Dietary fat is a major source of energy and helps the body absorb certain vitamins. Fat is also important for proper growth, development, and maintenance of good health. However, one kind of fat, trans fat, also called trans-fatty acid, is unhealthy; there are no known health benefits that come trans fat.
Types of fat
There are several types of dietary fat — some good, some bad, some well understood and some less so.
Saturated fats are saturated with hydrogen molecules. Saturated fat comes from animal sources, such as red meats, poultry and dairy products. Saturated fats are solid at room temperature; lard, for example. Saturated fat is linked to high cholesterol levels and an increased risk of cardiovascular disease, according to the American Heart Association (AHA).
Unsaturated fats are not saturated with hydrogen molecules. They are liquid at room temperature. They come from plant-based liquid oils, avocados, nuts, seeds and some fish. These fats can help reduce bad cholesterol levels in the blood, which can lower the risk of heart disease, according to the Harvard School of Public Health.
There are two types of trans fat, according to the U.S. Food and Drug Administration (FDA)
Naturally formed trans fat: This type is produced in the gut of some grazing animals, so small quantities of trans fats can be found in meat, milk and milk products.
Trans fat formed during food processing: Artificial trans fats are created when hydrogen is added to (unsaturated) liquid vegetable oils to make them more solid. Food manufacturers use partially hydrogenated oils (PHOs) to improve texture, shelf life and flavor. PHOs are the main source of this type of trans fat in the United States, according to the FDA.
PHOs were discovered in 1902 by scientist Wilhelm Normann. For many years, it was thought that eating shortening or margarine made from PHOs was preferable to butter because they didn't contain saturated fat. It wasn't until the 1980s that researchers started uncovering the health hazards that come from consuming PHOs.
In 2015, the FDA determined that partially hydrogenated oils are no longer "generally recognized as safe" (GRAS) in human food and took steps to restrict its use. According to the new restrictions, companies must remove PHOs from their food products by June 2018. Removing trans fat could prevent up to 20,000 heart attacks, and 7,000 deaths from heart disease each year in the United States, the Centers for Disease Control and Prevention estimated.
The FDA recommends eating as little trans fats as possible. Finding out if a product has trans fats can be tricky, though. A food can list "0 grams of trans fats" on the label but still contain less than 0.5 grams of trans fat per serving in the United States, according to the Mayo Clinic. The FDA also noted that trans fats have no percent daily value (%DV) on nutrition labels, so the grams (g) labeling is all that is posted on the label. A better indicator of trans fat content may come from reading the ingredients list. If a food contains partially hydrogenated oils, it contains trans fats.
The benefits of a low-fat diet, overall, are contested. Many studies show very little benefit from cutting out all fats. For example, the Women’s Health Initiative (WHI) Dietary Modification Trial, an eight-year trial of almost 49,000 women, found that a low-fat diet had no effect on breast cancer, heart disease, colorectal cancer or weight. Another study published in the October 2015 journal The Lancet Diabetes & Endocrinology found that low-fat diets don't help long-term weight loss.
Cutting out trans fats, specifically, though, can be very beneficial. Trans fats can raise bad (LDL) cholesterol levels, which can harden and narrow arteries, and lower good (HDL) cholesterol levels, according to the Mayo Clinic. They can also increase the risk of developing heart disease and stroke and is associated with a higher risk of developing type 2 diabetes, according to the American Heart Association.
There are many ways that consumers can cut down on their trans fat intake. "The No. 1 thing we can do to cut down on trans fats from the diet is to limit our intake of pre-packaged foods that have really long shelf lives or prepackaged foods with the ingredient 'partially hydrogenated' oil," said Dana Hunnes, senior dietitian at Ronald Reagan UCLA Medical Center and an adjunct assistant professor at the UCLA Fielding School of Public Health. "The No. 2 thing we can do is avoid stick margarines, as they tend to be very high in trans fats. Lastly, avoiding/limiting intake of highly fried foods is a good idea, as some restaurants may still be using trans fats to cook their products."
Cutting back on meats and animal products, such as milk, or switching to leaner cuts and lower fat milk, can also help.
Luckily, the damage done by trans fats can be reversed with a healthy diet. "Eating a healthy diet of low saturated fat, high soluble fiber (from beans, oats and greens) and monounsaturated fats (such as olive oil cold-pressed at room temperature) — in addition to produce with antioxidants and anti-inflammatory properties – will also help reverse the damage from trans fats over time," said Lisa Cohn, a registered dietitian with miVIP Surgery Centers.
- Cleveland Clinic: Avoid These 10 Foods Full of Trans Fats
- United States Department of Agriculture: Saturated, Unsaturated and Trans Fat
- The Atlantic: When Trans Fats Were Healthy