If you're convinced that everything you eat immediately turns into artery-clogging goo, a new study may confirm your suspicions. In the midst of the current holiday gorge-a-thon comes the news that dieting to control cholesterol doesn't work for everyone.
Research conducted at the University of Texas Southwestern Medical Center in Dallas showed that people eating similar diets may have a wide variation in their cholesterol levels and that genes play a major role in the effectiveness of an unsaturated fat diet.
"The study demonstrates that there are people who, despite being very careful, can't overcome their genetic predisposition," said Dr. Ronald M. Krauss, head of the molecular medicine department at Lawrence Berkeley National Laboratory at UC Berkeley.
This genetic trait is found in about 15% to 20% of Americans, according to Krauss, who had done pioneering research suggesting a correlation between genetics and cholesterol levels.
In the study of 46 families, the researchers contracted with a local bakery to produce cakes, cookies, brownies and bread that had either butter, a saturated fat, or margarine, an unsaturated fat. Then the researchers followed the families, who used either the butter products or margarine products, for five weeks.
Most of the people on the margarine diet achieved an average drop of 10% in their LDL cholesterol (low-density lipoproteins). This so-called bad cholesterol sticks to the walls of blood vessels, contributing to the blockages in blood flow that trigger heart attacks and strokes. But a small number of participants had no appreciable change.
Strikingly, 40% of the children in the study had the same response to the diets as their parents, said Dr. Margo A. Denke, one of the study's coauthors.
The high familial correlation among those who responded to dietary changes and those who didn't suggests there's a significant genetic component to these dietary variations.
For the virtuous souls whose cholesterol levels remain stubbornly high in spite of their most strenuous efforts, this comes as a vindication of sorts. Now they won't have to endure the gimlet-eyed stares of their doctors who don't believe they're really sticking to a heart-safe regimen. For them, diet and exercise aren't enough to keep down cholesterol; they may need to take medication to counteract their genes.
"Right now, we use the buckshot approach and put everybody on the same therapy," said Dr. Howard N. Hodis, director of atherosclerosis research at USC. "But one size doesn't fit all, and research like this helps us to understand differences in people's genetic makeup so we can better calibrate combinations of diet, drugs and exercise to prevent heart disease."
What's more, this study also illuminates the fact that just because someone is vigilant about diet doesn't guarantee that he or she will be immune to heart disease.
"Heart attacks can occur in people who follow a perfect lifestyle because a lot of the risk of heart disease is genetic," said Dr. Gregg C. Fonarow, an associate professor of medicine at UCLA. Unfortunately, adds Krauss, "people who have a cholesterol problem very often have this genetic disorder too."
So are those who were dealt a bad genetic hand just wasting their time skimming fat from their diets? Can they guzzle fat-laden eggnog with guilt-free abandon? "That's what people would like to do--just say they take after their mother, so it isn't their fault," Denke said.
She points out that the study also found we're not totally at the mercy of our genes: Overweight people on the unsaturated fat diet didn't experience the same drop in cholesterol levels as those of normal weight. "Environment is still important," Denke said. "People who were overweight had a double whammy: They were less responsive to the diet and also had higher cholesterol levels." This was true for the kids too, even those who were only five to 10 pounds overweight.
Shedding excess weight, even as little as 10 pounds, can cut down cholesterol from dangerously high levels, and boost the effectiveness of low-fat diets.
But we now have a better handle on why one person can wolf down Big Macs with relative impunity while someone else who consumes the same diet can have arteries that are as clogged as the 405 during rush-hour. Life simply isn't fair--and now we have scientific proof.