As the demand for larger portion sizes has been answered, the average American waistline has expanded accordingly.  New research from Duke University calls on the food and beverage industry to adjust serving sizes for calorie-laden soft drinks in an effort to slim down America and improve the nation’s overall level of health.

According to Duke’s Joel Huber, Kathryn M. Sharpe, and Richard Staelin, consumers shun the smallest and largest sizes when choices are available.  To increase profits, the research team says fast-food restaurants eliminated small (12-ounce) soft drinks because the larger, 16-ounce, beverage was more popular.  Once the 16-ounce beverage was the smallest on the menu, sales of the next larger (21-ounce) soft drinks went up while sales of 16-ounce beverages dropped.

At the opposite end of the scale of size options, the sale of 21-ounce beverages was higher than the largest size offered, the 32-ounce beverage.  When a 44-ounce serving size was introduced, however, sales of the 32-ounce beverages rose.

The research team believes adding bigger sizes has shifted the curve of demand to ever-larger portion sizes when there are many consumers who’d actually prefer to purchase a 12-ounce soft drink.

The team suggests these size-shifting policies within the fast-food industry amount to an increase in soft drink consumption by as much as 15%.  It calls on the industry to voluntarily return 12-ounce servings and eliminate the largest drink sizes in an effort to curb consumption and thereby generate improved public health, an effort likely to cost the industry less than 2% of its profit margin.

In the absence of voluntary down-sizing, the research team proposes a flat 28-cent tax on all soft drinks as a means of reducing consumption by 10%.  A reduction in consumption based on such a tax would reduce the industry’s profit margin by more than 7%, according to the research.

The Duke University researchers have published their work in the latest issue of the Journal of Consumer Research.