12 July 2005
A BBC news item reports on a twin study of diet-related cholesterol levels. There is considerable variation between individuals in terms of their lipoprotein responses to low-fat diets, and previous studies have linked this to genetic differences. Researchers at the Berkeley National Laboratory in the US looked at 28 pairs of genetically identical male twins with significantly different exercise levels. Either one twin was sedentary whilst the other ran at least 32km a week, or if both twins ran then one ran at least 40km a week further than the other. Running twins ran on average 50 km/wk more than the sedentary twins and weighed significantly less, although twin pairs showed a high degree of correlation for body mass index and blood cholesterol levels despite their divergent levels of physical activity [Williams PT et al. (2005) Am J Clin Nutr 2005 82: 181-187].Each twin ate either a high fat or a low fat diet for 6 weeks, followed by six weeks on the opposite diet, with cholesterol levels monitored before and after each stage. The response to these changes in dietary fat was generally very similar for each member of a twin pair, especially for changes in low-density lipoprotein (LDL) cholesterol. Dr Paul Williams, who led the study, reportedly said: "If one of the twins could eat a high-fat diet without increasing his bad cholesterol, then so could his brother. But if one of the twins' LDL cholesterol shot up when they went on the high-fat diet, his brother's did too". The researchers concluded that there are strong genetic influences over responses to dietary fat that operate even where physical activity levels are markedly different, and proposed that around 50% of the variation in LDL cholesterol levels could be genetic in origin. People with high levels of cholesterol who do not respond well to changes in diet to lower cholesterol intake currently require medication such as statins to reduce their blood cholesterol; it is suggested that identification of key genes involved in the physiological response to dietary cholesterol might help doctors to design special diets that such individuals would respond to.