SciCafe: Orangutans, Obesity, and Human Evolution

ERIN VOGEL (RUTGERS UNIVERSITY): While Louis Leakey is best known for his transformative fossil discoveries, he also knew that in order to understand the evolution of diet and behavior, and ultimately gain an understanding of how humans were so evolutionarily successful, we really need to take a comparative approach and study our closest living relatives, the primates.

He knew that fossils alone could not tell us what early hominids were doing, and how they survived in a changing environment. But what we could do is study primates in their natural habitats and really begin to unravel some of these mysteries of human evolution. We could begin to ask questions like, what were they eating? How did they survive the lean periods? How social were they, and how did they compete for limited resources?

And many of you may ask, why orangutans? Orangutans, their lineage split from the human lineage about 14 million years ago. So why not study chimpanzees, that split only about six million years ago?

Well, through the work that we’ve been doing in my lab, we found that orangutans have a lot in common with humans, particularly when we’re thinking about diet and health. For example, orangutans have a great propensity to put on body fat when they’re in an energy rich environment. They get really fat when you give them high energy foods.

So the work in my lab particularly focuses on how this changing environment and the variation and the availability of food resources, and particularly fruit and the habitat, influences the dietary strategy of orangutans. And how that, in turn, affects their health.

And I hope that through this research, I’m able to gain an understanding of perhaps how this changing environment influences their health, and we can begin to get a better understanding of how we’ve gotten ourselves into this incredibly, this worldwide obesity epidemic. So how has the human diet changed over time?

So the story I’m going to tell you about today begins with the orangutan, the only great ape other than ourselves found in Asia. And orangutans are found in Indonesia, on the islands of Sumatra, shown here, and Borneo, shown here. And where I work is the Tuanan Orangutan Research Center, which is located right there. It’s in central Kalimantan in Indonesia.

And what’s interesting is that the rain forests of Borneo are often viewed as impoverished habitats for the frugivores that inhabit them. And these forests are different than the rain forests that we find in other parts of the world, and the reason is that these forests are characterized by these high periods of fruit availability, but these periods are quite unpredictable, and they’re often followed by long periods of low fruit availability.

Now these rises and low periods of fruit availability have been closely linked to El Niño events, and what we’re also seeing is that when we have these major fires, and they’re becoming more and more common in Indonesia due to rising temperatures, what we’re seeing is that these periods become much longer. And so for a large arboreal frugivorous primate like an orangutan, they’ve got to figure out how to survive during these periods of very low food availability and fruit availability. And this is really what my research focuses on.

So today, I’m going to run you through how this unique ecology that we see in Southeast Asia influences the dietary strategy of wild orangutans, and how that strategy then interacts with their physiology and ultimately influences their health. And then I’m going to bring that back, bring this all back to what’s going on with the human obesity epidemic that we’re currently experiencing.

So through the research in my lab, we found that one way that orangutans are able to survive these really long periods of low fruit availability is that they feed on a really high number of species. They consume over 248 species of plant food items in the forest—just species alone. If we look at the different items of those plant species, like bark and leaves and flowers and fruit, what we find is that they’re feeding on about 416 unique species parts.

Now that’s quite a lot of different food items to feed on. But if we compare them, say, to chimpanzees found in Uganda, in Kibale Forest National, they’re only feeding on about 111 species of plant items, and about 179 unique species and parts. So what orangutans are doing is they’re feeding on a real big variety, a large variety of different resources.

And what we’ve also found is that during the high fruit availability, they prefer to eat fruit. They spend about 75 percent of their time feeding on fruit, and they spend a small amount of time eating leaves and bark and flowers and other vegetation for some of the macronutrients that they need to get that they can’t get from fruit.

But during this low fruit availability period when they can’t find fruit, instead of traveling further to look for fruit, they switch, and they do what we call dietary switching, and they switch to what we often refer to as fallback foods. And these are foods that tend to be lower in nutritional composition, lower in overall calories. And they spend more time feeding on bark and leaves and flowers as well.

