WebMD BlogsFrom Our Archives

Hydrogenated Oils and Trans Fats

finger pointing to nutrition label
August 19, 2007
From the WebMD Archives

How can food products containing partially hydrogenated oils be trans fat free?

For years, nutrition experts have been recommending that people avoid foods with partially hydrogenated oils on the label because they contain dangerous trans fats. Now, products are appearing that contain hydrogenated oils, but are labeled “trans fat free.” Confused?

I was at a child’s birthday party this weekend, and the conversation turned, as it often does when I’m around, to nutrition and health. An old friend of mine asked me how it was that health food store-brand margarine could both contain hydrogenated oils and also claim to be trans fat free.

There are at least two ways that I’m aware of. But to understand them, we’d better take a detour into food chemistry. Unsaturated fats usually make up the bulk of vegetable oils. These fats are unsaturated because they have less hydrogen per gram than saturated fats. Unsaturated fats are cheap, but they are also liquid and less stable (spoil more quickly) than saturated fats, making a big problem for food manufacturers.

Manufacturers have made vegetable oils more solid and more stable by adding in extra hydrogen in an industrial process called hydrogenation. They traditionally haven’t added in enough hydrogen to fully saturate the fat, leading to the description “partially” hydrogenated oils. Partially hydrogenated oils are popular in processed foods because they are cheap, stable, widely available, and add a nice mouth-feel.

In this process, a small percentage of the unsaturated fats become something called trans fats, fats that are thought to have particularly destructive effects on the human body even in small amounts. For example, trans fats are thought to increase bad LDL cholesterol, decrease good HDL cholesterol, and have been correlated with increased risk of heart attack. For these reasons, and ensuing regulatory pressure, the food industry is moving away from adding hydrogenated oils into food.

So, how does a product that contains hydrogenated fats call itself trans fat free? One way is by shrinking serving size. The FDA allows products containing up to half a gram of trans fats per serving to be labeled as trans fat free. When adverse effects of intake can be seen at levels as low as two grams per day or less, those almost half-gram servings could end up being more significant than you would guess. By defining servings on the small end, fatty foods like margarines can look low calorie and trans fat free, when they are, in fact, neither.

Alternately, companies can fully saturate the vegetable oil with hydrogen, creating an all saturated fat product. Since this product is very solid, it needs to be artificially thinned down by whipping with water before using. Although fully hydrogenated oils do not contain trans fat, they are by no means a health food. Saturated fats, whether naturally occurring or produced industrially, have the same adverse effects on cholesterol as trans fats, and are potentially worse for blood sugar control.

When possible, try to use liquid fats like organic canola, safflower, or sunflower oil in cooking instead of solids. For spreads and other mildly heated items, extra virgin olive oil is often a good choice. For those recipes that require more solid fats, use the non-hydrogenated margarines sold in health food stores, or just plain old organic butter.


  • de Roos NM, Bots ML, Katan MB. Replacement of dietary saturated fatty acids by trans fatty acids lowers serum HDL cholesterol and impairs endothelial function in healthy men and women. Arterioscler Thromb Vasc Biol. 2001 Jul;21(7):1233-7.
  • Lichtenstein AH, Erkkila AT, Lamarche B, et al. Influence of hydrogenated fat and butter on CVD risk factors: remnant-like particles, glucose and insulin, blood pressure and C-reactive protein. Atherosclerosis. 2003 Nov;171(1):97-107.
  • Odegaard AO, Pereira MA. Trans fatty acids, insulin resistance, and type 2 diabetes. Nutr Rev. 2006 Aug;64(8):364-72.
  • Thomsen C, Rasmussen O, Lousen T, et al. Differential effects of saturated and monounsaturated fatty acids on postprandial lipemia and incretin responses in healthy subjects. Am J Clin Nutr. 1999 Jun;69(6):1135-43
  • Zaloga GP, Harvey KA, Stillwell W, Siddiqui R. Trans fatty acids and coronary heart disease. Nutr Clin Pract. 2006 Oct;21(5):505-12.
WebMD Blog
© 2007 WebMD, Inc. All rights reserved.

Latest Blog Posts on WebMD

  • photo of
    Multiple Sclerosis

    Grieving Over MS

    A few weeks back, I had a miserable night with bowel issues related to my multiple sclerosis (MS). The next day, I started noticing the useful and fun things people were ...

  • photo of business meeting
    Sickle Cell Disease

    How I Work With Sickle Cell Disease

    Others in the sickle cell disease community have asked me a few times whether it’s wise to disclose having sickle cell when applying for a job ....

View all blog posts

Important: The opinions expressed in WebMD Blogs are solely those of the User, who may or may not have medical or scientific training. These opinions do not represent the opinions of WebMD. Blogs are not reviewed by a WebMD physician or any member of the WebMD editorial staff for accuracy, balance, objectivity, or any other reason except for compliance with our Terms and Conditions. Some of these opinions may contain information about treatments or uses of drug products that have not been approved by the U.S. Food and Drug Administration. WebMD does not endorse any specific product, service or treatment.

Do not consider WebMD Blogs as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare provider because of something you have read on WebMD. You should always speak with your doctor before you start, stop, or change any prescribed part of your care plan or treatment. WebMD understands that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified health care provider. If you think you may have a medical emergency, call your doctor or dial 911 immediately.

Read More