The study, which echo results from China last year, may have important implications for soy product manufacturers who may emphasise studies that have linked soy isoflavones to improved blood cholesterol levels.
However, this point is controversial and a recent scientific statement by the American Heart Association (AHA) in the journal Circulation concluded that soy had little effect on cholesterol levels, and raised doubts about health claims associated with soy.
The research, published recently in the International Journal of Food Sciences and Nutrition, looks set to muddy the waters further, and, if repeated in subsequent trials, could demand a refining of the 'soy for heart health' message.
The randomised, placebo-controlled, double-blind clinical study, led by Lars Hoie from Norway's NutriPharma in collaboration with researchers from the Karolinska Institute in Stockholm and the University of Potsdam, reports that consumption of a UHT soymilk led to increases in LDL-cholesterol levels of up to 20 per cent.
Raised LDL-cholesterol levels has been proposed to significantly increase the risk of cardiovascular disease, the cause of almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169 billion ($202 billion) per year.
According to the American Heart Association, 34.2 percent of Americans (70.1 million people) suffered from some form of cardiovascular disease (CVD) in 2002.
The researchers recruited 80 subjects with high cholesterol levels (hypercholesterolemia) and randomly assigned them to receive either an ultra-heat-treated milk containing a soy protein preparation containing 12.5 or 25 g soy protein or placebo (casein) everyday for four weeks. The researchers measured total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol levels.
"Unexpectedly, at the end of the study, low-density lipoprotein cholesterol concentrations were significantly increased compared with baseline in all study groups," wrote the researchers.
Hoie reports that the magnitude of LDL increase, ranging from 17 to 19 per cent observed from the soymilk groups was similar to the rise observed in the placebo group.
"Soy protein supplements previously shown to be effective in reducing serum cholesterol had in this study no such lipid-lowering effect after ultra heat treatment," concluded the researchers.
The research was welcomed by NutriPharma CEO, Trond Syvertsen, who said in a statement: "This unexpected result is a positive one for Nutri Pharma, as it confirms the effectiveness of our patented soy compositions to reduce cholesterol when included in non UHT-treated formats."
While additional study needs to be performed for other soymilks and other study populations, the results do appear to be in-line with results published last year by Chinese scientists from the South China University of Technology in Guangzhou.
The study, published in the Journal of the Science of Food and Agriculture (Volume 86, pp 1110-1114), investigated the effect of heat on degradation of three isoflavones - genistein, daidzein and glycitein - in soymilk processed over a range of temperatures and time, and reported that both pasteurization and UHT decreases the amount of isoflavones in soymilk.
Isoflavones are found in high concentrations in soybeans, and appear to act like the female hormone oestrogen. They have been widely researched for their potential to prevent diseases related to lower levels of this hormone, such as osteoporosis, breast cancer and prostate cancer.
Source: International Journal of Food Sciences and Nutrition Volume 57, Number 7-8, Pages 512-519 "Ultra heat treatment destroys cholesterol-lowering effect of soy protein"
Authors: L.H. Hoie, A. Sjoholm, M. Gulstrand, H-J.F. Zunft, W. Lueder,H-J. Graubaum, J. Gruenwald