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Coronary Heart Disease

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And You Think Saturated Is Bad...

Though dietary fat is much maligned, a certain amount is essential for life. After they are absorbed, fats are used as an immediate and stored source of energy as well as to insulate body tissues, protect organs, aid in the absorption of fat-soluble vitamins (A, D, E, and K), and maintain skin and hair. Dietary fat, which is absorbed more slowly than other nutrients (proteins and carbohydrates), also makes people feel full and prompts them to stop eating. But choosing the wrong dietary fats can increase the risk of heart disease, diabetes, and some cancers. And a recent study shows that trans fatty acids (TFAs)—a type of fat that is frequently added to commercially processed foods—are probably even more harmful to the heart than had previously been thought.

The good and the bad

Fats are made up mostly of fatty acids (which contain carbon, hydrogen, and a small number of oxygen atoms) and glycerol (a type of alcohol). There are three main types of fat: saturated, monounsaturated, and polyunsaturated. Saturated fats have hydrogen atoms attached to every carbon atom; monounsaturated fats are missing one pair of hydrogen atoms; polyunsaturated fats are missing two or more pairs. Virtually all foods plant- or animal-based, contain at least one of these fats. TFAs are modified unsaturated fats characterized by a different arrangement of hydrogen atoms.

When consumed in appropriate amounts, all monounsaturated and all polyunsaturated fats except TFAs are beneficial because they lower harmful low density lipoprotein (LDL) cholesterol. Conversely, all saturated fatty acids and TFAs are undesirable because they raise levels of LDL cholesterol and total cholesterol and have been associated with coronary heart disease (CHD) and stroke. In addition, saturated fats are associated with an increased risk of cancer of the colon, rectum, prostate, pancreas, uterus, and breast. A diet high in saturated fats also contributes to obesity, which raises the risk of life-threatening, chronic medical problems such as diabetes and CHD.

The really ugly

Saturated fats have long had a reputation for being the most harmful type of fat. But recent studies indicate that TFAs may pose an even greater risk of CHD and diabetes. Naturally occurring TFAs are found primarily in dairy products, beef, and pork. Synthetic TFAs are found in nearly all commercially prepared foods. They are formed by attaching additional hydrogen atoms to polyunsaturated vegetable oils, a process known as hydrogenation. Partially hydrogenated oils (in which a hydrogen atom has been added to some carbon atoms) are added to foods to retain their shape, enhance their flavor, and extend their shelf life. About 25% of the TFAs in the diet are from natural sources; the remainder are synthetic.

A recent Dutch study published in Arteriosclerosis, Thrombosis, and Vascular Biology examined the effect of TFAs on two CHD risk factors: arterial function and cholesterol levels. Twenty-nine healthy adults (average age 30) used a specially made margarine high in TFAs for a month and then switched to a margarine high in palm kernel oil (a saturated fat) for another month. Arterial function in the brachial artery (located in the arm) and cholesterol levels were measured at the end of each month. Levels of helpful high density lipoprotein (HDL) cholesterol were 21% lower on the high-TFA margarine; harmful LDL cholesterol levels were unchanged, but the ability of the brachial artery to dilate (widen) had decreased by one third.

In another Dutch report, published in The Lancet, 667 men aged 64 to 84 who were free from CHD completed a dietary history and were followed for ten years. At the end of the follow-up period, the incidence of CHD was higher in the men who had greater TFA intake at baseline (the start of the study).

A third study, published in the American Journal of Clinical Nutrition, examined TFA intake and diabetes risk in women. The researchers analyzed data from 84,000 women who were followed for 14 years as part of the Nurses' Health Study. Higher TFA intake was associated with a significant increase in diabetes risk; saturated and monounsaturated fat intake had no effect on diabetes risk.

These and other studies are so convincing that one Food and Drug Administration (FDA) expert estimates that removing all TFAs from margarine and 3% from baked items would prevent more than 17,000 heart attacks and more than 5,000 CHD-related deaths a year. Although prepared foods currently list the types of oils they contain, and whether any oils have been hydrogenated, listing the percentage of TFAs is not required. The FDA is currently considering mandating this information.

Meanwhile, you can choose healthy fats and avoid harmful ones by:

Limiting intake of whole-fat milk products (cheese, yogurt, whole milk), fatty meats, tropical oils (palm, palm kernel, and coconut), egg yolks (notable for their high cholesterol content), hydrogenated oils, and fried fast food.

Keeping total daily fat intake at less than 35% of total calories. Saturated fat and TFA intake should not exceed 7% of total calories.

Avoiding stick margarine. Instead, use tub or liquid products like olive oil, which contain fewer hydrogenated oils, or products that contain plant-based fats known as stanols (Benecol, Take Control, and others), which can help reduce cholesterol.

 

How Unsaturated Is Your Diet?

Monounsaturated: Vegetable oils such as olive, canola, and peanut; avocados; almonds, pecans, and peanuts.

Polyunsaturated: Vegetable oils such as safflower, sunflower, corn, flaxseed, and soybean; most nuts; fatty fish including salmon, tuna, mackerel, trout, and sardines.

Saturated: Animal products, especially beef, full-fat dairy products, any type of fried meat, and any type of ground meat that may have the skin mixed in to add moistness; tropical oils including palm, palm kernel, and coconut.

TFAs: Some margarines; virtually all prepackaged, prepared foods including frozen dinners, breakfast foods, vegetable dishes, and desserts; dry mixes for dressing, rice, macaroni, and hamburger dishes; chips; baked goods including breads, cookies, cakes, and crackers; fried fast food.

 

From The Johns Hopkins Medical Letter: Health After 50, March 2002.

 


 

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Coronary Heart Disease

The Coronary Heart Disease White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Johns Hopkins physicians.


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