Fit, Fat, & Cold

It is rare when I truly love something I write or an idea that I have. I tend to be hypercritical and continually play devil’s advocate with myself. And though that is likely a good thing for science, it often means I get less joy from the grueling process I put myself through. This new article, however, is the exception.

Dr. Alexandra Niclou and I recently published a commentary in Evolution, Medicine, and Public Health. In this article, we not only tear down the current concept and broad use of body mass index (BMI), but also present how the suite of features we typically see among cold climate populations may confer a metabolically healthy obese phenotype (or the fit and fat phenotype). The idea of a fit and fat phenotype has been around for a short while – it suggests that individuals can have a high BMI/high body adiposity but not suffer any of the cardiometabolic consequences often association with a high BMI/high body adiposity.

I have been percolating this idea for a fair amount of time since working through the data on reindeer herders, who despite having high BMI/body adiposity, have relatively healthy indicators of cardiometabolic health. There is a growing body of evidence, though not without controversy, that a metabolically healthy obese phenotype is a reality, rare, but a reality. I began to wonder how some of the interesting physiological and morphological variation we ascribe to cold climate populations may predispose these folks to a metabolically healthy obese phenotype.

Schematic representing how the different suite of morphological, physiological, and behavioral characteristics of cold climate populations may lead to a metabolically heathy obese phenotype.

In this paper, Alex and I work through the evidence and present a fit, fat, and cold hypothesis that still needs a great deal of testing. Theoretical though it may be, I think this is an intriguing possibility and one that could impact how individuals with high adiposity (and low adiposity) are treated by medical doctors.

How Climate Change is Affecting Finland

I was fortunate enough to be invited to contribute to an American Journal of Human Biology special issue on extreme weather events and they impact they can have on human health and wellbeing. Thank you to Asher Rosinger for the invite and putting together a timely and important series of articles!

My main research focuses on how reindeer herders of subArctic Finland cope with a physically demanding occupation in extreme cold. However, it is hard to work in Finland and not see the dramatic impacts that climate change are having on the landscape and the people. My wonderful collaborators, Drs. Minna Turunen and Päivi Soppela, have conducted a great deal more research on how climate change has impacted the reindeer herding occupation. For this contribution, the three of us worked with Dr. Sirpa Rasmus to review the ways in which climate change has increased the number of extreme events, in particular icing events in Finland and in turn how these events impact the landscape, the reindeer, reindeer herding, and the herders themselves.

Change in winter temperatures in Finland

In short, an increased number of rain-on-snow events that create icing conditions dramatically impact the reindeer herding livelihood from forcing herders to increase greater control of their herd, needing to increase agricultural production to feed reindeer, poor reindeer health, and negatively impacted herder heath through increased risk of cold related injuries and mental health concerns. Reindeer herders demonstrate a wide range of resilience behaviors for confronting these extreme events; however, there is likely a limit to what can be done.

This schematic depicts some examples of the downstream effects climate change has on the environment, reindeer herds, herding husbandry, and herder health. The solid lines represent the impact of climate change on various features of reindeer herding husbandry, and the hashed lines represent the aspects of reindeer husbandry that may exacerbate the effects of climate change.

Proud to introduce Dr. Alexandra Niclou

It has been a wonderful and fruitful journey (not without its troubles thanks to COVID and my changing institutions), but I am so VERY PROUD to say that my student, Alexandra Niclou, is now Dr. Alexandra Niclou.

Alex (right) and I (left) after the hooding ceremony.

Alex is beyond brilliant, and I consider myself exceptionally lucky to have been a part of this process. Watching her grow, manage so many obstacles, and surpass me has truly been an honor and humbling experience.

Alex’s dissertation work focused on brown adipose tissue (BAT) among individuals in Samoa. This work is not only fascinating, but unique and groundbreaking, as it is the first time BAT has been measured among an adult tropical population. This work provides critical insight into the question, “Do all humans have BAT?” and, if so, “How does BAT function differently in different populations?” In order to conduct this work successfully, she developed collaborations with colleagues who work in Samoa. This includes Dr. Nicola Hawley from Yale and the Samoan Obesity, Lifestyle and Genetic Adaptations Study (OLaGA) team.

