Phytosterols

Phytosterols (also called plant sterols) are a group of steroid alcohols, phytochemicals naturally occurring in plants. They are white powders with mild, characteristic odor, insoluble in water and soluble in alcohols. They have many applications as food additives, and in medicine and cosmetics.

Specific phytosterols

Uses

Plant structure

Plants contain a range of phytosterols. They act as a structural component in the cell membrane, a role which in mammalian cells is played by cholesterol.

Detection of organic matter

Due to its presence in terrestrial plant matter and only rare occurrence in unicellar algae, β-sitosterol can be used as a biomarker indicating the amount of terrestrially derived organic matter present in a sample. As these sterols are generally insoluble in water, they will partition onto suspended or settled solid matter (e.g. sediments). Due to grain surface area effects, muds will have greater concentrations by weight than sands or coarser grained sediments. To overcome this effect, ratios of individual sterols to total sterol content or cholesterol are usually used to indicate organic matter source.

Detection of adulteration

Presence of brassicasterol, together with auxiliary markers α-linolenic acid and erucic acid, is a marker of adulteration of soybean oil and sunflower oil with rapeseed oil. As there is no brassicasterol in sunflower and soybean oil, but its concentration in rapeseed oil is about 1400 mg/kg, the amount of rapeseed oil added can be calculated. [1]

Physiological Effects

As a food ingredient or additive, phytosterols have cholesterol-lowering properties (reducing cholesterol absorption in intestines).^[1] Phytosterols occur naturally in small quantities in vegetable oils, especially sea buckthorn oil (1640mg/100g oil),^[2] corn oil (968mg/100g),^[3] and soybean oil (327mg/100g oil).^[4] One such phytosterol complex, isolated from vegetable oil, is cholestatin, composed of campesterol, stigmasterol, and brassicasterol, and is marketed as a dietary supplement. Sterols can reduce cholesterol in human subjects by 10% to 15%.^[5]

The mechanism behind phytosterols and the lowering of cholesterol occurs as follows: the incorporation of cholesterol into micelles in the gastrointestinal tract is inhibited, decreasing the overall amount of cholesterol absorbed. This may in turn help to control body total cholesterol levels, as well as modify HDL, LDL and TAG levels. Many margarines, butters, breakfast cereals and spreads are now enriched with phytosterols and marketed towards people wishing to lower their cholesterol levels.

Researchers in Uruguay who conducted a small case cohort study suggested an association between dietary sterol intake and decrease risk for the development of gastrointestinal cancers; ^[6]; however, a subsequent large-scale study from the Netherlands reported that high dietary intake of plant sterols was not associated with a lower risk of colon and rectal cancers.^[7]

Caution about phytosterols is warranted. The main health concern are atherosclerosis and the vulnerable plaques which produce heart attacks, stroke, and other cardiovascular and cerebrovascular events. Evidence does not exist that lowering total blood cholesterol levels by any means is healthy, and there are no large clinical trials which verify the efficacy of phytosterols in reducing heart attack rates. Furthermore, there is some evidence that phytosterols can promote atherosclerosis, particularly in susceptible individuals.^[8]. A 2008 study conducted in Finland showed that sterols can accumulate in heart valves, suggesting that dietary sterols might increase the risk of aortic valve stenosis.^[9]

References

^ Ostlund RE, Racette, SB, and Stenson WF (2003). "Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ". Am J Clin Nutr 77 (6): 1385–1589.
^ Li, Thomas S. C.; Beveridge, Thomas H.J., Drover, John C.G. (1633-1639). "Phytosterol content of sea buckthorn (Hippophae rhamnoides L.) seed oil: Extraction and identification". Food Chemistry 101 (4): 1633–1639. Elsevier. doi:10.1016/j.foodchem.2006.04.033. Retrieved on 2006-11-20.
^ Pennington & Douglas, Food Values of Portions Commonly Used, 18th ed. (2005)
^ "The Marketing Edge: Phytosterols Qualisoy" (Brochure (PDF)). Qualisoy. Retrieved on 2006-11-20.
^ "Consumption of a Functional Oil Rich in Phytosterols and Medium-Chain Triglyceride Oil Improves Plasma Lipid profiles in Men" (Article (PDF)) . Journal of Nutrition (133): 1815–1820.
^ De Stefani, Eduardo, et al (2000). "Plant Sterols and Risk of Stomach Cancer: A Case-Control Study in Uruguay". Nutrition and Cancer 37 (2): 140–144. doi:10.1207/S15327914NC372_4.
^ "Plant sterol intakes and colorectal cancer risk in the Netherlands Cohort Study on Diet and Cancer" (2000). Am J Clin Nutr 74 (1): 141–148. Retrieved on September 27, 2008.
^ Patel MD, Thompson PD (May 2006). "Phytosterols and vascular disease". Atherosclerosis 186 (1): 12–9. doi:10.1016/j.atherosclerosis.2005.10.026. PMID 16325823.
^ "Accumulation of cholesterol precursors and plant sterols in human stenotic aortic valves." (2008). J Lipid Res 49 (7): 1511-8. Retrieved on September 28, 2008.

Contents