Banishing trans fats from foods is linked to reductions in the number of heart attacks and cardiovascular deaths in the years after the bans are implemented, according to data from cities and counties in New York that have made the cut.

After three years, the areas banning trans fats from eateries seemed to have an extra 6.2 percent reduction in heart attacks and strokes compared with those that didn’t, researchers report in JAMA Cardiology. Last year, other researchers reported in the Journal of Health Economics that the New York bans appeared to cut deaths from cardiovascular disease by 4.5 percent—that is, they spared about 13 lives from cardiovascular deaths per 100,000 people each year.

While the decade of bans that have gone into effect in the state offer “natural experiments” on how cutting out trans fat may affect health, the results back up a slew of older studies—animal, controlled trial, and observational studies—that found harms of trans fats, plus benefits of ousting them from people’s diets.

Further Reading FDA follows through on its plan to ban trans fats

In June of 2015, the Food and Drug Administration ruled that trans fats were no longer considered generally safe. Food manufacturers have until June 18, 2018 to ditch partially hydrogenated oils , the source of most industrial trans fats.

Trans fats—or trans fatty acids—are a type of unsaturated fat found rarely in nature (sometimes there’s a little in animal products, for instance). But they’re found readily in processed foods. Manufacturers figured out a while back that they’re a good way to make liquid fats into solid fats at room temperature—think transforming vegetable oils into a block of margarine.

The way this works is all about manipulating the tails of carbons that hang off all fats. Saturated fatty acids, found in meats, cheeses, and butter, have carbon tails that are straight. That is, their chains lack double bonds between the carbons, freeing the carbons to instead bond to their max amount of hydrogens; they’re saturated with hydrogens. This helps them have useful properties for foods, like being a solid instead of a liquid at room temperature. Unsaturated fatty acids, on the other hand, have kinky carbon tails with double bonds and fewer hydrogens.

By blasting unsaturated fatty acids in vegetable oil with hydrogen, manufacturers can make them into solid fats. But, as a side effect, they also create a weird form of unsaturated fatty acids. These still have double bonds between their carbons, but those bonds are oriented in such a way that allows the tails to be straight-ish.

These straight-ish unsaturated fatty acids in the partially hydrogenated oils are the trans fatty acids. They can be found in all sorts of junk food, fast foods, prepacked baked goods, ready-made frostings, margarine, premade doughs that often come in tubes, coffee creamers, and fried foods in restaurants.

A straight diet

Yet, they are bad for human health. Studies have found that artificial trans fats reduce high-density lipoprotein cholesterol levels in the blood, which have been linked to positive health effects, while increasing low-density lipoprotein cholesterol levels that are linked to bad health effects. Artificial trans fats are also linked to systemic inflammation markers and to causing dysfunction in cells lining our organs. Eating them is linked to higher risks of stroke, heart disease, and sudden cardiac death. (The same isn’t true for eating the tiny amounts of natural trans fats found in some animal products.)

In 2007, New York City went ahead and restricted artificial trans fats in food served in eateries, that is restaurants, bakeries, catering, mobile vending machines, street-fair food booths, etc. (But not prepackaged foods). Several counties in the state followed suit in the following years. Together, they offer a glimpse at the potential health effects that will follow the nation-wide restrictions in 2018.

In the latest study, which followed the data suggesting that the bans cut cardiovascular deaths, researchers wanted to look at non-fatal heart attacks and strokes. Scanning health records and other demographic data, the researchers compared rates of heart attack and stroke among 11 areas with restrictions to those of 25 areas without restrictions.

While rates of stroke and heart attacks were on the decline throughout the state, those with trans fat restrictions saw slightly steeper declines. When the researchers clumped the heart attack and stroke rates together, they found that the areas with restrictions for three years or more had an extra 6.2 percent reduction that was statistically significant. That’s about 43 fewer events per 100,000 people. Individually, there was a 7.8 percent reduction in heart attacks, and a non-statistically significant 3.6 percent reduction in strokes.

In coming up with those numbers, the researchers did their best to control for variables, such as age, race, gender, income, age-adjusted mortality, and how urban each area was. They even estimated each area’s commuters to make sure that people living in one county and eating in another wouldn’t throw off the calculations. Last, they ran their calculations with and without New York City, which had other big health campaigns going on that could have skewed the results. The city didn’t affect the overall results, though, the researchers found.

Of course, the researchers couldn’t control for everything. Trans fats were still in packaged foods. The researchers don’t know what people were eating exactly or even how faithful restaurants were about following the restrictions. However, other studies found that New Yorkers did get less trans fats after the restrictions and that restaurants did generally follow the restrictions. And, the authors note, some fast foods had enough trans fat in a single serving that cutting just that serving could drive health effects. Eating just 2 grams a day is associated with risks.

Yet, “for example, a large order of Popeye’s Louisiana Kitchen cajun fries contains 3.5 g of TFAs [trans fatty acids] per serving, Taco Bell’s Cinnabon Delights (12-pack) contain 2.0 g of TFAs per serving, and multiple varieties of Pillsbury Shape sugar cookies contain 2.5 g of TFAs per serving,” the authors write. (The amount of trans fats in a packaged food can be found on the nutrition label.)

Overall, the data falls in line with mounting evidence that the upcoming nationwide restrictions are a good thing.

JAMA Cardiology, 2017. DOI: 10.1001/jamacardio.2017.0491 (About DOIs).