Fats are a critical component of the diet, ranging from basic biological functions in metabolism maintenance to supporting glowing skin and shiny hair. But not all fats have the same impact on health—some are better for us than others.  By now, you’ve probably heard of trans fats and followed the advice to avoid or limit your intake of them. But not everybody has, which is why there are still a variety of news articles and media coverage dedicated to the topic. Recently, the World Health Organization made news by issuing updated draft guidelines on the intake of trans fat. Dietary fats can be a complicated topic, so use this handy Q&A to help further your understanding of trans fats.

Let’s first start with the basics: What are dietary fats?

There are two types of dietary fats: saturated and unsaturated. The difference between the two depends on the amount of hydrogen atoms that surround the fatty acid structure, called “saturation.” Saturated fatty acids are “saturated” with hydrogen atoms and are typically solid, while unsaturated fatty acids are not “saturated” with them and are typically liquid.

So what exactly is a trans fat?

Trans fats are technically unsaturated but, when formed, have characteristics more similar to saturated fats. They are formed by adding hydrogen to unsaturated fats through a process called hydrogenation, which results in oils becoming more solid and stable at room temperature.

As an example, hydrogenating vegetable oil to make a stick of margarine is a process that increases the stability of fats, therefore, increasing the shelf life.

What are some common sources of trans fats?

The trans fat found in our diet comes from two sources—foods from ruminant animals (such as sheep, goats and cows) and some fats and oils used as ingredients in certain packaged foods.

Back up, I am confused. What is the difference between trans fats and partially hydrogenated oils (PHOS)?

While often used interchangeably, PHOs are a type of trans fat and are created by heating oil in the presence of hydrogen. PHOs are the largest source of trans fats in most people’s diet.

I have heard a bunch about trans fats and PHOs in the news. What is this referencing?

As new research has emerged, there have been changing regulations on the use of trans fat in food. In 2006, the FDA required labeling of trans fats on the Nutrition Facts panel. In 2013, the FDA issued a Federal Register notice with a preliminary determination that PHOs would no longer be generally recognized as safe (GRAS), with a final determination in 2015 that trans fats are not GRAS and a compliance date of three years to allow for reformulation or petitioning for specific use.

This year, the World Health Organization issued draft guidelines recommending that people who consume greater than 1 percent of their calories from trans fat reduce their intake. The strongest evidence supporting this recommendation comes from randomized controlled trials showing LDL cholesterol-lowering effects of reducing trans-fatty acid intake.

Can you walk me through the timeline of PHOs and trans fats?

PHOs were originally developed and patented in the 1900s as a more affordable replacement for animal fats because of a shortage of butterfat at the time. Widespread use of PHOs began in the 1950s, and increased in the 1970s and 1980s, as many people were looking for an alternative to saturated fats, which were a health concern. 

PHOs were found to improve many qualities in some of our tastiest foods. They extend shelf-life and enhance the texture, firmness/spreadability, flakiness, creaminess and crispiness of a product. As research has demonstrated the negative health effects associated with high intakes of PHOs, they have largely been removed or are in the process of being removed from the food supplies of many countries around the globe. The continued removal of PHOs from the global food supply is a priority action identified by WHO between 2019 and 2023.

How has trans fat consumption changed in the U.S. over time?

In the 1980s, intake in the U.S. was around 8 grams/day. Intake would continually drop over the years, with 5.3 grams/day in the 1990s and 4.6 grams in the 2000s. By 2012, intake in the U.S. was around 1.3 grams/day.

What will be the replacement for PHOS?

Palm oils, derived from tropical palms, which are highly saturated and used to enhance the texture of products, are one replacement. Interesterified (IE) oils are another replacement, which change the structure of the oil (i.e. inserting saturated fatty acids into vegetable oils) for enhanced stability.

Should I be worried about fully hydrogenated oils?

Nope. Interestingly, fully hydrogenated oils do not have the same negative health effects as PHOs. Fully hydrogenated oils become saturated fats, such as stearic acid, but contain no trans fat.