Paper contains a measurable amount of chemical energy, but it provides virtually zero usable calories to the human body. Understanding the true caloric value requires distinguishing between the total energy locked within a substance and the energy our bodies can extract. Paper is composed primarily of complex carbohydrates that are inaccessible to the human digestive system.
Measuring the Energy Potential of Paper
To determine the total energy potential of any material, scientists use a device called a bomb calorimeter. This instrument works by completely burning a sample in a sealed container filled with pure oxygen, measuring the heat released to the surrounding water. This measurement provides the material’s gross energy, which is its total chemical energy.
Because paper is mostly cellulose, a carbohydrate polymer, it has a significant heat of combustion, registering approximately 4 kilocalories per gram (or 17 kilojoules per gram) of gross energy when fully burned. This total chemical energy is comparable to that found in digestible starches or sugars. However, this figure only represents the energy released under intense laboratory conditions, not the energy a human can metabolize.
The Biological Reason We Can’t Digest Paper
The reason paper delivers no usable calories is rooted in the specific chemical structure of its main component, cellulose. Cellulose is a polysaccharide, meaning it is a long chain made up of many individual glucose sugar molecules. Despite being made of glucose, the building block of human energy, the way these molecules are linked together makes them impenetrable to human digestive enzymes.
The glucose units in cellulose are joined by a specific chemical bond known as a beta-1,4-glycosidic linkage. Humans possess enzymes, like amylase, that can easily break the alpha-1,4-glycosidic bonds found in starches. However, we do not produce the necessary enzyme, called cellulase, which is required to cleave the beta bonds in cellulose. This lack of cellulase means the paper passes through the gastrointestinal tract largely intact.
Cellulose acts as an insoluble fiber in the human diet, providing bulk and aiding in intestinal movement, but it yields no energy. This inability to digest cellulose contrasts sharply with the digestive systems of ruminants, such as cows, or certain other herbivores. These animals house symbiotic bacteria that produce cellulase, allowing them to break down and absorb the energy from plant matter.
Health and Safety Concerns of Ingestion
While paper is not calorically significant, consuming it introduces physical and chemical risks beyond the nutritional discussion. The most immediate concern with ingesting any non-food material is the potential for physical obstruction in the digestive tract. Paper is a fibrous material that does not break down, and large or frequent consumption can lead to the formation of a mass that may cause an intestinal blockage, which is a serious medical issue.
There are also chemical considerations depending on the type of paper consumed. Many papers are treated with various chemicals for bleaching, binding, or coating purposes. Some bleaching processes have historically left trace amounts of chemicals like dioxins in the paper, which can be toxic upon regular ingestion.
Furthermore, inks, dyes, and coatings used in magazines, thermal receipts, or colored papers can contain heavy metals or other substances that are not meant to be consumed.