SA Forum is an invited essay from experts on topical issues in science and technology.
Last month the U.S. Food and Drug Administration made the welcome, belated determination that partially hydrogenated oils—the primary source of trans fats—could no longer be considered “generally regarded as safe” (GRAS). Although the ruling is preliminary, it is expected to become permanent. If it does, it will virtually eliminate industrially produced trans fat in the U.S, saving thousands of lives each year with minimal cost to industry.
Artificial trans fats, or trans unsaturated fatty acids, have been around for a little more than a century. In 1901 the German chemist Wilhelm Normann discovered the process of partial hydrogenation, which converts inexpensive liquid vegetable oils into shortenings and margarines and creates trans fats as a by-product. Because these cheaper, longer-lasting products mimicked the traditional cooking fats of European and North American cuisines, many countries quickly incorporated them into their food supplies. World War II–era food shortages and economic stresses greatly expanded the presence of trans fats in the U.S. diet. But because fat was primarily considered a metabolic fuel, no one paid much attention to its potential health effects. In fact, in 1912 the inventors of partial hydrogenation received the Nobel Prize.
It took decades for scientists to realize how deadly trans fats could be. When coronary heart disease (CHD) first emerged as a national epidemic in the U.S., physicians quickly came to suspect that saturated fat and dietary cholesterol, delivered mainly in butter and lard, were important causes. But they did not make a connection to trans fats. On the contrary, because margarines and vegetable shortenings were low in saturated fat and free of cholesterol, they were widely promoted as healthy alternatives to butter and lard beginning in the 1960s.
Then in the mid 1970s a few scientists began suggesting that trans fats should be given a closer look. Fred Kummerow of the University of Illinois at Urbana–Champaign reported that trans fats had adverse effects on arteries in his studies of pigs. Mary Enig of the University of Maryland, College Park, described the correlation over time between increases in trans fat intake and higher rates of coronary heart disease. I was particularly concerned about the process of partial hydrogenation itself: the vegetable oils being processed are primarily composed of linoleic acid and alpha-linolenic acid, precursors of molecules with many critical biological functions in the human body. But the process of partial hydrogenation changes the shape of those molecules, which almost certainly alters their function in unpredictable ways.
Despite the mounting questions, the food industry and the cardiovascular prevention community both dismissed these concerns.
In 1980 my colleagues and I set out to examine in greater detail the relation between intake of trans fat and risk of CHD. We included trans fat in a comprehensive assessment of diet in the Nurses’ Health Study cohort of over 100,000 women and developed a regularly updated database of the trans fat content of foods. After eight years of follow-up, and after accounting for known risk factors for heart disease, we found that women with the highest intake of trans fat had a 50 percent greater risk of hospitalization or death due to coronary heart disease. Margarine, the primary source of trans fat in 1980, was also associated with greater risk.
We were not the only ones subjecting trans fat to greater scrutiny. Around the same time, the Dutch researcher Martijn Katan and colleagues were investigating the metabolic effects of trans fats among healthy volunteers, doing carefully controlled feeding studies lasting several weeks. They found that trans fat and saturated fat increased “bad” LDL cholesterol to a similar degree—but unlike any other type of fat, trans fat also reduced “good” HDL cholesterol. Other researchers confirmed these findings and documented additional adverse metabolic effects, including increases in blood concentrations of triglycerides and inflammatory factors. Calculations suggested that eliminating industrially produced trans fats would prevent approximately 20 percent of avoidable CHD deaths in the U.S.
By 2003, the FDA found the evidence compelling enough to require that trans fat be included on food labels. Most manufacturers responded by eliminating trans fat entirely. Soon thereafter New York City banned the use of trans fats in restaurants, and other cities nationwide followed. By 2012, approximately 75 percent of the trans fat had been removed from the U.S. food supply. Blood cholesterol levels responded nationally, just as expected.
The U.S. Centers for Disease Control has estimated that the 25 percent of trans fats still coursing through the American food supply account for approximately 7,000 premature deaths per year. The FDA’s most recent action would prevent those deaths. The food industry is likely to take the new ruling in stride. It has already phased out the large majority of trans fat, and in Denmark trans fats have already been banned for a decade, proving that full elimination is feasible.
The FDA’s action is cause for a bit of celebration. It means that the efforts of many scientists from many disciplines will soon lead to the elimination of a major cause of premature death. Because of the FDA’s global leadership role, the ruling is even likely to stimulate similar changes worldwide. But we should not get too carried away with the celebration. It is sobering that it has taken more than a century for this moment to arrive. The case of trans fats should provoke us to consider how future risks might be prevented, detected or eliminated more quickly.