Alex found the cold adaptive BAT among the tropical Samoans. This unexpected finding suggests that BAT may be present in all humans. However, she also found that it functioned differently than among the Albany population she worked with previously and work conducted among cold climate populations by other researchers. By examining the presence or absence of this tissue in a tropical population, she has greatly added to our understanding of the role brown adipose tissue plays in human evolution and adaptation as well as addressing human variation and the unique morphologies exhibited by Polynesian populations. Furthermore, this work has the potential to reveal a therapeutic role for BAT in treating the global obesity epidemic and diabetes given the metabolic and glucose disposal properties. This is all to say that Alex’s work is not only exceptional within the field of human biology and anthropology, but also has real world implications.

Brown adipose tissue thermogenesis among a small sample of reindeer herders from sub-Arctic Finland

Yes, I am WAY behind on updating my website with various things! Here is another brown adipose tissue article recently out. This one is done in collaboration with Drs. Päivi Soppela, Minna Turunen, Ville Stenbäck, and Karl-Heinz Herzig.

We measured brown adipose tissue activity (using indirect calorimetry, thermal imaging, and mild cold exposure) among reindeer herders in Finland. We found that herders do indeed have active brown adipose tissue (BAT). When activated, resting metabolic rates increase significantly by 8.7%, warmer supraclavicular temperatures (BAT positive region) relative to sternum temperatures (BAT negative regions), and BAT among this sample preferentially uses fatty acids for fuel (a low RQ – respiratory quotient). This is different from other studies that have shown a preference for glucose or mixed glucose-fatty acid as fuel among other populations.

Resting metabolic rate at room temperature and during cold exposure when BAT is activated.

There were no correlations of BAT with any anatomical or physiological variables with the exception of a negative correlation between a change in RQ and the change in supraclavicular surface temperatures. Based on work by Dr. Stephanie Levy, this lack of correlation with various anatomical and physiological variables might be due to BAT activity being determined or at the very least influenced by cold exposure during key developmental periods in childhood.

Supraclavicular (BAT positive) and Sternal (BAT negative) surface temperatures during room temperature and mild cold exposure. The supraclavicular region stayed significantly warmers than the sternal region.

This study shows that BAT activity is highly variable even among different cold climate populations, and that like high altitude populations, there are often different ways the body copes and adapts to similar environments.

Weather Permitting: Increased seasonal efficiency of nonshivering thermogenesis through brown adipose tissue activation in the winter

Very proud to share this new article written by the newly minted Dr. Alexandra Niclou (my now former PhD student).

This work looked at brown adipose tissue activation between summer and winter among folks in Albany, New York. We compared changes in metabolic rate, respiratory quotient, & supraclavicular heat dissipation between room and mild cold temperatures in summer & winter. The participant pool was largely the same between the two seasons.

During cold exposure – when brown fat is activated – supraclavicular temperatures were greater in winter compared to summer while metabolic rate did not change. RQ – an index for substrate utilization – significantly increased in winter compared to summer, suggesting increase in preference for carbohydrates as fuel in winter.

This demonstrates that inferred brown fat activity is greater, more efficient, & increases glucose use in winter. Brown adipose tissue may play a role in seasonal cold acclimatization and glucose disposal in humans.

These figures show the metabolic rates, respiratory quotients, and supraclavicular temperatures for females, males, and the sample overall for summer and winter measures of brown adipose tissue.

First paper of 2022 came out today in the International Journal of Circumpolar Health! For this paper we looked at potential associations between body mass index and body adiposity with cholesterol and glucose levels among a small sample of reindeer herders in sub-Arctic Finland.

Despite over 70% of the herders being classified as having obesity or being overweight, blood biomarkers were largely normal. Though total cholesterol was high, this appears to be largely driven by high HDL cholesterol levels. Furthermore, glucose levels were also relatively normal.

Though the sample size is small, there does not appear to be a strong correlation between BMI, body adiposity and some indicators of cardiometabolic health, which has been seen among other populations.

This adds further evidence that using BMI and its health correlates as a diagnostic tool is not particularly helpful especially as the individual level.

Furthermore, as the reindeer herders are highly physically active and have a variety of cold climate adaptations, we could be seeing a demonstration of the fat and fit (and cold) hypothesis playing out.

