For years, only true diet detectives knew whether a particular food contained trans fat. This phantom fat—the worst type of fat for the heart, blood vessels, and rest of the body—was found in thousands of foods; but only those familiar with the “code words” partially hydrogenated oil and vegetable shortening knew when it was present. Fortunately, after a large body of research in the 1990s sounded the alarm on its deleterious health effects, a series of policy initiatives led to the near elimination of artificial trans fat in the U.S. food supply by 2018. However, the road to eliminating trans fat was not so straightforward, and outside the U.S. there’s still more work to be done. In many developing nations, trans fat intake remains high.
Where Do Trans Fats Come From?
In the late 19th century, chemists discovered that they could add hydrogen atoms to unsaturated fats by bubbling hydrogen gas through vegetable oil in the presence of a nickel catalyst.  This was far more than a chemical curiosity. Partially hydrogenated oils don’t turn rancid as easily as non-hydrogenated fats. They can withstand repeated heating without breaking down, and the process can turn a liquid oil into a solid, which allowed for easier transportation and wider uses. This solid fat was also much less expensive than many solid animal fats. These characteristics were attractive to food makers, and partially hydrogenated oils became a mainstay in margarines, vegetable shortenings, doughnuts, commercial baked goods like packaged pastries and cookies, other snack foods, and in fast-food restaurant deep fryers.
At the time, switching from butter or lard (both of which contain high amounts of saturated fat) to a product made from healthy vegetable oil seemed to make sense—and intake of trans fat increased dramatically. Before the advent of partial hydrogenation, the only trans fat that humans consumed came from eating cows (or dairy products), lamb, and deer. In ruminant animals like these, bacteria living in the stomach naturally make small amounts of trans fat. But due to the growth of partial hydrogenation, by the early 1990s, trans fat intake in the United States averaged 2% to 3% of total calories—with many Americans consuming up to three times this amount.
Harvard Chan’s This Week in Health Podcast takes a closer look at the history of trans fat, and the decades-long effort to remove it from the U.S. food supply. You’ll hear from two experts who were on the front lines of the battle against trans fats: Walter Willett, professor of epidemiology and nutrition at the Harvard Chan School, and Michael Jacobson, senior scientist and former executive director of the Center for Science in the Public Interest (CSPI).
Research Sounds the Alarm
Today, thanks to a series of research studies, we know that trans fats should be avoided. Eating trans fats increases levels of low-density lipoprotein (LDL, or “bad” cholesterol), especially the small, dense LDL particles that may be more damaging to arteries. It lowers levels of high-density lipoprotein (HDL, or “good” cholesterol) particles, which scour blood vessels for bad cholesterol and truck it to the liver for disposal. It also promotes inflammation,  an overactivity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions. Additionally, consuming trans fat reduces the normal healthy responsiveness of endothelial cells, the cells that line all of our blood vessels. In animal studies, eating trans fat also promotes obesity and resistance to insulin—the precursor to diabetes. So when did the research on this harmful fat begin?
In 1981, a group of Welsh researchers speculated that trans fats from partially hydrogenated oils might be linked with heart disease.  In 1990, a controlled feeding study by two Dutch researchers showed that trans fat consumption increased LDL cholesterol and reduced HDL cholesterol.  A 1993 Harvard study strongly supported the hypothesis that intake of partially hydrogenated vegetable oils contributed to the risk of having a heart attack.  In this study, researchers found that replacing just 2% of energy from trans fat with healthy unsaturated fat would decrease the risk of coronary heart disease by about one-third. An influential symposium on trans fat later in the 1990s drew public attention to the issue.
Science and Advocacy Lead to Change in the U.S.
In 2003, following a long campaign led by Dr. Fred Kummerow, along with the Center for Science in the Public Interest and researchers from the Harvard School of Public Health’s Department of Nutrition, the U.S. Food and Drug Administration (FDA) ruled that trans fats must be declared on the Nutrition Facts label by 2006. 
Despite intense lobbying efforts against the label addition by some parts of the food industry, this ruling sparked a major makeover of the American food supply. The FDA once estimated that approximately 95% of prepared cookies, 100% of crackers, and 80% of frozen breakfast products contained trans fat. When food companies realized that consumers—armed with this new information—would avoid products containing trans fat, many found ways to make their products without partially hydrogenated oils. For example, major manufacturers started using trans-free oils for making tortilla chips and other crunchy snacks; frozen food makers introduced frozen fried chicken products without trans fat; and many major restaurant chains reformulated their products to reduce trans fats.
Impacts of the 2006 ruling:
- By 2010, a survey of 83 major-brand grocery store products and restaurant dishes offered encouraging news: when most of these food makers reformulated their products, they cut back on trans fat without increasing saturated fat. 
- A study from the Centers for Disease Control and Prevention found that Americans’ blood-levels of trans fats dropped 58 percent from 2000 to 2009—evidence that the labeling law has had its desired effect. 
