Why do we get hungry and have to eat food?
Your body is made up of matter which consists of the chemical elements. The four elements that make up more than 95% of it are hydrogen (H), carbon (C), oxygen (O) and nitrogen (N), and the remaining 5% consists mostly of sodium (Na), potassium (K), chlorine (Cl), calcium (Ca), phosphorus (P) and iron (Fe). The laws of nature allow specific atoms to join together in a specific order to form specific molecules. Some of the more important molecules for life are (molecular) oxygen (O2), water (H2O), glucose (C6H12O6) and amino acids (which contain nitrogen). The only useful molecule the lungs bring into the body is O2 which helps your cells release the chemical energy stored within the glucose molecule. But your body needs all of the other atoms and molecules mentioned above, and more. In fact, everything else is brought into your body through the gastrointestinal system. In other words, you literally are what you eat (and drink).
The seven basic types of molecules your body uses to get what it needs into the blood through the gastrointestinal system are water, carbohydrates, fats, proteins, salts, minerals, and vitamins. Water is needed for your cells to work properly and for your body to have enough blood volume so the circulation can feed your cells what they need. Carbohydrates are made up of sugar molecules (e.g. glucose) which your body uses as its main source of energy, and joins to other molecules to form things like DNA and RNA. Fats consist of fatty acids joined to glycerol which your body uses as an alternative source of energy and to make the plasma membrane surrounding your cells and insulation that surrounds your nerves to help them work properly. Proteins are made up of twenty different amino acids which your body uses to make all the cellular structures and molecular machinery needed for them to work properly, the proteins that allow for muscle contraction, antibodies to fight infection, clotting and anti-clotting factors, and the hormones needed to control body development and the metabolism. Salts (e.g. sodium and potassium chloride) are the main atoms that dissolve in your body’s water which maintains not only cell function and blood volume but also gland and nerve function as well. Minerals (e.g. calcium, phosphorus and iron) are used to make things like your bones (so you can stand, move around and manipulate things) and hemoglobin (so your body can transport enough oxygen to its cells). Finally, vitamins (e.g. B vitamins, A, C, D, E and K) are molecules your body can’t produce but needs for some of its vital chemical reactions and structures.
But when it comes to trying to bring these various chemicals into the body, the gastrointestinal system faces a dilemma. It turns out that many of these chemicals are locked inside larger and more complex ones, which, because of their size, the gastrointestinal system can’t bring in and place inside the blood. The solution to this problem can be found by looking at how a pulp and paper mill works. Large logs are trimmed and chopped up into smaller pieces, and then various chemicals are used to breakdown the wood fibers to form pulp, which is then used to make paper and other products. So too, the large and complex molecules that are present in what we eat and drink must go through a similar process, called digestion, to release the chemicals the body needs to live. By digesting these large and complex molecules, the gastrointestinal system is then able to bring the resulting smaller and simpler atoms and molecules into the blood in a process called absorption. Here’s how it works.
Just as your body has a respiratory center that tells you to breathe in air, and a thirst center that tells you to drink water, it also has a hunger center that tells you to eat food. Understanding it is still a work in progress, but scientists think that there are centers within the brain that receive information (through nerves and hormones) about blood glucose and fat stores, stretching of the stomach wall, and nutrients being released into the intestine. The brain takes this information and, with emotional and other factors, decides when to signal the hunger center to tell you to eat.
Smelling and tasting food stimulates your mouth to produce saliva that helps you swallow what you've eaten and contains enzymes that starts the digestive process. At the same time your stomach begins to churn, produces fluid containing acid, and releases other enzymes that mix with the food that enters to help break down its physical and chemical structures. It then slowly pushes this liquid into the intestine, which has already been stimulated to release fluid containing bicarbonate to neutralize the acid (from the stomach) and is also acted upon by many other different enzymes from the intestine and the pancreas and also by bile (from your liver) to finish off the job of digestion. The intestine then absorbs what it needs of the water, carbohydrates, fats, proteins, salts, minerals, and vitamins it encounters while the colon picks up mostly water and salt. What’s left over comes out as feces. Without the gastrointestinal system’s ability to digest food and absorb water and all the nutrients the body needs, life would be impossible, so, that’s why we get hungry and have to eat food.
Three Questions for Mr. Darwin
- Besides wondering which urge (breathing, thirst or hunger) developed first, and in what order (since all of them are needed for survival), how does my hunger center know when and how strong a message to send, when to turn off, and where did this information come from?
- Besides wondering which of the many different enzymes, needed to digest the different types of molecules in our food, developed first and in what order (since all of them are needed for survival) where is the information that tells my body how much of each of them need to be sent out to get the job done right?
- Besides wondering which of the chemicals (e.g. sugars, fats, amino acids) was the first to be absorbed by the intestine (since all of them are needed for survival), how does it know, not only how to do it, but also how much it should bring into the body and where did this information come from?
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Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
Copyright 2017 Dr. Howard Glicksman. All rights reserved. International copyright secured.
