Review

International Journal of Obesity (2008) 32, S137–S142; doi:10.1038/ijo.2008.250

Obesity and the built environment: changes in environmental cues cause energy imbalances

D A Cohen1

1Department of Health, RAND Corporation, Santa Monica, CA, USA

Correspondence: Dr DA Cohen, RAND Corporation, 1776 Main, Santa Monica, CA 90407, USA. E-mail: Deborah_Cohen@rand.org

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Abstract

The past 30 years have seen dramatic changes in the food and physical activity environments, both of which contribute to the changes in human behavior that could explain obesity. This paper reviews documented changes in the food environment, changes in the physical activity environment and the mechanisms through which people respond to these environments, often without conscious awareness or control. The most important environmental changes have been increases in food accessibility, food salience and decreases in the cost of food. The increases in food marketing and advertising create food cues that artificially stimulate people to feel hungry. The existence of a metabolic pathway that allows excess energy to be stored as fat suggests that people were designed to overeat. Many internal mechanisms favor neurophysiologic responses to food cues that result in overconsumption. External cues, such as food abundance, food variety and food novelty, cause people to override internal signals of satiety. Other factors, such as conditioning and priming, tie food to other desirable outcomes, and thus increase the frequency that hunger is stimulated by environmental cues. People's natural response to the environmental cues are colored by framing, and judgments are flawed and biased depending on how information is presented. People lack insight into how the food environment affects them, and subsequently are unable to change the factors that are responsible for excessive energy consumption. Understanding the causal pathway for overconsumption will be necessary to interrupt the mechanisms that lead to obesity.

Keywords:

automaticity, cues, food environment, physical activity environment, non-conscious behavior

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Introduction

The obesity epidemic is affecting an estimated two of every three Americans and has become the most important nutritional problem on a global basis.1 Worldwide, more people suffer from conditions related to overweight and obesity than from malnutrition and underweight.2 The increase in obesity in the United States began in the late 1970s. In the three decades since, the increase in the number of severely obese has been substantial, and the problem appears to be accelerating. Between 2000 and 2005 alone, the number of people with body mass index (BMI)>50kg/m2 (equivalent to a 5′5″ person weighing 300lbs) has increased by 75%.3 In this short period of 30 years, it does not appear that there has been any change within people—no mutations, metabolic changes or physiologic alterations. Given that there are no recognizable changes within individuals, sources outside of individuals need to be considered as causal factors for obesity. By definition, these sources must emanate from the environment. Indeed, the past 30 years have seen dramatic changes in the food and physical activity environments, both of which contribute to the changes in human behavior that could explain obesity. This paper will review documented changes in the food environment, changes in the physical activity environment and the mechanisms through which people respond to these environments, often without conscious awareness or control.

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Changes in the food environment

The most dramatic change in the food environment over the last 30 years has been the increased accessibility of foods and the decline in the relative price of food. The major accomplishment of the Green Revolution was to increase the productivity of cereals, rice, wheat and maize, which are staples for much of the world. Improvements in variety, as well as in cultivation techniques and fertilizers, improved crop yields substantially. For example, before the Green Revolution, the maximum yield potential of rice was four tons per hectare.

After improving the variety and adding fertilizer, the yield was increased to 10 tons per hectare. Second, the growth duration was also reduced from 150–180 days to 110 days, making it possible to plant two cycles of crops rather than just one in a year. Yield was also improved by developing varieties that were disease-resistant and could tolerate problems with soils, temperatures and insects. The increase in rice production has resulted in a decrease in cost, and, on average, people are paying 40% less (adjusted for inflation) for rice now than they did in the mid-1960s.4 The increasing yields of all staples have led to lower food prices overall in relation to income, and in the United States, in 2006, the average family spent only 9.9% of their income on food compared with 14.8% just 40 years ago. In addition, owing to the relative decline in the cost of food, more people can afford the convenience of purchasing food away from home. In 1966, only 24% of all food expenses went toward food prepared away from home; in 2006, the percentage increased to 42%.5

Along with the real decrease in food cost, in the 1980s, per capita food availability increased by about 15% compared with 1970. Per capita carbohydrate availability increased by 27%, whereas fat increased by only 3% per capita.6 Beyond the overall increase in food in the environment, its accessibility has dramatically changed. In a 10-year period between 1986 and 1996, the number of commercial food establishments increased by 78%, with the number of fast-food outlets increasing by 85% and the number of restaurants and lunchrooms increasing by 62%, although food stores decreased by 15%.7 The real accessibility of food is likely to be many times higher, as a large percentage of retail outlets that do not sell food as their primary business now have food available on their premises, either in vending machines, as ‘impulse buys’ at the cash register, or as an add-on to their other merchandise. Chocolate, candies, chips and sodas are now sold in gas stations, hardware stores, book stores, car washes, office buildings and clothing stores. Typically, the types of food sold in these non-food establishments are highly processed, non-perishable items, which tend to be high in sugar and fat with very low nutrient value. Furthermore, there is no system that provides inspection or control, or keeps track of the scope of food availability.

