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Genes key in how diet affects cholesterol levels

July 12, 2005

By Amy Norton

NEW YORK (Reuters Health) – Anyone who has ever renounced
dessert and failed to be rewarded with low cholesterol levels
may be able to blame it on genetics, a new study suggests.

The study of 28 pairs of male twins — one a lean athletic
type, the other a bit rounder and sedentary — found that
brothers tended to show the same cholesterol response to
high-fat and low-fat diets, even though their exercise habits
were starkly different.

Because identical twins share the same genetic makeup, the
findings point to the importance of genes in determining how a
person’s cholesterol levels respond to diet and lifestyle
changes, according to the study authors.

It’s a well-known phenomenon that some people can eat
whatever they want yet stay thin and have normal cholesterol
levels, while others send up their cholesterol just by looking
at cheesecake. Likewise, some people with high cholesterol can
manage the problem by altering their eating habits, while
others need medication.

For those who fail to better their cholesterol profile with
diet, genes — rather than a lack of will — could be the
reason, said Paul T. Williams, a researcher at the Lawrence
Berkeley National Laboratory in California and the study’s lead
author.

He and his colleagues report their findings in the July
issue of the American Journal of Clinical Nutrition.

For the study, the researchers recruited 28 pairs of male
identical twins; in each case, one brother was an avid runner,
while the other tended to stay on the couch. The researchers
looked at the men’s cholesterol responses to each of two 6-week
diets — a high-fat diet where 40 percent of calories came from
fat, and a low-fat regimen with 20 percent of calories coming
from fat.

The study found a high degree of similarity in how
brothers’ LDL cholesterol (the “bad” form of cholesterol)
responded to the switch from the high-fat diet to the low-fat
one. On average, the men’s LDL declined on the low-fat diet,
but any individual’s response seemed to depend largely on
genes.

“What’s remarkable is that we found such a high
correlation” between twin brothers’ LDL responses, Williams
told Reuters Health. This suggests, he said, that “there’s a
lot to be found” in the hunt for genes that help regulate
cholesterol levels.

Scientists have identified a few genes that appear to be at
work, but these cannot explain the wide variance seen in
individuals’ cholesterol responses to diet changes, Williams
and his colleagues note.

In general, low-fat diets tend to lower LDL concentrations,
but can also decrease “good” HDL cholesterol and raise
triglycerides, another type of blood fat. So cutting dietary
fat may not have a net benefit, depending on the individual.

If researchers can uncover the genes that govern
cholesterol responses, Williams said, then it may be possible
to identify people who are “good candidates” for dietary
management of high cholesterol, and those who may need to try
medication sooner.

Other research, Williams noted, has shown that a person’s
response to cholesterol medication may also depend on genes.

SOURCE: American Journal of Clinical Nutrition, July 2005.