After transforming part of a fast food restaurant in Illinois with milder music and lighting, researchers found that customers ate 18 per cent fewer calories than other people in the unmodified part of the restaurant.
"When we softened the lights and softened the music in the restaurant it didn't change what people ordered, but what it did do was lead them to eat less and made them more satisfied and happier," said Brian Wansink, a professor of marketing and consumer behaviour at Cornell University in New York.
In the study published in the journal Psychological Reports, Wansink and his co-author Koert Van Ittersum, of the Georgia Institute of Technology, said the bright lights, stimulating colors, sound-reflecting surfaces and loud music in fast food restaurants are not designed to be relaxing.
So they improved the mood in a section of a Hardee's restaurant for the study, adding plants, paintings, indirect lights, tablecloths, candles and instrumental music.
After seating customers in both the original and restyled sections of the restaurant, they timed how long their meal lasted and how many calories they consumed. Customers in the modified section ate longer than those in the main dining area, consumed fewer calories and rated the food as more enjoyable.
"Spending that extra time eating a little more slowly at a more relaxed pace made a world of difference, not just to how much they ate but how much they liked it," said Wansink, a former executive director of the US Department of Agriculture Center for Nutrition Policy and Promotion and the author of the book "Mindless Eating: Why We Eat More than We Think."
"These results suggest that a more relaxed environment increases satisfaction and decreases consumption," he added.
About one in three adults and one in six children and teens in the United States is obese, according to government figures. Wansink, who is sending the findings to restaurant chains, said some simple changes could help people eat better and enjoy food more.
"If softer music and softer lighting seem to get people to eat less in a fast food situation, why not try the same thing at home?" said Wansink.