Cholesterol in plants
The other pages in this series are in urgent need of updating
(and the information in this one needs to be checked in the light of all current textbooks).
The biochemical principles have not changed, of course, but textbooks have: some of
those that were current when I first prepared these pages in 2000 have appeared in new editions, and
others have ceased to be widely used. New books have appeared that are not discussed. Unfortunately
I do not have easy access to any of the commonly used textbooks, as I work in a research (not teaching)
environment in a country where English is not the everyday working language. I could buy them, of course,
but that would represent rather a large investment for the sake of a few web pages.
Accordingly
I should be grateful if someone would collaborate with me in the revision. If you have access to
all of the textbooks published in English in the past ten years (say 1996 or later)
that are commonly used for teaching biochemistry, and if you would like to
help, please contact me at acornish@ibsm.cnrs-mrs.fr.
Sterols in plants
Behrman and Gopalan (2005) suggest the following as an accurate account of the real sterol
content of plants:
More than 250 steroids have been described in plants. Of these, perhaps
sitosterol, which differs from cholesterol by an ethyl substituent at position 24, is the most
common. But plants also contain cholesterol both free and esterified. Cholesterol occurs as a
component of plant membranes and as part of the surface lipids of leaves where it is sometimes the
major sterol. The quantity of cholesterol is generally small when expressed a percent of total lipid.
While cholesterol averages perhaps 50 mg/kg total lipid in plants, it can be as high as 5 g/kg (or more)
in animals.
Examples of the problem
Textbooks typically assert that plants do not contain cholesterol, for example,
According to Horton et al. (2002, p. 275),
Cholesterol ... is only rarely found in plants.
Similarly, Zubay (p. 385) says that
Plant cells have no cholesterol.
Other books make statements that are partially correct. For example Voet and
Voet (2004, p. 389) follow a correct sentence by one that is more dubious:
Plants contain little cholesterol. Rather, the most common sterol
components of their membranes are stigmasterol and β-sitosterol.
Why does it matter?
Correct appreciation of the cholesterol content of different food components is important because
diets are often intended to control cholesterol intake, and need to be based on true information.
Although the cholesterol content of plants is typically much less than that of animals it is by no means
negligible: It can be as high as 5 g cholesterol per kilogram of total lipids in animals, but averages
about 50 mg cholesterol per kg of total lipids in plants, and is much lower than this average in
certain oils. For example olive oil typically contains 0.5–2 mg cholesterol per kg and
sesame oil about 1 mg cholesterol per kg. For designing diets it is also important to understand
that labelling laws in the USA (and probably elsewhere) allow amounts less than 2 mg per serving to be shown
as zero
.
Further reading
I am grateful to Dr E. J. Behrman, of the Ohio State University, for bringing this problem to
my attention. The information given here is based on the following forthcoming article:
E. J. Behrman and V. Gopalan (2005) Cholesterol and plants
J. Chem. Educ. in press.
Textbook checklist
The list is not complete, because not all the textbooks referred to on other pages have been checked,
and those that have been checked are in some cases of more recent publication than those referred to on
other pages.
Other common errors in textbooks
List of books considered
