Food is any substance consumed in order to provide nutrition to the organisms for life. Life cannot exist without food, since without food we will not live. Food is generally of animal, plant or fungal origin and includes essential vitamins, including proteins, carbohydrates, fats, and minerals. Plants need food in the form of sugars, starch, and chlorophyll, while animals need meat, fat, protein and other nutrients to survive. In fact, animals and plants are different only in that plants secrete food for their growth and maintenance while animals secrete waste products that pollute the soil and must be disposed of through excreting them or by excreting them through their pores.

The major groups of foods that we consume are animal sources, plant sources and both animal and plant sources. Animal sources include red meats, poultry, game, milk, eggs and fish. Plant sources include vegetable oils, fruits, roots, vegetables, nuts, spices, grains, legumes, seeds, mushrooms and nuts. The main difference between plant and animal sources of nutrition is that animal sources contain much higher levels of fat, salt and cholesterol and therefore are more harmful to our health than plant sources are.

Most of our food comes from animal source food which consists mainly of pork, beef, lamb and poultry, although milk, cheese, butter, cream, yoghurt and milk products are also important for human consumption. Meat, dairy and eggs are high in saturated fats, which increase the risk of heart diseases and various cancers. Dairy products also contain different kinds of hormones, antibiotics and growth promoters. Plant products such as nuts, vegetables, spices, grains and legumes are rich in unsaturated fatty acids and are essential for maintaining a healthy weight. Eating smaller portions of oily foods on a daily basis is the best way to reduce the consumption of saturated fatty acids.