Evolutionary Drivers of our Taste Preferences for Vegetables

Penn State undergraduate student Hannah Marchok interviews Assistant Professor of Geography, African Studies, and Anthropology Bronwen Powell about her research into factors that may drive dietary practices across different groups of people in different regions of East Africa. Powell also shares her passion for wild foods, international collaborations, and inter-disciplinary approaches to dietary behavior change.

HOST:
Hannah Marchok, Penn State Biobehavioral Health, with a minor in Global Health; member of the Shriver Lab hair team

GUEST:
Dr. Bronwen Powell, Assistant Professor of Geography, African Studies, and Anthropology

Transcript

Mark Shriver:

From Penn State’s Center for Human Evolution and Diversity, this is Tracking Traits

[THEME MUSIC]

Nina Jablonski: 

Hello and welcome to the fifth episode of the Tracking Traits podcast. I’m Nina Jablonski , co-director of CHED – the Center for Human Evolution and Diversity at Penn State University. 

Mark Shriver:

And I’m Mark Shriver, the other co-director of CHED. Welcome to the podcast. 

Nina:

For today’s episode, we brought back interviewer Hannah Marchok, a Penn State Undergraduate Student in Biobehavioral Health with a minor in Global Health.

Mark:

Hannah currently works in my lab with Tina Lassi as part of the team researching human hair. In episode two, Hannah interviewed me about my life and work as a scientist. 

Nina:

She did a great job on that episode, asking you a lot of really thoughtful questions, Mark. In this fifth episode Hannah interviews Bronwen Powell, Assistant Professor of Geography, African Studies, and Anthropology here at Penn State. Bronwen is a research associate for the Center for International Forestry Research, and she looks at the social, cultural and environmental determinants of diet.

Mark:

A nd the research project that she talks about on this podcast is a great example of that. Like all the projects we talk about on Tracking Traits, this one was seed-funded by CHED – the Center for Human Evolution and Diversity. 

Nina

Bronwen’s CHED project, which she is conducting in collaboration with Helene Hopfler and Larry Gorenflo, seeks to understand the cultural and environmental factors that have shaped culturally-bound preferences for traditional and wild vegetables in East Africa.

Mark

Once again, we find ourselves examining the evolutionary interplay between human beings and other parts of the living world. 

Nina

Exactly. So much interesting research right now is focusing on these relationships that we have to place, and plants and animals. These relationships have tremendous impacts on who we are, who we become, and how we continue to co-evolve within this larger systems of life.

Mark

As usual, this episode’s conversation between student and scientist goes beyond the research as well. It touches on some of the personal dimensions of why Bronwen has gone into this subject matter, and some of her inspirations and international collaborations.

Nina:

And also as usual, we hear about how important it is for scientists from different disciplines to collaborate with one another to paint a bigger picture of what’s going on. 

Mark:

It really is a classic episode of Tracking Traits, if we can say that about a podcast that’s still in its first season.

Nina:

That it is! Well, why don’t we give it a listen? 

Mark:

Sounds good Nina. OK, here is Hannah Marchok interviewing Bronwen Powell about evolutionary drivers of our taste preferences for vegetables.

[MUSICAL INTERLUDE]

Hannah Marchok:

Thank you so much for joining us today, Bronwen. We're very excited to be discussing this topic with you and your research. Would you mind getting us started with just like a brief summary of what your research is?

Bronwen Powell:

Sure. My research looks at the social, cultural, and environmental determinants of diet nutrition and food security. A main focus of my research has looked at how landscapes and forests and wild foods contribute to human nutrition. And generally my research is somewhat applied. I really aim to inform policy about ways to improve food security and nutrition. With the CHED Project, the goal of that research is to try and determine if we can understand how preferences for traditional vegetables in East Africa evolve and whether they're shaped more by cultural or environmental factors, or maybe an interplay of both.

