Dietary fat intake and prevention of cardiovascular disease: systematic review
BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7289.757 (Published 31 March 2001) Cite this as: BMJ 2001;322:757All rapid responses
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EDITOR- The findings of the systematic review by Hooper et al [1] do
not justify their support for a “central role of dietary fat intake in the
causation of cardiovascualar disease”, and implicitly in its prevention.
Instead, they should have referred to the alternative dietary hypothesis
on milk and lactose. [2-5] The challenge for researchers was well
expressed by Artaud-Wild et al: “The strong association of milk and many
of its components with CHD mortality, both before and after adjustment for
CSI [Cholesterol-Saturated Fat Index], suggested that something about milk
must be strongly related to CHD mortality”.[4]
That challenge should now be met by a randomised comparison of a
lactose (and galactose) free diet with a diet of reduced and modified fat
intake.
Jeffrey J Segall
general practitioner (retired)
London NW2
1. Hooper L, Summerbell CD, Higgins JPT, Thompson RL, Capps NE, et
al. Dietary intake and prevention of cardiovascular disease: systematic
review. BMJ 2001;322:757-63.
2. Wells WW, Anderson SC. The increased severity of atherosclerosis
in rabbits on a lactose-containing diet. J Nutr 1959;68:541-49.
3. Segall JJ. Is milk a coronary health hazard? Br J Prev Soc Med
1977;31:81-5.
4. Artaud-Wild SM, Connor SL, Sexton G, Connor WE. Differences in
coronary mortality can be explained by differences in cholesterol and
saturated fat intakes in 40 countries but not in France and Finland. A
paradox. Circulation 1993;88:2771-79.
5. Segall JJ. Epidemiological evidence for the link between dietary
lactose and atherosclerosis. In: Colaco CALS, ed. The glycation hypothesis
of atherosclerosis. Austin TX: Landes Bioscience, 1997:185-209.
Competing interests: No competing interests
Put it like this: The pills are labeled thusly, "This pill will
produce DEATH in exactly 5 years and 5 minutes". Then the pill label is
removed and each of a population swallows a pill and goes merrily on his
way. The population is monitored each week for a long while,--over a two
year period, say, or three years, or four. All is well! Alas, not one has
expired. The pills are harmless! Tobacco, asbestos, liberal laws and
courts, etc. The problem is one of degradation, and only when the
critical zone is reached do the visible results begin to appear. 5 yr, 6
min.? Health is in shades of gray, and symtoms often lag---
Just a Consumer
Competing interests: No competing interests
Dear Editor
It is disappointing to see how little real health benefit is gained
by the efforts of medical professionals to persuade their patients to
reduce their dietary intake of fat.
Coronary heart disease was almost unknown in the 19th century. The
emergence of coronary heart disease as a major cause of death in developed
nations in the 20th century may have many causes. However, it could be
argued that the rise in incidence of coronary heart disease follows some
20-30 years after the rise in the consumption of refined carbohydrates,
particularly sugar. We know that many of the conditions associated with
coronary artery disease (diabetes, hypertension and obestity)are
associated with insulin resistance.
Perhaps we are looking in the wrong direction. Could the dietary
villian be refined carbohydrates?
Competing interests: No competing interests
In spite of the trivial findings Dr Hooper and his coworkers
concluded that their meta-analysis of the cholesterol-lowering dietary
trials supports ”a central role of dietary fat intake in the causation of
cardiovascular disease”.1 This surprising conclusion is based on a
borderline significant improvement of the combined cardiovascular events,
and a subgroup analysis showing a significant improvement of the same
outcome in five trials of more than two years duration. These effects may
rather be due to bias. Most of the trials reviewed by Dr. Hooper et al
were open or single-blind. It is widely acknowledged that such trials are
prey to bias, and had they been drug trials they would never have been
accepted by any major medical journal to-day. The only double-blind
dietary trial with a favourable outcome for cardiovascular events was the
Veterans Administration Trial, but that trial was biased by a
significantly larger number of heavy smokers in the control group.2
Another disquieting finding was the higher degree of atherosclerosis at
autopsy in the treatment group, certainly not in support of a beneficial
effect of dietary intervention.
