Nutrition is chemistry. It is the study of how food it taken in and used by the body. “Taking in” food has two parts: digestion and absorption. Digestion is the body’s way of breaking down a “chunk” of food to its molecular level. Absorption is when the body takes the molecule into the bloodstream and uses it to support the tissues of the body.

Throughout this class we are going to use basic terminology and ideas from chemistry to discuss human nutrition. The following section describes some basic concepts that demonstrate chemistry within nutrition.

Atoms and Molecules

Everything around us and in us is made up of atoms which you can consider as minute spheres. They are very, very small. A page of a book is about one million (1 000 000) atoms thick. There are about 100 or so different types of atom including: oxygen atoms, carbon atoms, nitrogen atoms, gold atoms, and iron atoms.

Atoms provide the basic building blocks for everything. It is like having a “Lego” set with about a hundred different types of brick. Each type of atom is a different size and has a different mass from all the other types. Because atoms are so very small, chemists do not deal with their actual mass, but instead they give the smallest and lightest atom, which is hydrogen, a mass of 1 and then express the mass of all the other atoms relative to that. For example, an oxygen atom is 16 times as heavy as a hydrogen atom,  so it has a relative atomic mass of 16. The different types of atoms are called chemical elements or just elements for short. By using different atoms and joining them in different ways, you can produce water, sugar, salt, proteins, paper, rocks, and, in fact, everything in the Universe!

Different materials can exist as either a solid, a liquid, or a gas, but one of these “states” is most familiar. For example, water is generally thought of as a liquid, but it can freeze to a solid ice, and it can occur as a gas, water vapor, or steam.

Chemical Compounds

Many molecules consist of atoms of more than one type of element, and they are called compounds. Carbon dioxide, methane, and water from the list of gases above are all chemical compounds. Water is the most abundant compound in living matter, and indeed on Earth, accounting for an average of 60% of total human body mass. A molecule of water, whether it exists as a gas in the atmosphere, as liquid water in our bodies, or in lakes, rivers, or seas, or as a solid in the form of ice, always has the same structure. It is a compound of two of the elements we have already met as gases, hydrogen, and oxygen.

A water molecule consists of two atoms of hydrogen and one atom of oxygen and can be represented by a ball-and-stick model. Hydrogen is pink, and oxygen is white in this model.

To make things quicker to draw when we are dealing with larger molecules, the atoms are not usually represented as colored balls but by the chemical symbol for the element, and the bonds between the atoms are drawn as lines.

This chemical structure drawing of water uses the chemical symbols for oxygen (O) and hydrogen (H) instead of colored balls.

Elements of the Body

Throughout this course we will discuss elements needed in the human body. The following table describes the major elements of the body.