Hannah Marchok:

It sounds like a lot of your research is actually quite interdisciplinary and has the potential to have a wide array of effects on a variety of fields, but I want to know from your perspective, if your research progresses to what you would deem to be it's fullest potential, what implications do you propose it could have for the understanding of evolution and maybe even effects on daily living?

Bronwen Powell:

I've spent a lot of my career working with policymakers, specifically policymakers trying to shape a broad array of policies to improve food security and nutrition, and largely in African countries. And what I found is that there are a lot of legacies of colonialism in nutrition policy in many of the countries that I work in. So for example, nutrition experts would, when they arrive in a new place, not recognize many of the foods, especially wild vegetables that communities were consuming,  and therefore those vegetables ended up becoming very devalued. For example, one community I work in, in Ethiopia, when you ask women there what are healthy foods? They list canned tuna and pasta, which are foods they've never even consumed. And this is a result of nutrition education information being written by people who aren't familiar with their food system and their cultural preferences.

So there's a lot of work to be done to overcome some of these colonial legacies. And even today, nutrition experts from various countries are still trained in curriculum that isn't written for that local context. And so if this project is able to really highlight the potential health benefits of traditional vegetables and the fact that people and particular ethnic groups might have a genetic adaptation that enables them to benefit more than other communities from the consumption of certain vegetables, that would really help to counter some of these colonial legacies. Then that has really important implications for how we promote these healthy foods, fruits and vegetables. Low fruit and vegetable consumption is one of the top ten modifiable risk factors for mortality globally. And even in rural African communities, people don't consume enough vegetables. And we know that cultural identity can really shape our dietary choices and our dietary preferences. So if we can highlight that co-evolution of culture and diet, then I think there's a lot of room to use that to encourage more vegetable consumption and consumption of these traditional vegetables.

Hannah Marchok:

Just from listening to it, it sounds like the possibilities and potential really exciting affects are almost endless with your research. So I would appreciate you telling me what excites you when you wake up in the morning excited to go and work on this project. 

Bronwen Powell: 

I have a small obsession with wild food that comes from my childhood. I grew up just outside of Toronto in Canada, in a rural area. And my dad was also really fascinated with wild food, and so we would go and learn new things. But certainly fiddleheads and berries and other things were pretty central to my upbringing. Throughout my childhood we picked and sold fiddleheads to fancy restaurants. So whenever I get to work on projects that have something to do with wild food that's really exciting to me, but that research can fulfill my curiosity and at the same time have the potential to improve human wellbeing is a really big motivator for me.

Hannah Marchok:

Your work has often left you interacting with and working with people from many different countries and regions of the world, so how do you think working with people internationally has shaped your views of the importance of your work and research?

Bronwen Powell:

I've been very lucky to work in multiple research settings, and I've also been very lucky to have mentors from very diverse places. One of the mentors who's really shaped my thinking about this project is my dear mentor, Dr. Patrick Maundu who is a Kenyan ethnobiologist, one of Africa's most recognized and esteemed ethnobiologists. He also works on wild vegetables and he kept telling me, "Those Luo-speaking communities, they really love slimy vegetables." And so it was really thanks to him that I got interested in the evolution of cultural preferences for diet,    with regard to this project. And I can't emphasize enough how much my thinking has expanded in really neat and diverse interdisciplinary ways from having benefited from mentorship from people from all over the world.

Hannah Marchok:

Mentors can be especially helpful in shaping our own views about things and even bringing new ones to light. And I understand that some of the basis of your research is actually based off of one of your mentors’ theories, is that correct? 

Bronwen Powell:

Yeah. So in addition to this cultural preference seen, that Dr. Maundu hypothesized for Luo and other Nilotic-speaking communities for slimy vegetables, in East Africa, if you're lucky enough to travel around and get to know multiple communities, you see that some really express a strong preference for bitter vegetables and others really don't. And I found that really interesting. And at the same time, I have heard foreign experts warn against the consumption of traditional bitter vegetables, being fearful of potential toxicity from bitter phytochemicals in them. And so it really made me wonder if there was some adaptive function for those cultural preferences. 

