Colour-coding foods sold in hospital cafeterias may help guide people to make more nutritious choices.

Researchers in Massachusetts experimented with colour-coding foods into red, yellow and green categories depending on how healthy they were. Colour-coded hospital cafeteria foods such as pre-made sandwiches were moved around to make healthy items more visible. (Courtesy of Massachusetts General Hospital)

Some U.S. cities will soon be required to label calories on menus as a public health policy. The Massachusetts team was concerned that some consumers might have trouble interpreting the calorie information.

Instead, they put green labels to signify the healthiest items in the cafeteria, such as fruits, vegetables and lean meat, yellow to indicate less healthy items, and red for those with little or no nutritional value.

Signs were also posted in the cafeteria to encourage people to eat green items more, yellow less often and to consider something else besides red items.

Cash registers were programmed to record which items were purchased in each category during the six-month study.

The changes seemed to work.

"Our results demonstrate that a simple colour-coded labeling intervention increased sales of healthy items and decreased sales of unhealthy items in a large hospital cafeteria," Dr. Anne Thorndike of Massachusetts General Hospital in Boston and her co-authors concluded in the March issue of the American Journal of Public Health.

The study also included a second phase. Food and beverages were re-arranged to move the healthy items to more convenient and visible areas. That led to even better choices in the nutritional quality of the foods purchased, the researchers found.

Simple changes

The re-arrangements focused on cold drinks, pre-made sandwiches and chips that were likely to be bought by consumers on the run.

Cafeteria beverage refrigerators were arranged to place water, diet beverages and low-fat dairy products at eye level, while beverages with a red or yellow label were placed below eye level.

The sandwich refrigerator was also arranged to put green items at eye level while red or yellow items were placed above and below. Racks of chips had yellow items at eye level and red items below, and extra baskets of bottled water were placed near stations where hot food was served.

During the first part of the experiment:

• Sales of all red items decreased 9.2 per cent.
• Green item sales increased 4.5 per cent.

During the second phase of re-arrangements, red item sales dropped another 4.9 per cent compared with phase 1.

While sales of green items decreased 0.8 per cent in phase 2, sales of green beverages increased another 4 per cent, the researchers found.

"We believe this intervention was so successful because it was simple and easy to understand quickly," Thorndike said.