It seems like there is more
misinformation being spread about nutrition and natural medicine than
about any other biomedical science. With the drug industry conducting
questionably designed research (or interpreting research in a biased way) and
circulating their anti-natural medicine con-clusions in press releases that
the media is all too happy to turn into a story; with the hawkers of questionable
nutritional products exaggerating the benefits of those products or the strength
of the evidence supporting their use; and with some scientists or institutions
promulgating sensationalist inter-pretations of their research in order to
obtain publicity, many people are feeling like they are stuck in a strawberry
field where nothing is real.
Or perhaps, more appropriately, in a cornfield of dreams. One example of misinformation
is the FDA's recently approved qualified health claim that allows manufacturers
to state, "Very limited and preliminary scientific evidence suggests that
eating about one tablespoon (16 grams) of corn oil daily may reduce the risk
of heart disease due to the unsaturated fat content in corn oil." While
the approved claim includes an acknowledgment that there is only weak supporting
scientific evidence, it does not include an acknowledgment that the evidence
is pathetically weak and that the claim may be flat out wrong.
The idea that corn oil can prevent heart disease is based on a few small studies
(some conflicting) showing that substituting saturated fat with corn oil can
reduce serum cholesterol levels. While high serum cholesterol is a risk factor
for heart disease, it is only one of many. Corn oil may have certain deleterious
effects that outweigh its beneficial effect on serum cholesterol. For example,
corn oil contains a large amount of linoleic acid (an omega-6 fatty acid) and
virtually no omega-3 fatty acids. Consuming corn oil would tend to worsen the
excessive ratio of omega-6 to omega-3 fatty acids in the Western diet. A relative
deficiency of omega-3 fatty acids is believed to promote the development of cardiovascular
disease. In addition, because corn oil contains a large amount of unsaturated
fatty acids, cooking with corn oil would lead to the formation of heart-damaging
lipid peroxides.
One might debate which of these factors (i.e., serum cholesterol, omega-6/omega-3
ratio, or lipid peroxides) has the greatest influence on the risk of heart attacks
and heart disease-related deaths. However, such a debate may be unnecessary,
because there is already published research on the effect of corn oil on those
cardiac outcomes, research of which the FDA seems to be unaware. In a 1965 study
published in the British Medical Journal, 80 patients with ischemic heart disease
were divided into three groups. One group was advised to restrict intake of animal
fat (meat, milk, eggs, and butter), pastry, ice cream, and cakes, and received
a corn oil supplement. Another group was given the same dietary advice and received
an olive oil supplement. The amount of the respective oils consumed during the
study was approximately four tablespoons per day. The third group received no
dietary advice and served as a control group. After two years, the proportion
of patients who had died or experienced a myocardial infarction was nearly twice
as high in the corn oil group as in the control group (48% vs. 25%), even though
serum cholesterol levels fell significantly in the corn oil group and did not
change in the control group.1 The olive oil group fared only slightly better
than the corn oil group (and worse than the control group) in terms of death
rate and infarctions, but that is a discussion for another day. The adverse outcome
in the corn oil group, as compared with the control group, was of marginal statistical
significance (p < 0.10). However, the likelihood that the study failed to
detect a real benefit from corn oil was considered by the authors to be "extremely
remote."
If the FDA and the corn oil manufacturers that petitioned for the health claim
had examined all the evidence, then perhaps the result would have been not a
health claim, but a disease claim such as, "Very limited and preliminary
scientific evidence suggests that eating corn oil daily may give you a heart
attack and kill you."
Another bit of questionable information recently disseminated in the media is
the idea that cooking pizza at higher temperatures and for longer periods of
time is more healthful than cooking it at lower temperatures for shorter periods
of time, because the former results in the presence of higher concentrations
of antioxidants in the pizza. While the point about antioxidants may be true
(although it appears to be limited to whole wheat pizza, which very few people
eat), high-temperature, prolonged cooking destroys a wide range of beneficial
nutrients and leads to the formation of cardiotoxic advanced glycation end-products
and lipid peroxides. Cooking food at high temperatures also increases serum concentrations
of C-reactive protein, which is an independent risk factor for heart disease.
Thus, if the bulk of the evidence regarding high-temperature cooking points in
any direction, it is most likely in the direction of "don't do it."
Over the years, it has been my hobby to try to untangle misinformation. It is
my fervent hope that doing so will prevent the development of neurofibrillary
tangles.
Alan R. Gaby, MD
Note
1. Rose GA, Thomson WB, Williams RT. Corn oil in treatment of ischemic
heart disease. Br Med J. 1965;1:1531-1533.
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