High resting metabolic rate among Amazonian forager-horticulturalists experiencing high pathogen burden

Increases in regional brain volume across two native South American male populations

Industrialized environments, despite benefits such as higher levels of formal education and lower rates of infections, can also have pernicious impacts upon brain atrophy. Partly for this reason, comparing age-related brain volume trajectories between industrialized and non-industrialized populations can help to suggest lifestyle correlates of brain health. The Tsimane, indigenous to the Bolivian Amazon, derive their subsistence from foraging and horticulture and are physically active. The Moseten, a mixed-ethnicity farming population, are physically active but less than the Tsimane. Within both populations (N = 1024; age range = 46-83), we calculated regional brain volumes from computed tomography and compared their cross-sectional trends with age to those of UK Biobank (UKBB) participants (N = 19,973; same age range). Surprisingly among Tsimane and Moseten (T/M) males, some parietal and occipital structures mediating visuospatial abilities exhibit small but significant increases in regional volume with age. UKBB males exhibit a steeper negative trend of regional volume with age in frontal and temporal structures compared to T/M males. However, T/M females exhibit significantly steeper rates of brain volume decrease with age compared to UKBB females, particularly for some cerebro-cortical structures (e.g., left subparietal cortex). Across the three populations, observed trends exhibit no interhemispheric asymmetry. In conclusion, the age-related rate of regional brain volume change may differ by lifestyle and sex. The lack of brain volume reduction with age is not known to exist in other human population, highlighting the putative role of lifestyle in constraining regional brain atrophy and promoting elements of non-industrialized lifestyle like higher physical activity.

Age-related physiological dysregulation progresses slowly in semi-free-ranging chimpanzees

Background and objectives

Lifestyle has widespread effects on human health and aging. Prior results from chimpanzees (Pan troglodytes), one of humans' closest evolutionary relatives, indicate that these lifestyle effects may also be shared with other species, as semi-free-ranging chimpanzees fed a naturalistic diet show healthier values in several specific health biomarkers, compared with their sedentary, captive counterparts. Here, we examined how lifestyle factors associated with different environments affect rates of physiological aging in closely related chimpanzees.

Methodology

We compared physiological dysregulation, an index of biological aging, in semi-free-ranging chimpanzees in an African sanctuary versus captive chimpanzees in US laboratories. If the rate of aging is accelerated by high-calorie diet and sedentism, we predicted greater age-related dysregulation in the laboratory populations. Conversely, if costs of a wild lifestyle accelerate aging, then semi-free-ranging chimpanzees at the sanctuary, whose environment better approximates the wild, should show greater age-related dysregulation. We further tested whether dysregulation differed based on sex or body system, as in humans.

Results

We found that semi-free-ranging chimpanzees showed lower overall dysregulation, as well as lower age-related change in dysregulation, than laboratory chimpanzees. Males experienced lower dysregulation than females in both contexts, and the two populations exhibited distinct aging patterns based on body system.

Conclusions and implications

Our results support the conclusion that naturalistic living conditions result in healthier aging in chimpanzees. These data provide support for the proposal that lifestyle effects on human health and aging are conserved from deeper into our evolutionary history.

Total daily energy expenditure and elevated water turnover in a small-scale semi-nomadic pastoralist society from Northern Kenya

BACKGROUND

Pastoralists live in challenging environments, which may be accompanied by unique activity, energy, and water requirements.

AIM

Few studies have examined whether the demands of pastoralism contribute to differences in total energy expenditure (TEE) and water turnover (WT) compared to other lifestyles.

SUBJECTS AND METHODS

Accelerometer-derived physical activity, doubly labelled water-derived TEE and WT, and anthropometric data were collected for 34 semi-nomadic Daasanach adults from three northern Kenyan communities with different levels of pastoralist activity. Daasanach TEEs and WTs were compared to those of other small-scale and industrialised populations.

RESULTS

When modelled as a function of fat-free-mass, fat-mass, age, and sex, TEE did not differ between Daasanach communities. Daasanach TEE (1564-4172 kcal/day) was not significantly correlated with activity and 91% of TEEs were within the range expected for individuals from comparison populations. Mean WT did not differ between Daasanach communities; Daasanach absolute (7.54 litres/day men; 7.46 litres/day women), mass-adjusted, and TEE-adjusted WT was higher than most populations worldwide.

CONCLUSIONS

The similar mass-adjusted TEE of Daasanach and industrialised populations supports the hypothesis that habitual TEE is constrained, with physically demanding lifestyles necessitating trade-offs in energy allocation. Elevated WT in the absence of elevated TEE likely reflects a demanding active lifestyle in a hot, arid climate.

Limits of Ultra: Towards an Interdisciplinary Understanding of Ultra-Endurance Running Performance

Ultra-endurance running (UER) poses extreme mental and physical challenges that present many barriers to completion, let alone performance. Despite these challenges, participation in UER events continues to increase. With the relative paucity of research into UER training and racing compared with traditional endurance running distance (e.g., marathon), it follows that there are sizable improvements still to be made in UER if the limitations of the sport are sufficiently understood. The purpose of this review is to summarise our current understanding of the major limitations in UER. We begin with an evolutionary perspective that provides the critical background for understanding how our capacities, abilities and limitations have come to be. Although we show that humans display evolutionary adaptations that may bestow an advantage for covering large distances on a daily basis, these often far exceed the levels of our ancestors, which exposes relative limitations. From that framework, we explore the physiological and psychological systems required for running UER events. In each system, the factors that limit performance are highlighted and some guidance for practitioners and future research are shared. Examined systems include thermoregulation, oxygen delivery and utilisation, running economy and biomechanics, fatigue, the digestive system, nutritional and psychological strategies. We show that minimising the cost of running, damage to lower limb tissue and muscle fatigability may become crucial in UER events. Maintaining a sustainable core body temperature is critical to performance, and an even pacing strategy, strategic heat acclimation and individually calculated hydration all contribute to sustained performance. Gastrointestinal issues affect almost every UER participant and can be due to a variety of factors. We present nutritional strategies for different event lengths and types, such as personalised and evidence-based approaches for varying types of carbohydrate, protein and fat intake in fluid or solid form, and how to avoid flavour fatigue. Psychology plays a vital role in UER performance, and we highlight the need to be able to cope with complex situations, and that specific long and short-term goal setting improves performance. Fatigue in UER is multi-factorial, both physical and mental, and the perceived effort or level of fatigue have a major impact on the ability to continue at a given pace. Understanding the complex interplay of these limitations will help prepare UER competitors for the different scenarios they are likely to face. Therefore, this review takes an interdisciplinary approach to synthesising and illuminating limitations in UER performance to assist practitioners and scientists in making informed decisions in practice and applicable research.

