And You Think Saturated Is
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
foodsare 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
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
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:
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.
total daily fat intake at less than 35% of total calories.
Saturated fat and TFA intake should not exceed 7% of total
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
oils such as olive, canola, and peanut; avocados; almonds,
pecans, and peanuts.
oils such as safflower, sunflower, corn, flaxseed, and
soybean; most nuts; fatty fish including salmon, tuna,
mackerel, trout, and sardines.
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.
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.