Poverty and Obesity: Questioning the Causal Link

Introduction: The Poverty–Obesity Claim

The argument that obesity is correlated with poverty is one that is quite persistent in popular literature and in scientific research (e.g., Drewnowski, 2004; Pollan, 2006). To say that one thing is correlated with another should not be interpreted as meaning that one thing leads to or causes another. Yet writers like Pollan do precisely this. The actual relationship of obesity to income level or poverty turns out to be far more complex than such writers take the time to consider. In fact, the relationship of obesity to poverty is in actuality almost nil. It is the writings of individuals who skew and oversimplify these issues that lead to such misinterpretations.

Defining Obesity and Measuring Its Prevalence

This is not to imply that obesity is not a serious issue. There has been a dramatic rise in obesity rates in the United States over the last decade. For instance, the Centers for Disease Control and Prevention (CDC) recently estimated that 65% of adults in the United States are either obese or overweight (CDC, 2004a). The terms obese and overweight are not judgment calls but have been defined by accepted medical standards using the measurement of Body Mass Index (BMI). The BMI is a ratio measurement using a person's weight in kilograms to the square of their height in meters. Thus, a person with a BMI between 25 and 30 kg/m² is considered overweight, whereas a person with a BMI greater than 30 kg/m² is considered obese (National Institutes of Health [NIH], 2004).

Moreover, the World Health Organization (WHO) has divided obesity into different classes. Class I obesity is defined by a BMI of 30.0–34.9; Class II obesity by a BMI of 35.0–39.9; and Class III obesity by a BMI of 40.0 or greater (NIH, 2004). It is important to understand that, even though BMI is strongly correlated with the amount of body fat a person carries, it is not a direct measure of body fat. For instance, certain individuals such as bodybuilders or other athletes could have a BMI that would classify them as overweight or obese even though they carry low levels of excess body fat. Nonetheless, BMI is the index most commonly used to determine rates of obesity and is utilized in nearly every study on obesity in the United States.

Several different agencies, including government-sponsored agencies, have investigated the prevalence and incidence of obesity in the United States. The National Health and Nutrition Examination Survey (NHANES) is a program of studies assembled by the CDC. These studies are designed to measure the health and nutritional standing of adults and children in the United States. The surveys are unique in that they combine both interviews with physical examinations to derive their results. National data collected during 1999–2002 indicated that one adult in three had a BMI of 30 or higher. Comparing this figure to data collected in 1994 — when 23% of adults had a BMI greater than 30 — indicates a clear trend of rising obesity (Flegal, Carroll, Ogden, & Curtin, 2010). One of the most disturbing aspects of this trend is the rise of obesity in children and adolescents. The percentage of overweight children and adolescents between the ages of six and nineteen has tripled since 1980 (CDC, 2004b). This consistent increase in obesity among young people is of special concern because overweight children and adolescents are far more likely to become overweight adults. The risk of contracting serious health problems is significantly higher in overweight children and adults (CDC, 2004a).

Causes of Obesity and the Role of Environmental Factors

The causes of obesity have been investigated and include the following (NIH, 2004):

1. Genetic factors — research indicates that obesity tends to run in families.
2. Environmental factors — including lifestyle behaviors such as eating patterns and level of physical activity.
3. Psychological factors — such as the tendency for some people to eat in response to emotional states, including boredom, stress, or depression.
4. Certain physical factors — such as symptoms of medical conditions (e.g., hypothyroidism) or the effects of aging.

Notice that income level does not appear among the NIH's identified causes. The effects of rising obesity in this country are only beginning to manifest, and they will continue to worsen. The cost of obesity-related conditions in the United States is well over $100 billion (NIH, 2004). Dietary factors have been associated with at least four of the ten leading causes of death in the United States. In addition, people who are obese may experience significant emotional and psychological difficulties as well as discrimination and social prejudice.

For practical purposes, this paper focuses on environmental factors — such as socioeconomic status (SES), food access, and food choices — that have been linked to obesity. If we consider the causal factors listed above, we would have to conclude that environmental factors are the most important contributors to the dramatic rise in obesity prevalence over the last decade. Specifically, increased food consumption and the consumption of certain types of food over others are the two key factors that explain this rise (Block, Scribner, & DeSalvo, 2004; Bray, 2004).

Conclusion: Correlation Is Not Causation

The research clearly indicates that obesity has risen substantially in the United States and that certain risk factors increase the probability of an individual becoming obese. However, these risk factors center on family biological history and behaviors shaped by personal choice — not on SES. The complicated, multifactorial nature of the data reviewed here makes it untenable to single out income level as a meaningful cause of obesity. Authors who promote the notion that poverty drives obesity have failed to examine the evidence thoroughly, conflating a weak and variable statistical association with a causal mechanism. A more careful reading of the literature reveals that education, ethnicity, gender, and individual dietary behavior are all more nuanced and contextually variable explanatory factors than socioeconomic status alone.

References

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