When it comes to heart-healthy eating plans, reducing fat intake may not be the only answer to keeping your cholesterol within limits.
A study of almost 200 people whose diets were strictly controlled shows that lowering saturated fat by replacing it with monounsaturated fat - such as olive or canola oils - could be just as effective as a very low-fat diet.
Called the DELTA study (Dietary Effects on Lipoprotein and Thrombogenic Activity), it ran from 1992 to 1996 at four geographically diverse universities using adult men and women, black and white, young and old. It is to date the most thorough study of dietary fats and fatty acids in which the food consumption was controlled.
In the study, which was run in two parts, the researchers provided all the meals and snacks for the participants. In the first part, 46 women and 51 men, a quarter of them African-American, were fed one of three different 2,000-calorie diets over eight weeks: an average American diet with 37 percent fat calories and 16 percent saturated fat; a 30 percent fat diet with 9 percent saturated fat; or a low-fat diet (26 percent) with 5 percent saturated fat.
The diets were changed for a second eight weeks, then changed again for an additional eight weeks so that each subject followed each diet.
When results were compiled, researchers found what they expected: Eating less saturated fat lowered both total cholesterol and low-density lipoproteins (LDL, the so-called “bad cholesterol”).
But on the negative side, high-density lipoprotein (HDL, the “good cholesterol”) levels also dropped and triglyceride levels went up. Triglycerides are fat molecules in the blood that, like cholesterol, may be associated with coronary heart disease.
The results, for the most part, were the same regardless of sex and race.
The second part of the study - using 85 men and women, 11 percent of whom were black - also included three different diets: the average American diet with 37 percent total fat, 16 percent saturated and 14 percent monounsaturated; a 30 percent fat diet with 8 percent saturated and 15 percent monounsaturated; and a high-monounsaturated diet with 37 percent total fat, 8 percent saturated and 22 percent monounsaturated.
These results showed drops in total cholesterol and LDLs for both the low-fat and high-monounsaturated diets. However, HDLs went up in the high-monounsaturated diet while they dropped in the reduced-fat diet. Triglycerides did the opposite.
What’s the message here?
“DELTA indicates that no single diet is optimal for everyone,” says Wahida Karmally, director of nutrition for the Irving Center for Clinical Research at Columbia University, one of the four universities involved in the study.
For some people, such as those with a carbohydrate sensitivity (insulin resistance), the study shows that lowering total fat could be more detrimental than substituting monounsaturated fat.