INTAKE

INTAKE. Intake is an umbrella term that refers to the act of taking something in. The term "intake" is often used in relation to food and drink, to describe how and how much is ingested. It also relates to behavior, since mental processing is involved in the action of eating and drinking. That is, physical and social stimuli are involved in feeding and drinking behaviors in terms of controlling the movements of gathering and ingesting materials; internal stimuli such as metabolism and circulating substrates also play a role. Intake of food and drink interests natural and social sciences as it is a vital behavior to sustain life that is also shaped by culture and society.

Behavioral Organization of Intake

The behavioral organization of intake involves perception of the sensory characteristics of food and drink. Physical and chemical properties of food and drink that can be sensed by the eater provide information about their nature. Orosensory attributes (that is, those relating to both taste and the other senses) can be detected by sight and sound, smell, irritance, taste, and touch. Food and drink can be appealing based on their orosensory properties. And the first mouthfuls of food can send substrates around the body within minutes.

Intake can be adjusted according to nutritional needs when orosensory characteristics are associated with the postingestive (metabolic) effects of food and drink. Orosensory characteristics can thus become cues that predict postingestional effects specific to foods and drinks. These cues can be unlearned (innate, sweet taste) or learned (acquired, bitter taste). While sweet stimuli mean energy, perhaps from carbohydrate, bitter stimuli are a cue to alkaloid toxins. From an evolutionary standpoint, it has been hypothesized that the liking for sweetness ensured animals' survival. In animals and humans, learning plays an important role in food intake. The acquisition of a taste for nutrients and an aversion for toxic substance are also vital. Behavioral and physiological analysis of the learning of pre-and postingestive control of intake was developed by French physiologist Jacques Le Magnen. His original contributions include findings on conditioned sensory aversions, carbohydrate-conditioned sensory preferences, and control of meal size.

Social and Cultural Organization of Intake

Intake is also organized according to food availability. In terms of the latter, we see the great contrast between industrialized countries where food is available in abundance and Third World countries where hunger afflicts poor people due to food scarcity. Our ancestors' intake was mainly dependent on plant food gathering, hunting, and fishing. Later on, domestication of food and animals and the development of food preservation enabled human societies to improve food availability. However, in parts of the world not well suited for cultivation, pastoralists still acquire their food from their herds of domesticated animals. Herding allows them to transform nonedible plant matter into animal products.

Intake is also determined by the culture of human groups. Learned cultural knowledge affects food choices. Socially transmitted knowledge about food includes norms, religious, or cult values, as well as myths, superstitions, taboos, and fads. The intake of certain kinds of plant and animal foods can be culturally prohibited. For example, cattle are killed for meat in many parts of the world, while traditional Hindus forbid killing cattle for meat because of their use in agriculture. Dogs serve as pets and companions in American culture while serving as food in other cultures, illustrating how intake is motivated by symbolic values of the food rather than its survival value. However, sociocultural influences do not act alone and interact with the individual's biology to determine intake.

Control of Intake

Investigations concerned with the control of intake have used various peripheral and central approaches. This has led to theories of the mechanisms controlling intake, such as the glucostatic (transient change of blood glucose), the lipostatic (fat metabolism and body fat stores), the thermostatic (thermic effect of food), and the aminostatic (essential amino acid) hypotheses. Although intake was shown to be facilitated or inhibited by a variety of substrates, the behavioral mechanisms remain to be identified. Neural bases of food intake have evolved from the those prevalent in the 1950s, focusing on appetite and satiety brain centers located in the hypothalamus, to the current hypothesis that macronutrient intake is controlled by precise synaptic pathways. Food intake might indeed be guided by macronutrient selection. However, experiments that involve presenting laboratory animals with two or more diets differing in their nutrient content in an attempt to understand brain mechanisms that control intake involves the inclusion of confounding factors. Indeed, many drugs that affect central nervous system neurotransmitters and peptides also act on sensory pathways. Therefore, unless the confounding sensory attributes of food have been excluded, one cannot conclude that the subsequent food intake is controlled by the macronutrients. This principle was applied by examining studies using sensorily contrasting forms of various macronutrients, and only brain serotonin was found to affect carbohydrate intake while the effects of catecholamines and opiates on macronutrients were not substantiated.