Well, what this results in is over a 50 percent reduction in total caloric intake during these low fruit periods. So they’re drastically reducing their caloric intake. And more recent studies by Herman Pontzer and his group has found that if we look at body mass on the X axis here, and energy expenditure on the Y, and we look at orangutans, Pongo, in orange here, they’re significantly shifted down compared to gorillas, chimpanzees in blue, and humans.

So on a per unit body mass, or on a cellular level, orangutans have actually slowed everything down. They’ve just kind of slowed down their cellular processes. And what we see is even when we look at resting or basal metabolic rate, we see that they’re significantly lower than other ape species, including ourselves.

And so perhaps this partially may explain why orangutans get so obese in zoos and in captive settings, when they’re exposed to a high energy environment. But this can’t explain everything.

So to look at the relationship between nutrition and health, I go to central Kalimantan on the island of Borneo, and my field site is located along the Kapuas River. It’s called Tuanan, and it’s represented by that star. And these red lines here represent the trail system that we have throughout the forest, where we study a population of orangutans. And we’ve been working there now since 2003, and we have been collecting data year round for the past 15 years, with a very large research team.

This is what our camp looks like, in case you’re curious. We don’t have cellphone communication, we don’t have Wi-Fi, we don’t have electricity. But we have solar energy and a generator, so you can charge things up for a little bit.

And over the past 15 years we’ve been studying approximately 61 habituated animals. So that means that they’re used to us, and they no longer alarm at us or react to our presence.

We follow these animals from the time they wake up in the morning in their nest to the time they go to bed at night and make a new nest. So we call those nest to nest follows, and during that time, we record everything they’re eating and everything they’re doing throughout the whole day. And we follow an individual for five to 10 days each, and we’re often doing several simultaneous follows at one time.

We also are able to monitor trees in the habitat to gain an understanding of the availability of food resources in their habitat. So we monitor every month 2,400 trees that have their own numbers and tags, and we go and we look to see if they’re producing fruit, how much, what stage of ripeness, how many new leaves they have, are they producing flowers. And we do this every month.

So we’ve got this really wonderful long term data. Now a lot of people ask me, how do you collect data on nutrition? Well, we can’t go up into the trees when the orangutans are there feeding, so we often wait for the orangutans to come down from the trees, we mark the trees, and then we climb up the trees and collect the fruit that they’re feeding on. And in fact, one of my grad students who is here has done a lot of tree climbing, so he knows.

So we go up, we collect these fruit samples here, and then we process them in camp for the parts that the orangutans are feeding on. We dry them in our ovens, and then we send them to a lab in Indonesia. And basically what comes back to us is the nutrition facts label for all of the species and items that they’re feeding on. And we have an idea of how much fat, how much protein, how much carbohydrates, how much fiber in each food item.

We can take these data and combine them with the behavioral data, so all the feeding data that we’re collecting, and we can estimate how much, how many calories they’re getting on a daily basis, how much protein, how much fat, how much fiber. And then we can relate that back to health.

A lot of people ask me, how do we monitor their health? These are our boreal mammals in the trees. So what we do to monitor their health is the same thing that happens when you go to your doctor’s office for an annual physical and they collect a cup of pee. Only we can’t ask the orangutans to give us a cup of urine. So instead, when they come out of their nests, they wake up in the morning and the first thing they do is urinate. So we go out, before they come out of their nests, and we prepare our bags on a stick, and we wait for them to urinate and catch their pee in a bag. And it’s been actually voted one of the top worst jobs in science by Popular Science Magazine, which is pretty cool, I think. I think that’s pretty awesome.

So once we collect these urine samples we process them in the forest and we use the same kind of chemistry strips that your doctors use in the doctor’s office to look for different indicators of health. And then we take these samples and we freeze them in our solar freezer in camp and we then send them to my lab at Rutgers. And in my lab, we can look at a number of markers of health, energy status, and inflammation from this urine. We can get a lot of information from these urine samples, and I’ve got a full freezer of orangutan urine.

