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food — news, coverage & facts — IJR

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. Other organic substances (e.g., vitamins) and minerals (e.g., salts) can also be found in food. Plants, algae, and some microorganisms use photosynthesis to make some of their own nutrients. Water is found in nearly all foods and has been defined as food by itself. Water has no food energy, and fibers have low energy densities, or food energy relative to volume, some providing none, while fat is the most energy-dense component. Some inorganic substances are also essential for plant and animal functioning.

Human food can be classified in various ways, either by related content or by how it is processed. The number and composition of food groups can vary. Most systems include four basic groups described by their origins and relative nutritional functions: vegetables and fruit, cereals and bread, dairy, and meat. Studies that look into diet quality group food into whole grains, refined grains, vegetables, fruits, nuts, legumes, eggs, dairy products, fish, red meat, processed meat, and sugar-sweetened beverages. The Food and Agriculture Organization and World Health Organization use a system with eighteen or nineteen food classifications, including: cereals and their products; roots, tubers, plantains and their products; pulses, seeds and nuts and their products; milk and milk products; eggs and their products; fish, shellfish and their products; meat and meat products; insects, grubs and their products; vegetables and their products; fruits and their products; fats and oils; sweets and sugars; spices and condiments; beverages; foods for particular nutritional uses; food additives; composite dishes; and savory snacks. (The source claims nineteen but lists eighteen, numbered 1–15 and 17–19.)

Plants

Plants as a food source are divided into seeds, fruits, vegetables, legumes, grains and nuts. Where plants fall within these categories can vary, with botanically described fruits such as the tomato, squash, pepper and eggplant or seeds like peas commonly considered vegetables. Food is a fruit if the part eaten is derived from the reproductive tissue, so seeds, nuts and grains are technically fruit. From a culinary perspective, fruits are generally considered the remains of botanically described fruits after grains, nuts, seeds and fruits used as vegetables are removed. Grains can be defined as seeds that humans eat or harvest, with cereal grains (oats, wheat, rice, corn, barley, rye, sorghum and millet) belonging to the Poaceae (grass) family and pulses coming from the Fabaceae (legume) family. Whole grains are foods that contain all the elements of the original seed (bran, germ, and endosperm). Nuts are dry fruits, distinguishable by their woody shell.

Fleshy fruits (distinguishable from dry fruits like grain, seeds and nuts) can be further classified as stone fruits (cherries and peaches), pome fruits (apples, pears), berries (blackberry, strawberry), citrus (oranges, lemon), melons (watermelon, cantaloupe), Mediterranean fruits (grapes, fig), tropical fruits (banana, pineapple). Vegetables refer to any other part of the plant that can be eaten, including roots, stems, leaves, flowers, bark or the entire plant itself. These include root vegetables (potatoes and carrots), bulbs (onion family), flowers (cauliflower and broccoli), leaf vegetables (spinach and lettuce) and stem vegetables (celery and asparagus).

The carbohydrate, protein and lipid content of plants is highly variable. Carbohydrates are mainly in the form of starch, fructose, glucose and other sugars. Most vitamins are found from plant sources, with the exception of vitamin D and vitamin B12. Minerals can also be plentiful or not. Fruit can consist of up to 90% water, contain high levels of simple sugars that contribute to their sweet taste, and have a high vitamin C content. Compared to fleshy fruit (excepting bananas) vegetables are high in starch, potassium, dietary fiber, folate and vitamins and low in fat and calories. Grains are more starch based and nuts have a high protein, fiber, vitamin E and B content. Seeds are a good source of food for animals because they are abundant and contain fiber and healthful fats, such as omega-3 fats. Complicated chemical interactions can enhance or depress bioavailability of certain nutrients. Phytates can prevent the release of some sugars and vitamins.

Animals that only eat plants are called herbivores, with those that mostly just eat fruits known as frugivores, while leaf and shoot eaters are folivores (pandas) and wood eaters termed xylophages (termites). Frugivores include a diverse range of species from annelids to elephants, chimpanzees and many birds. About 182 fish consume seeds or fruit. Animals (domesticated and wild) use as many types of grasses that have adapted to different locations as their main source of nutrients.

Humans eat thousands of plant species; there may be as many as 75,000 edible species of angiosperms, of which perhaps 7,000 are often eaten. Plants can be processed into breads, pasta, cereals, juices and jams or raw ingredients such as sugar, herbs, spices and oils can be extracted. Oilseeds are pressed to produce rich oils – ⁣sunflower, flaxseed, rapeseed (including canola oil) and sesame.

Many plants and animals have coevolved in such a way that the fruit is a good source of nutrition for the animal, who then excretes the seeds some distance away, allowing greater dispersal. Even seed predation can be mutually beneficial, as some seeds can survive the digestion process. Insects are major eaters of seeds, with ants being the only real seed dispersers. Birds, although being major dispersers, only rarely eat seeds as a source of food and can be identified by their thick beak that is used to crack open the seed coat. Mammals eat a more diverse range of seeds, as they are able to crush harder and larger seeds with their teeth.

Taste

Animals, specifically humans, typically have five different types of taste sense: sweet, sour, salty, bitter, and umami. The differing tastes are important for distinguishing between foods that are nutritionally beneficial and those which may contain toxins. As animals have evolved, the tastes that provide the most energy are the most pleasant to eat while others are not enjoyable, although humans in particular can acquire a preference for some substances which are initially unenjoyable. Water, while important for survival, has no taste.

Sweetness is almost always caused by a type of simple sugar, such as glucose or fructose, or disaccharides, such as sucrose, a molecule combining glucose and fructose. Sourness is caused by acids, such as vinegar. Sour foods include citrus, especially lemons and limes. Sour is evolutionarily significant as it can signal a food that may have gone rancid due to bacteria. Saltiness is the taste of alkali metal ions such as sodium and potassium. It is found in almost every food in low to moderate proportions and enhances flavor. Bitter taste is a sensation considered unpleasant, caused by foods such as unsweetened dark chocolate, caffeine, lemon rind, and some types of fruit. Umami, commonly described as savory, is a marker of proteins and characteristic of broths and cooked meats. Foods that have a strong umami flavor include cheese, meat and mushrooms.

While most animals' taste buds are located in their mouths, some insects' taste receptors are located on their legs, and some fish have taste buds along their entire bodies. Dogs, cats, and birds have relatively few taste buds (a chicken has about 30), and an adult human has between 2000 and 4000, while a catfish can have more than a million. Herbivores generally have more than carnivores as they need to tell which plants may be poisonous. Not all mammals share the same tastes: some rodents can taste starch, cats cannot taste sweetness, and several carnivores (including hyenas, dolphins, and sea lions) have lost the ability to sense up to four of the five taste modalities found in humans.