Over the past 30 years, research has clearly identified the adverse health effects of trans fatty acids, most notably on coronary heart disease.

Epidemiological estimates attribute upward of 100,000 deaths annually to trans fats. It is unknown what levels of trans fatty acids are clinically significant, yet after two decades a research group at Indiana University concluded, “On a per-calorie basis, trans fats appear to increase the risk of (coronary heart disease) more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3% of total energy intake).”

With the exception of a handful of naturally occurring trans fats, TFAs are created by hydrogenation. This chemical process bubbles hydrogen through unsaturated oils to stabilize them, to prevent them from becoming rancid and to keep them solid at room temperature.

Fatty acid molecules are chains of 12 to 24 carbon atoms attached to a unit of carbon, oxygen and hydrogen atoms, abbreviated “COOH.”

Fat and oil molecules consist of different combinations of three fatty acid chains bonded to a molecule of glycerin, hence the name “triglyceride.”

Carbon atoms can each form four bonds. In a carbon chain, two of the bonds attach a carbon atom to its neighbors. Hydrogen atoms usually occupy the other two bond sites. If not, then the two carbon atoms form a second bond, called a double bond.

Unsaturated fats have double bonds in their structures. These are called unsaturated chains because each double bond repre­sents a potential bonding site for a hydrogen atom, to “saturate” the chain with hydrogen.

The viscosity and melting temperature of fats are higher when there are fewer double bonds, so monounsaturated fats have a higher melting point than polyunsaturated fats.

Isomers are two molecules that have the same chemical formula but different structures. The two hydrogen atoms can be either on the same side of the chain or on opposite sides. A “cis” isomer occurs when they are on the same side, and a “trans” isomer occurs when they are on opposite sides.

Trans fatty acid chains are linear, whereas cis chains have a bend due to the mutually repulsive hydrogen atoms crowded onto the same side of the chain.

Trans fats are easy to use, inexpensive to produce, last a long time and give foods a good taste and texture. Many restaurant and fast-food establishments use trans fats to deep-fry because oils with TFAs resist rancidity and can be used many times in commercial fryers.

Fatty acids of both types cannot be metabolized directly because they are not soluble in blood. A sequence of metabolic events packages them into blood- soluble packets of cholesterol and other proteins. In that form they may either be stored as fat or used as energy, depending on metabolic needs.

Although little is known about the mechanisms by which trans fatty acids actually function at the cellular level, it is becoming increasingly clear that they are bad news, whether banned by edict or by choice.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.