Decoding Nutrition Fact Labels: Fats
As you munch idly on your morning bowl of Froot Loops, you find yourself glancing over the back of the cereal box. The nutrition facts label seems simple enough at first — after all, you’ve been hearing about proteins, carbohydrates, and fats since elementary school health class. As you look beneath “Total Fat,” however, you’re surprised to find a whole slew of big, unfamiliar words; everything from “trans fat” to “monounsaturated fat.” Is this even English? you wonder dazedly. Before long, you develop a headache and cast the box to the side, reassuring yourself that proper nutrition is overrated anyway.
Fat plays a large number of roles in the human body. In addition to being a source of energy, it helps with vitamin and mineral absorption, composes cell membranes, and is essential for proper blood clotting. Unfortunately, there is a general misconception that fat is unhealthy and should be limited as much as possible in one’s diet. While it is true that excessive fat intake may lead to adverse health effects, including heart disease and high cholesterol, the complete relationship between fat and health is far more complex.
In order to properly understand this relationship, we need to understand that there are a number of different types of fats that each have a specific structure and effect on the body. The four main categories of fats delineated on most nutrition facts labels are saturated fat, polyunsaturated fat, monounsaturated fat, and trans fat. Of these, saturated fat and trans fat are generally viewed as “harmful fats,” whereas polyunsaturated and monounsaturated fat are classified as being “helpful fats.” But why?
At the molecular level, fat consists largely of hydrocarbons, in which hydrogen molecules are bonded to a backbone of carbon molecules. In general, a carbon molecule can form up to four bonds with other molecules. In a saturated fat, each carbon molecule in the interior of the backbone is bonded to two other carbons by single bonds. This leaves room for two more bonds with hydrogen molecules. Because each carbon is bonded to the maximum number of hydrogen molecules, a saturated fat is “saturated” with hydrogens. This tight packing causes saturated fat to assume a solid state at room temperature — think butter and fatty meats. It may also link diets rich in saturated fats to high cholesterol levels and an increased risk of heart disease.
Whereas the carbon molecules in a saturated fat are linked entirely by single bonds, an unsaturated fat has one or more double bonds in the carbon backbone. The carbon molecules involved in the double bond can then only bond to one additional hydrogen molecule each. Since the fat molecule no longer contains the maximum number of hydrogens, it is described as being “unsaturated.” The double bond also puts a kink in the hydrocarbon structure, which prevents fat molecules from tightly packing. This is why unsaturated fats are liquids at room temperature — think oils.
A monounsaturated fat contains only one double bond in the carbon skeleton, meaning that it has two fewer hydrogen atoms than a saturated fat of the same length. Common sources of monounsaturated fats include olive oil, avocados, and most nuts.
It follows that a polyunsaturated fat contains more than one double bond in the carbon skeleton. Polyunsaturated fats are also known as omega-3 and omega-6 fatty acids, which are commonly found in corn oil, canola oil, and fatty fish. Both types of unsaturated fats are believed to improve heart health when consumed in place of saturated fat.
While small amounts of trans fat do occur in nature, the large majority is artificially produced through a process called partial hydrogenation. This injects liquid unsaturated fat with hydrogen atoms to convert it into a form that is more solid at room temperature — think margarine and shortening.
Partial hydrogenation also converts the type of double bond present in the carbon skeleton. Double bonds can exist in two forms, “cis” and “trans,” which correspond to different molecular shapes. Naturally-occurring unsaturated fats have “cis” double bonds; after partial hydrogenation, these are changed to “trans” double bonds. While this increases shelf life and enhances flavor, it can have disastrous health effects. High trans fat intake has been shown to increase harmful cholesterol levels, contribute to inflammation that can induce heart disease and stroke, and increase the risk of type 2 diabetes. Hence, processed foods that contain trans fat or “partially hydrogenated oils” should absolutely be avoided.
Rather than shunning fat altogether, it’s important to distinguish between the different types of dietary fat and make appropriate eating choices. There is a huge difference between big words like “saturated” and “polyunsaturated,” and picking one over the other can produce a variety of health benefits. The next time you find yourself reading a nutrition facts label, keep in mind that proper nutrition may not be so overrated after all.
“Dietary fats: Know which types to choose.” Mayo Clinic, 2 Feb. 2016, https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fat/art-20045550. Accessed 18 Nov. 2018.
“The truth about fats: the good, the bad, and the in-between.” Harvard Health Publishing, 13 Aug. 2018, https://www.health.harvard.edu/staying-healthy/the-truth-about-fats-bad-and-good. Accessed 18 Nov. 2018.
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