QuickTime Movie: Low-fat diet doesn't benefit everyone (5.6 MG) (You can view and hear this with Sparkle on a Macintosh; Simple Player on the Mac does not the play the sound.)
ANAHEIM, CA -- Before going on a stringent diet to try and lower their risk of heart disease, individuals should be aware of their overall heart disease susceptibility, according to medical researchers at the Ernest Orlando Lawrence Berkeley National Laboratory. Two new studies led by Ronald M. Krauss, M.D., head of the Berkeley Lab's Department of Molecular Medicine, suggest that only those at high risk significantly benefit from certain low-fat, heart-healthy diets.
"The benefit of major dietary changes may best be assessed by determining the individual's genetic and metabolic profiles," said Krauss. The findings were presented here this week at the American Heart Association's (AHA's) 68th Scientific Sessions.
In the studies presented at the AHA meeting, registered dietitian Dr. Darlene M. Dreon, from Dr. Krauss' group, investigated whether levels of low-density lipoprotein (LDL) in subjects with low amounts of small, dense LDL (pattern A) and those with high amounts (pattern B) respond differently to diets aimed at reducing heart disease risk.
Dreon and Krauss studied the dietary responses of 133 healthy men to determine the effects of replacing saturated fat with either carbohydrates or monounsaturated fats, such as olive and canola oil. The results showed that for both diets, the greater benefit was derived in the higher-risk pattern B subjects. Unlike the healthy pattern A men, the pattern B men experienced significant lowering of small, dense LDL. The monounsaturated fat diet also reduced levels of triglycerides and a protein called apoB, both of which are associated with increased risk of heart disease.
In a related study, Dreon and Krauss studied a group of 43 healthy men who reduced their dietary fat consumption in 10 percent increments from 40% to 20% by replacing fat with carbohydrates. They found that in the 30 pattern A men on the high fat diet, there was a relatively small reduction in LDL on the low-fat diets, whereas the pattern B group experienced significant, progressively greater reductions in levels of small, dense LDL as dietary fat content was reduced.
Krauss noted that the low-risk individuals who cut down their fat intake decreased their levels of high density lipoproteins ("good cholesterol"), while their levels of small, dense lipoproteins escalated.
"Healthy pattern A individuals in our study showed minimal beneficial effects in response to a reduced saturated fat diet, and in some cases, surprisingly, they experienced adverse changes that could conceivably increase their risk for heart disease," Krauss said.
Krauss and his associates were the first to develop a test that identifies heart disease susceptibility based on levels of a particularly pathologic form of LDL in the blood. Those with a predominance of small, dense versions of LDL--a submicroscopic particle that transports cholesterol through the bloodstream--tend to have a higher risk of heart disease than those with larger LDL.
"Within the next few years, specific tests for these genetically-influenced traits will provide more appropriate dietary guidelines for individuals to reduce their risk for cardiovascular disease," Krauss said, adding that the high-risk trait affects an estimated 25-30% of healthy men and 40-50% of men with heart disease.
According to Krauss, the latest studies emphasize the importance of working with a physician to determine one's risk of heart disease before embarking on a major dietary program.
The test for small, dense LDL developed by Krauss' group is already available for research purposes and a clinical version is currently being developed.
The Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, Calif. It conducts unclassified scientific research and is managed by the University of California.