with their size. Metabolic rates vary based on size. Animals with who have a large body masses have low metabolic rate and animals with size a small body mass have high metabolic rates.
- Adenosine triphosphate (ATP) is the most important energy currency in the body. It is formed by oxidation of glucose during cellular resperation and its ultimate use is to perform physical work. The way in which energy is provided for the ATP is through macronutrients. This uses carbs, proteins, fats, and alcohol to provide energy for the ATP. The amount of macronutrients consumed effects the dietary patterns for different cultures.
When the expenditure of energy is greater than the energy consumption the body’s mass, fat, and tissue are reduced. When the expenditure of energy is less than the energy consumption then the body retains fat. The body fat percentage varies in different cultures as well as mammals species. Cultures with more plentiful calories have higher body fat.
- BMR is the amount of energy used while awake. This occupies 45-70% of the total energy expenditure (TEE). The TEE is the total metabolic costs that come from physical activity within a 24 hour period. The BMR is correlated with body mass and varies between different sexes and can fluctuate with age.
- Maintenance costs contribute to a populations energy requirements . Thermic effect of food (TEF), thermoregulation, immune function, physical activity, growth, and reproduction are all ways in which energy costs can be measured. TEF measures the cost of energy through the digestion, absorption, and oxidation of food. Thermoregulation consists of two components: obligatory and facultative thermoregulation. Obligatory thermoregulation produces heat from maintenance metabolism and maintains the human body temperature in the thermoneutral range (77-81° F). Facultative thermoregulation allows the body to maintain homeostasis. Immune functions are the cost of energy for the body to fight diseases, maintain core temperature, and producing antibody responses. Physical activity measure the energy costs through voluntary activity. Growth and reproduction take into account the amount of energy it takes for the body to change over time and for the female body to undergo pregnancy.
Measuring Energy Intake and Energy Balance
- Energy intake is measuring the energy intake available in the food supply in a population. Ways of measuring this are by dietary records which are sometimes followed by and dietary recalls. The dietary records requires participants to record all nutrients consumed over a specific time period (usually a few days). They must record ingredients and volume of the food and liquids they’ve consumed. This allows for more accurate results of a dietary recall is to follow.The dietary recall requires participants to recall the quantity of food they have consumed over the last 24 hours. This can be performed through surveys or interviews and allows researchers to analyze nutrition consumption amongst populations. These records allow for anthropologists to analyze a population’s energy intake by the energy available in their diets.
- Nutritional intake refers to body size and body fat as long-term measures of energy balance. Ways of measuring body fat are by measuring skinfolds (sum of four skinfolds taken at a skin fold site), using bioelectrical impedance analysis, and calculating the body mass index (BMI).
Physical activity is the cost of human movement. This is measured in Activity energy expenditure (AEE)
- Measuring Physical Activity- The book discusses two main methods that help measure physical activity patterns in everyday life.DLW (doubly labeled water) uses two isotopes of water to calculate the TEE. By orally taking the isotopes and monitoring them for a week or two, the carbon dioxide production made from the disappearing isotopes helps calculate the TEE. The second HR (heart rate) Monitoring uses the HR and energy expenditure to calculate the TEE. A HR monitor is worn during the time in which the participant is active. The participant’s average energy expenditure is analyzed by the HR monitor over the span of a few days.
Have any of you ever used a HR monitor before? If so, what was your experience using it?
Why do you think it is important that we measure physical activity?
Energetics and Human Evolutionary History
- What are some of the evolutionary adaptations along the early hominin line and what energy trade-offs occurred based on these changes?
- Bipedalism- Conserves more energy than quadrapedalism at walking speeds, but requires more effort to move faster
- Encephalization- While overall caloric intake remains at a level predicted by trends among other primate species, a far greater portion of those calories is dedicated to brain functions (~20%)
- Dietary switch to more nutrient dense foods
- Required a subsequent reduction in colon size and dietary thermogenesis
Energetics and Adaptations in Modern Populations
- What are some environmental stressors that require changes in energetics within the human populations that live there?
- Thermal Stress
- ~3% increase in BMR for every 10 degrees C drop in temperature (below the baseline of 10 degrees C)
- High heritability effect, since a study has revealed higher BMRs in the indigenous population than the non-indigenous immigrants
- Genetic studies focus heavily on mitochondrial DNA and the corresponding haplogroups
- Thermal Stress
- Seasonal Stress
- Several populations faced with severe, season-based energy shortages
- Compensations include cultural adaptations such as migration and food storage
- A major adaptation: seasonality of reproduction, helps pregnant women sustain a healthier weight during term and to buffer the extra energy requirements of lactation
Energetics and Health
- What are some of the problems that humans face when attempting to regulate energetics?
- Can be either acute or chronic
- Particular problematic in juveniles
- Stunted= Low height for weight
- Wasted= Low weight for height
- Underweight= Low weight for age
- Results in reduced physical activity and down regulation of the BMR
- Many communities facing a double-edged sword: Undernutrition among adolescents and overnutrition among adults
- Heavily correlated with the obesity epidemic
- Previously considered a disease of affluence, but the reduction in price of refined carbs and sugars has made them more available to groups of a lower social economic status
- People are receiving a surplus energy supply but not enough micronutrients
- Accompanied by a reduction in overall activity level