Food

"Everything we eat depends on the sun. This statement probably seems obvious, but it’s key to understanding why we need both plants and animals working together in a sustainable food system. Living things that make their own food by using energy from the sun and carbon dioxide in the air are known as autotrophs. Autotrophs provide the energy that allows all of us on earth, from bacteria to humans to elephants, to live. A key principle in ecology is that every time energy moves from one trophic-level to the next, about 90% of the energy is lost as heat and only 10% is captured by the organism. For example, when cattle eat grass, 90% of the energy in the grass is lost as heat, and if we humans eat beef, 90% of the energy in beef is lost as heat. As a result, we humans are only capturing about 1% of the energy in the original plant eaten by the cow for ourselves. The more trophic levels you get away from the original source—the plant—the more energy is lost."

Logically, this basic truth of energy loss in the food web has driven some to call for “eating lower” on the tropic scale—eat more plants and fewer animal-sourced foods. In some ways, we already do this in the United States—about 70% of the calories in the average American diet come from plant-sourced foods. If this inefficiency exists when you move from one trophic-level to the next, why eat animal-sourced foods at all? The answer is two-fold: the energy contained in plants eaten by animals is often unavailable to humans by eating plants directly, and food security is more than simply calories available."