So a couple of things that we’ve been looking at are ketone bodies. Ketones are produces as a byproduct of fat metabolism, so if you’re burning fat and you were to stick one of these Chemstrips into your urine sample, you would have evidence of ketone bodies.

We also look at C-peptides of insulin. C-peptides are produced in equal proportion to insulin. So when there’s a lot of sugar, elevated sugar in the blood your body will produce these C-peptides, and they’re actually excreted in urine, so we can measure them in urine as well.

And we also look at urea. Now urea is basically nitrogen, and protein is made out of nitrogen. So urea gives us a very good marker of protein balance state, and how much excess protein they have in their diet. And it can also give us an indicator if they’re actually going into starvation, and starting to digest their own skeletal muscle, so their own muscle. And we also look at other markers of muscle wasting as well that I’m not going to go into today.

So when I think about nutrients and nutrition, I like to think about multiple nutrients within a nutritional space, and that’s what we do when we study these animals in the wild. We look at what they’re feeding on, what types of leaves they’re selecting, and then we do our nutritional analyses of these. So we can think about the interaction of nutrients with health in these animals.

So one way to think about what these animals are doing is that they’re actually going out on a daily basis and targeting certain nutrients, and certain amounts of these nutrients.

So here, for example, we have protein and carbohydrates. And this target basically represent what the animals need on a daily basis. And animals can reach this target in a number of ways. For example, one thing they can do is feed on foods that are really high in carbohydrates but low in protein, like this durian fruit here. But if they only ate durian fruit, they would end up with a protein deficit. Now they could also just feed on leaves that are really high in protein and low in carbohydrates, but if they only ate leaves they would end up with a carbohydrate deficit.

So what we see is that most primate species and most species in the wild in general will combine a variety of different types of food items to reach their nutritional goals. And so this is what we’re looking at. How do they reach their nutritional goals?

What research has found is that certain species, like folivorous mammals, tend to tightly regulate the amount of non-protein energy. So folivorous primates, for example, like mountain gorillas, you see very little variation in the amount of non-protein energy, so things like fat and carbohydrates. But you see great variation in the amount of proteins. So they’re over-shooting their protein needs to get enough carbohydrates.

Other primate species, like the more frugivorous spider monkey, tends to tightly regulate the amount of protein in their diet. No matter what, they always get about the same amount of protein, but they have a lot of variation in this non-protein energy.

So we went out and we were really curious as to what orangutans were doing. Given that they do this dietary switching, we wanted to know what their nutrient regulation looks like. And what we found is that they look very similar to spider monkeys. In fact, what we see is that there’s very little variation in the amount of protein eating, regardless of whether it’s the high or low fruit period, relative to the amount of non-protein energy.

We have a lot of variation in non-protein energy ranging from 200 calories to over 6,000 calories. But when we look overall at the ratio of protein to the amount of non-protein energy they’re eating, it’s about one to 10.5. And I want you to remember this number because it comes back again. Spider monkeys are doing something similar, but it’s about one unit of protein to eight units of non-protein energy. But they look very similar.

So in 2015 I was in the field with a few of my colleagues, Jessica Rothman and David Raubenheimer, and we decided we wanted to see how these animals were doing this. How do they regulate their nutrients?

So we went out and we followed Juni. And here the blue line represents fruit, and the green line represents leaves. So we started following Juni at about five o’clock, and she was feeding on leaves and green here. And then she fed on some fruit, more fruit, leaves, fruit, and so on. And we did this for the day. And what we found, by the end of the day she had eaten a mix of fruit and leaves and fruit and leaves. But what was remarkable was that at the end of the day, she landed right on that one to 10.5 ratio.

So we were like, wow, this is really amazing. Let’s go and follow her for a few more days and see if she does the same thing. And what she did was exactly that. She kept selecting for that one to 10.5 ratio. So we went out and we were like, okay, this is Juni. Let’s go follow Mindi. And Mindi was another adult female with a newborn infant, that was about a month old.

And we followed Mindi and we found that Mindi was doing the same exact thing. The only difference is that she had the same macro-nutrient balance, but she had higher consumption overall, which is expected with a female with a newborn infant that’s investing a lot in the energetics of lactation.

