Saturated Fats: What does the literature say?

February 20, 2005

http://www.sciencenews.org/articles/20041127/food.asp

" In the study, " the beneficial effects [of saturated fats] were the

greatest in women with the lowest fat intake overall, " Mozaffarian

points out.

He speculates that similar antiplaque benefits might also have

occurred if the women had eaten more heart-friendly monosaturated

fats, such as in canola and olive oils, in place of the saturated

fats, so long as overall fat intake was low. "

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The study participants were:

* all were postmenopausal women

* three-fourths were overweight postmenopausal women

* forty percent were obese postmenopausal women

* one-quarter had diabetes

The study results apply to this group and to postmenopausal women with

metabolic syndrome. Sharon

Science News Online

Week of Nov. 27, 2004; Vol. 166, No. 22

Saturated Fat Shows Unexpected Benefit

Parsell

It's been an article of faith in the medical community for more than

40 years that diets high in saturated fats put people at risk of heart

disease. Most saturated fats boost blood concentrations of harmful,

low-density-lipoprotein (LDL) cholesterol and lead to the buildup of

plaque in arteries. So researchers at the Harvard School of Public

Health were " surprised " by the results of a new study showing exactly

the opposite effect in a group of postmenopausal women.

Dariush Mozaffarian and his colleagues examined the daily diets and

coronary artery conditions of 235 U.S. women. The women's average age

was 66 at the beginning of the 3-year study, and all had some plaque

buildup at that time.

The scientists took X-ray images at 10 places along each woman's heart

arteries at the start and end of the study. The women all provided

comprehensive records of what foods they ate and how much, including

details such as the kinds of oils used for frying and baking.

The researchers analyzed the women's intake of various nutrients in

relation to plaque buildup during the study, adjusting for factors

such as age, education, smoking habits, and use of medication. The

X-rays after 3 years showed that those women who had regularly eaten

the highest amounts of saturated fats had the least amount of

additional plague buildup in their arteries.

The women who ate more saturated fat also had a healthier balance of

good and bad cholesterols, as well as more desirable blood

concentrations of various kinds of fats.

The body needs a variety of dietary fats for energy, for proper

functioning of the body, and for processing the fat-soluble vitamins

A, D, E, and K. But excessive saturated fat can increase blood

cholesterol, which circulates through the body in molecules called

lipoproteins. When cholesterol builds up on the lining of blood

vessels—a condition known as atherosclerosis—it constricts blood flow

and can cause heart attacks and strokes.

Saturated fats come from meat and dairy products, as well as oils in

some tropical plants such as coconut and palm trees.

No single answer

The Harvard researchers also examined the women's carbohydrate intake

in relation to plaque progression. The women with the highest amounts

of carbohydrates in their diets over the 3 years had the most plaque

buildup. This was especially evident among women who ate a lot of

low-fiber carbohydrates and those who had less physical activity.

Mozaffarian says the results, published in the November American

Journal of Clinical Nutrition, shouldn't be construed as an

endorsement of diets that advocate eating high amounts of fats and

avoiding carbohydrates.

The outcome does support the advice of nutritionists who argue that

people should be careful about what kind of carbohydrates they eat, he

adds. " The women [in the study] who ate carbs in the form of

whole-wheat grains did fine, " he says. " The problem was with women who

ate highly-refined carbohydrates. "

An important distinction in this study, Mozaffarian cautions, is that

the participants weren't typical in a number of ways.

For one thing, all the women were postmenopausal. Moreover,

three-fourths of them were overweight, and 40 percent were obese. A

quarter had diabetes.

Other studies have shown that women generally experience changes in

their lipid, or fat, levels as they age. Concentrations of good,

high-density lipoprotein (HDL) cholesterol tend to decline after

menopause, for example.

Most other dietary studies have linked saturated fat intake with high

blood concentrations of bad LDL cholesterol. That effect wasn't seen

in this study, however.

Another significant trait of the group that may help explain the

results is that most of the women consumed relatively low amounts of

fat compared with those in typical U.S. diets. About 25 percent of

this group's calories came from fats, whereas the fat content of most

U.S. diets may be 40 percent or more.

In the study, " the beneficial effects [of saturated fats] were the

greatest in women with the lowest fat intake overall, " Mozaffarian

points out.

He speculates that similar antiplaque benefits might also have

occurred if the women had eaten more heart-friendly monosaturated

fats, such as in canola and olive oils, in place of the saturated

fats, so long as overall fat intake was low.

Dietary mystery

What interplay of factors affected plaque formation among the

menopausal women in the study is a " paradox " that can't be fully

explained, lipid experts Knopp and Barbara Retzlaff of the

University of Washington in Seattle acknowledge in an editorial

accompanying the published study.

Knopp says the answer probably lies in the specific combination of

characteristics of the women in the group.

Most of them, he notes, were " sort of a model for metabolic

syndrome " —a set of physiological conditions that puts a person at risk

of diabetes and other diseases involving problems processing insulin.

Furthermore, he points out, two-thirds of the women were taking

hormone supplements.

Mozaffarian says the study highlights the complex way in which dietary

fats interact, which is not well understood. " Fats are not just inert

metabolic substances, they have wide-ranging metabolic effects in the

body, and these effects are different for different kinds of fats, " he

says.

Also, he says, " there's greater appreciation today of the fact that

the effects of dietary nutrients are different in different people. "

The researchers were " initially surprised by the findings, but not so

much so " after considering possible explanations, Mozaffarian says.

Results of studies of saturated fat intake and coronary artery–disease

risk have been inconsistent. And most of those studies have focused on

men, while the effects of diet on heart disease may differ in men and

women.

The volunteers in the Harvard dietary study were a subset of women

from six cities who were enrolled in a randomized trial designed to

evaluate whether hormone replacement therapy curbs atherosclerosis.

The results, which showed that female sex hormones did not prevent

coronary artery disease in the postmenopausal women, were " a great

disappointment, " Knopp and Retzlaff note.

References:

Knopp, R.H., and B.M. Retzlaff. 2004. Saturated fat prevents coronary

artery disease? An American paradox. American Journal of Clinical

Nutrition 80(November):1102-1103. Available at

http://www.ajcn.org/cgi/content/full/80/5/1102.

Mozaffarian D., E.B. Rimm, D.M Herrington. 2004. Dietary fats,

carbohydrate, and progression of coronary atherosclerosis in

postmenopausal women. American Journal of Clinical Nutrition

80(November):1175-1184. Abstract available at

http://www.ajcn.org/cgi/content/abstract/80/5/1175.

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