To date, what we've done is we have a map of where all of the different ethnic groups are across East Africa. And we combed the literature to create a new data set of which of those ethnic groups consume or prefer bitter vegetables. And what we see is that the communities that have historically, at least, of course there's migration and intermixing and intermarrying, but the communities that have historically lived in places with high malaria prevalence are consuming more bitter vegetables and that's a fairly statistically significant relationship.

With the slimy preference, which isn't as much a focus in the proposal that we submitted to CHED, it seems to be more cultural. We're hypothesizing that there might be a microbiome link, because slimy vegetables have a lot of soluble fiber and soluble fiber is really important for microbiome. We see a lot of slimy vegetable consumption in Nilotic-speaking groups. Nilotic-speaking groups also tend to be pastoralists, right? So there may be some adaptive function where the slimy vegetables support a microbiome that supports a dietary pattern associated with pastoralism that then doesn't cause negative health outcomes that would otherwise come from a diet based primarily on animal-sourced foods.

Hannah Marchok:

Do you see a time in the future where we'll be able to use our own genome to determine what an individual's perfect diet could be?

Bronwen Powell:

Yeah, for sure. And I don't think it's so much in the future as already happening. There are companies out there that do your genetic profile for you and then make dietary recommendations. I think it's complicated because it's not just genetics, it's also microbiome. And how those, and culture, and genetics, and microbiome all interact, and our environmental exposures and potentially the environmental exposures of our parents all come together to shape which foods are most healthy for us. And I think the nutrition community is aware of this, but it takes a while for practice to catch up. We know that microbiome, for example, shapes how efficiently we use energy from food, but we still, when we talk about dietary advice, it's still calories in equals calories out. And so it takes a while sometimes for the dietary advice to catch up with the science.

Hannah Marchok:

So another thing that you've kind of mentioned here during our discussion is that through colonialism and certain dietary recommendations, preferences for certain vegetables have almost been ostracized or looked down upon. Do you think that a better understanding of the complex evolutions of these dietary preferences could lead to more of an appreciation of diversity rather than fear or ostracization because of it?

Bronwen Powell:

Yeah, certainly that's the hope. You know, I t's very fine for a researcher from Europe to say, "Oh, I'm afraid to eat that vegetable. I worry it might make me sick." But that researcher has a very different genetic makeup than communities in East Africa and they come from a different ecological setting. And so what we've hypothesized for our project is that communities that live in places where there's high malaria prevalence have evolved, whether it's culturally or genetically is yet to be determined, but have evolved to have a preference for consumption of bitter vegetables.

And there's enough evidence to suggest that bitter compounds may have anti-malarial activity. Of course quinine, being the original anti-malarial drug, is very bitter. People are familiar with quinine because it is put in tonic water. And so even those colonial experts originally would have drunk gin and tonic as an anti-malarial prevention. So the idea that communities are consuming bitter vegetables to help mitigate the risk of malaria it's plausible. So I think if we can demonstrate that, then it will really help to promote and revive the preference and consumption of traditional vegetables.

Hannah Marchok:

That's so interesting to think that what people are eating could sincerely be affecting their resistance to something as potentially devastating as malaria. 

[MUSICAL INTERLUDE]

Hannah Marchok:

Now, even just what you've mentioned here, really requires an understanding of history of colonialism and obviously of diet preferences and perhaps some basic biology, of course, so your work is incredibly interdisciplinary, could you explain to the audience just how interdisciplinary it is in terms of how you would promote healthy eating, if it is in fact understood that these could really be helpful vegetables to consume?

Bronwen Powell:

Well, I think the food and nutrition community have been trying to change the trajectory of dietary change for a long time. The global food and nutrition community have spent a lot of effort trying to get people to eat better, right? And increasingly we realized that just telling people what's healthy isn't going to get behavior change. And so it's increasingly apparent that in order to achieve changes in what people eat, the food and nutrition community has to partner with anthropologists, psychologists, economists, other social scientists, even people working on marketing and in other disciplines. And that drawing on theory and work from across all of these disciplines, we might then be able to see more efficient behavior change through policy and programming.

