Chemically-Altered Fats

Interesterified 'margarine'

Interesterified ‘margarine’

By Cat, January 2007 (Photo, right, from I Can’t Believe It’s Not (9))

This article discusses three types of chemically-altered fats (synthetic fats):

  1. Partially-hydrogenated fats (Trans fats), such as margarine and vegetable shortening, which have been making negative headlines of late, and for good reason;
  2. Fully hydrogenated, trans-fat-free fats, such as the “new” Crisco and margarines like I Can’t Believe It’s Not Butter (pictured above), which could be even worse than trans fats, especially for glucose and fat metabolism.
  3. Interesterified (IE) fats, such as some trans-free fats that chemically combine a saturated fat such as palm oil (or fully hydrogenated vegetable oil) and a liquid vegetable oil such as soybean or safflower oil to achieve the desired consistency.  These might be even worse than trans fats. These fats claim to be “a blend of oils” (9), but its not that simple.

When Is a Fat Not a Fat?

The answer: when it is made of any of the following:

  • Mono- or di-glycerides. The FDA defines a fat as a triglyceride, because this is the form of stored fat in all animals and plants. Yet mono-and di-glycerides have one or two fatty acids bound to the glycerol backbone, so they behave similar to try-glycerides and chemically are a “fat.” The issue is that may include trans fatty acids, but because mono/di-glycerides are not included in the definition of a fat, they hence avoid being labeled at trans fat.
  • Interesterified fats (IE fats), which are unnatural triglycerides that have been chemically altered. While these are included in the FDA’s definition of ‘fat,’ they are un-natural and can cause serious health issues.

Why should you care?  Because it affects food labeling, and allows food manufacturers to mislead the consumer. They can use trans fatty acids in the food and yet declare their food as trans-fat-free (4); they can lead the consumer to believe the product is all-natural, when in fact you would never find the fat in a natural plant or animal.

Interesterified (IE) fats are also a way of misleading the consumer. They lead the buyer to believe that a saturated fat like palm or coconut oil and an unsaturated fat like soybean or canola oil are simply ‘mixed’ together to be solid at room temperature. For example, “Smart Balance;” according to their ingredients label, they use “canola oil, palm fruit, fish and olive oils” (10). Note that ‘palm fruit’ is the source of palm oil, which is solid at room temperature; canola, fish and olive oils are liquid at room temperature.

But they are not simply mixed; rather, the fatty acids of each fat are removed from the triglyceride before mixing, then induced to re-form triglycerides. The problem with this is that while unsaturated fatty acids in a natural triglyceride will never be in the middle position because of the kink in the fatty acid, the chemical process called ‘interesterification’ allows unsaturated fatty acids to be in the middle position, creating an unnatural fat. This in turn causes problems for the body’s enzymes and signaling mechanisms that can lead to serious health issues (11).

A short history of chemically-altered fats

A review of history (12, 13):

  • In the 1890s and early 1900s, several scientists developed the method to hydrogenate oils to make then solid at room temperature. They believed they were saturating the fatty acids in the oils, but this would later be refuted.
  • 1911: The first hydrogenated vegetable shortening, “Crisco’ was marketed in the US. This product was first made from liquid cottonseed oil, but later from soybean oil.
  • Late 1940s, research began on the relationship between these hydrogenated fats and cancer. This research led to the discovery that the hydrogenation process did not fully saturate the fatty acids, but rather merely changed the arrangement of atoms in the fatty acid molecule from ‘cis‘ to ‘trans.’ The name of the process was changed from ‘hydrogenation’ to ‘partial hydrogenation; the resulting product became known as ‘trans fats’ in the scientific literature, but was not yet known to the general public.
  • At about the same time, scientists discovered a way to fully hydrogenate vegetable oils (and avoid the creation of trans fats), but the resulting product was too hard and stiff for most culinary uses.
  • In 1956, research suggested in the scientific literature that the use of trans-fats could be a cause in the large increase of coronary artery disease and heart disease, but this was not shared with the public at large.
  • By the 1980s, animal fats (saturated fats) were the largest concern of dietitians, who generally recommended that people switch from butter and lard to margarine and vegetable shortening, despite the fact that margarine and shortening were known in scientific circles to be the actual cause of the health issues blamed on animal fats.
  • By the 1990s, this began to change when renewed interest in the study of trans fats revealed the real truth to the public. “In 1994, it was estimated that trans fats caused 20,000 deaths annually in the US from heart disease” (12).
  • In 1995 mandatory labeling of trans fats in foods became law and took effect on January 1, 2006, mainly through the efforts of Mary G. Enig,, Ph.D. and the Weston Price Foundation (13).
  • Meanwhile, in the 1970s, research had begun on an alternative way to solidify vegetable oils as a replacement for margarine and its trans fats. This is done by randomly incorporating a saturated fatty acid known as stearic acid (produced by the hydrogenation process) into the triglycerides of natural soybean oil. The resulting product has a similar consistency to margarine (7).
  • This new process is known as interesterification (IE). Crisco was one of the first products to switch to this new method. However, the resulting product is an unnatural fat (not present in nature).
  • In 2007, several studies found a correlation between consumption of interesterified (IE) fats and increased risk of cardiovascular disease, but this risk was not attributable to increased levels of LDL cholesterol (‘bad’ cholesterol) as originally believed.
  • Continued research revealed that stearic acid (used in the IE process) is immediately converted into oleic acid (a type of mono-unsaturated fatty acid) in our body. This explained why stearic acid does not raise LDL cholesterol (6).
  • Another 2007 study isolated the molecular problem responsible for this problem. (7, 12). More on this below.

