Last week, the U.S. Food and Drug Administration (FDA) finally took a step toward banning trans fats.
The agency announced its preliminary finding that partially hydrogenated oils (PHOs) – the primary source of artificial trans fat in processed foods – are not “generally recognized as safe” for use in food.
As their press release said, the FDA's preliminary determination “is based on available scientific evidence and the findings of expert scientific panels”.

This move is long overdue. More than 30 years ago, Welsh researchers speculated that trans fat might be linked with heart disease (Thomas LH et al. 1981), and 1993 Harvard study strongly linked intake of PHOs to the risk of heart attack. 

In that Harvard study, the researchers estimated that replacing just two percent of calories from trans fat with regular unsaturated fat would reduce the risk of coronary heart disease by about one-third (Willett WC et al. 1993).
Health & Human Services Secretary Margaret Hamburg quantified the potential benefits of a ban on trans fats:
“The FDA's action today is an important step toward protecting more Americans from the potential dangers of trans fat. Further reduction in the amount of trans fat in the American diet could prevent an additional 20,000 heart attacks and 7,000 deaths from heart disease each year – a critical step in the protection of Americans' health.”
(The FDA's finding does not apply to the small amounts of harmless trans fats that occur naturally in meat and dairy foods, some of which – such as trans-10 conjugated linoleic acid – appear actively healthful.)
Trans fats are created during the process of making partially hydrogenated oils (PHOs), and almost all artificial trans fats in processed foods are omega-6 fats.

This is because the oils most commonly subjected to partial hydrogenation — soy, corn, safflower, sunflower, and cottonseed — are very high in omega-6 fats, and contain almost no omega-3 fatty acids, which are virtually eliminated by that process.

Why are trans fats bad for heart health?
Eating trans fats does several bad things for cardiovascular health:
  • Promotes inflammation linked to cardiovascular disease. 
  • Raises levels of LDL ("bad") cholesterol, especially small, dense LDL particles damaging to arteries. 
  • Lowers levels of HDL ("good") cholesterol.
  • Reduces the responsiveness of endothelial cells that line blood vessels.
  • Promotes obesity and resistance to insulin, the precursor to diabetes, n animals.
In a complaint filed with the Illinois Central District Court earlier this year, University of Illinois emeritus professor Dr. Fred Kummerow said that the “use of partially hydrogenated vegetable oils in the American food supply has contributed to a national epidemic of coronary heart disease”, and promotes to diabetes, cancer and Alzheimer's disease.
And as he wrote in a 2009 citizen's petition, “Trans fat calcifies both the arteries and veins and causes blood clots [and] leads to the reduction of prostacyclin that is needed to prevent blood clots in the coronary arteries.” (Pressey D 2009)
Dr. Kummerow also pointed out that a nursing mother who eats trans fats would pass along substantial amounts to her infant (Pressey D 2009): 
“To date, the FDA has not considered the daily intake of trans fat relevant to the health of small children since they do not exhibit overt heart disease. In cases where children have died of unknown causes and had been autopsied, 99 percent of them showed the beginning stages of hardening (calcifications) of the arteries, which ultimately can lead to heart disease.”
As it turns out, even non-hydrogenated vegetable oils are bad for your heart when consumed in the excess typical of the standard American diet … see “Most artificial trans fats are omega-6 fats”, below.
The U.S. Centers for Disease Control and Prevention says that the death rate from coronary heart disease in the U.S. more than doubled during the 50-year period when margarine and shortening had a high percentage of trans fat (39 to 50 percent) … and that a widespread reformulation of PHOs around 2004 raised their trans fat levels from 20 percent to nearly 40 percent.
The independent Institute of Medicine (IOM) concluded that artificial trans fat provides no known health benefit, that there's no safe intake level, and the semi-official body recommends keeping consumption as low as possible.
Since trans fat content began appearing in the Nutrition Facts label of foods in 2006, trans fat intake has declined from 4.6 grams per day in 2003 to about 1 gram per day in 2012.
Many food manufacturers have found that their products can be made without PHOs high in artificial trans fats, though this change will shorten processed food products' absurdly long shelf lives.
If and when the FDA action happens, PHOs would be considered food additives and could not be used … unless the agency granted an exception in response to a manufacturer's petition and proof of safety.
Most artificial trans fats are omega-6 fats
Partially hydrogenated oils (PHOs) were invented early in the 20th century, but were not widely used until the 1970's.
Why did that change happen? During the 1960's, deeply flawed epidemiological research inaccurately damned saturated fats as a cause of heart disease. (See “Heart-Diet Myths Get a Busting”)
That bad science led manufacturers to replace butter and lard with vegetable oils high in polyunsaturated omega-6 fats: mostly soy, corn, safflower, sunflower, and cottonseed oils.
And food makers usually subjected those oils to partial hydrogenation, to render their (mostly omega-6) fatty acids resistant to oxidation and resulting rancidity, thereby extending their products' shelf lives by months.

The process also turns liquid oils into a solid substance that's much less expensive than solid animal fats, and allows for easier transportation and storage of processed foods and wider uses for cheap vegetable oils.
But America's relatively recent turn to oils high in omega-6 fats — and the packaged and takeout foods made with them — was way too much of a good thing, no matter whether they were PHOs or not.
A fast-growing body of evidence reveals real harm from Americans' relatively recent shift (since the late 1960's) to radically higher intake of omega-6 fatty acids.
For example, a rigorous evidence review published three years ago refuted the American Heart Association's 2009 finding that Americans' extremely high intake of omega-6 fats is heart-healthy poses no heart risks (see “Heart Group's Omega-6 Advice Takes a Huge Hit” and “America's Sickening Omega Imbalance”.
Americans' omega-3/6 intake ratio shifted dramatically over the past 150 years, and is now about 25 parts omega-6s to one part omega-3s, versus the estimated four-to-one average ratio of pre-industrial diets, to which humans adapted over many millennia.
This extremely high intake of omega-6s creates a need for more omega-3s, and a drastic drop in omega-6 intake would limit the average American's need for supplemental omega-3s from fish oil.  
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