Food is any material food consumed to supply the necessary nutrients to an organism for its survival. In simple terms, food is food that is suitable for humans to eat, and that can be converted into the needed energy or other nutrients. More specifically, food is generally of animal, plant or fungi origin, and consists of necessary nutrients, including proteins, carbohydrates, vitamins, or iron. The five main food groups are carbohydrates (e.g., glucose), proteins, vegetables, fruits, and milk products.

Carbohydrates, like sugar, are used in the body in many ways, especially as fuel for energy production and as part of building and maintaining a healthy weight. Some carbohydrates are converted into glucose, which is used for energy and is stored in some cells as glycogen. Some carbohydrates are metabolized by the liver for energy, but most are stored in the muscles as glycogen. Some carbohydrates are used locally by the body to give nutrition, while others are used globally to supply the body with vital nutrients. Examples include honey, which serves both a digestive and an energizing role, and vegetables, which are an extremely important source of vitamins, minerals, fiber, and various antioxidants.

Fruits and vegetables are low in fat and contain high amounts of water, fiber, vitamins, and phytochemicals, which are powerful nutrients that strengthen the immune system, prevent cancer, and promote good overall health. They contain a variety of carbohydrates and vitamins that are immediately available for consumption and can help to reduce the risk of many types of cancer, including colon, breast, prostrate, bladder, and ovarian cancer. Vegetables and fruits are so versatile that they are often used in salads, sprinkled on sandwiches, or marinated in juices and added to other foods instead of pureed.

Animal origin foods contain meat, which provides essential protein, calcium, iron, zinc, vitamin B12, vitamin C, and vitamin E. Because animal origin foods are generally lower in fat than plant origin foods, they help to control weight. However, studies have shown that consuming animal source foods may cause higher cholesterol levels and increased risks of type 2 diabetes. This is because animal sources of carbohydrates tend to have a shorter half-life than plant-based carbohydrates. Animal proteins also contain large amounts of non-nutrient absorbable fats.

Foods that are high in sugar, especially refined sugar, are digested too quickly and are stored as fat. They cause spikes in blood sugar and lead to obesity, which is associated with increased chances of developing heart disease and cancer. Even though refined sugar is metabolized more slowly than natural sugars, it contributes to excess fat storage. Sweeteners such as aspartame and saccharin are widely used as sweeteners. Since the chemical structure of these sugars is identical to that of insulin, they stimulate the pancreas to release more insulin, which causes further weight gain.

A diet that does not include any fruits, vegetables, or other fibrous foods can provide energy and make you feel fuller for a long time. Some fruits, however, provide more calories per serving than other types of fruits do. Therefore, it is necessary to balance the amount of calories by including other foods with fewer calories. Fruits and vegetables are a good source of fiber, minerals, and other nutrients, because they are low calorie and high fiber. For example, apples contain almost twice as much fiber as whole wheat bread, which provides almost twice the amount of calories and almost three times the volume of pulp.