Nutrition Nuts and Bolts

Guest post by Carrie Dennett

A revolution is under way in the food industry, spurred by science, consumer demand and legal pressure. Trans fats, otherwise known as hydrogenated and partially hydrogenated oils, are surely and steadily being removed from our food. It’s a good thing.

Once hailed as a healthier alternative to saturated fats, trans fats are now being called “metabolic poison” by some health and nutrition experts. Unfortunately, these artificially derived fats made their way into all areas of our food supply, and stayed there for decades, before their true nature was revealed.

What is a “fat”? What is a “fatty acid”?

A fat, also known as a triglyceride, is composed of three fatty acids attached to a glycerol “backbone.” A triglyceride can have three matching fatty acids, or contain a mix (see image below). A fatty acid is made up of a chain of carbon atoms with hydrogen atoms attached. Each type of fatty acid is defined by the length of its carbon chain and how “saturated” it is with hydrogen atoms.

Why is some fat solid at room temperature while others are liquid?

A saturated fatty acid is filled up with hydrogen atoms, which makes the carbon chain straight. An unsaturated fatty acid is missing one (monounsaturated) or more (polyunsaturated) hydrogen atoms, causing the carbon chain to bend at each missing hydrogen.

A triglyceride with saturated fatty acids is compact because the straight fatty acid “tails” fit neatly together, and the resulting fat is solid at room temperature (i.e., butter or the fatty streaks in bacon). If the triglyceride contains unsaturated fatty acids, the bends in the carbon chains create space between the fatty acid tails, and that space makes the resulting fat fluid at room temperature (i.e., oils) (see image below).

A trans fat is an unsaturated fat (usually polyunsaturated) that has been hydrogenated. The hydrogenation process forces extra hydrogen atoms  into the empty slots on the carbon chain, creating an unsaturated fatty acid that looks like a saturated fatty acid. Because saturated fats were linked to heart disease and unsaturated fats were known to be heart-healthy, it was believed that trans fats, would offer the best of both worlds: Heart-healthy unsaturated fats with the culinary properties of saturated fats. As anyone who likes to bake knows, there are some recipes that require a solid fat like butter or shortening.

As it turns out, once unsaturated fats are hydrogenated, they are no longer heart-healthy. In fact, they are even worse for heart health than saturated fats. One reason may be that hydrogenated trans fats are artificial—they don’t occur in nature (very small amounts of natural trans fats are present in meat and dairy products).

Why did it take so long to do something about trans fats?

Although some experts expressed concern about trans fats in their early days, it took decades before their voices (together with mounting scientific evidence) grew loud enough that the mistake could no longer be ignored. In the meantime, trans fats had seeped into all areas of food preparation. Restaurants were frying in hydrogenated oils (trans fats) instead of beef tallow (saturated fat). Home cooks got the message that margarine (trans fats) was heart-healthy and that butter (saturated fat) was not. You would be hard pressed to pick up a box of crackers or cupcakes without seeing hydrogenated oil in the ingredient list.

Finally, we’ve arrived at the point where restaurants and food manufacturers are turning away from trans fats. Trouble is, when you remove a major ingredient, you need to replace it with something.

What exactly is taking the place of trans fats?

Trans fats, and saturated fats before them, were valued for their stability at high heat. Any replacements for trans fats need to have similar qualities.

For commercial frying, partially hydrogenated oils are being replaced by vegetable oils that are naturally stable at high heat (corn, cottonseed, palm, peanut and rice bran) as well as sunflower, soybean and canola oils that have been modified to make them less likely to break down and become rancid at high heat.

The situation becomes trickier when looking for a replacement for solid hydrogenated fats, such as those used for baking. Any candidate must have the right texture and creaming ability, and it can’t turn to liquid too soon. It’s also important that the fat doesn’t go rancid quickly, so the product will be shelf-stable. The trend so far is to produce trans fat-free shortenings using either palm oil or interesterified vegetable oil.

What is palm oil? What are the pros and cons?

Palm oil is a tropical oil that comes from the fruit portion of the palm fruit (as opposed to palm kernel oil, which comes from the kernel of the palm fruit). Palm oil is rich in palmitic acid, a saturated fat, but there is disagreement among scientists and health experts about the effect palmitic acid may have on blood cholesterol and heart disease. Additionally, there are environmental concerns about the harvesting of palm oil.

What is interesterified oil? What are the pros and cons?

Interesterified oils have been used since the 1930s, but interest in them increased as trans fats began to be taken out of foods. Interesterified oils take a small amount of unsaturated triglycerides (usually soybean or cottonseed), fully hydrogenate them, then mix them with a lot of the non-hydrogenated oil. The triglycerides in the mixture are broken apart and their fatty acids rearranged, producing oil that is solid at room temperature. If you buy trans fat-free shortening or chocolate bars that have had their cocoa butter removed, you’re using interesterified oil.

The concern is that whether interesterified oil is harmful to our health or simply neutral may depend on exactly how the fatty acids in the triglyceride get rearranged. Scientists are finding that it’s not just the type of fatty acid that matters, it’s also the position it occupies on the triglyceride. The interesterification process is not precisely controlled, and some of the random arrangements produce triglycerides that are not found in nature.

What are health experts saying about these trans fat “alternatives”?

Most health and nutrition experts agree that palm oil is a lesser evil than trans fats, even if they don’t agree on whether palm oil is good, bad or neutral for health. Many experts also agree that research needs to continue on the possible effects of interesterified oil on health, especially if our consumption of it goes up due to increased use in commercial food preparation.

What can I do now until we know more about these fats?

• First, don’t assume that the words “trans fat free” on a food package means that food is healthy. It’s wise to also consider what else is in the food. Is it high in…
  • Sugar?
  • Refined flour?
  • Artificial ingredients?
• Second, if you eat more whole foods and fewer processed foods, you’ll naturally be eating less of whatever type of fat is used in place of trans fats. This means you will be less affected if years from now it turns out that these trans fat alternatives aren’t any better for us.

If you’d like to read more, Harvard School of Public Health’s Nutrition Source website has a nice page on trans fats.

Also read…

• Health Effects of Rancid Fat

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