Research reviewEvolutionary and anthropological perspectives on optimal foraging in obesogenic environments
Introduction
Ninety-eight percent of hominid existence has been shaped by hunting and foraging with selection for cognitive and behavioral repertories, nutritional requirements and physiological patterns adapted to harsh environments with fluctuations in food availability, food shortages and periodic high energy expenditures (Chakravarthy & Booth, 2004; Eaton, Shostak & Konner, 1988; Kuzawa, 1998; Loos & Rankinen, 2005; Mann, 2004). In this environment, an advantage accrued to hominids who had biological and behavioral mechanisms that insured (over)consumption of available food to meet immediate physiological needs as well as efficient storage of energy and macro- and micronutrients (Chakravarthy & Booth, 2004; Kuzawa, 1998).
These once adaptive cognitive, behavioral and physiological genotypes and phenotypes persist today in evolutionary-novel environments characterized by an abundance of supersized energy-dense foods with low energy-cost availability (Boon, Stroebe, Schut & Jansen, 1998; Booth, Pinkston & Poston, 2005; Brownell & Horgan, 2003; Nestle, 2003; Speakman, 2004). Modern environments, especially urban settings, afford lifestyles conducive to a surfeit of calories and consequent obesity (Popkin, 2001; Popkin & Gardon-Larson, 2004; Winterhalder & Smith, 1981).
This epidemic of overweight and obesity has now reached more than 1.1 billion persons worldwide with some adult populations reaching a prevalence of nearly 80% (International Obesity Task Force, 2004; Kuczmarski, Flegal, Campbell & Johnson, 1994; Lobstein, Baur, Uauy, & IASO International Obesity Task Force, 2004). In 2000, the World Health Organization (2000), World Health Organization. (2003) estimated that worldwide there were 22 million overweight children and adolescents. A number of studies indicate that 15–30% of children in developed countries are overweight with percentages in developing countries rapidly rising (de Onis & Blossner, 2000; International Obesity Taskforce, 2004; Lobstein et al., 2004). This paper addresses this pandemic by using models from evolutionary behavioral ecology to elucidate obesogenic features and human behaviors in contemporary environments.
Section snippets
Foraging theory applied to the obesogenic environment
Foraging theory is a component of behavioral ecology that utilizes cost/benefit models to predict food-related behaviors, prey (including plants)–predator interactions and characteristics of the environment. Most cost/benefit models use energy as the currency. Because food is essential to meet nutrient and energy requirements for survival, growth and reproduction, foraging theory provides explanatory models linking the environment through adaptive food-related behaviors that, theoretically,
Optimal foraging: energy costs and profitability
A central theorem of foraging theory is that animals operate to increase energy intake and reduce energy costs (MacArthur & Pianka, 1966). Profitability defined as energy gain per unit time or effort has markedly increased in modern environments. Foraging in obesogenic landscapes requires little energy expenditure to acquire big energy payoffs (Popkin & Gordon-Larsen, 2004; Winterhalder & Smith, 1981). A number of factors account for this.
First, search time is significantly reduced because of
Optimal foraging: Marginal Value Theorem
The Marginal Value Theorem describes decisions about when, where and how long to stop for a feeding bout among widely scattered food patches (Sinervo, 1997). Under most circumstances, as animals and humans feed, the energy gain declines as the food becomes scarcer in the patch. However, in obesogenic environments there is an endless supply of food, there is no decreasing rate of return for time invested. There are often few time constraints as food is available 24 hours a day with little
Convenience and the built environment
The built environment, daily habits and cultural values can make small but consistent differences in energy intake and expenditure that lead to big differences in obesity prevalence. For example, Frenchmen are physically active based on necessities of the built environment (e.g., few elevators), convenient walking distances (e.g., small markets in mixed residential and commercial neighborhoods) and traditions of walking and biking (Rozin, 2005). These aspects of lifestyle account, in part, for
Globalized food trends and dietary breadth
As big-brained omnivores, we enjoy and seek dietary variety to balance nutrient requirements. Plant and animal evidence from Paleolithic sites to the present documents dietary breadth and geographic and seasonal dietary variation (Eaton et al., 1988; Unger & Teaford, 2002). Extensive studies of three species of apes show that they consume an average of 94 plant species while a classic hunting and foraging population, the !Kung of the Kalahari desert, consume 110 species of plants (Lee & Devore,
Globalized food trends: large portion sizes
Larger portion sizes of foods characterize obesogenic environments. Supersizing, which began in the 1990s, costs the industry pennies because most of the cost is in advertising, packaging and labor (Brownell & Horgan, 2003; Nestle, 2003; Spurlock, 2005). Therefore, larger portions are actually more profitable for the fast food companies; consumers expect them and get more food for their money (Spurlock, 2005).
Portion size is a potent environmental determinant of how much a person eats (
Globalized food trends: ubiquitous visual food cues
Modern environments are filled with an array of visual stimuli of actual food items, their representations in the media, and universally recognized iconic images and logos (e.g., McDonald's golden arches). These images transcend cultural and linguistic boundaries. The visual appeal is purposeful and effective because vision is the primary primate mode of perception (Jones, Martin & Pilbeam, 1992). As the architecture of the primate face evolved, rotation of the eye orbits to the front of the
Conclusion
In summary, in obesogenic environments, the foraging costs are low (minimized) and the benefits in caloric intake are high (maximized) relative to prehistoric and historic feeding patterns. The demographic shift to urban and suburban environments affords both adults and children access to energy-saving conveniences, inexpensive processed foods and sedentary leisure activities. Optimal foraging models in these environments with abundant visual food cues predict behaviors in high density and
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