Effect of influenza vaccination on resting metabolic rate and c-reactive protein concentrations in healthy young adults

OBJECTIVES

Chronic immune activation and severe inflammatory states are positively associated with resting metabolic rate (RMR; kcal/day), but the impacts of mild immune stimuli on metabolism are poorly understood. This study investigates the within-individual association between the inflammatory response to influenza vaccination and RMR in young adults.

METHODS

We evaluated RMRs through indirect calorimetry and circulating c-reactive protein (CRP) concentrations (mg/L)-a direct measure of inflammation-via high-sensitivity immunoassays of dried blood spots (n = 17) at baseline and two- and seven-days post-vaccine. Wilcoxon matched-pairs signed-rank tests were used to evaluate the magnitude of the CRP and RMR responses. Type II Wald chi-square tests of linear mixed-effect models assessed whether those responses were correlated.

RESULTS

Baseline CRP was 1.39 ± 1.26 mg/L. On day two post-vaccine, CRP increased by 1.47 ± 1.37 mg/L (p < 0.0001), representing a 106% increase above baseline values. CRP remained higher on day seven post-vaccine, 1.32 ± 2.47 mg/L (p = 0.05) above baseline values. There were no statistically significant changes in RMR from baseline to day two (p = 0.98) or day seven (p = 0.21). Change in CRP from baseline did not predict RMR variation across days (p = 0.46).

CONCLUSIONS

We find no evidence that adult influenza vaccination results in a corresponding increase in RMR. These results suggest that the energetic cost of an influenza vaccine's mild inflammatory stimulus is either too small to detect or is largely compensated by a temporary downregulation of energy allocated to other metabolic tasks.

The 24-h activity cycle and cardiovascular outcomes: establishing biological plausibility using arterial stiffness as an intermediate outcome

This review proposes a biologically plausible working model for the relationship between the 24-h activity cycle (24-HAC) and cardiovascular disease. The 24-HAC encompasses moderate-to-vigorous physical activity (MVPA), light physical activity, sedentary behavior (SB), and sleep. MVPA confers the greatest relative cardioprotective effect, when considering MVPA represents just 2% of the day if physical activity guidelines (30 min/day) are met. While we have well-established guidelines for MVPA, those for the remaining activity behaviors are vague. The vague guidelines are attributable to our limited mechanistic understanding of the independent and additive effects of these behaviors on the cardiovascular system. Our proposed biological model places arterial stiffness, a measure of vascular aging, as the key intermediate outcome. Starting with prolonged exposure to SB or static standing, we propose that the reported transient increases in arterial stiffness are driven by a cascade of negative hemodynamic effects following venous pooling. The subsequent autonomic, metabolic, and hormonal changes further impair vascular function. Vascular dysfunction can be offset by using mechanistic-informed interruption strategies and by engaging in protective behaviors throughout the day. Physical activity, especially MVPA, can confer protection by chronically improving endothelial function and associated protective mechanisms. Conversely, poor sleep, especially in duration and quality, negatively affects hormonal, metabolic, autonomic, and hemodynamic variables that can confound the physiological responses to next-day activity behaviors. Our hope is that the proposed biologically plausible working model will assist in furthering our understanding of the effects of these complex, interrelated activity behaviors on the cardiovascular system.

Energetic costs of testosterone in two subsistence populations

OBJECTIVE

Testosterone plays a role in mediating energetic trade-offs between growth, maintenance, and reproduction. Investments in a high testosterone phenotype trade-off against other functions, particularly survival-enhancing immune function and cellular repair; thus only individuals in good condition can maintain both a high testosterone phenotype and somatic maintenance. While these effects are observed in experimental manipulations, they are difficult to demonstrate in free-living animals, particularly in humans. We hypothesize that individuals with higher testosterone will have higher energetic expenditures than those with lower testosterone.

METHODS

Total energetic expenditure (TEE) was quantified using doubly labeled water in n = 40 Tsimane forager-horticulturalists (50% male, 18-87 years) and n = 11 Hadza hunter-gatherers (100% male, 18-65 years), two populations living subsistence lifestyles, high levels of physical activity, and high infectious burden. Urinary testosterone, TEE, body composition, and physical activity were measured to assess potential physical and behavioral costs associated with a high testosterone phenotype.

RESULTS

Endogenous male testosterone was significantly associated with energetic expenditure, controlling for fat free mass; a one standard deviation increase in testosterone is associated with the expenditure of an additional 96-240 calories per day.

DISCUSSION

These results suggest that a high testosterone phenotype, while beneficial for male reproduction, is also energetically expensive and likely only possible to maintain in healthy males in robust condition.

Comparative life history patterns of female gorillas

OBJECTIVES

Several theories have been proposed to explain the impact of ecological conditions on differences in life history variables within and between species. Here we compare female life history parameters of one western lowland gorilla population (Gorilla gorilla gorilla) and two mountain gorilla populations (Gorilla beringei beringei).

MATERIALS AND METHODS

We compared the age of natal dispersal, age of first birth, interbirth interval, and birth rates using long-term demographic datasets from Mbeli Bai (western gorillas), Bwindi Impenetrable National Park and the Virunga Massif (mountain gorillas).

RESULTS

The Mbeli western gorillas had the latest age at first birth, longest interbirth interval, and slowest surviving birth rate compared to the Virunga mountain gorillas. Bwindi mountain gorillas were intermediate in their life history patterns.

DISCUSSION

These patterns are consistent with differences in feeding ecology across sites. However, it is not possible to determine the evolutionary mechanisms responsible for these differences, whether a consequence of genetic adaptation to fluctuating food supplies ("ecological risk aversion hypothesis") or phenotypic plasticity in response to the abundance of food ("energy balance hypothesis"). Our results do not seem consistent with the extrinsic mortality risks at each site, but current conditions for mountain gorillas are unlikely to match their evolutionary history. Not all traits fell along the expected fast-slow continuum, which illustrates that they can vary independently from each other ("modularity model"). Thus, the life history traits of each gorilla population may reflect a complex interplay of multiple ecological influences that are operating through both genetic adaptations and phenotypic plasticity.

