Researchers Adam Drewnowski, director of the Center for Public Health Nutrition, and Pablo Monsivais, a research fellow in the center, argued that their study provides evidence that obesity is ever more an economic problem, not a personal one.
"The gap between what we say people should eat and what they can afford is becoming unacceptably wide," said Drewnowski. "If grains, sugars and fats are the only affordable foods left, how are we to handle the obesity epidemic?"
The study, published this month in the Journal of the American Dietetic Association, compared the prices of more than 370 food items at three supermarket chains in the Seattle area in 2004 and 2006.
Foods were stratified by quintiles of energy density and the differences in energy cost and in percent price change were tested using analyses of variance.
In 2004, the researchers found the foods that are less energy-dense, such as fresh fruits and vegetables, were much more expensive than energy-dense foods, such as those high in refined grains, added sugars, and added fats.
Furthermore, the disparity in food prices worsened with time. In 2006, energy cost of foods in the bottom quintile of energy density, beverages excluded, was $18.16 per 1,000kcal as compared to only $1.76 per 1,000kcal for foods in the top quintile.
The cost of low-calorie foods jumped by about 19.5 per cent over the two years, while the prices of foods rich in calories stayed stable or even dropped slightly, with a general decrease of 1.8 per cent.
The general rate of food price inflation in the United States was about 5 per cent during that period, according to the US Department of Labor.
The study looked at price inflation in foods grouped by energy density, or calories per gram of food. The researchers said that because many energy-dense foods tend to be low in nutrients, people who eat energy-dense foods may consume more calories than they need.
"We are an overfed but undernourished nation," said Drewnowski.
According to the report, the energy density of the American diet has allegedly risen , suggesting that consumers are seeking out lower-cost foods. It claims the finding that energy-dense foods are not only the least expensive, but also most resistant to inflation, may help explain why the highest rates of obesity continue to be observed among groups of limited economic means.
According to the Center for Disease Control and Prevention, in 2006 only four states had a prevalence of obesity less than 20 per cent. Washington had a prevalence of obesity between 20 and 24 per cent.
According to figures published by the World Health Organisation, in the year 2015 some 2.3 bn adults will be overweight and more than 700 million will suffer from obesity, a pathology that is increasingly being seen in children.
Monsivais concluded: "We need to focus on bigger-scale changes, like the farm bill or other policy measures that can address the disparity in food costs."
Research conducted by the University of Washington Center for Obesity Research had previously shown that per calorie food costs in the US and Europe were much higher for fresh produce and other recommended foods than for fats and sweets. The recent study went deeper to consider food quality as well.
The project was supported by the US Department of Agriculture and the National Institute of Dental and Craniofacial Research in the National Institutes of Health.
Source: Journal of the American Dietetic Association
December 2007, Volume 107 Number 12
"The Rising Cost of Low-Energy-Density Foods"
Authors: P. Monsivais and A. Drewnowski