Here's why:

* Cells are the fundamental units of life. They are responsible for all the processes that keep an organism alive.

* Cells use energy from food to build complex molecules. This process is called anabolism.

* Food provides the building blocks and energy for anabolic processes. These complex molecules include:

* Proteins: For building and repairing tissues, enzymes, and hormones.

* Carbohydrates: For energy storage and structural components.

* Lipids (fats): For energy storage, insulation, and cell membranes.

* Nucleic acids (DNA and RNA): For carrying genetic information and protein synthesis.

In summary: Cells use the energy from food to create the complex molecules necessary for life through the process of anabolism.