Total daily energy expenditure has declined over the past three decades due to declining basal expenditure, not reduced activity expenditure

Obesity is caused by a prolonged positive energy balance1,2. Whether reduced energy expenditure stemming from reduced activity levels contributes is debated3,4. Here we show that in both sexes, total energy expenditure (TEE) adjusted for body composition and age declined since the late 1980s, while adjusted activity energy expenditure increased over time. We use the International Atomic Energy Agency Doubly Labelled Water database on energy expenditure of adults in the United States and Europe (n = 4,799) to explore patterns in total (TEE: n = 4,799), basal (BEE: n = 1,432) and physical activity energy expenditure (n = 1,432) over time. In males, adjusted BEE decreased significantly, but in females this did not reach significance. A larger dataset of basal metabolic rate (equivalent to BEE) measurements of 9,912 adults across 163 studies spanning 100 years replicates the decline in BEE in both sexes. We conclude that increasing obesity in the United States/Europe has probably not been fuelled by reduced physical activity leading to lowered TEE. We identify here a decline in adjusted BEE as a previously unrecognized factor.

Impact of energy availability and physical activity on variation in fertility across human populations

Human reproduction is energetically costly, even more so than other primates. In this review, we consider how the energy cost of physical activity impacts reproductive tasks. Daily energy expenditure appears to be constrained, leading to trade-offs between activity and reproduction expenditures in physically active populations. High workloads can lead to suppression of basal metabolic rate and low gestational weight gain during pregnancy and longer interbirth intervals. These responses lead to variation in fertility, including age at first reproduction and interbirth interval. The influence of energetics is evident even in industrialized populations, where cultural and economic factors predominate. With the decoupling of skills acquisition from food procurement, extrasomatic resources and investment in individual offspring becomes very costly. The result is greater investment in fewer offspring. We present a summary of age at first reproduction and interbirth interval trends across a diverse, global sample representing 44 countries and two natural fertility populations. While economic factors impact fertility, women in energy-rich, industrialized populations are capable of greater reproductive output than women in energy-stressed populations. Thus, energetic factors can be disentangled from cultural and economic impacts on fertility. Future research should focus on objective measurements of energy intake, energy expenditure, and physical activity in a broader sample of populations to elucidate the role of energetics in shaping reproductive outcomes and health.

Natural selection of immune and metabolic genes associated with health in two lowland Bolivian populations

A growing body of work has addressed human adaptations to diverse environments using genomic data, but few studies have connected putatively selected alleles to phenotypes, much less among underrepresented populations such as Amerindians. Studies of natural selection and genotype-phenotype relationships in underrepresented populations hold potential to uncover previously undescribed loci underlying evolutionarily and biomedically relevant traits. Here, we worked with the Tsimane and the Moseten, two Amerindian populations inhabiting the Bolivian lowlands. We focused most intensively on the Tsimane, because long-term anthropological work with this group has shown that they have a high burden of both macro and microparasites, as well as minimal cardiometabolic disease or dementia. We therefore generated genome-wide genotype data for Tsimane individuals to study natural selection, and paired this with blood mRNA-seq as well as cardiometabolic and immune biomarker data generated from a larger sample that included both populations. In the Tsimane, we identified 21 regions that are candidates for selective sweeps, as well as 5 immune traits that show evidence for polygenic selection (e.g., C-reactive protein levels and the response to coronaviruses). Genes overlapping candidate regions were strongly enriched for known involvement in immune-related traits, such as abundance of lymphocytes and eosinophils. Importantly, we were also able to draw on extensive phenotype information for the Tsimane and Moseten and link five regions (containing PSD4, MUC21 and MUC22, TOX2, ANXA6, and ABCA1) with biomarkers of immune and metabolic function. Together, our work highlights the utility of pairing evolutionary analyses with anthropological and biomedical data to gain insight into the genetic basis of health-related traits.

Human total, basal and activity energy expenditures are independent of ambient environmental temperature

Lower ambient temperature (Ta) requires greater energy expenditure to sustain body temperature. However, effects of Ta on human energetics may be buffered by environmental modification and behavioral compensation. We used the IAEA DLW database for adults in the USA (n = 3213) to determine the effect of Ta (-10 to +30°C) on TEE, basal (BEE) and activity energy expenditure (AEE) and physical activity level (PAL). There were no significant relationships (p > 0.05) between maximum, minimum and average Ta and TEE, BEE, AEE and PAL. After adjustment for fat-free mass, fat mass and age, statistically significant (p < 0.01) relationships between TEE, BEE and Ta emerged in females but the effect sizes were not biologically meaningful. Temperatures inside buildings are regulated at 18-25°C independent of latitude. Hence, adults in the US modify their environments to keep TEE constant across a wide range of external ambient temperatures.

The energetics of uniquely human subsistence strategies

[Figure: see text].

Reindeer herders from subarctic Finland exhibit high total energy expenditure and low energy intake during the autumn herd roundup

OBJECTIVE

High levels of total energy expenditure (TEE, kcal/day) have been documented among numerous human populations such as tropical climate horticulturalists and high-altitude agriculturalists. However, less work has been conducted among highly physically active cold climate populations.

METHODS

In October 2018, TEE was measured using the doubly labeled water (TEE_DLW , N = 10) and flex-heart rate methods (TEE_HR , N = 24) for 6-14 days among reindeer herders (20-62 years) in northern Finland during an especially physically demanding, but not seasonally representative, period of the year for herders-the annual reindeer herd roundup. Self-reported dietary intake was also collected during TEE measurement periods. TEE was then compared to that of hunter gatherer, farming, and market economies.

RESULTS

During the herd roundup, herders expended a mean of 4183 ± 949 kcal/day as measured by the DLW method, which was not significantly different from TEE_HR . Mean caloric intake was 1718 ± 709 kcal/day, and was significantly lower than TEE_DLW and TEE_HR (p < .001). Herder TEE_DLW was significantly higher than that of hunter gatherer (p = .0014) and market (p < .0014) economy populations; however, herder TEE_DLW was not different from that of farming populations (p = .91).

CONCLUSION

High TEE and low caloric intake among herders reflect the extreme demands placed on herders during the annual herd round up. Although TEE_DLW was similar between cold climate herders and hot climate farming populations, there are likely differences in how that TEE is comprised, reflecting the local ecologies of these populations.

Household Food Insecurity, Hair Cortisol, and Adiposity Among Tsimane' Hunter-Forager-Horticulturalists in Bolivia

OBJECTIVES

This study examined how household food insecurity (HFI) and chronic stress relate to adiposity among Tsimane' hunter-forager-horticulturalists in remote Bolivia with limited access to energy-dense processed foods that promote weight gain among industrialized populations.