Hannah Marchok:

Could you describe some of the biggest frustrations that you may experience during your research process?

Bronwen Powell:

Certainly with this project, COVID-19 has had a huge impact. We had planned to go to Tanzania and actually test people's taste preferences for bitter vegetables using food science methodologies, where we give people samples of foods and ask them to rank which they prefer, using a non-bitter vegetable and adding bitter compounds to it to see if people from different ethnic groups do prefer bitter or not.

Of course with COVID-19, number one, we can't go to Tanzania and number two, we certainly can't sit face to face with people and feed them stuff. And of course, Tanzania is a particularly interesting case in terms of COVID-19. And as I, a researcher, committed to decolonial approaches to health, Tanzania has rejected the WHO's involvement in their COVID-19 response and stopped reporting COVID-19 caseloads early on during the pandemic. And so, the uncertainty around that and uncertainty around when we'll actually get to do this next phase of our research project has been probably the biggest frustration for this project.

Hannah Marchok:

So sort of opposite to that, what do you feel would make a strong research project?

Bronwen Powell:

Well  you know, next steps, I would love to include a genetic testing and of course that's sensitive. But there's so few actual demonstrated co-evolution of human and diet examples. And the preliminary research we've done, which includes an extensive literature review and spatial analysis looking at vegetable preferences reported in the literature for ethnic groups across East Africa really we do see a statistically significant association between malaria prevalence and preference and consumption of bitter vegetables. And so it would seem that this may be another case of co-evolution. So I would love to be able to actually demonstrate that with pairing the food science work of taste preferences with genetic assessment.

Hannah Marchok:

That's very interesting. Once again, using interdisciplinary models to give more explanation and just more context to your research and hypothesis. So I suppose that genetic testing and field work are what is next for you and your research?

Bronwen Powell:

Well, certainly with the current project, we hope to do the field work for taste preferences. The genetic testing we would need another collaborator that currently on our project we have geographers, I have a PhD in nutrition, and we have a food scientist involved as well, but we don't have anybody with the expertise on human genetic evolution, so I hope that that will be a next step after the CHED project.

Hannah Marchok:

Adding a teammate to make the team even stronger, nice.

Bronwen Powell:                                                                                                                        And some more funds I think. (LAUGHS)  

Hannah Marchok:

So I am really interested to know, first of all, what impact you would like your research to have, which we've touched upon here thus far, but also if this has changed over the course of your work and your research on this project or even as a nutritionist?

Bronwen Powell:

I'm not sure it has changed. I think I'm pretty focused on that broader impact of informing policy to really promote consumption of fruits and vegetables, given that we have this very clear evidence of the association between fruits and vegetables and chronic disease, as well as micronutrient deficiencies. And we know that fruit and vegetable consumption is low worldwide, including in communities in East Africa. That to me is always the end goal. But certainly this project has really engaged my curiosity with that co-evolution of dietary preference and human genetics in a way that I hadn't really focused on previously. And the other thing that's really neat is that it's so trendy these days, right? We hear all these things about eating right for your genetics and yet there's not a whole lot of evidence for that. So I think it's an area of research that I'll continue to be interested in moving forward.

Hannah Marchok:

I love what you mentioned about it being a sort of trend right now, but you're out here doing the research to prove that it's actually something viable. When it comes to actually being in the kitchen, getting ready to prepare a meal, how do you make a meal attractive to a child? How do you make a meal attractive that culturally it may not be the most exciting thing to a five-year-old, a six-year-old?

Bronwen Powell:

Yeah, that's a great question. It's not just about knowing what to eat, it's about knowing how to change behavior. And I always use myself as a good example. I have a PhD in nutrition and I don't always make good dietary choices. I think that's true of all of us. Even women in rural communities, they know that they shouldn't feed their kids candies and soda, but sometimes they do. So telling them that they shouldn't feed their kids candies and soda isn't necessarily going to change behavior. Increasingly, the food and nutrition community are aware of this and so they are seeking input from fields such as anthropology and sociology. So one example of a behavior change strategy or something that affects what people choose to eat is that identity and that cultural attachment to foods. French sociologist Claude Fischler who drew on the work of Levi-Strauss and others said, "If we are what we eat, then it's natural for people to try and shape their identity by eating specific foods."

