New study details the saturated fat/cholesterol link
provided by American Heart Association
hether you are male or female, black or white, old or young, taking fat out of your diet will lower blood cholesterol levels and reduce the risk of a heart attack or stroke, according to a study in the March 1998 issue of Arteriosclerosis, Thrombosis, and Vascular Biology: Journal of the American Heart Association. The study's authors say they are the first to show in a single study that there is a uniform response on cholesterol levels from cutting out fat in the diets of people of different ages, ethnic backgrounds, races and gender. The study also revealed several unexpected and disconcerting responses to lower-fat diets. Blood levels of high-density lipoprotein, HDL, which can lower the risk of heart disease, also fell, although the declines in black people and older white men were less affected.
Cholesterol, a pearly fat-like substance found in animal fats and oils, can collect inside the blood vessels, causing obstructions that may set the stage for a heart attack or stroke. Cholesterol is transported through the blood on "carriers" called lipoproteins. Low-density lipoprotein, LDL, is called the "bad" cholesterol because it takes cholesterol to the blood vessel walls. HDL, the "good" cholesterol carries cholesterol to the liver and away from the blood vessels.
The study tested the American Heart Association and the National Cholesterol Education Program Step 1 and Step 2 diets on reducing cholesterol. LDL dropped about one percent for every one percent drop in saturated fat calories, says lead author Henry N. Ginsberg, M.D., professor of medicine and head of the division of preventive medicine and nutrition at Columbia University College of Physicians and Surgeons in New York City.
Step 1 and Step 2 diets are for treatment of high blood cholesterol. Initial dietary recommendations for patients on Step 1 are similar to those advocated by the AHA for the public. For those already on the Step 1 diet, further reductions in saturated fat and cholesterol Step 2 should achieve more cholesterol lowering.
The Step 1 diet contains 30 percent or fewer calories from fat, with no more than eight to ten percent from saturated fat. Cholesterol intake is 300 milligrams a day or less. The Step 2 diet reduces saturated fat to seven percent and total cholesterol to 200 milligrams a day or less.
Total cholesterol fell for the whole group by 5 percent on the Step 1 diet and 9 percent on the Step 2 diet. LDL averaged 7 percent lower when people ate the Step 1 diet and 11 percent lower on the Step 2 diet. These kind of reductions may translate into a 15 to 20 percent reduction in risk of coronary heart disease, say the researchers.
Other studies, particularly those comparing countries with different diets and culture, have indicated that lower HDL cholesterol concentrations in populations consuming low-fat diets do not lead to an increased risk of coronary heart disease, the cause of heart attacks. "HDL declines whenever you remove saturated fat from the diet," Ginsberg explains. "The question of whether this drop in HDL might affect heart risk remains open," he says, "but no one questions the value of lowering LDL." To their surprise, the researchers found that blood levels of lipoprotein (a) a cousin to LDL that at elevated levels appears to increase the risk of coronary heart disease went up 15 percent as saturated fat fell from 15 percent of calories to 6 percent of calories. "On face value, it would appear this is not the best thing to happen," Ginsberg acknowledges. "We know that lowering LDL is good for you. We don't know exactly what it means when you eat a low-fat diet and your lipoprotein (a) levels go up. We need to look at this more closely with further studies."
Triglycerides, another fatty substance associated with increased heart risk at high levels, rose about 10 percent on the American Heart Association Step 1 diet in comparison to the average American diet, but showed no further rise when people ate the low-saturated fat diet, Ginsberg says. The lipoprotein (a) and triglycerides findings aside, Ginsberg sees the lower-fat diet as a healthier diet. "The message is unchanged. Follow the American Heart Association recommendations and take the saturated fats out of your diet and eat more fruits and vegetables," he says.
Researchers at four medical centers Columbia University, Pennington Biomedical Research Center, Penn State University and University of Minnesota each recruited 25 to 30 healthy individuals with normal concentrations of blood fats. Of the 103 volunteers who completed the study, 46 were men and 57 women, ranging in age from 22 to 67 years old. Thirty percent of the women and 20 percent of the men were black. Eighteen of the women were postmenopausal and 16 of the men were 40 or older. The volunteers ate three different diets for eight weeks each, although not in the same order, with a break of four to six weeks between each diet.
In the average American diet, 34.3 percent of the calories came from total fat and 15 percent from saturated fat. In the American Heart Association Step 1 and Step 2 diets, the calorie counts were 28.6 percent and 25.3 percent total fat and 9 percent and 6.1 percent saturated fat. Carbohydrates replaced the calories lost by reducing the fat content in the two lower-fat diets. All three diets contained 300 milligrams a day of cholesterol. Blood fats were measured weekly during the final four weeks on each diet.
"This is really the gold standard study," Ginsberg says. "No study had ever monitored the chemical nutrient makeup of the diet on an ongoing basis throughout. We were sending weekly samples to a laboratory to make sure the diet was on target the entire way." Most dietary-fat studies have included young middle-aged white males, but no one knew for certain if these findings about fat held true for other groups. Some small studies suggested men might respond differently from women and blacks differently from whites. "Now we can say that when you lower saturated fat in the diets of healthy people, it doesn't matter how old you are or if you are black or white, a man or a woman," says Ginsberg. "Everybody in our field could have predicted our results in terms of lowering cholesterol, LDL cholesterol in particular, as we lowered saturated fat in men," Ginsberg says. "However, they would have been really guessing if they had said this would happen in postmenopausal women exactly as it happens in premenopausal women or that it would happen in blacks exactly as it happens in whites. The data weren't there."
|Contact: Carole Bullock (214) 706-1279 or Brian Henry (214) 706-1135. For copies of the study, please telephone: (214) 706-1173.|