METHODS

Retrospective cross-sectional data on HFI (via the Household Food Insecurity Access Scale [HFIAS]), hair cortisol concentration (HCC), adiposity (BMI, body fat percentage [%BF]), and sociodemographics were collected from 171 men, 164 women, and 167 children. Linear mixed-effects models tested linear, quadratic, joint, and interactive relationships between adiposity measures and both the HFIAS score and HCC.

RESULTS

Among children, each 3-point HFIAS score increase was associated with a 0.44-point higher %BF (SE = 0.22, P = 0.04). However, each 20% increase in HCC was associated with a -0.29-point difference in %BF (SE = 0.12, P = 0.01). Among men, a slight curvilinear relationship emerged between HFIAS and BMI. HFIAS and HCC were unrelated to adiposity measures among women. HCC did not modify relationships between HFIAS and adiposity in any subgroup.

CONCLUSIONS

These findings from a remote, small-scale population suggest that positive associations between HFI and adiposity are not isolated to contexts of industrialized food environments and heavy reliance on processed foods. However, these dynamics and the role of stress appear to differ by sex and age group.

Hotter and sicker: External energy expenditure and the tangled evolutionary roots of anthropogenic climate change and chronic disease

BACKGROUND

The dual crises of climate change and chronic, or non-communicable, disease (NCD) have emerged worldwide as the global economy has industrialized over the past two centuries.

AIMS

In this synthesis I examine humans' dependence on external (non-metabolic) energy expenditure (e.g., fire, fossil fuels) as a common, root cause in these modern crises.

MATERIALS AND METHODS

Using fossil, archeological, and historical evidence I show that the human lineage has been dependent on external energy sources since the control of fire in the Paleolithic. This reliance has grown with the development of agriculture, the use of wind- and water-power, and the most recently with industrialization and the transition to fossil fuels. To place industrialization in context I develop a Rule of 50, whereby individuals in industrialized economies consume roughly 50-times more external energy and manufacture roughly 50-times more material than do hunter-gatherers.

RESULTS

Industrialization and mechanization, powered by fossil fuels, have promoted centralization and processing in food production, reduced physical activity, and increased air pollution (including greenhouse gas emissions). These developments have led in turn to NCD and climate change.

DISCUSSION AND CONCLUSION

Climate change and NCD are connected both to one another and to our species' deep evolutionary dependence on external energy. Transitioning to carbon-free energy is essential to reduce the existential risks of climate change, but will likely have only modest effects on NCD. With the impending exhaustion of oil, coal, and natural gas reserves, developing replacements for fossil fuels is also critical to maintaining our species' external energy portfolio.

The Diagnostic-Measurement Method-Resting Energy Expenditure Assessment of Polish Children Practicing Football

Establishing the amount of energy needed to cover the energy demand of children doing sport training and thus ensuring they achieve an even energy balance requires the resting energy expenditure (REE) to be estimated. One of the methods that measures REE is the indirect calorimetry method, which may be influenced by many factors, including body composition, gender, age, height or blood pressure. The aim of the study was to assess the correlation between the resting energy expenditure of children regularly playing football and selected factors that influence the REE in this group. The study was conducted among 219 children aged 9 to 17 using a calorimeter, a device used to assess body composition by the electrical bioimpedance method by means of segment analyzer and a blood pressure monitor. The results of REE obtained by indirect calorimetry were compared with the results calculated using the ready-to-use formula, the Harris Benedict formula. The results showed a significant correlation of girls’ resting energy expenditure with muscle mass and body height, while boys’ resting energy expenditure was correlated with muscle mass and body water content. The value of the REE was significantly higher (p ≤ 0.001) than the value of the basal metabolic rate calculated by means of Harris Benedict formula. The obtained results can be a worthwhile suggestion for specialists dealing with energy demand planning in children, especially among those who are physically active to achieve optimal sporting successes ensuring proper functioning of their body.

The Influence of Maturity Status on Resting Energy Expenditure, Body Composition and Blood Pressure in Physically Active Children

Peak height velocity (PHV) is the period where the maximum rate of growth occurs. The moment the sports player reaches PHV can be estimated by monitoring the growth of body structures. The aim of this study was to assess changes in resting energy expenditure (REE), body composition and blood pressure in young, male soccer players between the pre-PHV, circa-PHV and post-PHV periods. This transverse study was conducted among 184 children aged 9 to 17 and included measurements of the resting energy expenditure (REE) using indirect calorimetry, body composition (bioimpedance) and blood pressure (sphygmomanometer). In addition, births in each quartile were analyzed. Children in the pre-PHV group had significantly lower REE values compared to the other two groups (p < 0.0001). The differences in the value of the REE between the children in the circum and post groups were not statistically significant. Additionally, the fat-free mass was significantly lower in the pre-PHV period compared to the other two periods (p < 0.0001), and the same relationship concerned the z-score body mass index (BMI) and systolic blood pressure. Early-born players were overrepresented (p < 0.05).

Resting Energy Expenditure of Physically Active Boys in Southeastern Poland-The Accuracy and Validity of Predictive Equations

Optimization of energy intake in the diet of young athletes is of primary importance. In addition to the energy expenditure associated with their body development, the demand resulting from intensive physical activity also increases. The aim of this study was to compare the accuracy of formulas commonly used for resting energy expenditure (REE) calculations with values obtained from measurements using indirect calorimetry among male children and adolescents practicing football. The study was conducted among 184 boys aged 9 to 17 using a calorimeter and a device for assessing body composition by means of electrical bioimpedance using a segment analyzer. The mean error ranged from −477 kcal/d by the Maffeis formula to −182 kcal/d for the Institute of Medicine of the National Academies (IMNA) formula. A statistically significant difference was found for all formulas in the calculated value in relation to the measured REE value (p < 0.0001). Most “ready-to-use” formulas underestimate REE, which can be a risk in determining the total energy demand in a group that requires more calories, especially when due to intensive growth and development and the expenditure associated with regular training and increased physical activity.

