Up until a few years ago, only nutrition experts were aware of a certain type of fat known as trans fat. Since then, plenty of research has proven that trans fats (also known as trans fatty acids) play a significant role in the development of heart disease.
In the human body, trans fats raise levels of LDL (low-density lipids, bad) cholesterol and lower levels of HDL (good) cholesterol. When HDL levels are low and LDL levels are high, cholesterol builds up in the vessels that supply blood to your heart. This fatty plaque buildup causes a narrowing of the blood vessels and can eventually cause a complete blockage.
The most common cause of heart disease is this narrowing of the coronary arteries, which are the blood vessels that supply oxygen to the heart.
A heart attack occurs when these vessels become blocked: the heart muscle does not get enough blood and oxygen so cells in that area die. The damaged heart muscle becomes weakened and loses its ability to contract normally.
There are four types of fats found in our food:
Monounsaturated fat, found in peanuts, avocados, olive oil and canola oil. This is good fat that reduces blood cholesterol levels.
Polyunsaturated fat, found in nuts and seeds, as well as in sesame, safflower, sunflower, cottonseed, corn and soybean oils. Also, omega-3 fatty acids (found primarily in fish, flaxseed and walnuts) are a type of polyunsaturated fat. This is also good fat that reduces blood cholesterol levels.
Saturated fat is bad fat found in tropical oils (palm and coconut oil) and animal products (meat, eggs, butter, cheese, ice cream, and milk. Saturated fats are the main dietary cause of high LDL cholesterol levels.
Trans fat is the very bad fat found in products containing hydrogenated or partially hydrogenated vegetable oils, such as commercial baked goods (cakes, crackers, cookies), fried foods (doughnuts, French fries, fried chicken) and most types of margarine. There are also small amounts of trans fats naturally occurring in beef, pork, butter and whole milk.
Once upon a time, baked goods and fried food were made using butter or tropical oils. When the connection between saturated fats and heart disease became clear, the food industry began looking for substitutes for saturated fats.
They turned to hydrogenated and partially hydrogenated vegetable oils, made by adding hydrogen to the vegetable oil, which increases the shelf life and flavor of foods.
For decades, margarine was seen as a healthy alternative to butter with all its saturated fat. Now nutritionists recognize that the partially hydrogenated vegetable oils used to make margarine contain trans fats. However, liquid margarine or soft margarine found in tubs contains considerably less trans fat than stick margarine, and are the best choice.
All commercially prepared cookies, cakes, pies and crackers made with partially hydrogenated vegetable oil contain trans fats. Most deep-fried foods are fried in partially hydrogenated oils, too. Researchers have found that trans fats are found in about 40 percent of products found in supermarkets.
So, why aren't trans fats usually listed on the nutritional facts labels of foods you buy at the store?
Until the link between trans fats and heart disease became clear, the Food and Drug Administration did not take a stand on trans fats. Now that this link is known, the law has been changed. By Jan. 1, 2006, the amount of trans fats must be listed on all product labels.
Trans fats are so bad that the FDA has announced there is no healthy level of trans fats in the diet. Saturated fats are not much better, and should be kept to a minimum to reduce your risk of heart disease.
Next week's column will be about cholesterol and its relationship to heart disease.
Kathryn B. Brown is a family nurse practitioner with a master's degree in nursing from OHSU.
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