And so in places where soda marks social prestige, it's not surprising that people consume a lot of soda because it helps them to mark themselves as no longer poor. And so that certainly is the case when it comes to vegetables. All over the world, traditional vegetables have gotten a bad rap. They're not cool because they for years have been seen as weeds. Like just the word weed has a very strong impact on whether we think that's palatable. And so if we can build on these ideas that these foods are part of our heritage, they're part of, well, a community's heritage, they're part of their identity and build people's pride in those traditional foods, then maybe the kids will be more willing to consume them, right? If they're seeing them as something that marks prestige, marks social status, that will change choices about what to eat and what not to eat.

Hannah Marchok:

What you said made me think about college students. Some college students I know don't even want to drink, but they think that, well, everyone else is doing it, and it means something. If you're putting significance to a food or a drink or a meal, you're automatically changing how significant it is to consume a certain thing.

Bronwen Powell:

Marketing companies know this very well, right? They are very efficient at shaping what we think are prestigious foods and shaping what our children think are prestigious foods. And I'm always shocked by how much my five-year-old's willingness to eat a food is shaped by what she sees her peers eating and enjoying and valuing.

Hannah Marchok:

So sort of moving to a broader question here, why do you do what you do? What sparked your interest in science? What sparked your interest in nutrition?

Bronwen Powell:

Well, I mentioned that I've got a small obsession with wild food and that started in my childhood. I tell all my students here at Penn State that if they see me in a ditch it's probably because I'm trying to collect weeds for dinner. I try to practice what I preach. So as a kid I spent a lot of time in the forest learning different wild foods and learning how to cook them, and then having researched wild foods in many different around the world, now the ways I prepare wild foods here at home in North America and the species I use, have grown and diversified significantly, bringing home some of that knowledge I've learned in communities in Africa and elsewhere.

Hannah Marchok: 

I would love to know what is your favorite weed or random plant to cook up?

Bronwen Powell:

(LAUGHS) So there's a species that's consumed, it's slightly bitter. It's not as bitter as some species. It's called Bidens pilosa. Black Jack, it's called an English. It's a weedy species with a little yellow flower and it's consumed across Tanzania. In Swahili it's called kiso yangu which means “sticks to your clothing.” It is literally a weed that has a seed that will stick to you if you walk through a patch of it when it's in seed and that's most definitely my favorite wild vegetable. 

Hannah Marchok:

So this is actually my final question for you today, and we've asked it of everyone else who we've been interviewing for this podcast, what is one piece of advice that you would give to budding researchers?

Bronwen Powell:

Yeah, do something you love. If you don't love it, probably you shouldn't go to graduate school because it's a lot of work. And so you have to be curious, you have to be willing to put in the hard work. And if it's something you're really interested in, that really helps. 

Hannah Marchok:

The first step is having a passion for something, great. Thank you so much for taking the time to speak with me today. I have greatly enjoyed our conversation. I've learned quite a bit even more about you and your passion and just how important it is to take something you're really passionate about and hold on to that. And maybe you can make something really, really cool and impactful out of it.

Bronwen Powell:

Thank you, Hannah. It’s been fun.

[MUSICAL INTERLUDE]

Mark Shriver:

Tracking Traits is a production of Penn State’s Center for Human Evolution and Diversity. Our producer, audio engineer and musical theme composer is Cole Hons, and our logo was designed by Michael Tribone of mtribone design. 

If you enjoyed this podcast, please subscribe through your favorite app, and help us reach more people by sharing it with others and rating us on Apple podcasts. 

You can also follow us on social media and learn more about CHED and all of our interviewers and guests at our website, ched – that’s C H E D dot L A dot P S U dot E D U.