Rapidly declining body temperature in a tropical human population

Normal human body temperature (BT) has long been considered to be 37.0°C. Yet, BTs have declined over the past two centuries in the United States, coinciding with reductions in infection and increasing life expectancy. The generality of and reasons behind this phenomenon have not yet been well studied. Here, we show that Bolivian forager-farmers (n = 17,958 observations of 5481 adults age 15+ years) inhabiting a pathogen-rich environment exhibited higher BT when first examined in the early 21st century (~37.0°C). BT subsequently declined by ~0.05°C/year over 16 years of socioeconomic and epidemiological change to ~36.5°C by 2018. As predicted, infections and other lifestyle factors explain variation in BT, but these factors do not account for the temporal declines. Changes in physical activity, body composition, antibiotic usage, and thermal environment are potential causes of the temporal decline.

Faecal parasites increase with age but not reproductive effort in wild female chimpanzees

Energy investment in reproduction is predicted to trade off against other necessary physiological functions like immunity, but it is unclear to what extent this impacts fitness in long-lived species. Among mammals, female primates, and especially apes, exhibit extensive periods of investment in each offspring. During this time, energy diverted to gestation and lactation is hypothesized to incur short and long-term deficits in maternal immunity and lead to accelerated ageing. We examined the relationship between reproduction and immunity, as measured by faecal parasite counts, in wild female chimpanzees (Pan troglodytes schweinfurthii) of Kibale National Park, Uganda. While we observed higher parasite shedding (counts of eggs, cysts and larvae) in pregnant chimpanzees relative to cycling females, parasites rapidly decreased during early lactation, the most energetically taxing phase of the reproductive cycle. Additionally, while our results indicate that parasite shedding increases with age, females with higher fertility for their age had lower faecal parasite counts. Such findings support the hypothesis that the relatively conservative rate of female reproduction in chimpanzees may be protective against the negative effects of reproductive effort on health. This article is part of the theme issue 'Evolution of the primate ageing process'.

Immune function during pregnancy varies between ecologically distinct populations

BACKGROUND AND OBJECTIVES

Among placental mammals, females undergo immunological shifts during pregnancy to accommodate the fetus (i.e. fetal tolerance). Fetal tolerance has primarily been characterized within post-industrial populations experiencing evolutionarily novel conditions (e.g. reduced pathogen exposure), which may shape maternal response to fetal antigens. This study investigates how ecological conditions affect maternal immune status during pregnancy by comparing the direction and magnitude of immunological changes associated with each trimester among the Tsimane (a subsistence population subjected to high pathogen load) and women in the USA.

METHODOLOGY

Data from the Tsimane Health and Life History Project (N = 935) and the National Health and Nutrition Examination Survey (N = 1395) were used to estimate population-specific effects of trimester on differential leukocyte count and C-reactive protein (CRP), a marker of systemic inflammation.

RESULTS

In both populations, pregnancy was associated with increased neutrophil prevalence, reduced lymphocyte and eosinophil count and elevated CRP. Compared to their US counterparts, pregnant Tsimane women exhibited elevated lymphocyte and eosinophil counts, fewer neutrophils and monocytes and lower CRP. Total leukocyte count remained high and unchanged among pregnant Tsimane women while pregnant US women exhibited substantially elevated counts, resulting in overlapping leukocyte prevalence among all third-trimester individuals.

CONCLUSIONS AND IMPLICATIONS

Our findings indicate that ecological conditions shape non-pregnant immune baselines and the magnitude of immunological shifts during pregnancy via developmental constraints and current trade-offs. Future research should investigate how such flexibility impacts maternal health and disease susceptibility, particularly the degree to which chronic pathogen exposure might dampen inflammatory response to fetal antigens.

LAY SUMMARY

This study compares immunological changes associated with pregnancy between the Tsimane (an Amazonian subsistence population) and individuals in the USA. Results suggest that while pregnancy enhances non-specific defenses and dampens both antigen-specific immunity and parasite/allergy response, ecological conditions strongly influence immune baselines and the magnitude of shifts during gestation.

Relationship of sanitation, water boiling, and mosquito nets to health biomarkers in a rural subsistence population

OBJECTIVES

Throughout human evolutionary history, parasites and pathogens were a major cause of mortality-modern urban life with public health infrastructure has changed disease exposure. We examine associations between boiling water, using latrines, mosquito net usage, and biomarkers among the Tsimane, a nonindustrial subsistence population with little public health infrastructure.

METHODS

We conducted cross sectional surveys on water, latrines, and bed nets among 507 heads of households (aged 18-92 years, median age 41 years). Regression models estimated associations between behaviors and health biomarkers (ie, white blood cell count [WBC], hemoglobin, eosinophil count, and erythrocyte sedimentation rate) adjusting for age, sex, body mass index, wealth, schooling, and distance to the nearby market town.

RESULTS

Latrine use is associated with 6.5% lower WBC count (β = -679.6, P = .031, SE = 314.1), 17.4% lower eosinophil counts (β = -244.7, P = .023, SE = 107.2), and reduced odds of eosinophilia (adjusted OR = 0.40, P < .019, 95% CI = 0.18-0.86). Boiling water and mosquito net use are not significantly associated with any biomarkers measured.

CONCLUSIONS

In a subsistence population currently undergoing epidemiological transition, we find that latrine use was associated with several objective measures of health. This suggests that relatively low cost and low maintenance public health interventions may wish to focus on latrine use, as there is unmet need and potential health benefits for those who use latrines. Additionally, while the cost is higher, public health organizations aimed at improving sanitation may be able to use minimally invasive field-collected biomarkers as a diagnostic to objectively test the efficacy of interventions with greater specificity than anthropometric measurements.

Constraint and trade-offs regulate energy expenditure during childhood

Children's metabolic energy expenditure is central to evolutionary and epidemiological frameworks for understanding variation in human phenotype and health. Nonetheless, the impact of a physically active lifestyle and heavy burden of infectious disease on child metabolism remains unclear. Using energetic, activity, and biomarker measures, we show that Shuar forager-horticulturalist children of Amazonian Ecuador are ~25% more physically active and, in association with immune activity, have ~20% greater resting energy expenditure than children from industrial populations. Despite these differences, Shuar children's total daily energy expenditure, measured using doubly labeled water, is indistinguishable from industrialized counterparts. Trade-offs in energy allocation between competing physiological tasks, within a constrained energy budget, appear to shape childhood phenotypic variation (e.g., patterns of growth). These trade-offs may contribute to the lifetime obesity and metabolic health disparities that emerge during rapid economic development.

Longitudinal Changes in Measures of Body Fat and Diet Among Adult Tsimane' Forager-Horticulturalists of Bolivia, 2002-2010

OBJECTIVE

This study examined changes in body fat and diet among Tsimane' forager-horticulturalists and assessed how dietary shifts relate to increases in adiposity between 2002 and 2010.