The addition of trans fat on the Nutrition Facts label was certainly a victory for public health—but there was more work to be done. Despite the ruling, manufacturers could still claim “0 grams of trans fat” on the label if the product contained less than 0.5 grams of trans fats per serving. While seemingly minimal, even small amounts of trans fat could add up over the course of a day. In these cases, the only way consumers could avoid trans fats from packaged products was by identifying partially hydrogenated oils in the ingredients list.
Furthermore, since the ruling did not cover foods without labels—such as those sold in bakeries, cafeterias, schools, and restaurants—consumers couldn’t easily choose to avoid potentially trans fat-laden foods in these settings.
Still, word on the harm of trans fat was out, and states, counties, and cities spurred additional change with educational efforts and local bans on trans fats. In 2006, New York City became the largest city in the nation to require its restaurants, cafeterias, and schools to go trans fat-free, and other cities and towns such as Boston followed its lead. California was the first state to pass legislation phasing out trans fats from restaurants and baked goods by 2010 and 2011, respectively.
NYC leads by example:
“This will save many hundreds, and probably thousands, of premature deaths each year in New York and will also likely reduce the development of type 2 diabetes and dementia,” said Dr. Walter Willett, then chair of Harvard School of Public Health’s Department of Nutrition, in response to the ban.
Leading up to the decision, Willett and Dr. Dariush Mozaffarian detailed the many negative health effects associated with trans fat intake in testimony to the New York City Board of Health.
In 2015—over 10 years since the initial ruling and decades after research showed the harms of trans fat intake—the FDA ruled that partially hydrogenated oils are no longer “generally recognized as safe” for use in human food. Although earlier educational efforts and local bans had vastly reduced partially hydrogenated oils, this decision was the final nail in the coffin for industrial trans fat in America’s food supply. Given three years to comply, food manufacturers are banned from using partially hydrogenated oils as of June 18, 2018. (Industry will be allowed some minor manufacturing and petitioned uses, though even these are set to be phased out by 2021. However, the FDA denied a last-minute petition by the Grocery Manufacturers Association for certain continued uses.)
The story of trans fat in the U.S., while lengthy, serves as an excellent example where scientific evidence was translated into policy actions to improve public health. As early as 2006, researchers estimated that eliminating trans fats from America’s food supply could prevent up to 1 in 5 heart attacks and related deaths; which would mean a quarter of a million fewer heart attacks and related deaths each year in the U.S. alone!  Encouragingly, research has already found that earlier bans on the use of trans fats in New York State public eateries are associated with a drop in heart attacks and strokes. 
Work to be Done Worldwide
Outside of the U.S., a number of countries, such as Denmark, Switzerland, Canada, and Britain, have already restricted or banned trans fats. However, trans fat remains prevalent in many developing nations where inexpensive partially hydrogenated oils have become staples not only for the food industry, but also for home use. This shift away from traditional cooking oils toward partially hydrogenated oils is contributing to the growing global epidemic of cardiovascular disease. For example, trans fats in India are often found in “vanaspati,” a partially hydrogenated oil often used as a low-cost alternative in food preparation. 
Encouragingly, the World Health Organization (WHO) has also put trans fat in the spotlight on a global stage. Estimating that industrial trans fat intake leads to more than 500 thousand deaths from cardiovascular disease annually, the WHO campaign is calling on governments to eliminate, or “REPLACE,” trans fats by 2023 through six strategic actions:
- REview dietary sources of industrially-produced trans fats and the landscape for required policy change.
- Promote the replacement of industrially-produced trans fats with healthier fats and oils.
- Legislate or enact regulatory actions to eliminate industrially-produced trans fats.
- Assess and monitor trans fats content in the food supply and changes in trans fat consumption in the population.
- Create awareness of the negative health impact of trans fats among policy makers, producers, suppliers, and the public.
- Enforce compliance of policies and regulations.
Because the WHO has no enforcement capacity, it will be up to national and local governments to carry out these actions in to eliminate industrial trans fats.
Tips for Lowering Trans Fat Intake
If you live or spend time in a country where there is weak regulation or no ban on industrial trans fat, here are a few tips that may help you lower your intake:
- Choose liquid vegetable oils.
- Avoid eating commercially prepared baked foods (cookies, pies, donuts, etc.), snack foods, and processed foods, including fast foods. To be on the safe side, assume that all such products contain trans fats unless they are labeled otherwise.
- When foods containing partially hydrogenated oils can’t be avoided, choose products that list the partially hydrogenated oils near the end of the ingredient list.
- To avoid trans fats in restaurants, one strategy is to avoid deep-fried foods (since restaurants may use partially hydrogenated oils in their fryers) and desserts. You may be able to help change these cooking practices by asking your server, the chef, or manager if the establishment uses only trans fat-free oils and foods.
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