Twin Study Shows Genes Have Major Clout Over Cholesterol Levels

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Twin Study Shows Genes Have Major Clout Over Cholesterol Levels

By Katrina Woznicki, MedPage Today Staff Writer

Reviewed by Jasmer, MD; Assistant Professor of Medicine,

University of California, San Francisco

July 08, 2005

MedPage Today Action Points

* Advise patients that while cholesterol can be managed with

medication, diet and exercise, the findings from this study suggest

that genes may be the overriding factor in determining cholesterol

responses to lifestyle changes.

Review

BERKELEY, Calif., July 8-When it comes to cholesterol, the genes reign

supreme. So suggests a study of identical twins with diverse

lifestyles-one a health enthusiast and the other a couch potato.

The researchers found nearly identical LDL cholesterol responses to

high-fat and low-fat diets when they looked at 28 pairs of monozygotic

male twins where one brother was a regular runner and the other lived a

sedentary lifestyle. The findings were published in the July 8 issue of

American Journal of Clinical Nutrition.

Exercise, said , Ph.D., a researcher at Lawrence Berkeley

National Laboratory here, did not appear to be a major influence. If

one twin could eat a high-fat diet without increasing his LDL

cholesterol, then so could his brother. But if one of the twins' LDL

cholesterol shot up when on the high-fat diet, the brother's did too.

The vigorously exercising brothers ran an average of 50 km per week.

All participants had blood drawn at baseline. Then for six weeks the

twins were randomly placed on a diet that consisted of 40% fat and 45%

carbohydrates or a diet of 20% fat and 65% carbohydrates. After six

weeks, the participants switched diets.

Fifteen pairs of twins started out with the high-fat diet while the

remaining 13 pairs started off with the low-fat diet. To ensure dietary

compliance, participants were phoned weekly, and even their grocery

receipts were reviewed.

Blood samples were taken again after the first six weeks of dieting and

then again after the second diet had been completed. Prior to having

their blood drawn, all participants abstained from food and exercise

for up to 14 hours.

Despite the twins' different levels of physical activity, the study

results showed dietary changes produced " significantly correlated

changes (P<0.05) in the twins' total cholesterol (r=0.56), " Dr.

and colleagues reported.

The subjects showed a 0.7 correlation in responses to the two diets,

indicating that no matter which diets the brothers were on, their

reactions to the diet, whether positive or negative, were almost equal.

A zero correlation would signal no relationship between the brothers'

reactions to the diets while 1.0 would indicate their reactions were

identical.

" The strongest correlation between the running and sedentary twins'

lipoproteins was the correlation in the LDL-cholesterol response when

switching from a high fat to a low-fat diet, (r=.70) " the investigators

wrote.

The study also found correlated changes were both r=0.49 for both

apoliprotein A-1 (g/L) and lipoprotein. The correlation between the

twins' lipoprotein changes " could not be attributed to concordance in

their adherence to the dietary protocol, " the investigators reported.

" The correlations for changes in percentages of energy from protein and

carbohydrate and dietary cholesterol were all non-significant (0.06² r

² 0.08) when switching from the high-fat, low-carbohydrate diet to the

low-fat, high-carbohydrate diet. "

The study results confirmed earlier suspicions that genes, not diet or

exercise, have the major effect on cholesterol.

" Our results suggest there are genes that strongly influence the

LDL-cholesterol response to diet, even in the presence of large

differences in physical activity, " the research team wrote. " These

genes appear to primarily affect the dietary response of the larger,

more buoyant LDL particles. "

People who carry the apo E e4 allele " experience greater reductions in

LDL cholesterolÉthan do those lacking the allele, " they said.

http://www.medpagetoday.com/Cardiology/Cholesterol/tb1/1325