How well your cholesterol levels will respond to a low-fat diet may very well be genetic. And people who are healthy and not prone to coronary heart disease may actually increase their chances of developing it if they consume an "extreme" low-fat diet.
The difference seems to be a matter of genetics, said Dr. Ronald Krauss, physician and visiting professor from the University of California, Berkeley, at the Utah Dairy Council's annual "Breakfast and Briefing" Wednesday. "We must incorporate genetic information into development of individualized dietary guidelines based on individual risk."Coronary heart disease is the leading killer in the United States. And while some risk factors, such as smoking, high blood pressure, high blood cholesterol levels and physical inactivity, can be modified, genetics seem to play a strong role in what works and what can actually do harm.
For a long time, scientists have told people who have high cholesterol to reduce their saturated fat intake. Now research has shown that not everyone benefits from that diet. And some individuals might be harmed.
Here's how Krauss and others explain the difference:
The goal is to reduce the bad cholesterol, low-density lipoprotein (LDL), and to increase the good cholesterol, high-density lipoprotein (HDL). But scientists have decided that a person's genetically determined LDL subclass pattern, A or B, decides how blood lipoprotein responds to dietary changes.
Pattern A folks have "large, buoyant" LDL particles and are at low risk of developing coronary artery disease. Pattern B folks, on the other hand, have mostly small, dense LDL particles and a high risk of both coronary artery disease and myocardial infarction.
Pattern B folks thrive on the low-fat diet. But it has been shown, in a very short period of time, to convert some of the people who were healthy Pattern A types to the more artery-clogging, heart-disease prone Pattern B. The ones who converted apparently had a susceptibility inherited from a parent who was Pattern B.
They're not sure why it seems to work that way, but several studies have reached the same conclusion, Krauss said.
"We don't fully understand how factors like cholesterol are affected by genes and diet," he said. "We are all different in how we respond to different diets and we don't know how genes influence the response. But they do."
That's not to say that genetics are the only thing that's important, according to Krauss. Diet, exercise and other factors all have an effect. It's possible that what an individual eats regularly, for instance, can trigger the inherited susceptibility.
There's no evidence for healthy individuals that a very low-fat diet does anything positive, Krauss said. And it seems to convert some people from the more healthy Pattern A to the more dangerous Pattern B, which is not a good thing.
"If you're a Pattern A and have a Pattern B parent, you'd better be very careful about going on a low-fat diet."
One size, he emphasized, doesn't fit everyone when it comes to genetics, diet and cardiovascular health.