Another dramatic change in the food environment has been the increase in portion sizes. Portions for beverages in 6 oz and 8 oz sizes are no longer sold in favor of 12, 16, 20 oz and larger sizes.6 The typical restaurant now serves portions that are 2–5 times in excess of what individuals typically require to stay in energy balance.8, 9, 10 Packaging sizes for goods have increased, and big box stores are making foods available in larger quantities as well. Moreover, larger supermarkets and warehouse stores are being increasingly utilized. Just 20 years ago, nearly 90% of food purchases were from traditional grocery stores. Today, grocery store purchases account for 69% of all at-home food purchases, and the difference has been allotted to nontraditional food stores, such as Costco, Target and WalMart.11

The variety of food available in the marketplace has also increased, although the variety in nutrient composition has not necessarily been affected. The food industry introduces in excess of 10000 new products each year, most of which have only minor changes in flavoring and texture but still contain the same sugar and fat ingredients.12

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Why we eat more than we need to

Even though the food environment has changed dramatically, it does not directly explain why people may be consuming more foods. What is necessary to connect the changes in the built environment with changes in eating behaviors are mechanisms, whereby the bounty of the built environment directly influences people's responses to food. Evidence for such mechanisms has been identified in a variety of fields, namely neurophysiology, behavioral economics, social psychology and commercial marketing. What follows is a brief review of the ways in which the environment influences our behaviors and results in overconsumption, often without awareness or control.

People are being artificially stimulated to feel hungry

Neuroimaging studies of the brain have identified that the brain secretes dopamine in responses to a variety of stimuli, including food and images of food.13 Dopamine creates the sensation of desire and craving and motivation to act.14 The response of the brain to images of drugs among drugs addicts is exactly the same as the response to food, although the magnitude of dopamine secretion is lower for food.15 The brain's response is automatic and is NOT mediated by consciousness. The reaction is largely uncontrollable. This suggests that the food and images of food in the environment stimulate the desire to eat, in addition to internal mechanisms such as low blood sugar.16 Translated on a larger scale, the ubiquitous accessibility of food and the omnipresence of food advertising is artificially stimulating people to feel hungry and overconsume. Given the increasing food availability over time, this stimulation is increasing, potentially explaining continuing rises in obesity.

Behavior is often NOT the result of deliberate, consciously planned decision-making

Once stimulated to desire food, people can potentially interrupt the action to eat. If people are aware that the stimulus to eat is artificial, it is easier to interrupt. However, when people are unaware of the stimulus, it may not be possible to avoid acting on what they perceive to be a real need.

Unfortunately, it appears that people have little insight into how much the environment influences their behavior. Studies of unplanned buying in supermarkets have documented that 65% of all supermarket decisions were made in the store with over 50% being unplanned. Of the factors that lead to unplanned purchases include supermarket displays, 67% were due to retail displays and manufacturing factors—all beyond the control of the individual.17

People's eating behaviors and preferences can be influenced without their knowledge or control

Although people may not be aware of them, they perceive subliminal cues. Many experiments have been performed in which images are flashed at durations too short for the conscious part of our brains to be aware of, yet the subjects so exposed react to the images, even though they report that they did not see them. One study using this technique flashed images of a person either frowning, with a neutral expression or smiling, which was then masked by another image, for which subjects were asked to identify the gender.18 Afterwards, subjects were asked to pour themselves an ‘energy’ drink, sample it and rate it. The subjects who were exposed to the frowning face poured themselves the least and rated the drink the lowest, whereas those exposed to the smiling face poured and drank more, and rated the drink the highest. Among the three groups subjects reported no noticeable differences in mood and arousal. Thus, individuals were influenced to consume different amounts in a manner that was beyond their awareness or control. Although this experiment took place in a laboratory setting, the same kind of phenomenon has been shown to occur in natural settings.

