Source: Norman Rockwell. Freedom From Want. This Image is in the public domain
Halloween is just passed and Thanksgiving is on the horizon, so maybe this is a good time to talk about eating. It’s a WAY more complex subject than you might think.
First off, let’s “set the table” and outline the basic facts about how and why we and all other living things “eat”. All living organisms require two things to live and grow—energy and a source of carbon, nitrogen and other basic building blocks to make all the complex organic molecules, like carbohydrates and proteins, that living things need to synthesize in order to survive. We, along with all other complex organisms that aren’t plants, are what are called heterotrophs. The word “heterotroph” means “other feeder”, which refers to the fact that these organisms get their carbon by consuming carbon-containing material from their environment. We are, even more specifically, chemoheterotrophs, which means that we also get our energy from what we consume from the environment. We’ve already touched on this process—when we eat something, we digest it and break down the chemical bonds in the food, releasing the energy in those bonds that we can then use for our own needs. There is another category of heterotrophs, called photoheterotrophs. They still get their carbon from the environment, but they get their energy from light, through photosynthesis. Some photosynthetic bacteria fit into this category. Plants are in the category of autotroph, or “self feeder”. Autotrophs don’t have to consume organic carbon—they can use a process called “carbon fixation” to take carbon directly from the environment. Most plants, for instance, use carbon dioxide from the air as their carbon source. Plants are photoautotrophs, meaning they also get their energy from light through photosynthesis. Lithoautotrophs are an interesting group. “Litho” means “stone” in Greek. They are autotrophs, so they get their carbon directly from the environment, but they also use chemicals (“stone” or “minerals”, hence the “litho” part) in the environment as their energy source. Lithoautotrophs are all microbes that mostly live in really extreme environments, like deep in the oceans where there is no light, in acidic ponds or in boiling hot springs.
We, however, as I said, are chemoheterotrophs. We have to eat. Most of the people reading this are probably in the very fortunate part of the human population that doesn’t have to think much about eating, beyond when they are going to eat and what do they feel like eating. Most of these lucky people look at eating as a pleasurable activity that adds quality to their lives, and sharing meals is an important social process. This is, unfortunately, not the case for everyone, and just avoiding hunger and malnutrition is sometimes a challenge for them. Somewhere around 13.5% of the households in the United States (that’s about 47 million people, including children) are food-insecure, meaning there is some question about whether or not there is going to be food to eat at all at mealtime. This is a science column, so we won’t go into the issues of poverty and hunger, but I just thought I’d toss that out there as food for thought. Anyway, most people in the “developed world”, spend only a tiny fraction of their effort (income) on food. We, here in the US, generally spend less than 11% of our resources on food. People in the lower income levels, spend 30% or even 45% of their resources on food. In some developing nations, the percent is even higher. I don’t mention that purely as something that we should all think about. I mention it to get you to thinking about how important eating is. Most animals, particularly herbivores (plant-eaters) like antelope, spend the vast majority of their day just trying to get enough to eat. Carnivores generally eat less often, but they also generally have to work harder to acquire their food (most of the time they have to hunt it down and kill it).
Much of the way organisms evolve is to improve their ability to compete for resources, like food, with other organisms that share their environment. For instance, animals run (or swim or fly) fast for one of two reasons: it either helps them to catch food or to avoid becoming food. Humans got to the top of the food chain by being smart, because aside from our brains and our thumbs, we are pretty much just slow, weak, claw-less, fang-less, hairless, flightless prey for anything faster than we are. If you look at some of the adaptations animals have for finding food and avoiding predators, you will be amazed. Look up “angler fish” or “cuttlefish”. Cheetahs can run faster than most cars drive on the highway. The list of adaptations is, practically, endless.
As you sit down to Thanksgiving dinner, as I hope you will, with people I hope you like, think a bit about what it represents. Yes, it is probably an expensive feast, but even at that, it probably didn’t cost that much, and all you had to do was drive to the grocery store to pick it all up. You didn’t have to hunt down the turkey (not easy, for those of you who have never hunted turkeys) or chase down the wild boar or spend hours wandering in the woods looking for nuts and berries. You are going to sit down, put WAY more food on your plate than you would really need in two or three days and eat. You will chew up your beans and your potatoes. You will enjoy the flavors. You will enjoy feeling full. You may even feel pain from being overly full. Been there, done that. The food you ate will undergo a chemical and physical process to break it down into components your body can use. You will use the carbohydrates for energy (and store some as fat). You will store away pretty much all the fats you just ate, because there are plenty of carbs available for immediate energy. Remember way back when we were talking about chemical bonds? The carbs in your potatoes are complex sugars (starches) made of chains of carbon, hydrogen and oxygen atoms all bonded together. The potato plant took carbon from the carbon dioxide in the air and hydrogen and oxygen from water in the soil and, using the energy of sunlight, bonded them together to make starch molecules, which were then stored in the potatoes. You eat the potatoes, and basically, digestion is the reverse of the process the plant went through to make the potato. You’re breaking the molecules down again to release the energy and use the other parts of the molecules for your own body’s needs.
Molecular Structure of Sugar Molecules, showing energy-rich chemical bonds. Source: OpenStax Biology
It’s just a bonus that it tastes really good. Taste, by the way, serves an important biological function. Things that taste bitter, for instance, are often poisonous. Things that taste sweet cause you to really want them, and when food is scarce, eating energy-dense things like sweet fruits is important for survival. So, there is way more to eating than just chewing and swallowing. Like all of Biology, particularly Physiology, eating is complex, intertwined with all kinds of other aspects of physiology, anatomy and behavior. That’s the true beauty of science, especially physiology. Everything is connected.