The metabolism’s work of turning food into energy and then using that energy to operate the body and to bounce back from everyday wear and tear is quite a process. Through our choices and actions, we can make that process more efficient or less so.

First, the process: After we’ve eaten, the body uses oxygen to convert food into energy. The nutrients providing that energy are either used to fuel the body, or they’re stored as fat. The byproduct, or waste, from converting food into energy is carbon dioxide. Here’s how the body uses each of the main nutrients from the foods we eat:

Carbohydrates are generally the body’s main source of energy. Carbs are broken down into sugars and stored in muscle cells as glycogen. The body can only store so many carbs, which have 4 calories per gram.

Proteins are used to build and maintain body tissues and are rarely used as energy. Like carbs, only so much protein can be stored. Protein also has 4 calories per gram.

Fat is the most energy-dense of the nutrients at 9 calories per gram, making it the most efficient source of fuel. Fat is also a long-term fuel reserve that guards against starvation. Sounds good, so what gives fat its bad rap? The body has a seemingly unlimited capacity to store it. And it’s not only fat that makes us fat: When the body is maxed out on other nutrients, especially carbs, those get stored as fat, too.

Which brings us to efficiency, and back to the car engine metaphor: A car that’s throwing off a lot of exhaust is wasting its fuel and getting terrible gas mileage. It may chug along and need frequent repair, and that can waste a lot of time and money. That’s a fairly reasonable sketch of what happens to our bodies, too.

Through proper diet, good lifestyle habits, and healthy exercise, we can teach the body to burn fuel with greater efficiency. At its most efficient, the body uses greater amounts of oxygen to convert more of our food into usable fuel (a bonus: the fat burns first!). Less carbon dioxide is produced as waste, and less of our fuel ends up stored as fat (double bonus!!).

Assessing your metabolism puts the info you need for healthy exercise and optimal nutrition right at your fingertips.

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