You've heard that hydrogenated oil is bad for you. Of course, you can take this information at face value and steer clear of hydrogenated oils without really knowing why. But sometimes it's easier to stick to a nutrition recommendation when you know why that recommendation exists in the first place.
Hydrogenated oil is bad for you because it contains a high level of hydrogenated fats, called trans fats, that increase your risk of developing heart disease and other health problems. There are some foods that also naturally contain trans fats, but these kinds of fats the biggest problem when they come from artificial and processed sources, like hydrogenated oil.
Hydrogenated oil, more specifically partially hydrogenated oil, contains a type of man-made fat, called trans fat, that increases the risk of heart disease, stroke and diabetes. Although once "generally recognized as safe," the FDA has declared that after January 1, 2020, no food manufacturers are allowed to add partially hydrogenated oils to their foods.
What Is Hydrogenation?
To define hydrogenation, it's best to keep it simple. Although the chemistry is advanced, in simple terms, hydrogenation involves adding hydrogen atoms to certain types of fats, like vegetable oils, to change their chemical structure to increase their shelf life, enhance taste and texture and make them more stable during cooking. The addition of hydrogen atoms breaks apart the natural bonds in the fat and creates new types of connections called double bonds.
There are two types of hydrogenation: full and partial. Full hydrogenation involves creating enough double bonds to make the fat completely solid at room temperature. In partial hydrogenation, just enough double bonds are created to make the fat semi-solid at room temperature.
According to experts from Berkeley Wellness, fully hydrogenated oils become a type of saturated fat that hasn't been linked to increased heart disease risk. On the other hand, partially hydrogenated oils end up containing trans fats, a type of fat that simultaneously increases your bad, or LDL, cholesterol, while lowering your good, or HDL, cholesterol.
What Are Trans Fats?
Because trans fats affect both of your major cholesterol markers negatively, the Mayo Clinic describes them as "double trouble" when it comes to your heart health, and Harvard Health Publishing calls artificial trans fats, like those made when partially hydrogenating vegetable oil, "the worst fats you can eat."
In addition to lowering your good cholesterol while also increasing your bad cholesterol, trans fats also contribute to chronic inflammation and increase your risk of developing blood clots. Together, all of these factors contribute to an increased risk of heart disease, stroke and diabetes, some of the leading causes of death in the United States.
A report published in the Annals of the New York Academy of Sciences in April 2016 adds that diets high in trans fats have been linked to cognitive decline and an increased risk of developing dementia.
The History of Hydrogenated Oil
Partially hydrogenated oil entered the food supply in the late 19th century when chemists were looking to create shelf-stable food products that didn't spoil quickly or easily. These chemists also found that, in addition to increasing a product's shelf-life, hydrogenated oils could withstand higher cooking temperatures than their non-hydrogenated counterparts, and they were cheaper.
After becoming a regular part of the food supply for decades, the risks associated with consuming the trans fats in partially hydrogenated oils started to become more apparent. As a response to this, the Food and Drug Administration (FDA) started requiring food manufacturers to list the amount of trans fats in their food products on nutrition labels in 2006.
Then, in 2015, the FDA announced that it was removing partially hydrogenated oils from its "Generally Recognized as Safe," or GRAS, list and that taking these oils out of processed foods could prevent thousands of heart attacks and diet-related deaths each year. According to a May 2014 report in the New England Journal of Medicine, that number is around 20,000 coronary events, such as heart attacks, and 7000 deaths from coronary causes each year in the United States.
Are Partially Hydrogenated Oils Banned?
Following the determination that trans fats and hydrogenated oils are bad for you, the FDA decided to start phasing them out of all processed foods and food products. After June 18, 2018, no new foods were allowed to include partially hydrogenated oils. However, there was a caveat for food items that were already in production.
For products that were produced before June 18, 2018, the FDA extended this date to January 1, 2020, or January 1, 2021, if the food company has an approved, petitioned used for the partially hydrogenated oil.
Sources of Partially Hydrogenated Oils
Other Sources of Trans Fats
The majority of trans fatty acids in the diet are man-made and come from the partial hydrogenation of various vegetable oils, including canola oil, soybean oil, palm oil and cottonseed oil. However, according to a review published in the Bulletin of the World Health Organization in October 2017, some meat and dairy products also naturally contain some small amounts of trans fats.
The American Heart Association notes that these natural trans fats are different in chemical structure than the artificial ones produced during hydrogenation and that there hasn't been enough evidence to show whether or not they cause the same negative health effects. The concentration of trans fats is also significantly lower.
According to a report published in Nutrients in August 2017, natural trans fats, like those found in meat, generally comprise up to 6 percent of a food's fat content, while artificial trans fats, like those found in partially hydrogenated oils, make up around 60 percent of a food's fat content.
- Bulletin of the World Health Organization: "Systematic Review of Dietary Trans-Fat Reduction Interventions"
- Berkeley Wellness: "Ask the Experts: Hydrogenated Oils"
- Mayo Clinic: "Trans Fat is Double Trouble for Your Heart Health"
- American Heart Association: "Trans Fats"
- Harvard Health Publishing: "Where the Worst Type of Fat Is Hiding in Supermarket Foods"
- The New England Journal of Medicine: "The Trans-Fat Ban — Food Regulation and Long-Term Health"
- Nutrients: "Trans Fat Intake and Its Dietary Sources in General Populations Worldwide: A Systematic Review"
- Harvard T.H. Chan School of Public Health: "Shining the Spotlight on Trans Fats"
- U.S. Food and Drug Administration: "Final Determination Regarding Partially Hydrogenated Oils (Removing Trans Fat)"
- Annals of the New York Academy of Sciences: "Nutrition and Risk of Dementia: Overview and Methodological Issues"
- Centers for Disease Control and Prevention: "Leading Causes of Death"