Macronutrients

Carbohydrates
Carbohydrates are the majority of what should be consumed in a teenager’s diet. One gram of carb provides 4 Calories of energy. 45-65% of the foods that active teenagers should consume are foods composed of carbohydrates. For older and more active teens, a diet composed of 55-65% of carbohydrates should be a goal to be set. Carbs are the body’s “preferred” source of energy. Some of our body’s most vital cells can only use carbohydrates for their energy usage needs, this list including red blood cells and brain cells.

All carbohydrates are composed of the basic building block called the glucose molecule. It consists of carbon, hydrogen, and oxygen atoms — three of the essential atoms for life — in the ratio 1 : 2 : 1. Due to the structure of a glucose molecule, it can to broken down more efficiently than most other compounds. They can either be split apart for energy (molecules create energy when broken down), or used to build larger molecules the body creates on its own.
All forms of carbs must be broken down into glucose for the body to use it. When any carb is at its final stage, it is broken down into individual glucose molecules. All carbs are grouped into one of two categories: simple and complex, based on their structure.

    Simple Carbohydrates

Simple carbohydrates, also known as “simple sugars” or just “sugars”, are either a single glucose molecule or a short chain of a few. The shorter the chain, the easier it is processed. Because of this, sugars make for a quick energy boost; however, they are also quickly depleted. Since they are so small, they are usually dissolved into fats and liquids. They are naturally abundant in fruit, dairy products, and grains, as these contain substances necessary to nurture new life, such as a seed or a newborn mammal.

    Complex Carbohydrates

In contrast simple carbohydrates, complex carbohydrates are long chains of glucose. There are three types of complex carbs: starches, glycogen, and cellulose. Starches are found in plants such as potatoes, rice, and corn. Glycogen is found in animal tissue, particularly the liver and muscles. Cellulose,  A.K.A. fiber, is found in all plant cells. Starch and glycogen must be broken down into simple sugars for absorption; cellulose cannot be digested, but is still beneficial. Fiber keeps you full throughout the day, regulates bowel movements, lowers blood cholesterol, and stabilizes your blood sugar. Since fiber is the main structure of all plants, it is found in whole grains,  fruits, and vegetables.

Proteins
Proteins are the things that  perform practically all cell functions. Everything that a cell does requires different kinds of proteins. If a cell is thought about as a factory, each different kind of protein is a type of machine that the factory requires to produce something or perform an action. A diet of an active teen should consist of 10-35% proteins.
Proteins are long chains of amino acids. There are twenty different kinds of amino acids and different proteins are made from different combinations of the amino acids. There are so many different kinds of proteins in the body that we need all 20 amino acids to survive. Only twelve of the twenty amino acids can be made in the human body, so that means the other eight have to be taken in through food. Proteins build and repair our bodies. Most of the things in our body are made of proteins. When we work out and our body needs something to burn for energy, protein ensures that our body burns fat and carbohydrates, and not muscle. The human body can’t store protein the way it does with fat and carbohydrates, so a constant flow of protein is needed to be healthy. Meat, milk, eggs, beans, and nuts are great sources of complete proteins, or proteins that have all the essential dietary amino acids.


Lipids (Fats)
Fats are the basic unit of energy storage in the body. They are essential for the creation of cells (being a major ingredient to the lipid bilayer and creating a means of transportation for cell intake and disposal of waste). 20-35% of a diet should be composed of lipids. Even though fat is often viewed as unhealthy and detrimental to your health, fat plays many vital roles in you body. Fat stores energy, insulates nerve cells, protects the internal organs, and makes up hormones that regulate bodily functions.
  All fats are composed of fatty acids. A fatty acid has a carbon-based "head" called a carboxyl group. Attached to it is a "tail" of carbon and hydrogen atoms.

A single "free" fatty acid.

A triglyceride molecule.

       The most common form of fat has 3 carboxyl groups chained together to form glycerol, and thus has 3 fatty acids. This is called a triglyceride.

       The fats we eat are basically different fatty acids grouped in triglycerides. Fatty acids differentiate based on the length of their tails and the number of double bonds in its tail. Notice that when a carbon chain is "maxed-out" on hydrogen atoms, it is straight; however, when some hydrogen atoms are missing, the carbon atoms bond to each other, and the fatty acid becomes bent due to the double bonds.

A saturated and an unsaturated fatty acid in a triglyceride.

       When all of the carbon atoms have attached to as many hydrogen atoms as they can, then the fat is saturated. If the fatty acid contains only one double bond in its tail, then the fat is monounsaturated ("mono" = single ; monounsaturated = single unsaturated area). If the fatty acid is unsaturated in lots of places, then it is polyunsaturated ("poly" = many ; polyunsaturated = multiple unsaturated areas).

       Saturated fats are solid at room temperature, since their structure allows them to pack tightly together. Most polyunsaturated and monounsaturated fats are liquid at room temperature due to their bent shape. Foods that contain saturated fat are butter, animal fat, and processed meat. Foods that contain polyunsaturated fats are walnuts, sunflower seeds, and olive oil. Foods that contain monounsaturated fats are avocados and peanut butter.

   When unsaturated fats are artificially saturated with hydrogen atoms, then they become trans fats. Like unsaturated fats, trans fat has double bonds; however, its tail is straight as if it were saturated. Foods that contain trans fat are doughnuts and fast foods.

A trans fatty acid in a triglyceride. Notice the double bond and the lack of a bend.

       There are also essential fatty acids the body cannot create on by itself. These are categorized into omega-3 fatty acids and omega-6 fatty acids. Both are polyunsaturated and used to make hormones that control cell growth, the immune system, and blood clotting, among other things. Omega-3 fatty acids are found in most fish, such as salmon, mackerel, and trout. Omega-6 fatty acids are found in seeds, nuts, and extracted oils, especially refined vegetable oil.






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