Reindeer Herder Total Energy Expenditure…Reindeer Herders Work Hard!

I am excited to share our new publication about Reindeer Herder total energy expenditure (TEE, kcal/day)! This work is the result of a collaboration with Dr. Päivi Soppela, Dr. Minna Turunen, Ville Stenbäck, Dr. Karl-Heinz Herzig, Dr. Rebecca Rimbach, and Dr. Herman Pontzer. We measured how many calories the reindeer herders in sub-Arctic Finland expend and consumed during an exceptionally busy time of year…the autumn herd roundup. We also included some pilot data from a much less busy time in the spring.

The herd round up consists of collecting reindeer from their summer pastures either on foot or with the aid of all-terrain vehicles, motorbikes, snowmobiles, or helicopters. During this time, herders count the number of reindeer, separate the animals to be left alive from those to be slaughtered, mark calves with the owner’s earmarks, and return any wayward reindeer to their proper owners.

A picture of the 2019 autumn herd round up. Photo taken by Dr. Minna Turunen.

Here are some of the key findings:

Herders are very active during the annual herd roundup!

We measured TEE using two methods: the gold standard doubly labeled water technique and the flex-heart rate method. During the herd roundup, herders expended a mean of 4183 ± 949 kcal/day with female TEE ranging from 2898-3887 kcal/day and male TEE ranging from 3463-5853 kcal/day. There was no significant difference between the two methods.

Herder total energy expenditure by sex and measurement method

Herders eat way fewer calories than they burn during the roundup, and their diet is relatively high in fat.

Females consumed 883-2195 kcal/day and males consumed from 854-3638 kcal/day, which is well under the number of calories they were burning each day. Diet information was collected via diet diaries, and this can be a rather inaccurate estimate of calories consumed. However, even if herders underreported calories by as much as 20%, they still would have expended ~1000 kcal more than they were consuming each day during the herd roundup. The herders’ diet consisted of a greater proportion of protein and fat than is recommended by the World Health Organization (WHO).

Herder diet composition (right) compared to WHO recommendations (left)

Herders expend a similar number of calories to farming economy populations like the Aymara speaking peoples and Shuar…at least during the herd roundup.

We compared the herder total energy expenditure to that of hunter-gatherers, farming economy populations, and market economy populations. Herder TEE was significantly higher than hunter gatherer and market economy populations, but very similar to that of the farming populations. However, herder TEE was much lower during the spring pilot study, though May is a particularly less busy time of the herder year.

Log TEE vs. Log Body Mass Regression. The herd roundup is represented in bold red and the herder spring pilot study in bold black.
TEE residuals for each of the comparative populations

Given exposure to extreme cold in addition to high physical activity levels, one might expect herder TEE to be significantly higher than, rather than equivalent to, equatorial farming economy populations with similar activity levels but a potentially reduced thermoregulatory burden. There are several potential explanations for the similar energy expenditure among the herders and the farming economy populations, all of which highlight how local ecologies and biologies likely play an important role in shaping energy expenditure.

  1. Herders are very good and very experienced at mitigating cold stress – using technology, alternating tasks, and eating warming foods, for example.
  2. The herders’ high levels of physical activity may help reduce the cost of trying to stay warm in their cold climate.
  3. The farming economy populations are also known to carry a high parasitic burden (though cold climate populations have their fair share of such burdens, too, though not to the degree of equatorial populations). This high parasitic burden can raise energy expenditure in the way that the need to keep warm may raise energy expenditure among the herders.

What’s Next?

Well, we are applying for funding in hopes of expanding TEE measurements across seasons to get a better, more detailed view of energy expenditure across the herder work year. We would also like to expand the number of participants, and begin to look at the impact of climate change on reindeer herder TEE and other physiological measures.

Cultural Cold Climate Coping Mechanisms among Reindeer Herders

Our new paper in ARCTIC is out! This paper looks at the cultural cold climate coping mechanisms among the reindeer herders we worked with in 2018 and 2019. We discuss different coping behaviors that range from physical activity style decisions, ecological knowledge, technology, clothing, food, and more!

A picture from this paper was also chosen to be the cover of the upcoming ARCTIC Issue.

Please contact me for a PDF!