Several aspects of this history of trans and interesterified fats disturb me:

  • Hydrogenated oils,’ in theory, are fully saturated, but no chemical reaction is 100% complete; there could still be some unsaturated trans fatty acids present.  This doesn’t worry the manufacturers, however, because the amount of trans fats is below the 5% threshold to mandate labeling as trans fat.
  • How are we to know that there is not some other, yet unknown harmful difference, between these chemically altered fats and the naturally occurring saturated version? This concern was eventually demonstrated by the 2007 study published in Nutrition and Metabolism (this is discussed below under ‘Toxic fats study.’
  • Stearic acid is a common saturated fat in foods, especially meats, providing 2-4% of daily energy.  It is an 18-carbon saturated chain, and indeed would result from a complete saturation of 18-carbon linoleic and linolenic acids, the two essential omega-3 fats present in vegetable oils. Stearic acid has indeed been observed to have a neutral effect on cholesterol and lipoproteins (7). However, what’s the point of saturating poly-unsaturated fatty acids to stearic acid, when stearic acid is readily obtained from natural dietary sources?  The point is, that big business stands to gain if consumers buy industrially-converted vegetable fats instead of the naturally occurring saturated fats falsely labeled as “artery-clogging.”

Toxic Interesterified Fats Study

Because it is now well known that trans fats are bad for us, manufacturers are replacing these known toxins with other chemically altered vegetable fats, in the hope that we will continue to prefer these industrial products to natural, whole counterparts (butter, lard,  and coconut oil).

A 2007 study in Nutrition and Metabolism (7) compared the impact of three types of vegetable fats on human fat and sugar metabolism.  These three types of fats are all currently available on our grocers shelves:

  1. Natural saturated fats (e.g., butter, coconut oil, and palm oil shortening)
  2. Trans, partially-hydrogenated fats (e.g., original Crisco shortening & margarines)
  3. Trans-free, hydrogenated & interesterified fats, which I call TFF for trans-free fats (e.g., “New Crisco,” & trans-free margarines)

The results of this study reflect undesirable changes in fat and sugar metabolism when subjects consumed the chemcially-altered fats (trans and TFF), compared with when they consumed the natural saturated fat (7):

  • Trans– and TFF fats caused undesirable changes in a lipid profile (LDL and triglycerides went up, HDL went down) compared with the natural fat.
  • TFF fat was slightly less bad than trans fats with respect to fat metabolism.
  • TFF fat was definitely worse for sugar metabolism than the toxic trans fats!

The researchers attribute the problems seen with TFF fats to the interesterification (IE) process, which allows fatty acids to combine randomly to the three positions on the glycerol backbone to make a triglyceride.  When a fatty acid is in a position the body’s enzymes cannot recognize, the substance is toxic, altering metabolic processes in ways harmful to health.

This is, in fact, what was found to be the problem. The process of interesterification is random (not controlled by enzymes) so that the individual fatty acids are free to attach to the glycerol backbone in any of its three positions. But in natural fats, an unsaturated fatty acid will never be found in the middle position, because of the kink in the unsaturated (cis) fatty acids. The body treats as toxic any interesterified fat molecule with a cis fatty acid in the middle position; this toxicity is known to affect sugar metabolism in a harmful way.

For more detail about this study, refer to my article Trans Fats: No longer Recognized as Safe. See also Mercola’s website for more on interesterified fats (11).


If our 100-year deadly experiment with trans and other unnatural fats has proven anything, it is that in biological systems, geometry is everything; just as the pieces of jig-saw puzzles will only connect in specific places, so it is with biochemical molecules.

  • Natural fatty acids have a specific geometry governed by the position and number of double bonds in the chain: natural unsaturated fats have bends and kinks, while trans fats are rigid and linear.
  • Natural triglycerides are formed by enzymatic action on glycerol and fatty acids, which ensures that the fatty acids are connected at the appropriate position on the glycerol backbone for metabolic processes.
  • Interesterified fats have fatty acids linked in the wrong position, making them toxic.


  8. by Mary Enig
  9. and
  12. Wikipedia on trans fat ( and on interesterified fat (
  13. FDA on labeling of trans fats:

About Cat

See my 'About' page
This entry was posted in Dairy, Diet, Fat or oil, Health and tagged , , , , . Bookmark the permalink.