So we thought this was really cool. And since this time, my grad students and I have looked at a number of different individuals, and we find that the pretty much all fall along this one to 10.5 line. So it’s pretty good evidence that in the wild, primates are regulating their macronutrients.

However, what we do see is during the low fruit period, there is a reduction in the amount of carbohydrates that they’re consuming. They actually reduce carbohydrates by about 33 percent, and increase protein by about 10 percent.

So we hypothesized that during these high fruit periods, they are actually building up body fat. They’re over-consuming their calories slightly, building up body fat, and then they’re using that body fat for energy during the low fruit period, and burning it. And we also see that they’re increasing protein consumption, and they’re very likely potentially using body protein as well for energy via a more costly pathway.

So in a negative energy balance state, these animals have high protein in their diet, and they have low carbs and fat. Sounds like most of these diets that we’re all going on all the time, these newer diets where they say high protein/low carbs/low fat. And this is the formula for orangutans to burn fat. This is what works for them.

So the question is, given what we’ve learned about orangutans, what can we learn from them? What can we learn about ourselves? And how do we compare with orangutans, and what are the implications for human health?

So we know that we’re in a worldwide obesity epidemic. This is no secret. We know that we need help, and we recognize that the main culprit is a transition in our diet from whole foods and real foods to foods that are processed, high in fat, and high in carbohydrates.

It’s very difficult to know what our early ancestors were feeding on, and how they coped with the changing environment. But what we do know from tooth morphology, isotope evidence, and also fossilized plant remains found in the teeth of these fossils, is that our ancestors primarily had a plant-based diet that was supplemented with nuts and with meat and with some honey.

However, we can’t take a time machine back to figure out how they coped with a changing environment. We know the environment was changing. But what we can do is instead study primates and our living relatives, and look at how they are coping with the changing environment, and then we can better understand how humans have gotten to where we have today.

So one way to think about the obesity epidemic is through, this is called the protein leverage hypothesis. And this hypothesis basically says that a very small change in the amount of protein in the diet will result in a much larger change in the amount of carbohydrates and fat. And this is if humans are like orangutans and they’re prioritizing or regulating the amount of protein. So if humans are regulating the amount of protein, we would expect this to lead to, perhaps, the obesity epidemic.

So you could imagine if we switch from a diet that was 14 percent protein to a diet that’s 12.5 percent protein, in order to regulate that same amount of protein in our diet, we would have to actually increase carbohydrates by 14 percent, and that’s quite a bit.

So the question is, could this explain the current obesity epidemic? Well, what we find in human populations is that they do look very much like what orangutans are doing. It’s very clear that humans are regulating protein. And even when we look at choice experiments in humans, we see that when humans are given a wide variety of foods with different ratios, they tend to regulate the amount of protein, regardless of what the diet is. So it seems that humans are doing something that’s very similar to orangutans, in that they’re selecting, they’re regulating the amount of protein in their diet.

Now the protein leverage hypothesis also predicts that the percentage of protein in our diets has actually decreased over time. And in fact, if we look at data from the United States, we do see that the percentage of protein in our diet has decreased. But what’s interesting is the amount of energy that we’re consuming has greatly increased over time.

So when I think about orangutans, I think about how the human diet has changed over time. And if we think about early hominids, they were likely consuming an energy limited diet that was higher in protein, something that we see in orangutans during the low fruit period.

But as we move through evolutionary time, we see a shift from an energy limited diet to a protein limited diet. And what we see is an increase in the amount of sugars in our diet due to the facilitating transportation, refining of sugars, and really an unlimited variety and quantity of foods that are processed.

So are humans like orangutans? Yes. We are both susceptible to fat retention when we’re placed in an energy rich environment. And indeed, it seems that we’re both very adapted to a feast and famine ecology. The only difference is that humans are generally—at least Western humans are not experiencing the cyclic famine that orangutans are going through. So we’re stuck kind of in this feast where we’re not experiencing a period where we actually can burn body fat.