The word “energy” is splattered across food labels and dietary supplement products as an enticement to buy the product and instantly be transformed from a couch potato into a marathon runner.  But what does the word energy actually mean in terms of nutrition?

The true definition of energy is a force that moves an object.  In biology, energy is an attribute of all biological systems that keeps the organism functioning properly.   When we talk about energy as a general term, we are usually referring to the opposite of fatigue – as in “I have a lot of energy today!”   The source of our energy that creates our ability to do work – from the kind we are aware of like walking and running to the stuff that happens behind the scenes, like digestion and heart beating – is food kilocalories (often shortened to just “calories”), provided by carbohydrate, protein, and fat.

Over the course of a day, a body needs a specific number of kilocalories in order to survive.  Too few calories and our body will shut down some functions in order to conserve energy.  Too many calories and the body will store the excess for future use, such as during times when adequate calories are not available.  The number of calories a person needs is based on a variety of factors, including gender, age, and activity level.

Carbohydrates contribute 4 calories per gram.  In biochemistry, a carbohydrate is an organic compound that consists of carbon, hydrogen, and oxygen.   The basic form of a carbohydrate is a saccharide or sugar.  You will sometimes hear table sugar called a “disaccharide” or a starch called a “polysaccharide”.  This describes how they are chemically put together, but the basic molecule is the same.  That is why when someone says “carb” it means anything made with a basic sugar molecule – from simple sugars in candies and simple starches in potatoes to the more complex carbohydrates in whole grains and fiber.

Proteins also provide 4 calories per gram.  The most basic part of a protein is an amino acid, which are grouped together to form different types of “peptides.”  Proteins for the most part are building blocks for structures inside the body, including virtually every cell such as muscle, bone, and even blood cells.  Proteins are also used for cells that carry out chemical reactions in the body, called enzymes, that is part of our metabolism.  If protein is taken in based on needs, it will be used to repair the daily damage that occurs in a functioning being.  Too much protein is not stored in muscle, contrary to popular belief; it is converted and stored as fat.

Fats are essential components of the diet, but contribute more calories per gram (9) than either protein or carbohydrate, which is why they are often suggested to be avoided when trying to cut calories to lose weight.   Chemically, fats (or oils or lipids) are composed of smaller fatty acids that can be grouped in such a way that they are considered “saturated” or “unsaturated”.  Fat is used for important body functions, like protein, in the skin, hair, and body organs.  Fat can also be stored for energy when the body is in need of an extra fuel source.

Alcohol is a compound that also contributes energy, but it is not frequently referred to as a nutrient because it interferes with the growth, maintenance, and repair of the body.  However, it does contribute 7 calories per gram, and can be stored as fat just like the other energy nutrients.

Products such as dietary supplements or “energy” drinks usually do not actually contribute true fuel to the body, unless they contain calories.  Energy supplements usually contain B vitamins, which are used as assistants in the process of metabolism, but do not actually provide energy on their own.  Many energy drinks contain caffeine, which produce a feeling of stimulation, but also does not provide any actual energy for bodily functions.  That’s not to say that these products don’t have their place in an overall healthy diet – but hopefully this will help squash some of the confusion around the use of the term “energy”. web archive . Loilafinworkme

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