The only outcome free of bias is total mortality. The mean weighted
rate ratio for that event was close to one in all subgroups, indicating
that dietary fat intake has no importance, and this conclusion is
supported by numerous epidemiological studies. Dynamic population studies
of more than hundred time periods in 35 countries found no association
between change of animal fat consumption and change of coronary mortality;
twenty-seven cohort and case-control studies including more than 150,000
participants did not find any difference between the character of dietary
fat in coronary patients and control individuals; and four cohort studies
found no supportive associations between dietary fat and degree of
atherosclerosis at autopsy.3 Add to that the numerous cross-sectional
studies, most of which found no or even contradictory associations between
fat consumption and the morbidity and mortality of cardiovascular
disease.3
Trans fat, a product of the industrial hardening of vegetable oils
with many unfortunate effects on experimental animals, is the only type of
fat that consistently has been found to be consumed more often by coronary
patients.4 It is time to tell the populations that the dietary advices
they have received since many decades are not only ineffective, they may
even have adverse health effects.5
Uffe Ravnskov. MD, PhD
Magle Stora Kyrkogata 9,
S-22350 Lund, Sweden
1. Hooper L, Summerbell CD, Higgins JPT, Thompson RL, Capps NE, Davey
Smith G, Riemersma RA, Ebrahim S. Dietary fat intake and prevention of
cardiovascular disease: systematic review. BMJ 2001;322:757-63 (31 March)
2. Dayton S, Pearce ML, Hashimoto S, Dixon WJ, Tomayasu U. A controlled
clinical trial of a diet high in unsaturated fat in preventing
complications of atherosclerosis. Circulation 1969;40,suppl II:1-63.
3. Ravnskov U. The questionable role of saturated and polyunsaturated
fatty acids in cardiovascular disease. J Clin Epidemiol 1998;51:443-60.
4. Oomen C, Ocké MC, Feskens EJM, van Erp-Baart MAJ, Kok FJ, Kromhout D.
Association between trans fatty acid intake and 10-year risk of coronary
heart disease in the Zutphen Elderly Study: a prospective population-based
study. Lancet 2001;357:746-51.
5. Ravnskov U. The Cholesterol Myths. Washington: New Trends Publishing,
2000.
Competing interests: No competing interests
Let's revisit fat intakes achieved...
I have reviewed study and the extra Table describing the papers
included in the Hooper et al. review and I feel I must make some comments.
To me, the studies included seem to fall into at least three different
categories...
Firstly, some of the studies appear to have achieved only very modest
fat intake changes (ie. reduction of 3-5% total fat and 2-3% sat fat).
Secondly, some studies do not record dietary results achieved at all.
Thirdly, a few studies actually increased fat intake quite
substantially with additions of corn/olive oil supplements.
As noted in the article, follow-up times were indeed disapointingly
short... and this cannot be helped, but inclusion of studies with no
intake data and/or very modest or increased intake effects can be helped.
I would like to see the review analysed on the basis of achieved
dietary change. I suspect that including studies with missing intake
data, short follow-up times, and overall very modest diet effects all
conspire to attenuate the results. I am also of the belief that the
baseline fat intakes are, in general, far too high a starting point. At
the turn of the century in North America, the diets of affluent people
provided approximately 20% of calories in the form of fat...by todays
standards, these (formerly)average people would have a diet comparable to
the intervention group in your included study #27 with intakes of 18%
total/6% sat fat. A study by the way that did show a positive effect even
with only a 1.7 year follow-up.
Allan Sinclair, M.H.Sc.,
Manager of Health Services,
Public Health
Lakeland Regional Health Authority,
Alberta, Canada.
Competing interests: No competing interests