For example, a British study of the influence of restaurant background music on consumption behavior compared consumption patterns among diners on days when the background music played was classical, pop music versus no music at all.19 The music could not be considered a subliminal cue, because people could hear the music, although they may not realize how it influences them. Although the researchers did not measure the amount of energy consumed, diners listening to classical music on average racked up higher bills, 32.5£ (Pounds Sterling) for classical music, 29.5£ for pop music versus 29.7£ among the group with no music. The group provided with classical music also spent significantly more on appetizers and coffee. The researchers hypothesized that music created an ‘upscale’ atmosphere that primed the constructs of wealth and increased purchase intentions, pointing to greater spending on optional features of a meal, the appetizer and coffee. Again, it is unlikely that individuals would be aware that the background music would affect how much food they order and consume.

Much of human behavior occurs automatically without conscious direction

Human beings are designed to be able to do several things at once. To walk, for example, we do not have to consciously direct our right foot to move in front of our left foot. We walk effortlessly and can direct our attention elsewhere while walking. Similarly, if we need to raise our foot a little higher to navigate over a raised curb or avoid a puddle in our path, we do not have to stop to calculate a change in our trajectory or stepping pattern; typically, we will do this either without noticing or we may realize we have taken the appropriate action, usually AFTER we have already done it. One study observed children eating when they were served an excessively large portion of food. The researchers noted that when their plates had more food, the children automatically opened their mouths wider to accommodate more. This action was completely unrecognized by the children.20 Libet et al.21 was the first to conduct a study that clearly showed that motor activity begins PRIOR to conscious awareness of that activity. However, people often have the illusion that they consciously direct their behavior.22

Mirror neurons have been identified as the mechanism through which people automatically respond to environmental stimuli, and mimic other individuals.23 Not only to do people unconsciously mimic many kinds of behavior but they even adopt others’ preferences unknowingly.24 The behaviors are completely automatic; thus, they are also largely uncontrollable.

Research on decision-making also shows that people lack insight into the processes that govern their decisions.25 When it comes to choosing and eating foods, many factors, including distractions,26 information overload,27 context,28 fatigue and stress29 and smells and ambience,30, 31 play a more important role than rational choice. Typically, evaluations and judgments are made instantaneously, and then subsequently people fabricate a reason for their behavior.32

Behavioral economics and the important of framing

The work of Amos Tversky and Kahneman33 showed that people make choices depending on how information is presented to them and the context. Their decisions are influenced by ‘framing and prospect theory’ and three basic heuristics, namely representativeness, availability and anchoring.34 As far as framing, people make different decisions, for example, based on whether choices are presented as gains or losses, even when the choices result in exactly the same outcomes. The three heuristics that influence our choices are based on how people evaluate their environments. People tend to make judgments that are frequently flawed or biased because they may inappropriately generalize from their prior experiences to what they see in front of them. The frequency of an event or perception of the event influences their judgments by creating an appearance of normality or acceptability. Judgments are often biased by an initial impression, which may prevent reassessments. As people do not have control over how information is presented to them or the context in which it is presented, the resulting actions cannot be considered to be independently chosen.

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Why people cannot easily resist an obesogenic environment

Obesity occurs to people in a way that is insidious and undetectable—people gradually put on weight, a few ounces at a time. An imbalance as low as 20 excess kcal per day will cause the average person to gain about 2 pounds (0.89kg) per year, or 10 pounds (4.4kg) in 5 years. These small amounts are next to impossible for people to recognize or keep track of, especially when there are so much energy available all around us and so many strong cues that bid us to eat.

Improvements in marketing and advertising

In 1957, Vance Packard wrote the popular book, The Hidden Persuaders, pointing out the influence of advertising techniques on consumer behavior. Since that time, not only has the sophistication of advertising increased enormously, but also the amount of dollars invested in marketing research and advertisements has increased geometrically. Eye-tracking technology is an example of how marketers can use technology to increase product sales. Visual fixations represent interest in a visual area and provide information about automatic processing of behavior.35 The longer people look at a product, the more likely they are to purchase it. Devices have been developed that track the retina and record where people look and how long they focus on any particular element in an image. Individuals cannot accurately report eye fixations themselves, but the technology can record it with great accuracy. Eye tracking technology allows measurement of both conscious and unconscious reactions to stimuli and choices presented to the respondent.36 With this information, marketers can constantly improve on designs and products that will automatically grab people's attention.

Another technique that is found to be powerful in increasing consumer behaviors is branding, which is a type of conditioning that creates automatic association between desired qualities and characteristics and a specific product.37 Again, this is something that is difficult for individuals to recognize and resist at the moment when they are making choices.

Changes in the physical activity environment

Although a great deal of the obesity epidemic can be ascribed to increases in energy caused by the increase in food cues, reductions in energy expenditure may also play a role. The history of the human race has been the struggle to develop labor-saving devices and other shortcuts—anything that will make life easier for people. The total energy expenditure needed to survive has declined considerably over time. And the search for convenience continues at an inexorable pace.

