All living things get energy through nutrition, which is the process by which an organism takes in and uses food. Foods supply nutrients, or raw materials needed to sustain healthy life functions. Nutrients provide energy, heal wounds, help to transport oxygen to cells, and regulate body functions. In other words, the body needs nutrients to maintain basic functions and to provide energy for daily activities.

Nutrients are constantly being consumed and depleted by bodily functions. Different foods provide different nutrients for the body, so eating a variety of healthful foods is important to get the nutrients needed. Key nutrients include carbohydrates, proteins, fats, vitamins, minerals, and water.


Carbohydrates are molecule chains made up of carbon, hydrogen, and oxygen that provide people with fuel and energy when consumed. There are three different kinds of carbohydrates: simple, starches, and fiber. Simple carbohydrates are sugars, such as sucrose (table sugar), fructose, and lactose. Sugars occur naturally in fruits, vegetables, and milk. They can also be added to processed food, such as cookies, cakes, and breads. Refined simple carbohydrates such as white rice and white bread should be eaten in moderation.

Starches are complex carbohydrates that can be found in breads, pastas, potatoes, rice, and other grains. These are long chains of sugars that must be digested before the body can use them as fuel. Starches are a more sustained energy source than simple sugars and act as fuel for metabolic functions.

Fiber is a complex carbohydrate that comes from the cell walls of plants, and is found in peas, beans, fruits, vegetables, and whole-grain breads and cereals. Fiber is essential for the smooth running of the digestive system.


Proteins provide the basic structural and functional components of all cells. Each protein is made up of combinations of 20 different amino acids. Amino acids are the building blocks of proteins, nine of which are considered essential. This means they cannot be built by the body. The nine essential amino acids need to be consumed in order to maintain healthy body structures, including skin, muscles, and hair.

Both plant and animal food sources contain proteins. Proteins that come from fish, milk, meat, and eggs contain all 20 amino acids and are known as complete proteins. Nuts, beans, and some grains are rich in protein, but lack some of the 20 amino acids. Quinoa is an example of a grain that is a complete protein containing all 20 amino acids. People on a vegetarian diet must plan their meals carefully so they obtain all the amino acids they need.


Fats and other lipids are an important part of cell membranes, nerve insulation, and hormones. The three types of fat molecules-saturated fats, unsaturated fats, and trans fats-are classified based on their chemical structure. Fats support some of the body’s functions and provide energy, but trans fats should be avoided.

  • Saturated fats usually come from animals. Saturated fats are also known as solid fats because they are solid at room temperature. Butter and lard are examples of saturated fats.
  • Unsaturated fats usually come from plants. Extracted unsaturated fats, such as com oil and olive oil, are typically liquid at room temperature. Nuts, avocado, and fish are just a few other foods rich in unsaturated fats. Unsaturated fats are, in general, considered more healthful than saturated fats. Eating unsaturated fats in moderate amounts may lower your risk of heart disease.
  • Trans fats are manufactured by adding hydrogen to vegetable oils. They are often used in processed foods and may have adverse effects on health, including an increased risk of stroke and heart disease.


All of the body’s cells contain water. Water is essential for most body functions. Cells cannot reproduce or grow without water. Water also lubricates the joints of the body and reduces protein breakdown of muscle tissue. Without water, neurotransmitters do not work efficiently, slowing down brain function, reaction time, and the ability to reason.

Every day the human body loses between two to three liters of water through respiration, perspiration, and urination. A person needs to consume at least two liters of water daily to maintain homeostasis in the body. While the human body can go weeks without food, it can survive only a few days without water. Dehydration can cause severe medical issues, including muscle weakness, slow reaction times, and even death.


Complex organic molecules that help the body build new tissues, regulate body functions, and fight disease are called vitamins. There are 13 different vitamins. Their sources, functions, and results of deficiencies are shown in the table below. Even though only a few hundredths of a gram of each vitamin is needed every day, deficiencies can cause severe health problems.



Inorganic elements the body needs for most of its metabolic functions are called minerals. Minerals contribute to making bones strong, enabling nerves to send impulses and allowing muscles to contract. Some of the many minerals the body needs, their sources, functions, and results of deficiencies, are shown in the table on the next page.


Eating a Healthy, Balanced Diet

When you eat meals that provide a variety of the nutrients your body needs, you are eating a balanced diet. Most foods contain more than one nutrient. For example, vegetables contain fiber, carbohydrates, vitamins, and minerals. Quinoa is a grain that contains carbohydrates, minerals, and protein. In order to have a healthy diet, it is important to include a variety of nutrient-rich foods that are low in fat and added sugars.

Calories and Maintaining a Healthy Weight

Calories measure the energy stored in food. People get all the calories they need from the foods they eat. Foods that are high in calories include foods high in fats, starches, simple carbohydrates, and many processed foods. Foods that are low in calories include lean meats, fruits, and vegetables. All metabolic functions, including respiration and maintaining body temperature, burn calories to maintain homeostasis in the body. However, most of these processes do not require a large amount of calories.

The number of calories a person needs depends on gender, age, and activity level. To maintain a healthy weight is to balance the calories consumed with the calories expended through physical activity. If a person eats more calories than his or her metabolism burns, the body will store the extra calories as fat.