METHODS

Longitudinal anthropometric and household-level dietary recall data from 365 men and 339 women aged ≥20 years in the Tsimane' Amazonian Panel Study were used. Multilevel mixed-effects models estimated how BMI, body fat percentage, waist circumference, skinfolds, and fat-free mass relate to household consumption of crops, hunted or fished foods, domesticated animal products, cooking oil, and refined grains and sugar.

RESULTS

Women's prevalence of overweight and obesity increased from 22.6% and 2.4% in 2002 to 28.8% and 8.9% in 2010, respectively, and BMI increased by 0.60% ± 0.12% per year (P < 0.001). Increases in fat-free mass accounted for some of this observed weight gain among women. Men's prevalence of overweight and obesity increased from 16.2% and 0.7% to 25.0% and 2.2%, respectively, and BMI increased by 0.22% ± 0.09% per year (P = 0.009). Household use of cooking oil increased and was positively associated with female BMI. Consumption of domesticated animal products did not change significantly but was positively associated with female BMI and male waist circumference.

CONCLUSIONS

Even small increases in energy-dense market-based foods can contribute to adiposity gains among a moderately active, subsistence-based population.

Evolutionary origins of polycystic ovary syndrome: An environmental mismatch disorder

Polycystic ovary syndrome (PCOS) is the most common female endocrine disorder and has important evolutionary implications for female reproduction and health. PCOS presents an interesting paradox, as it results in significant anovulation and potential sub-fecundity in industrialized populations, yet it has a surprisingly high prevalence and has a high heritability. In this review, we discuss an overview of PCOS, current diagnostic criteria, associated hormonal pathways and a review of proposed evolutionary hypotheses for the disorder. With a multifactorial etiology that includes ovarian function, metabolism, insulin signaling and multiple genetic risk alleles, PCOS is a complex disorder. We propose that PCOS is a mismatch between previously neutral genetic variants that evolved in physically active subsistence settings that have the potential to become harmful in sedentary industrialized environments. Sedentary obesogenic environments did not exist in ancestral times and exacerbate many of these pathways, resulting in the high prevalence and severity of PCOS today. Overall, the negative impacts of PCOS on reproductive success would likely have been minimal during most of human evolution and unlikely to generate strong selection. Future research and preventative measures should focus on these gene-environment interactions as a form of evolutionary mismatch, particularly in populations that are disproportionately affected by obesity and metabolic disorders.

LAY SUMMARY

The most severe form of polycystic ovary syndrome (PCOS) is likely a result of interactions between genetic predispositions for PCOS and modern obesogenic environments. PCOS would likely have been less severe ancestrally and the fitness reducing effects of PCOS seen today are likely a novel product of sedentary, urban environments.

High energy requirements and water throughput of adult Shuar forager-horticulturalists of Amazonian Ecuador

OBJECTIVES

We measured total energy expenditure (TEE; kcal/d) and water throughput (L/d) among Shuar forager-horticulturalists from Amazonian Ecuador to compare their daily energy and water demands to adults in other small-scale and industrialized populations.

METHODS

TEE and water throughput were measured using the doubly labeled water method among 15 Shuar adults (eight women, seven men; age range 18-60 years) living in a relatively remote village. We used multiple regression to assess the effects of anthropometric variables (body size, fat free mass, age, and sex) on TEE and water throughput. We also compared Shuar TEE and water throughput to those of other small-scale and industrialized societies.

RESULTS

TEE among Shuar adults (men: 4141 ± 645 kcal/d, women: 2536 ± 281 kcal/d) was most strongly correlated with fat free mass. Estimated physical activity levels (PAL) calculated as (TEE/estimated BMR), were greater for men (2.34 ± 0.29) than women (1.83 ± 0.14, P < 0.001). Water throughput was also greater among Shuar men (9.37 ± 2.34 L/d) than women (4.76 ± 0.36 L/d, P < 0.001). Shuar TEE and water throughput were elevated compared to adults in industrialized populations.

DISCUSSION

TEE and PAL of Shuar men are among the highest recorded during normal daily life, and likely reflect both high levels of physical activity and cultural dietary practices. Drinking large amounts of chicha, a traditional carbohydrate-rich drink made from manioc, likely contributes to the high levels of water throughput among Shuar men, and may contribute to elevated TEE.

Nutrition transition in 2 lowland Bolivian subsistence populations

Background

Traditional diets are often credited for the robust cardiometabolic health of subsistence populations. Yet, rural subsistence populations are undergoing nutrition transitions that have been linked to the increase in chronic noncommunicable diseases. Few studies have presented detailed dietary estimates in transitioning populations.

Objectives

We aimed to 1) characterize and compare dietary profiles of 2 neighboring subsistence populations in Bolivia who vary in market integration and 2) identify dietary factors contributing to low cardiovascular disease risk.

Design

We used a mixed longitudinal design to estimate nutrient intake via 24-h recall and dietary questionnaires among 1299 Tsimane (aged 30-91 y) and 229 Moseten (aged 30-84 y) men and women. We constructed population-level estimates of energy intake, dietary diversity, and nutrient shortfalls and analyzed dietary changes over time and space using multilevel models. Last, we compared Tsimane and Moseten dietary profiles with those of Americans (NHANES).

Results

The Tsimane diet was characterized by high energy (2422-2736 kcal/d), carbohydrate (376-423 g/d), and protein (119-139 g/d) intakes; low fat intake (40-46 g/d); and low dietary diversity relative to the average US diet. Most calories (64%) were derived from complex carbohydrates. Total energy and carbohydrate intake increased significantly during the 5-y study, particularly in villages near market towns. Tsimane consumption of food additives (lard, oil, sugar, salt) increased significantly [sugar (15.8 g ⋅ person-1 ⋅ d-1) and oil (4.9 mL ⋅ person-1 ⋅ d-1)] between 2010 and 2015. The more-acculturated Moseten consumed substantially more sugar (by 343%) and oil (by 535%) than the Tsimane.

Conclusions

A high-energy diet rich in complex carbohydrates is associated with low cardiovascular disease risk when coupled with a physically active lifestyle. A transition away from a high-fiber and low-fat, low-salt, and low-processed-sugar diet is a salient health risk for transitioning populations. Evidence of a nutrition transition in Bolivia parallels trends of increasing body fat and body mass index, which suggests that a low prevalence of cardiovascular disease may not persist.

