The study suggests cafeteria-goers made healthier food choices when following the labels modelled after traffic light signal colours.
Nutrition labelling on food packages aim to address unhealthy eating patterns that are based on lack of knowledge, habit and a preference for convenience, say researchers who labelled foods as red, green or yellow, based on positive and negative criteria.
The labels modelled after a traffic light break down the choices this way:- Green: fruits, Vegetables and lean sources of protein.
- Yellow: Less nutritious foods.
- Red: Foods with little or no nutritive value, and high fat or caloric content.
In Tuesday's issue of the American Journal of Preventive Medicine, researchers in Boston say they found the proportion of sales of red items decreased from 24 per cent at the start of the study to 20 per cent after 24 months.
What's more, green sales increased from 41 per cent to 46 per cent after two years.
"These results suggest that simple food environment interventions can play a major role in public health policies to reduce obesity," Dr. Anne Thorndike of Massachusetts General Hospital and her co-authors said.
The team used sales data from cash registers at the main cafeteria at Massachusetts General to track purchases, excluding weekend and holiday sales.
Food labelling urged
During the 27 months of the study, transactions from 2,285 employees who used the cafeteria regularly were also analyzed along with sales for all cafeteria customers.
The changes remained similar for all categories of employees (such as service workers, technicians and professionals). Overall, cafeteria sales were stable.
"These findings are the most important of our research thus far because they show a food labelling and product placement intervention can promote healthy choices that persist over the long term, with no evidence of 'label fatigue,'" Thorndike said in a release.
"The next steps will be to develop even more effective ways to promote healthy choices through the food service environment and translate these strategies to other worksite, institutional or retail settings."
The researchers said the food industry has opposed nutrition and menu labelling strategies, arguing there is scientific uncertainty about the effectiveness of calorie labels for example.
Unlike previous observational studies where researchers surveyed people about their choices, the Boston team used objective sales data.
They weren't able to separate out the effects of the labelling and another phase of the project that involved rearranging displays of foods. For example, baskets of bottled water were placed throughout the cafeteria and prepackaged salads were put next to the pizza counter.
In the first six months of the experiment, the researchers said the largest changes in green and red choices occurred when the labels were introduced, but sequentially adding rearrangements further hit red sales and promoted green purchases.
The study was funded by the Robert Wood Johnson Foundation and the Donaghue Foundation.