To be more specific, you are what you eat eats. There is a whole web of intertwined plants and animals and bacteria and fungi tied to each carrot and each burger. There probably aren't six degrees of separation between bacon and Kevin Bacon.
How much life is there? There is a lovely, big word for this. Biodiversity is a term that describes the number and kinds of life forms that exist in a given place and time. A place that has great biodiversity has many life forms and many different kinds of life.
All life is part of larger systems that are interdependent. Whoa. We are not getting metaphysical here. We are getting physical. One basic law of physics is that matter is neither created nor destroyed. What we eat today becomes part of something else later. It all comes back around. Nutrients are cycled through the ecosystem, though all the kingdoms of life. Biodiversity is a crucial part of this recycling process.
Our food supply—what we grow and catch and raise—depends on the diversity of organisms that support natural systems. It isn't just sun, water, and air that grow our crops, but also earthworms, nematodes, and insects. Organisms in the soil break down nutrients for plants and ensure the quality of soil. These organisms in turn depend upon others. Without these, the whole system starts to fall apart and so does our food supply.
We are part of this system and we are also great at manipulating it, though not always to our long-term benefit. Modern agricultural techniques provide one example. Earthworms are necessary for soil health, but are harmed by frequent tilling and some chemicals used to control plant and animal pests. We need a diversity of creatures in the soil and the trick is to maintain this while still controlling pests.
The food we catch is also equally dependent on biodiversity. For instance, the fish and seafood we eat depend upon a healthy aquatic ecosystem. There are plenty of things in rivers, lakes and the ocean that we don't eat. However, those other animals are also part of the nutrient cycling and prey-predator balance that keeps the whole thing healthy for the ones we do eat.
So, the next time you bite into a carrot, give earthworms a little shout out.