Hunter-gatherers as models in public health

Hunter-gatherer populations are remarkable for their excellent metabolic and cardiovascular health and thus are often used as models in public health, in an effort to understand the root, evolutionary causes of non-communicable diseases. Here, we review recent work on health, activity, energetics and diet among hunter-gatherers and other small-scale societies (e.g. subsistence farmers, horticulturalists and pastoralists), as well as recent fossil and archaeological discoveries, to provide a more comprehensive perspective on lifestyle and health in these populations. We supplement these analyses with new data from the Hadza, a hunter-gatherer population in northern Tanzania. Longevity among small-scale populations approaches that of industrialized populations, and metabolic and cardiovascular disease are rare. Obesity prevalence is very low (<5%), and mean body fat percentage is modest (women: 24-28%, men: 9-18%). Activity levels are high, exceeding 100 min d^-1 of moderate and vigorous physical activity, but daily energy expenditures are similar to industrialized populations. Diets in hunter-gatherer and other small-scale societies tend to be less energy dense and richer in fibre and micronutrients than modern diets but are not invariably low carbohydrate as sometimes argued. A more integrative understanding of hunter-gatherer health and lifestyle, including elements beyond diet and activity, will improve public health efforts in industrialized populations.

Estimating the agreement between the metabolic rate calculated from prediction equations and from a portable indirect calorimetry device: an effort to develop a new equation for predicting resting metabolic rate

BACKGROUND

Many studies have been performed over time in order to determine the reliability of metabolic rate prediction equations.

PURPOSE

To evaluate the agreement, in terms of bias, absolute bias and accuracy between metabolic rate prediction equations and measured metabolic rate using indirect calorimetry system (IC), investigating also the factors affecting this agreement.

METHODS

The anthropometric features of 383 Caucasian participants of all Body Mass Index (BMI) classes were recorded and Resting Metabolic Rate (RMR) was measured by using the IC Fitmate portable device. The resulting values were compared with the predictive values of Harris & Benedict, Schofield, Owen, FAO-WHO-UNU, Mifflin and Harrington equations.

RESULTS

A closer approximation in agreement was obtained using the Harrington equation (based on BMI, age and gender). The equations using variables, such as weight, height, age and gender demonstrated higher agreement than the equations using merely weight and gender. Higher educational level was associated with normal weight, while higher calorific ratio was found in the class of normal-weighted individuals. An inverse relationship between ΒΜΙ and RMR was also observed and a logarithmic equation for calculating RMR was created, which was differentiated in relation to BMI classes, using the weight and gender variables.

CONCLUSION

A better measurement agreement between RMR prediction equations and IC may be achieved due to BMI consideration. The present findings contributed to a better understanding of the measured parameters, confirming the inverse relationship between BMI and RMR. Age group and gender variables may also exert significant role on the bias response of some RMR equations.

The inflammation paradox: Why are Tsimane protected against Western diseases while Westerners are not?

We here describe two apparent paradoxes concerning high CRP levels and NCD risk. One has emerged from observational studies in the Amazon region showing that the indigenous Tsimane in Bolivia appear protected against non-communicable diseases (NCDs) such as obesity, type 2 diabetes, and cardiovascular diseases despite increased inflammatory markers. These findings stand in contrast to Western societies, where an increasing body of evidence demonstrates that low-grade-inflammation is the driver of NCDs. The second paradox has emerged from two field studies (Eifel studies) conducted in 2013 and 2014 with Westerners who returned to a simulated Palaeolithic lifestyle in a National park for 4 days. We had detected elevated inflammation markers, despite otherwise anti-inflammatory effects of these interventions as indicated by metabolic blood parameters. We here propose three hypotheses for this second inflammatory paradox.

Expanding the insurance hypothesis of obesity with physiological cues

Food insecurity relates to fat storage, but cannot explain fat storage in excess of levels optimal for buffering - that is, obesity. However, factors related to food unpredictability in the past, including stress, disease, micronutrient content of food, and physical activity, may cue physiological processes that change intake or fat deposition even in the absence of actual food unpredictability.

Association between infection burden and adult height

Although highly heritable, adult height is also associated with numerous environmental factors, including exposure to infection. Particularly in developing regions of the world, infection burden appears to slow growth during childhood. Using a large database representative of the US population, we examined associations between adult height and leg length and an infection-burden index based on past exposure to Toxocara species, Toxoplasmosis gondii, cytomegalovirus, hepatitis A, hepatitis B, hepatitis C, herpes simplex virus 1, and herpes simplex virus 2. In models controlled for age, sex, educational attainment, socioeconomic status, and race-ethnicity, we found that the infection-burden index predicted height (β=-0.10 [95% CI: -0.15, -0.05], p .001<0.001) but not leg length (β=-0.04 [95% CI: -0.12, 0.04], p=0.357). Both sex and race-ethnicity moderated this association. In addition, exposures to Toxocara species, cytomegalovirus, and hepatitis A were each individually associated with reduced height and reduced leg length. While associations between growth and infection have been found principally in children in developing regions of the world, our findings suggest that the effects of infection on height may persist into adulthood even in developed nations.

The Tsimane Health and Life History Project: Integrating anthropology and biomedicine

The Tsimane Health and Life History Project, an integrated bio-behavioral study of the human life course, is designed to test competing hypotheses of human life-history evolution. One aim is to understand the bidirectional connections between life history and social behavior in a high-fertility, kin-based context lacking amenities of modern urban life (e.g. sanitation, banks, electricity). Another aim is to understand how a high pathogen burden influences health and well-being during development and adulthood. A third aim addresses how modernization shapes human life histories and sociality. Here we outline the project's goals, history, and main findings since its inception in 2002. We reflect on the implications of current findings and highlight the need for more coordinated ethnographic and biomedical study of contemporary nonindustrial populations to address broad questions that can situate evolutionary anthropology in a key position within the social and life sciences.

Horticultural activity predicts later localized limb status in a contemporary pre-industrial population

OBJECTIVES

Modern humans may have gracile skeletons due to low physical activity levels and mechanical loading. Tests using pre-historic skeletons are limited by the inability to assess behavior directly, while modern industrialized societies possess few socio-ecological features typical of human evolutionary history. Among Tsimane forager-horticulturalists, we test whether greater activity levels and, thus, increased loading earlier in life are associated with greater later-life bone status and diminished age-related bone loss.

