Inexpensive food a key factor in rising obesity

Today, two in three Americans are overweight or obese, with rates climbing steadily over the past several decades. Many factors have been suggested as causes: snack food, automobiles, television, fast food, computer use, vending machines, suburban housing developments, and portion size. The authors say forming a coherent picture is a challenge, but is necessary to assess whether the many proposed solutions, from encouraging physical activity and decreasing access to high calorie foods, to building more exercise-friendly environments, increased labeling, or even levying taxes on some foods, can make a difference.

After examining available evidence, the authors say widespread availability of inexpensive food appears to have the strongest link to obesity. They write: "Americans are spending a smaller share of their income (or corresponding amount of effort) on food than any other society in history or anywhere else in the world, yet get more for it." In the 1930s, Americans spent one-quarter of their disposable income on food. By the 1950s, that figure had dropped to one-fifth. The most recent data show the share of disposable income spent on food is now under one-tenth.

The authors review the evidence for other factors, and say the rise of electronic entertainment, increased use of cars, a shift in jobs away from those with physical demands, and increased urbanization also contribute to obesity. But they say the evidence for those associations is less strong, saying: "Examining time trends for which there are data, what jumps out are changes in food availability, in particular the increase in caloric sweeteners and carbohydrates."

The authors also suggest that policy interventions that focus on "positive" approaches or messages, such as increasing fruit and vegetable consumption and increasing physical activity, may not be the optimal approach. They conclude a more promising tactic is an emphasis on reducing calorie consumption, particularly sugar sweetened beverages and salted snacks. They write, for example: "Although increasing fruit and vegetable consumption may be a laudable goal for other health reasons, it is unlikely to be an effective tool for obesity prevention.