Over
forty years ago, from 1968 to1973, a double blind randomized controlled trial
called the Minnesota Coronary Experiment was performed to determine the effects
of lowering saturated fat on health. The British Medical Journal (BMJ) did a
re-evaluation of data from the experiment and published their results yesterday
in the article, “Re-evaluation
of the traditional diet-heart hypothesis: analysis of recovered data from
Minnesota Coronary Experiment (1968-73).”
The
experiment divided participants from one nursing home and six state mental
health hospitals in Minnesota into two groups. The first group was fed a
control diet, the standard hospital food at the time, which consisted of 18.5%
of calories as saturated fat and 3.4% of calories as linoleic acid. The second
group, ate an intervention diet which had a mean reduction in saturated fat by
about 50% (from 18.5% to 9.2% of calories) and a more than 280% increase in
linoleic acid intake (from 3.4% to 13.2% of calories).
The
hypothesis was that the intervention diet, which decreased saturated fat and
increased linoleic acid (mostly from corn oil), would (1) result in a reduction
of cholesterol levels and (2) result
in a reduction in death of the participants in this group. This study was done
when the prevailing wisdom was “that the serum cholesterol lowering effects of
replacing saturated fat with vegetable oil rich in linoleic acid will diminish
deposition of cholesterol in the arterial wall, slow progression of
atherosclerosis, reduce coronary heart disease events, and improve survival.”
The
results of the experiment show a 13.8% reduction in cholesterol in the
intervention group compared with just a 1% reduction in cholesterol in the
control group. However, unexpectedly, there turned out to be a correlation
between decreasing blood cholesterol and an increased risk of death in
participants who were 65 or older at the start of the study, specifically every
30 mg/dL decrease in cholesterol was associated with a 35% higher risk of death
from all causes. For participants under age 65 at the start of the study there
was no relation between the change in serum cholesterol and death. Furthermore,
of the 149 participants autopsied after death, twice as many participants in
the intervention group had at least one myocardial infarct as in the control
group.
From
1975-1989 this data was published multiple times in support of replacing
saturated fats with vegetable oil to reduce cholesterol and reduce the risk of
heart disease. Yesterday’s BMJ article was the first to report that the data
showed a relationship betweem reducing cholesterol was linked to an increase in
risk of death in participants over 65 years old.
The
BMJ article goes into possible reasons why this part of the analysis was
omitted, including that “the crude study results were clearly at odds with
prevailing beliefs”. And honestly I think that’s the most important take-away
from this re-evaluation published by the British Medical Journal. Unless we see
the actual data and all the analysis, we are at the mercy of the authors for
their interpretation of the results. In this case the authors were not
falsifying findings- they were just omitting findings that didn’t agree with
the original hypothesis. This is irresponsible and unfortunately it happens all
the time, including the debacle with Vioxx causing
heart attacks and misleading information about estrogen supplementation in
post-menopausal women in the Women’s
Health Initiative (WHI).
The
good news is that these days scientific articles are easy to access and thus
anyone can take a look at the actual data. In both the Vioxx and WHI studies
the information that later “surprised” everyone was in the data that was
published in scientific journals- it just wasn’t mentioned in the results or
conclusions. So, please, don’t just read the results and/or discussion and/or
conclusion sections. Take a look at the data (including charts, graphs and
tables) and draw your own conclusion(s). And unless you see the data for yourself, take anything you read about the data results with a grain of salt.
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