Entropy and Meals 1/16/19


By Richard E. Bleil, Ph.D.

A friend of mine was video-chatting with me as she was eating a meal today. She is an artist through and through, and showed me her plate before she began, and it was just gorgeous. All it had was a few crackers, two cherry tomatoes, cheese and blueberries, but the way it was arranged looked similar to an inverse of the Cross of St. Andrews national flag of Scotland. Seeing this plate reminded me of a conversation we had regarding meals.

We all know that food is our primary source of energy. Calorimetry is the technique chemists use to determine the caloric content of food. The simple explanation (perhaps overly simplified) is that the food is burned and the amount of heat released is measured in calorimetry. In the body, the exact same amount of energy is released from the food in the metabolic process as when the food is simply burned, but the way in which it is released is broken down into smaller steps that can be converted to physical changes (ADP is converted to ATP as a more useful form of energy to the body). This is actually the first law of thermodynamics, namely, conservation of energy.

But the truly fascinating theory that I had heard in my thermodynamics class comes from a chemistry who suggested that, perhaps, when we eat meals it is the entropy that is more important than the energy.

Personally, I don’t believe the entropy is more important, but it’s an aspect of the consumption of food that is rarely thought of. Let’s begin, though, with a brief review of the second law of thermodynamics, and the term “entropy”. Entropy is typically thought of as a state of disorder. The higher the entropy of a system, the higher the disorder. Personally, I prefer to think of entropy in terms of information knowledge which has a closer relation to the quantum foundation of the second law. “Disorder” is a term that is subject to interpretation (remember when an adult would complain about the disorder of your bedroom?), but think about finding a remote. In a high entropy room (high disorder), one would be less likely to be able to find the remote than in a low entropy room (low disorder).

But, I digress. Back to the basic concept of entropy. We all have an innate sense that the natural direction of processes is towards increased entropy (higher disorder). There was a very silly comedy from the ’80’s that featured a scene that was filmed backwards. They did a very good job at it, so while it seemed a little bit awkward in the beginning, one might not realize how it was filmed. It just seemed…off. However, in the midst of the scene, the shop keep blew onto an old book, but rather than having the dust blow off and disperse into a more disordered state, it accumulated onto the book into less disorder. If we drop a camera, it’s more likely to break than repair itself; the disorder, and hence the entropy, increases naturally.

We also realize that we can decrease entropy by doing work on the system. Back to the messy room, how do we decrease the disorder (decrease the entropy)? We clean the room. We do work. We pick up our nasty unmentionables off of the floor, but the items on the flat surfaces where they belong, and vacuum to accumulate the dust all in one location. But, understanding entropy is not quite enough, as we also need to discuss the second law of thermodynamics which, arguably, may be the least well understood law in science.

The second law of thermodynamics states that through any process the total entropy of the universe cannot decrease. In principle it can remain constant, but it never does in practice. So in any process, like cleaning the room, must increase entropy of the universe. The entropy of the system (namely, the room) can decrease and is doing so, but that means that the entropy of the environment (the rest of the house, the yard, the neighborhood, the country, the world and so forth) must increase at least as much as the decrease of the room entropy so when you add them together, the net entropy is increasing. This might seemcounter-intuitive; how can cleaning increase the entropy of the universe? Well, throughout action, we are converting sugar into carbon dioxide which is a great increase in entropy on a molecular scale. There are other ways in which the entropy of the surroundings is also increasing, but the point is that the entropy of the surroundings must increase to make up for the entropy decrease of the system.

As living creatures, we are constantly decreasing the entropy of our body. This is how we survive and grow. Think about how organized our body systems are, and how organs like the liver removes things that don’t belong to decrease the entropy of our body. Even our skin continually sheds dead cells and replaces them with new ones, cells that fall into our room and becomes dust that makes us eventually need to clean our room!

But, if our body is constantly decreasing entropy, that means that somehow, the entropy of our surroundings must be increasing (that pesky second law again). Our processes do burn sugar, just as cleaning did, which increases entropy, but what this chemist was suggesting was that our meals also increase entropy. Our meals start as part of our surroundings, and much work goes into preparing those meals (either by us or others), to make them look good, separate the components of the meal or mix them just so in order to maximize flavor. For example, we might like gravy on our mashed potatoes, but certainly not on that cookie we will have for dessert.

This lovely, low entropy meal first goes into our mouth, which, through the process of mastication, becomes paste like which has a much higher entropy than before we began. This then goes through a process in our body where its entropy is decreased even further until it becomes, well, I think we all know where this is going. On a cellular level, we are starting with foods organized in a low entropy level as well, and our bodies will break down those cells creating entropy even at microscopic levels.

So, in eating, we are increasing the entropy of our surroundings in the meal. This may not be intentional, as we have no organs that can absorb “entropy” the way that we can absorb energy, which is why I think the original statement may be too bold. However, it’s fascinating, at least to me, to think that, indeed, the process of eating and digestion does help to satisfy the second law of thermodynamics, which is good because I would not want to end up in quantum court!

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