In some parts of the world, it’s now the norm rather than the exception to be overweight. This is an evolutionarily novel situation. Up until quite recently in our evolutionary history, virtually nobody was overweight or obese. Not only have we, via the changes we’ve made to our environment, been fattening ourselves up, but we’ve built up the adipose stores of certain other animals as well, most notably the ones we’ve domesticated for food production purposes. The result is that we’ve created a situation that differs markedly from the situation that is – and has been for millions of years – the normal situation in nature.
The natural state of things
Animals that live in a natural environment are typically fairly lean. Wild animals (e.g., deer) carry much less fat than modern, domesticated animals (e.g., cows), and the meat derived from such animals also has a different fatty composition. This is important to note, in part because it has major implications for human health and well-being. As we’ve transitioned over from eating primarily wild meat to eating industrially produced meat, our intake of saturated fatty acids has increased markedly, whereas our intake of long-chain omega-3 fatty acids has gone down.
Some animals carry a significant amount of fat, but that’s only because they need that fat in order to survive and/or reproduce. Whales and dolphins, for example, have a thick layer of adipose tissue under their skin, known as blubber, which helps them maintain a healthy body temperature. These animals don’t suffer the same health problems as overweight humans, for the simple reason that they are evolutionarily designed to be somewhat plump. They don’t carry excess fat; rather, they carry a desirable amount of fat in specific places where it serves a purpose to have lipids stored.
Moreover, unlike overweight humans, most wild animals are not fat year-round. They merely store fat during times of abundance in order to survive during times of hardship or food insecurity, or periods when they don’t eat at all. Black bears, for example, eat a lot prior to when they go into hibernation. By doing so, they build up their adipose stores, which they depend on in order to survive for long periods of time without eating.
Unlike black bears, human hunter-gatherers rarely fast for many days or weeks at a time. They certainly don’t have unlimited, easy access to food though. Their body fat levels vary somewhat depending on the season and climate, among other things, and they will build up fat if they have the chance to do so. However, their body fat levels barely register when compared to those of obese people. This is true irrespective of what time of the year it is and whether we’re talking about men or women (women (including female hunter-gatherers) naturally carry more body fat than men). The average BMI value of African hunter-gatherers like the Hadza and !Kung San is roughly 20 for both men and women (1, 2, 3). In the U.S., however, it’s closer to 30! (4)
In nature, there’s a natural balance between the energy that animals expend and the energy they take in!
The reason why animals that live in a natural environment tend to be fairly lean is simple: In nature, where everything is a competition, it’s usually a disadvantage to be fat! All else being equal, a fat animal will typically have a harder time getting a hold of food, evading dangers, and otherwise doing what’s required to survive than a lean animal. Just picture an obese zebra trying to escape a nimble lion, and you probably get what I mean. A fat animal is an easy prey, as well as a bad hunter.
With that said, as pointed out earlier, under some environmental conditions, it’s better to be somewhat fat than to be lean. It would obviously be a disadvantage for a zebra living on the African savanna to be carry around a lot of adipose tissue; however, the same cannot be said for a black bear that has to survive a long winter with little to no access to food.
The fact that everything is a competition means that everything is brought towards a state of “natural equilibrium”. Hypothetically, let’s say that a terrestrial animal that lives in a warm part of the world manages to get a hold of a lot of food and build up its adipose stores. The animal will now likely be at a disadvantage, in terms of energy procurement, when compared with leaner animals that exploit similar nutritional resources, as it will be bigger and slower. Moreover, it will be an easier target for predators. Hence, it’ll either lose the weight because it’s not able to eat as much as before, or it’ll be killed and eaten.
If for some reason there is so much food of a particular type available that all of the animals that exploit that food resource are able to “live like kings” for a time, one would expect the animals to produce more offspring, which in turn would mean increased exploitation of the food resource. Moreover, one would expect that other organisms would start to exploit the resource in question. That would bring about a “normalization” of the situation.
Given that this is the case, it’s not surprising that the normal phenotype of most animals is a lean phenotype. It’s only when animals leave nature in favor of an environment they are not genetically programmed for that their body fat levels may start deviating substantially from the evolutionary norm. This is clearly seen in the case of domesticated animals and humans living in an industrialized milieu…
By changing our environment, we’ve reduced the amount of energy we need to expend to get a hold of food, as well as increased the amount of energy we’re able to take in through the consumption of food
Part of the reason why our waistlines have been expanding lately is that we’ve changed our food procurement practices. By domesticating and confining plants and animals and mass-producing food in an industrial manner we’ve changed the rules of the game. We no longer fight with other animals for access to limited nutritional resources, at least not to the same extent as before, and we no longer have to expend significant amounts of energy in order to get a hold of energy. Moreover, we have the option of eating foods that are markedly more energy dense than the foods our ancestors had available to them. (Caveat: This is not the situation in every corner of the world.)
In nature, calorie-dense foods are typically hard to come by; wild animals rarely have the option of bingeing on very sugary, fatty stuff. Even when wild animals do what they can to maximize the number of calories they get, while minimizing the amount of energy they have to expend; they will be hard-pressed to get a hold of a lot more food than they need to maintain energy balance.
When compared with modern, processed fast food, most of the eatable stuff that one can get a hold of in nature has a relatively low energy density, meaning that one has to eat a lot of it in order to make some headway towards attaining the energy that’s needed to counterbalance the energy that’s been expended. This, coupled with the fact that the gastrointestinal systems of animals are limited with respects to their size and the amount of food they can process in a day, helps explain why it’s difficult for wild animals to get fat. It’s only when processed food with an abnormal nutrient composition and a supernormal caloric content enters the equation that obesity rears its ugly head.
Pictures: 1: Creative commons picture by Aalia19. Some rights reserved. 2: Photo by Laura College on Unsplash. 3: Creative commons picture by FlickrWarrior. Some rights reserved. 4. 5: Photo by Nils Öhman on Unsplash.
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There is some larger context to keep in mind. Wild caribou, for example, have more saturated fat than grain-fed cows. Also, hunter-gatherers always prioritized hunting the fattest animals at the time of year when they were the fattest. A few mass kills could create enough fatty meat to be saved for the rest of the year, combined with hunting smaller game in between.
It was much easier during the millions of years when megafauna were around, as the megafauna were at least 50% fat and a lot of it saturated, but also a lot of it Omega-3s as well. Paleolithic hunter-gatherers only ever hunted less fatty animals when the megafauna weren’t available. The megafauna die-off probably contributed to the rise of agriculture because hunting wasn’t as easy as it once was in procuring the large amounts of fat such a lifestyle required.