The food chain is a complex network of all the food types and their relationships. Food is any material consumed to supply nutrition to an organism. A primary function of food is to provide the energy necessary for growth and development. In most animals, food is generally of animal, plant or fungi origin, and consists of various essential nutrients, including proteins, carbohydrates, vitamins, or iron. Plants derive nourishment from the sun, rain, and weeds.

Humans eat food in three main ways: to provide energy to move to and from living bodies; to store food for future consumption; and to facilitate digestion of food. Humans need a wide range of food to survive. They have mouths to feed; a series of stomachs to digest food before swallowing it; and the reproductive system to feed future generations. Humans can survive on little food supplied by nature, but they have developed a variety of habits to help them acquire food and maintain healthy diets.

The human diet includes a combination of carbohydrates, protein, vegetables, fruits, and fat. All these food types contain different components, with differing proportions in different foods. The proportion of each component varies in different foods and can be affected by food type, area of the world, population, activity level, and the overall makeup of the diet. These food types are separated into five broad categories: carbohydrates, proteins, fibres, vitamins, and minerals

Carbohydrates include starches, unrefined vegetable oils, bread products, cereals, pasta, rice, and some fruits. These foods provide energy and are available in diverse forms, including concentrated and unprocessed sugars, and products made from plants (e.g., sugar, corn syrup, yeast, soy sauce, milk, and cheese). Some carbohydrates are soluble in water and some are not, which gives some carbohydrates the potential to cause diarrhea when they become too much for the body’s digestive system to process and metabolize. However, because carbohydrates are a main food source for energy in the body, they are also an important source of nutrients.

Proteins are the primary elements in food, supplying the essential amino acids, which are required for the building of muscles, tissues, organs, bones, and teeth. Animal products are the most common sources of protein, including meat, milk, eggs, fish, poultry, and other seafood. The meat is the richest source of protein, with little animal-derived food available in the form of dairy products, cheese, yogurt, and butter. Fish and dairy products are low in fat and cholesterol and provide a wide range of nutrients. Other plant-based foods include fruits (fresh and dried), vegetables (onions, beans, and grains), whole grains (i.e., bread), nuts, seeds, and legumes (peas, beans, and lentils).

Fats are a main food source for many people. They provide the body with a number of benefits, including being the main source of energy for walking and exercising, since they are absorbed rapidly by the body. Unfortunately, high levels of consumption can be harmful, leading to obesity. Since fats are digested slowly, consuming too many on a regular basis can result in weight gain, which in turn can lead to the development of serious health problems like coronary disease and diabetes. The best dietary sources of fat are nuts, avocados, peanuts, olives, and walnuts, as well as sunflower and olive oils.