Trans Fats: Health Effects

by Health Canada

Scientific evidence has shown that dietary trans fats can increase your risk of developing heart disease. You can reduce this risk by choosing healthier foods that contain little or no trans fat.

Fat is an important part of a healthy diet because it provides essential fatty acids and energy (calories). It also helps your body absorb Vitamins A, D and E.

Fats and oils are made mostly of fatty acids. There are four main types of fatty acids. Most fats and oils contain a mixture of all four types, but such mixtures usually have a higher proportion of one particular type of fatty acid. The four main types of fatty acids are:

Polyunsaturated fatty acids - Many common vegetable oils (e.g., soybean, corn and sunflower oil), fatty fish (e.g., salmon, mackerel, smelt, herring and trout), fish oils, flaxseed, sunflower seeds, soybeans and some nuts (e.g., walnuts) contain a high proportion of polyunsaturated fatty acids.

Monounsaturated fatty acids - Olive oil, canola oil, high oleic sunflower oil, avocados and certain nuts (e.g., cashews, pecans, almonds and peanuts) contain a high proportion of monounsaturated fatty acids.

Saturated fatty acids - Coconut, palm and palm kernel oils, animal fats (e.g., pork and beef), butter, cheese and other dairy products contain a high proportion of saturated fatty acids.

Trans fatty acids - These are found naturally in small amounts in certain foods (e.g., dairy products, beef and lamb). Also, small amounts of trans fats are formed during the refining of liquid vegetable oils (e.g., canola and soybean oil). Trans fats are also created when manufacturers use a process called "partial hydrogenation." This process turns liquid oil into a semi-solid form, such as shortening or margarine.

Food products made with fats or oils with a high proportion of saturated or trans fatty acids have a longer shelf life than products made with oils that contain a higher proportion of other fatty acids. Saturated and trans fatty acids also play a role in producing the textures and flavours that make many bakery products and snacks so tempting. For example, it is the saturated and trans fatty acids that give pastries that "melt in your mouth" feeling.

The Health Effects of Dietary Fats

In general terms, polyunsaturated and monounsaturated fatty acids tend to lower your risk of heart disease. They are the healthier fats, and they should be included in your diet. Saturated and trans fatty acids are unhealthy fats because they tend to raise your risk of heart disease.

Trans fats do two things that raise the risk of developing heart disease:

Trans fats raise blood levels of so-called bad cholesterol (LDL-cholesterol). LDL-cholesterol is a risk factor for heart disease.

Trans fats lower blood levels of so-called good cholesterol (HDL-cholesterol). HDL-cholesterol protects against heart disease.

Saturated fats also raise blood levels of "bad" cholesterol. However, at the same time, they also raise blood levels of "good" cholesterol.

Main Dietary Sources of Trans Fatty Acids

Most of the trans fat in a typical Canadian diet comes from margarines (especially hard margarines), commercially fried foods and bakery products that are made with shortening, margarine or oils containing partially hydrogenated oils and fats. These products include crackers, cookies, donuts, cakes, pastries, muffins, croissants, snack foods and fried foods, such as french fries and breaded foods. In these products, up to 45% of the fat content may be trans fatty acids.

Trans fatty acids are also present at low levels (2 to 6% of the fat) in such foods as dairy products, beef and lamb. Some refined liquid oils may contain small amounts of trans fatty acids (0.5 to 2.5% of the oil).

About the Author

www.hc-sc.gc.ca
Health Canada is the Federal department responsible for helping Canadians maintain and improve their health, while respecting individual choices and circumstances.