• Adenosine Triphosphate (ATP): Our bodies need energy. We get this energy through a pathway called metabolism. ATP is the most common "currency" used to trade energy between cells. ATP is a small coenzyme the cells in our body use as an energy source in most of their processes.
• The Krebs Cycle: The body produces ATP through a series of biochemical reactions called the Krebs Cycle. It starts with Acetyl-CoA molecules. During the reactions, the energy inside this molecule is set free to produce ATP.

• The foods we eat are broken into three basic units: carbohydrates, fats, and proteins. They form the macronutrients.
• The macronutrients need to be further broken into simpler units that will be used to produce Acetyl-CoA.
• There are three metabolic pathways: Glycolysis pathway breaks down carbohydrates, Beta-oxidation breaks down fats, and Transamination breaks down proteins.
• The body converts fats, proteins and other substrates into glucose through Gluconeogenesis.

Glucose is the primary "fuel" that produce energy.

• Fats are packed into small units called lipoproteins and stored as body fat for later use.
• Proteins are broken into amino acids used to build new proteins, enzymes or tissues, such as muscle tissue.
• Amino acids and proteins are still available to be converted into glucose or used as a source of energy through the Transamination metabolic process.
• This glucose is stored in the muscles as glycogen.

While fasting, the body consumes the glycogen first, then fats, then proteins.

Electricity can light your lamps or power your appliances. But electricity needs to be produced first. We need a fuel that can be converted into electricity, such as petroleum (carbohydrates) that is converted into gasoline (glucose). Or solar energy (fats) or wind power (proteins).

We store the petroleum in warehouses (adipose tissue) for later use. The energy produced by electricity is used to build new materials (amino acids) and used to construct bridges or houses (muscular tissue).