Intake is also motivated by factors external to the food or the drink itself. Age, sex, physiological state, nutritional state, emotions, stress, number of people present, peer groups, food trends, social pressures (body image), as well as beliefs related to food safety (for example, food beliefs related to mad cow disease, genetically modified foods, pesticide-free or organic food) are known to influence intake. Other external factors that affect intake include food availability, food cost, as well as environmental factors (season, temperature, and so forth). In addition, animal and human studies have revealed that food and macronutrient intake is related to circadian rhythms, and that food intake is concentrated during the period of main activity (for example, during the day) and is related to predictable rhythms of macronutrient selection.

Expressing Intake

Intake of food and drink is often estimated by dietary measurement of daily intake of energy (kilocalorie [kcal], kilojoules [kJ]) and nutrients (carbohydrate, protein, lipid, vitamins, and minerals. Units such as the gram (g), milligram (mg), microgram (μg), International Unit (IU), and so forth are used, as well as established human nutrition methodologies such as food diary, food recalls, food frequency questionnaires, and so on. Intakes are then qualified as adequate or inadequate based on nutritional recommendations. Nutritional research methods need to be improved by assessing cognitive perception and control of eating.

Facilitated intake and its inhibition are expressed in various ways. Among terms used to describe facilitated intake or events surrounding it are appetite, hunger, palatability, motivation to eat, and (sensory) preference. If intake is inhibited, terms such as satiety, satiation, appetite inhibition, or even satiety disinhibition are used. These terms are often used to interpret sets of quantitative data such as amount eaten during the day, meal size, ingestion rate, or numbers calculated from scales rating the hunger state. Although these measurements do not assess cognitive processes controlling intake, their direction is translated into words describing behaviors. The experimental design is therefore crucial to identify causal processes involved in intake; for example, unchanged quantitative intake while rate of intake is reduced could be interpreted as decreased pleasure while sensory preference remains unaffected.

Implications

Insufficient intake results in chronic malnutrition and periodic massive starvation. Related health problems are numerous, and include the impact of the permanent effect of energy–protein deficiency on brain development (in early childhood), parasitic diseases, and high rates of infant mortality. Controlling population growth and a better allocation of resources were proposed as solutions to world hunger. The problem of hunger could also be alleviated by technology transfer in which new technologies and crop variety could improve food production.

Disordered intake can lead to health problems such as obesity, cardiovascular disease, diabetes, alcoholism, as well as disordered eating in athletes and the eating disorders of restrictive eaters, anorexics, and bulimics. Interestingly, these health problems often arise in countries where food is abundant. Intake of specific macronutrients has been linked to diseases, for example, intake of carbohydrates has been linked to diabetes, and fat intake has been linked to heart disease, as well as to some cancers. Therefore, a better understanding of how intake is controlled could provide precious tools enabling one to intervene effectively or even prevent the development of nutrition-related pathologies.

See also Acceptance and Rejection; Appetite; Assessment of Nutritional Status; Eating: Anatomy and Physiology of Eating; Health and Disease; Malnutrition; Metabolic Imprinting and Programming; Sensation and the Senses.

BIBLIOGRAPHY

Berthoud, Hans-Rudolf, and Randy J. Seeley. Neural and Metabolic Control of Macronutrient Intake. Boca Raton, Fla.: CRC, 2000.

Booth, David A. Psychology of Nutrition. London: Taylor & Francis, 1994.

Peoples, James, and Garrick Bailey. Humanity: An Introduction to Cultural Anthropology. Belmont, Calif.: West/Wadsworth, 1997.

Stricker, Edward M. Handbook of Behavioral Neurobiology, vol. 10, Neurobiology of Food and Fluid Intake. New York: Plenum, 1990.

Thibault, Louise, and David A. Booth. "Macronutrient-Specific Dietary Selection in Rodents and Its Neural Bases." Neuroscience and Biobehavioral Reviews 23 (1999): 457–528.

Thibault, Louise, and David A. Booth, eds. "The Role of Orosensory and Postingestional Effects of Food in the Control of Intake. Jacques Le Magnen, 1955–1963." Appetite 33 (1999): 1–59.

Louise Thibault

in·take / ˈinˌtāk/ • n. 1. an amount of food, air, or another substance taken into the body: your daily intake of calories | his alcohol intake. ∎  an act of taking something into the body: she heard his sharp intake of breath | a protective factor is the intake of cereal fiber. 2. a location or structure through which something is taken in, e.g., water into a channel or pipe from a river, fuel or air into an engine or machine, commodities into a place, etc.: cut rectangular holes for the air intake. ∎  the action of taking something in: facilities for the intake of grain by road.

intake f. phr. take in; see TAKE, IN1.