 How do we gather enough energy to do a high jump, run a sub five minute mile, or even just walk around the block after a day of work? These all depend on your body processing fuel to make energy. For us, this fuel takes the form of food and water. Our bodies are able to convert the food and water that we consume into compounds that our cells can use for energy. At the molecular level, most of this energy is stored in the form of adenosine triphosphate, or ATP. And the processes to create and use these ATP molecules are collectively known as your metabolism. Your metabolism involves multiple steps, many enzymes, and overlapping paths. There are also many checkpoints that ensure everything is working properly. Metabolism can be impacted in many ways, for example, eating different foods, exercising or disease. Let's walk through some of these details together. The major metabolic pathways are those for carbohydrates, or sugars, fatty acids, or fats, and ketones. Once these foods have been digested in our stomach and intestines, the nutrients head on into our bloodstream and off to the cells that need them. Once inside the cell, the broken down products of nutrients are used to fuel production of ATP. This can happen both inside and outside the mitochondria, an organelle famous for being the powerhouse of the cell. Most of these nutrients get broken down into acetyl-CoA. If this is inside the mitochondria, this metabolite enters the Krebs cycle, also known as tricarboxylic acid cycle. This cycle is named after Hans Krebs, who first described it in 1957. The Krebs cycle uses acetyl-CoA to produce much of the ATP produced within the cell. Our knowledge of how metabolism works allows us to understand what happens when things go wrong, resulting in disease. We can use clever imaging methods to study metabolism at multiple levels, such as in cells, tissues, and entire living organisms. These methods can use massive magnets, magnetic resonance imaging, or MRI, or radioactive versions of fuels to look inside the body. We can also extract cells and tissues from these organisms, and use methods, such as mass spectrometry, to provide even more information on a huge number of metabolites that our bodies make from food. When things go wrong, metabolism can be a key factor in disease. For example, the healthy heart uses fats and sugars in a 70 to 30 ratio. But in type 2 diabetes, the amount of fat it uses increases even further, as it responds to the higher levels of circulating fat in the bloodstream. The healthy brain runs almost entirely on sugar, but in Alzheimer's disease, the brain's ability to use sugar goes down. Research is underway to figure out exactly why this is. This even happens to some extent in normal aging. These medicines or changes to lifestyle can be used to return the metabolism to normal. Lifestyle changes can be powerful, such as improvements in diet or more exercise, as they not only improve disease symptoms, but also lower the risk for many other diseases. Fun fact, there are laboratories with metabolic chambers in which volunteers live for short periods of time. Everything that they eat and even excrete can be measured, allowing us to examine the effect of different diets, exercise, or disrupted sleep on how fuels are broken down. It's important to carefully control metabolic experiments, since what volunteers had for breakfast might influence the results. We are each unique, 1 in 8 billion, and metabolism is a perfect example of that. We all vary in how we process and store food, how much we exercise and regulate the heat, but the underlying pathways are mostly the same, so we can all expect to keep making that ATP to get us up in the morning and around the block.