However, it is very difficult to track population physical activity over time. The changes may be more subtle than can be detected by gross surveys. Jobs have been sedentary well before the obesity epidemic accelerated in the late 1970s. Nevertheless, even though jobs were sedentary before, people are probably even more sedentary since the mid-1980s when personal computers became widely available and the 1990s when internet communications were available. Now it is easier to send an email to colleague, than to walk 30s down the hall to have a conversation. For a person weighing 70kg, the same amount of energy conserved from avoiding a 30-s walk seems negligible, about 1.75kcal. But if this is now avoided six times per day (back and forth three times), that is a total of 10kcal no longer burned on daily basis and could accumulate to an extra pound (0.45kg) per year. Moreover, there are increasingly more gadgets sold to decrease everyday labor, including riding lawn mowers, leaf blowers, remote control devices for garages, doors and televisions, automatic sprinklers, all of which may save a few kcal of expenditure here and there. These differences cannot be easily measured, but cumulatively could make a significant overall difference in energy balance. These changes are also quite subtle and are likely below our awareness and control.

Although there have been changes in the design of our communities and streets, these changes occurred well before the obesity epidemic accelerated in the late 1970s. It is likely that social factors and physical features of our microenvironments play a more important role than the gross features of urban design and land use in explaining changes in our daily energy expenditure. Studies that have tried to measure an association between physical activity (PA), BMI and land use typically can only find a modest association between physical activity and the environment and rarely, if at all, an association between physical activity and BMI.38, 39, 40

Another problem with research on physical activity has been the reliance on self-report. According the CDC's Behavioral Risk Factor Surveillance System (BRFSS) in 2005, 49.1% of US adults reported that they met recommended physical activity guidelines of exercising 30minday−1, at least 5 days per week.41 In contrast, the National Health and Nutrition Examination Survey (NHANES) used accelerometers on 6329 people to actually measure moderate-to-vigorous physical activity and showed that fewer than 5% of adults met the guidelines.42 Just as shown with respect to eating behaviors, it is likely that individuals have little insight into their own physical activity behaviors. The lack of insight is also likely due to the fact that our motor activities are generally automatic, do not need conscious direction, so that while we are in motion, we are attending to other environmental cues, such as looking at the world around us, thinking about other problems, events or engaged in other activities.

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Conclusion

Eating behaviors as well as physical activity behaviors have earlier been characterized as a matter of conscious choice that people make to satisfy their own desires and cravings or to achieve their own goals. This model assumes that people are rational players who make decisions in their best interests and are aware of everything they do. Yet in reality, many people do not want to eat more than they need to, because they do not want to be overweight or obese, but they are unable to control their intake in a sustained manner. Similarly, in the past, more people had to be active (whether or not they wanted to), whereas now, labor-saving devices mean we do not have to expend as much energy to complete daily routines and communications. Given that the majority of individuals are now overweight or obese and that obesity exists across all subgroups, including minority and majority populations, low and high income and well-educated and poorly educated groups, suggests that excess eating and reduced physical activity may not be a conscious choice, but is probably the result of automatic and largely uncontrollable responses to unappreciated environmental cues. It can be clearly shown that changes in food presentation, portion sizes and other environmental factors precede and cause changes in food consumption. Similarly, changes in environmental cues, such as signs that promote climbing the stairs,43, 44, 45 also result in increases in physical activity in a causal manner. The existence of mechanisms that facilitate automatic and unconscious eating and responses to cues for physical activity are the critical link in the chain of causation between the environment and behavior.46

A more accurate conceptualization of the obesity epidemic is that people are responding to the forces in their environment, rather than lacking in will power and self-control. A metaphor that more truly captures the phenomenon is the tsunami. The environmental tsunami of cues and stimuli artificially make people hungry and lead them to unintentionally overconsume and to remain excessively sedentary. The societal response to the tsunami has been to provide swimming lessons and cheerleaders. The response has clearly not been proportional to the threat. People cannot change their responses to cues they do not perceive. Unless we focus on a more appropriate response, the obesity epidemic will continue. The real solution would be to control and reduce those forces that are causing the tsunami, change the cues we are exposed to on a daily basis or make explicit the cues we cannot change. Only then will people be able to make good use of the swimming lessons they receive, and bring themselves into energy balance according to their individual preferences.

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Notes

Conflict of interest

Deborah A Cohen has received lecture fees from Kompan and grant support from the National Institute of Health, National Institute of Alcohol Abuse and Alcoholism (#R01AA013749).

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