Association between dietary patterns and obesity
To help address growing public health concerns about rising obesity rates, ERS research illuminates differences in dietary patterns by social, demographic, and economic factors. For example, a greater share of low-income men consumes excessive calories and has Body Mass Indices (BMIs) in the obese range than do high-income men. Among women, however, low incomes tend to be associated with high BMIs but lower caloric intakes. Determining the underlying causes of disparities between patterns of caloric intake and body fat measures across sociodemographic groups may lead to a better understanding of the causes of disparities in overweight and obesity (see "Food Stamps and Obesity: Ironic Twist or Complex Puzzle?" and "U.S. Per Capita Food Supply Trends: More Calories, Refined Carbohydrates, and Fats 16x16 - PDF ").
ERS has examined the association between fruit and vegetable consumption and obesity and found a negative relationship between fruit consumption and BMI. That is, people who eat more servings of fruit each day have lower BMIs. In fact, healthy-weight children and adults eat significantly more fruits than their overweight and obese counterparts (See table below). Vegetable consumption, however, showed no consistent correlation with BMI. Why is fruit consumption a more accurate predictor of body weight status than vegetable consumption? The answer may lie in the way many Americans incorporate these foods into their diets.
BMI definitions and classifications
|BMI* and Weight||Healthy weight||Overweight||Obese
|BMI (index points) ||18.5-25 ||25-30 ||over 30
|Corresponding weight (6'0") ||137-185 lbs. ||185-220 lbs. ||over 220 lbs.
|Corresponding weight (5'6") ||115-155 lbs. ||155-185 lbs. ||over 185 lbs.
|*Note: Body Mass Index (BMI) = Weight (kilograms) / Height² (meters)
Causes of obesity—an economist's view
The prevalence of obesity and overweight has increased dramatically in the United States since the mid-1970s. The prevalence of overweight has tripled among children and adolescents, and nearly two of three adult Americans are either overweight or obese. Although high costs-in health, social, and economic terms-are known to be associated with obesity, how the U.S. population reached this point is less well understood. In most cases, weight gain and obesity are the result of individual choices. Examining the causes of the increase in obesity and proposed interventions under an economist's lens may help identify potential solutions to the obesity crisis.
An overview of leading health economics research on the causes and consequences of rising obesity in the United States can shed light on the issue (see The Economics of Obesity: A Report on the Workshop Held at USDA's Economic Research Service"). This research shows how the technological changes driving modern economic growth have raised household incomes, reduced the price of food, and increased the price of physical activity. The resulting increase in energy consumption (food intake) and flattening of energy expenditure (physical activity) has tilted the weight equation in favor of a steady weight gain across all segments of U.S. society ( "The Price is Right: Economics and the Rise in Obesity").
Although the incidence of obesity has risen among all population groups, not everyone is equally at risk of becoming overweight or obese. Understanding weight differences is one way to find solutions to obesity and its associated health costs. ERS research found that weight differs among demographic subgroups, and differences in specific behaviors, health awareness, and eating patterns can be linked to weight outcomes. These results suggest that income, household composition, and formal education help explain variation in behaviors and attitudes that are significantly associated with weight outcomes ( The Role of Economics in Eating Choices and Weight Outcomes).
Differences between adults' actual weight status and their perceived weight status show which individuals are mistaken in their self-perceptions. Women tend to make more accurate self-assessments than men but they are also more likely to overestimate their weight status-healthy-weight women are much more likely to indicate they think they are overweight, while overweight men are more likely to underestimate their weight status and think they are healthy. Mistakes in self-assessments are associated with demographic factors, socioeconomic status, and knowledge and attitudes toward diet and health. Federal information programs targeting obesity and overweight will be more likely to influence diet and lifestyle choices if the programs issue distinct messages to different subgroups.
ERS has also examined how dietary choices and attitudes toward diet and health contribute to obesity and whether those factors differ by gender (contact Biing-Hwan Lin for reprint). Findings indicate that:
- Choices and attitudes do matter, and the choices males and females make often have quite different effects on BMI.
- A male's belief or lack of belief that weight status is genetic has no influence on BMI.
- Women who do not believe that their weight is predetermined have lower BMI values than those who believe weight is genetically determined.
Can policies reduce obesity rates?
Action to combat obesity and overweight considers the many variables that influence diet and lifestyle choices. The wide range of factors affecting food choices is compounded by the incredible variety of foods and consumption opportunities available today. Lifestyle choices about diet quality and exercise also affect food choices. Because consumers are faced with nearly unlimited choice, public policy targeting specific foods or lifestyle choices could have surprising unintended consequences.
ERS has examined some of the potential intended and unintended consequences of three widely discussed obesity policies—nutrition labels in restaurants, taxes on snack foods, and restrictions on food advertising to children—with a focus on the likely effect of each program on producer and consumer incentives and on health outcomes. An apparently straightforward policy proposal can have surprising effects that would dampen the policy's success in reducing overweight and obesity: mandatory nutrition information at fast food restaurants could lead to reformulations or price promotions that do not necessarily contribute to more healthful diets; taxes on snack foods could lead some consumers to substitute equally unhealthy foods for the taxed food; and restrictions on food advertising could ultimately lead to lower prices for food subject to the restrictions. ( Obesity Policy and the Law of Unintended Consequences).