The ban that New York City authorities introduced in 2006 to restrict use of trans fats in fast-food restaurants has led to residents eating healthier fast food meals that are substantially and significantly lower in trans fats. Also, those meals have not increased their saturated fat content to compensate.

These are the findings of a new study published online in the Annals of Internal Medicine on Tuesday. According to the authors, all employed by the New York City Department of Health and Mental Hygiene at the time of the analysis, this is the first hard evidence that trans-fat regulations in local communities can make a difference in their dietary intake.

Although existing at low levels naturally in animal-derived foods such as meat and dairy, trans-fats in the diet come mainly from oils that have undergone hydrogenation to make them hard, easier to use in cooking and frying, and to increase shelf life of processed foods.

New York City authorities introduced a restriction on the use of trans-fats in chain restaurants because of evidence that their consumption can increase risk of coronary heart disease. Just 40 calories of trans-fat a day can raise the risk of heart disease by up to 23%, which is particularly significant in the US, where more than one-third of daily calorie intake comes from food bought outside the home.

For the study, the researchers surveyed customers at 168 randomly selected outlets of 11 fast food chains in New York City and asked them questions about what they had bought at lunchtime.

In the meantime they also compared the trans-fat and saturated fat content of nearly 7,000 fast food meals bought before the 2006 ban to meals bought after the ban.

The results showed the fast food meals that the surveyed customers bought were different before and after the ban in terms of their fat content. The average lunchtime purchase dropped by an average of 2.4 grams of trans-fat per customer.

The biggest drop in trans-fat content was in purchases bought at hamburger chains, followed by Mexican food and fried chicken chains.

There was also an increase in the number of meals that contained no trans-fats at all. Had the customers bought their meals before the ban, 32% of them would have had no trans-fats: after the ban this went up to 59%.

When they analyzed the locations of the outlets, the researchers found “the poverty rate of the neighborhood in which the restaurant was located was not associated with changes“.

In an accompanying editorial, Alice Lichtenstein, a nutrition specialist at Tufts University, writes:

“The regulation may serve as a model for future successful public health initiatives.”

The study was funded by the City of New York and the Robert Wood Johnson Foundation Healthy Eating Research program.

Written by Catharine Paddock PhD