Friday August 21 2009
Fast food is thought to be high in oxycholesterol
“A form of junk food cholesterol virtually unknown to the public may pose the biggest threat of heart disease,” according to The Daily Telegraph. The newspaper says that oxycholesterol, formed when cholesterol combines with oxygen, “gives an extra boost to blood cholesterol levels and is more likely to damage arteries than ordinary cholesterol”. There are high levels of the substance in fried food, processed food and take-aways, The Daily Telegraph's article on oxycholesterol says.
This news comes from the results of animal experiments presented orally at a scientific conference in the US. The research is not yet available in print. In these experiments the scientists heated cholesterol to oxidise it, and added it to the feed of 20 hamsters out of a group of 50.
While it appears the substance was harmful in the doses given to hamsters, it is an assumption to suggest that these amounts of oxycholesterol are found in burgers or that it would have the same effect in humans. These claims do not appear to be supported by the available scientific evidence.
What is oxycholesterol?
Oxycholesterol is formed when foods containing cholesterol, such as steaks and burgers, are fried or grilled. The cholesterol these foods contain reacts with oxygen to form oxidised cholesterol, also known as oxycholesterol. Saturated and unsaturated fats in fried foods react with oxygen in a different way.
The other types of non-oxidised cholesterol are better known. For example, elevated levels of total cholesterol and LDL cholesterol (often called "bad" cholesterol) can increase the risk of heart attacks, whereas high levels of HDL cholesterol have a protective effect.
How does oxycholesterol affect you?
It is not yet known how oxycholesterol affects humans. These scientists say that they do not yet know whether statins, the commonly prescribed anti-cholesterol drugs, lower oxycholesterol.
Where did this study come from?
This study was conducted by Dr Zhen-Yu Chen and colleagues from the Food and Nutritional Sciences Programme at the Chinese University of Hong Kong. Funding was provided by the Hong Kong Grant Research Council.
The study was presented orally at the 238th American Chemical Society’s national meeting in Washington, DC this week.
What did the scientists do and find?
The scientists measured the effects of a diet high in oxycholesterol on 50 hamsters, which were divided into five groups of 10. They prepared oxycholesterol by heating pure cholesterol at 160ºC in air for 72 hours, and then added this oxycholesterol to hamster feed. They compared two strengths of this test feed with two strengths of non-oxidised cholesterol feed and with a control feed without either cholesterol. The strengths of the cholesterol mixture chosen were 0.05% and 0.10%.
Blood serum levels of total cholesterol in the two groups of hamsters that were fed oxidised cholesterol increased more than in the two corresponding groups that were fed ordinary cholesterol (P<0.05). This increase was 12% in those fed the lower-strength mixture and 22% in those fed the higher-strength mixture.
There were larger atherosclerotic plaques (fatty deposits) and deposits of cholesterol in the aortas of hamsters fed oxycholesterol than in those of the hamsters fed non-oxidised cholesterol. These fatty deposits are found in humans and increase the risk for heart attack and stroke.
What did the scientists say?
The scientists say that antioxidants can counter these effects and may block the process of oxidation that forms oxycholesterol. Good sources of antioxidants include fruit, vegetables and beans.
The researchers went on to say that fast food raises oxycholesterol, and that foods containing wholegrains, fresh fruit and vegetables, seeds and nuts are healthier.
How reliable is this research?
This small animal study cannot yet be fully assessed as it has not yet been published in full or peer-reviewed. Even if this is a valid study it is important to assess how relevant it might be to humans.
- The feeding of relatively large doses of oxidised cholesterol to animals may produce changes similar to the atherosclerosis found in humans; however, it will be important to compare the doses used in these animal experiments with the levels found in human food.
- Cholesterol metabolism is complex, and the oxidation of cholesterol in this experiment (heating to 160ºC) may not reflect a biological process that occurs in humans.
- Healthy foods may be healthy due to constituents other than antioxidants and unhealthy food may be unhealthy because of such things as saturated fats. Searching for a single constituent for either a benefit or a harm, is likely to be unrewarding.
Overall, this orally presented study will need to be followed by publication and human research before any reasonable conclusions can be reached with regard to the role of this “new” cholesterol. In light of this, the headlines based on this science and news release seem overstated.
Too much cholesterol in the body causes coronary disease such as angina, heart attack and stroke. Dr Jonathan Morrell explains who is at risk and the treatments available.
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