Food

Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells to provide energy, maintain life, or stimulate growth. Different species of animals have different feeding behaviours that satisfy the needs of their unique metabolisms, often evolved to fill a specific ecological niche within specific geographical contexts.

Omnivorous humans are highly adaptable and have adapted to obtain food in many different ecosystems. The majority of the food energy required is supplied by the industrial food industry, which produces food with intensive agriculture and distributes it through complex food processing and food distribution systems. This system of conventional agriculture relies heavily on fossil fuels, which means that the food and agricultural system is one of the major contributors to climate change, accountable for as much as 37% of total greenhouse gas emissions.

The food system has significant impacts on a wide range of other social and political issues including: sustainability, biological diversity, economics, population growth, water supply, and access to food. Food safety and food security are monitored by international agencies.

Definition and classification
Food is any substance consumed to provide nutritional support and energy to an organism. It can be raw, processed or formulated and is consumed orally by animals for growth, health or pleasure. Food is mainly composed of water, lipids, proteins and carbohydrates. Minerals (e.g. salts) and organic substances (e.g. vitamins) can also be found in food. Plants, algae and some microorganisms use photosynthesis to make their own food molecules. Water is found in many foods and has been defined as a food by itself. Water and fiber have low energy densities, or calories, while fat is the most energy dense component. Some inorganic (non-food) elements are also essential for plant and animal functioning.

Human food can be classified in various ways, either by related content or by how the food is processed. The number and composition of food groups can vary. Most systems include four basic groups that describe their origin and relative nutritional function: Vegetables and Fruit, Cereals and Bread, Dairy, and Meat. Studies that look into diet quality often group food into whole grains/cereals, refined grains/cereals, vegetables, fruits, nuts, legumes, eggs, dairy products, fish, red meat, processed meat, and sugar-sweetened beverages.

Production of food
Originally, people got food as hunter-gatherers. The agricultural revolution changed that. Farmers grew crops including those invented and improved by selective breeding. These improvements, for example the invention of maize, allowed feeding more people, and further improvements gave it a better taste.

Food shortage has been a big problem throughout history. Many people do not have enough money to buy the food that they need. Bad weather or other problems sometimes destroy the growing food in one part of the world. When people do not have enough food, we say that they are hungry. If they do not eat enough food for a long time, they will become sick and die from starvation. In areas where many people do not have enough food, we say that there is famine there.

Food and water can make people sick if it is contaminated by microorganisms, bad metals, or chemicals.

If people do not eat the right foods, they can become sick. People may often have a variety of eating disorders that cause them to either eat too much, or not be able to eat certain things or amounts. Common diseases like Coeliac disease or food allergies cause people to experience ill effects from consuming certain foods that are normally safe. If people eat too much food, they can become overweight or obese. This causes numerous health problems. On the other hand, eating too little food, from lack of access or anorexia could cause malnutrition. Therefore, people have to balance the amount, the nutrition, and the type of food to be healthy.
 * If people do not eat enough protein, they get the disease called kwashiorkor.
 * If they do not eat enough vitamin B1 (thiamine), they get the disease called beriberi.
 * If they do not eat enough vitamin C, they get the disease called scurvy.
 * If children do not eat enough vitamin D, they get the disease called rickets.