Diet, fats and cholesterol

Part 2: Oxidised LDL and plant sterols

It has long been known that LDL, itself, is not the problem. The problem with atherosclerosis occurs when LDL is oxidised. But LDL is NOT cholesterol, it is merely a vehicle which carries cholesterol - as well as fatty acids, proteins and other sterols. This is an important distinction as the cholesterol in LDL turns out not to be the causal factor.

Because cholesterol is found only in animal products, more and more people have been turning away from meat and towards eating foods from plants. But chole -sterol is only one of a whole family of sterols. Cholesterol is found only in animals; the other sterols are found in plants. Dr J Plat and colleagues at Maastricht University's Department of Human Biology in the Netherlands, say that these plant sterols may actually be more important in heart disease than cholesterol. Because plant sterols are structurally related to cholesterol, Plat and colleagues examined whether oxidized plant sterols ( oxyphytosterols ) could be identified in human blood and soya-based fat emulsions. They could: Approximately 1.4% of the plant sterol, Sitosterol, in blood was oxidised. This may not seem very much, but it is 140 times as much as the 0.01% oxidatively modified cholesterol normally seen in human blood. The same was also found in two soya emulsions.[1]

If any sterols are to blame, plant sterols are much more likely candidates than cholesterol because the popular idea that animal products, specifically protein, cholesterol, and saturated fatty acids, somehow factor in causing atherosclerosis, stroke, and/or heart disease is not supported by any available data, including the field of lipid biochemistry.[2 - 5]

On this point, it is interesting that Dr Ancel Keys, whose 1953 hypothesis began the fatty-diet-causes-heart-disease dogma did not recommend cutting down on animal fats. He recommended cutting vegetable oils.

Oxidised LDL

Where the problem with LDL lies is when fatty acids that are transported with LDL are attacked by oxygen and oxidised.[6] In 2004 a study was conducted with patients eating two different diets.[7] Both had reduced total fat and saturated fat intakes and increased polyunsaturated fat intakes. Conventional wisdom says that these revised diets should be 'healthier'. In fact, what happened was that the levels of oxidised LDL in the bloodstream rose in both - by 27% and 19%. Another contributor to heart disease, lipoprotein (a), also rose by 7% and 9%.

Polyunsaturated fatty acids

Fatty acids come in a variety of lengths. As the chain length of a fatty acid increases, it acts more and more like an oil which will not mix with water or blood. Short and medium chain fatty acids will mix in blood; they exit the intestine bound to the protein, albumin, whereas long chain fatty acids with more than 12 carbon atoms do not mix and must be transported in lipoprotein carriers.

LDL is used to transport these long-chain fatty acids. LDL is only likely to be 'bad' if you eat a large proportion of 'healthy' polyunsaturated oils. This may be why, in a 10-year study of fats and the numbers of heart events, researchers found that only polyunsaturated fats significantly increased heart disease.[8]

References

1. Plat J, et al. Oxidized plant sterols in human serum and lipid infusions as measured by combined gas-liquid chromatography-mass spectrometry. J Lipid Res 2001; 42: 2030-2038.
2. Ravnskov U. The Cholesterol Myths. New Trends Publishing Inc, Washington DC, 2000. p 109.
3. Enig M. Know Your Fats: The Complete Primer on Fats and Cholesterol . Bethesda Press; Maryland, 2000, 76-81.
4. Smith R, Pinckney E. Diet, Blood Cholesterol, and Coronary Heart Disease: A Critical Review of the Literature. Vector Enterprises, California, 1991
5. George V. Mann, ed. Coronary Heart Disease: The Dietary Sense and Nonsense. Veritas Society; London, 1993.
6. Cherubini A, et al. The VASA Study Group. High vitamin E plasma levels and low low-density lipoprotein oxidation are associated with the absence of atherosclerosis in octogenarians. J Am Geriatr Soc 2001; 49: 651-4
7. Silaste M-L, et al. Changes in Dietary Fat Intake Alter Plasma Levels of Oxidized Low-Density Lipoprotein and Lipoprotein(a). Arterioscler Thromb Vasc Biol. 2004; 24: 498-503.
8. McGee DL, et al. Ten year incidence of coronary heart disease in Honolulu Heart Programme - Relationship to nutrient intake. Am J Epidemiol 1984; 119: 667-676.

for more on cholesterol and heart disease, see Cholesterol-and-Health.org.uk