Obviously, avoiding the freshman fifteen is a good reason to eat well and take care of your body while you're in college, but it's not the only reason. Food isn't just about how your body looks on the outside; in fact, it's how your body looks on the inside that's most important.

For this reason, it's a good idea to get acquainted with the basics of nutrition in order to understand the fuel aspect of the food you eat. In other words, things like vitamins, minerals, protein, calcium, and all that jazz.

First of all, it's very important to try to avoid eating processed foods whenever you can. College is perhaps the most difficult environment in which to do this, but it is possible — and the benefits are many. Try to always choose the whole foods that are complete as nature intended them.

Processed foods such as grains, sugars, and flours are often stripped of their natural nutrients. Even when vitamins and minerals are added back in later — a process called “enriching,” which means that the nutrients lost during refining are added back in to enrich the product — the total effect is never the same.

Take the example of rice: White rice may cook faster and have a more adaptable taste, but when the outer bran layer is stripped away, the rice grains lose much of their beneficial fiber and minerals. As proof, 1 cup of brown rice contains 3.5 grams of fiber. One cup of white rice contains less than 1 gram. Even enriching white rice doesn't make up the difference in the loss of fiber and minerals.

Now that you know to avoid processed foods that have all the good stuff stripped out of them, it's time to cover what you do want in your food. Key nutrients that your body needs include protein, iron, calcium, zinc, and vitamins A, D, and B12. You will also need a source of omega-3 fatty acids, important for preventing heart disease.

Your body's nerves, tissues, and bones are all made up of proteins, so proteins are necessary for growth and repair. Protein is found plentifully in meats and other animal-based foods, but that doesn't mean you should eat a cheeseburger every day to get your protein. Meats and other animal-based foods contain a lot of fat and cholesterol, so you'll want to find other sources of protein as well.

Dairy foods such as milk, cheese, and yogurt are excellent protein sources. Such nondairy sources as eggs, beans, and soy products contain enough protein to round out even a vegetarian diet.

Your body needs iron for the red blood cells carrying oxygen throughout the body. While iron is found plentifully in red meats, eggs, and seafood, and in lesser quantities in white meats, you can also get your daily allowance of iron from foods like spinach, kidney beans, lentils, and whole-wheat baked goods.

Calcium is the key mineral needed for forming and maintaining strong bones and teeth, but it also helps with other body functions. To get enough calcium, make sure to eat plenty of dairy products as well as calcium-rich vegetables like leafy greens.

You've heard about taking a zinc supplement if you begin to feel sick? That's because the mineral zinc helps bolster the immune system, assists in healing wounds, and helps sustain the senses of smell and taste. Zinc occurs naturally in red meat and poultry, in some seafood, and in beans, nuts, whole grains, and dairy products.

Vitamin A prevents eye problems, promotes a healthy immune system, is essential for the growth and development of cells, and keeps skin healthy. Good sources of vitamin A are milk, eggs, darkly colored orange or green vegetables (such as carrots, sweet potatoes, pumpkin, and kale), and orange fruits (such as cantaloupe, apricots, peaches, papayas, and mangoes).

Your body may need only small amounts of vitamin B12, but it is essential for the proper growth of red blood cells and for the health of some nerve tissues. Signs of a B12 deficiency include numbness and tingling in hands and legs, weakness, disorientation, and depression, among others. Vitamin B12 occurs in animal proteins, but you can also get plenty in your daily diet by eating eggs and dairy products.

The most abundant natural sources of omega-3 fatty acids, which help prevent heart disease, are fish and fish oils. Other good sources include flaxseed oil and such vegetable oils as olive oil and canola.