MATERIALS AND METHODS

We used quantitative ultrasonography to assess radial and tibial status among adults aged 20+ years (mean ± SD age = 49 ± 15; 52% female). We conducted systematic behavioral observations to assess earlier-life activity patterns (mean time lag between behavioural observation and ultrasound = 12 years). For a subset of participants, physical activity was again measured later in life, via accelerometry, to determine whether earlier-life time use is associated with later-life activity levels. Anthropometric and demographic data were collected during medical exams.

RESULTS

Structural decline with age is reduced for the tibia (female: -0.25 SDs/decade; male: 0.05 SDs/decade) versus radius (female: -0.56 SDs/decade; male: -0.20 SDs/decade), which is expected if greater loading mitigates bone loss. Time allocation to horticulture, but not hunting, positively predicts later-life radial status (β_Horticulture  = 0.48, p = 0.01), whereas tibial status is not significantly predicted by subsistence or sedentary leisure participation.

DISCUSSION

Patterns of activity- and age-related change in bone status indicate localized osteogenic responses to loading, and are generally consistent with the logic of bone functional adaptation. Nonmechanical factors related to subsistence lifestyle moderate the association between activity patterns and bone structure.

Growth references for Tsimane forager-horticulturalists of the Bolivian Amazon

OBJECTIVES

Growth standards and references currently used to assess population and individual health are derived primarily from urban populations, including few individuals from indigenous or subsistence groups. Given environmental and genetic differences, growth may vary in these populations. Thus, there is a need to assess whether international standards are appropriate for all populations, and to produce population specific references if growth differs. Here we present and assess growth references for the Tsimane, an indigenous population of Bolivian forager-horticulturalists.

METHODS

Mixed cross-sectional/longitudinal anthropometrics (9,614 individuals; 30,118 observations; ages 0-29 years) were used to generate centile curves and Lambda-Mu-Sigma (LMS) tables for height-for-age, weight-for-age, body mass index (BMI)-for-age, and weight-for-height (WFH) using Generalized Additive Models for Location Shape and Scale (GAMLSS). Velocity curves were generated using SuperImposition by Translation and Rotation (SITAR). Tsimane ≤5 years were compared to World Health Organization (WHO) standards while those >5 years were compared to WHO school age references. All ages were compared to published references for Shuar forager-horticulturalists of the Ecuadorian Amazon.

RESULTS

Tsimane growth differs from WHO values in height and weight, but is similar for BMI and WFH. Tsimane growth is characterized by slow height velocity in childhood and early adolescent peak height velocity at 11.3 and 13.2 years for girls and boys. Tsimane growth patterns are similar to Shuar, suggesting shared features of growth among indigenous South Americans.

CONCLUSIONS

International references for BMI-for-age and WFH are likely appropriate for Tsimane, but differences in height-for-age and weight-for-age suggest Tsimane specific references may be useful for these measures.

Fecal metabolome of the Hadza hunter-gatherers: a host-microbiome integrative view

The recent characterization of the gut microbiome of traditional rural and foraging societies allowed us to appreciate the essential co-adaptive role of the microbiome in complementing our physiology, opening up significant questions on how the microbiota changes that have occurred in industrialized urban populations may have altered the microbiota-host co-metabolic network, contributing to the growing list of Western diseases. Here, we applied a targeted metabolomics approach to profile the fecal metabolome of the Hadza of Tanzania, one of the world's few remaining foraging populations, and compared them to the profiles of urban living Italians, as representative of people in the post-industrialized West. Data analysis shows that during the rainy season, when the diet is primarily plant-based, Hadza are characterized by a distinctive enrichment in hexoses, glycerophospholipids, sphingolipids, and acylcarnitines, while deplete in the most common natural amino acids and derivatives. Complementary to the documented unique metagenomic features of their gut microbiome, our findings on the Hadza metabolome lend support to the notion of an alternate microbiome configuration befitting of a nomadic forager lifestyle, which helps maintain metabolic homeostasis through an overall scarcity of inflammatory factors, which are instead highly represented in the Italian metabolome.

Immune function in Amazonian horticulturalists

BACKGROUND

Amazonian populations are exposed to diverse parasites and pathogens, including protozoal, bacterial, fungal and helminthic infections. Yet much knowledge of the immune system is based on industrialised populations where these infections are relatively rare.

AIM

This study examines distributions and age-related differences in 22 measures of immune function for Bolivian forager-horticulturalists and US and European populations.

SUBJECTS AND METHODS

Subjects were 6338 Tsimane aged 0-90 years. Blood samples collected between 2004-2014 were analysed for 5-part blood differentials, C-reactive protein, erythrocyte sedimentation rate (ESR) and total immunoglobulins E, G, A and M. Flow cytometry was used to quantify naïve and non-naïve CD4 and CD8 T cells, natural killer cells, and B cells.

RESULTS

Compared to reference populations, Tsimane have elevated levels of most immunological parameters, particularly immunoglobulins, eosinophils, ESR, B cells, and natural killer cells. However, monocytes and basophils are reduced and naïve CD4 cells depleted in older age groups.

CONCLUSION

Tsimane ecology leads to lymphocyte repertoires and immunoglobulin profiles that differ from those observed in industrialised populations. These differences have consequences for disease susceptibility and co-vary with patterns of other life history traits, such as growth and reproduction.

Cardiovascular disease and type 2 diabetes in evolutionary perspective: a critical role for helminths?

Heart disease and type 2 diabetes are commonly believed to be rare among contemporary subsistence-level human populations, and by extension prehistoric populations. Although some caveats remain, evidence shows these diseases to be unusual among well-studied hunter-gatherers and other subsistence populations with minimal access to healthcare. Here we expand on a relatively new proposal for why these and other populations may not show major signs of these diseases. Chronic infections, especially helminths, may offer protection against heart disease and diabetes through direct and indirect pathways. As part of a strategy to insure their own survival and reproduction, helminths exert multiple cardio-protective effects on their host through their effects on immune function and blood lipid metabolism. Helminths consume blood lipids and glucose, alter lipid metabolism, and modulate immune function towards Th-2 polarization - which combined can lower blood cholesterol, reduce obesity, increase insulin sensitivity, decrease atheroma progression, and reduce likelihood of atherosclerotic plaque rupture. Traditional cardiometabolic risk factors, coupled with the mismatch between our evolved immune systems and modern, hygienic environments may interact in complex ways. In this review, we survey existing studies in the non-human animal and human literature, highlight unresolved questions and suggest future directions to explore the role of helminths in the etiology of cardio-metabolic disease.