Letters

Dietary fat intake and risk of stroke: Authors' reply

BMJ 2003; 327 doi: https://doi.org/10.1136/bmj.327.7427.1348-c (Published 04 December 2003) Cite this as: BMJ 2003;327:1348

The diet-heart idea is kept alive by selective citation

He
et al maintain that saturated fat is bad and polyunsaturated fat is good for the
cardiovascular system.1 They reject a large number of contradictory
epidemiologic and experimental studies2 by the argument that they are
inconsistent and inadequate. Instead they refer to a previous study from their
group.3 In that study the authors had calculated that a replacement
of 5% of energy from saturated fatwith the same amount of
polyunsaturated fat should be followed by a 50% lower risk of coronary heart
disease. They claimed that this calculation was supported by Sacks and Katan’s
review4 of four allegedly successful dietary trials.5-8
However, these authors had ignored four similar trials with a less favourable
outcome.9-12

Relevant
data from all eight trials are shown in the table (see below). As seen, the
accumulated relative risk of death in the four trials cited by Sacks and Katan
decreased by eight percent, but in the four trials that they had ignored, it
increased by nine percent, and the figures for coronary mortality was not much
better.2,13  Another
contradictory finding was that complicated atherosclerosis was significantly
more pronounced in the treatment group of the only trial that included a
post-mortem.
8

This
way of reviewing the literature is not unique. In a meta-analysis of all
controlled, randomised cholesterol lowering trials I found that trials
considered supportive were cited on average 40 times, but unsupportive trials
only seven times per year.14  Also,
in three of the most influential American reviews of the diet-heart idea, half
of a large selection of contradictory studies were ignored; 
the rest were quoted irrelevantly; or insignificant findings in favour of
the hypothesis were inflated; or unsupportive results were quoted as if they
were supportive.15 And in a recent letter in Science Scott Grundy,
one of the main figures in the cholesterol campaign, claimed that saturated
fatty acids are the main dietary cause of coronary heart disease, but the many
studies he used as support either had not addressed this question, or they were
inconclusive, or directly contradictory.
16

No
statistical operations are able to explain away the fact that an exchange of
saturated with polyunsaturated fats has no effect on mortality. This is also in
accordance with the findings of He et al. that intake of dietary fats are not
associated with the risk of stroke,17 and this is also what we should
expect because the idea that atherosclerosis in the coronary arteries should
have a different cause than atherosclerosis in the cerebral ones are highly
unlikely.

 References

  1. He
    K, Willett WC, Ascherio A. Dietary fat intake and risk of stroke. Authors'
    reply. BMJ  2003;327:1348-1349 [Full
    text
    ].
  2. Ravnskov
    U. The questionable role of saturated and polyunsaturated fatty acids in
    cardiovascular disease.
    J
    Clin Epidemiol

    1998;51: 443-60.
    [CrossRef][ISI][Medline]
  3. Hu
    FB, Manson JE, Willett WC.
    Types
    of dietary fat and risk of coronary heart disease: a critical review. J
    Am Coll Nutr
    2001;20: 5-19.[Abstract/Free
    Full Text]
  4. Sacks
    FM, Katan M. Randomized clinical trials on the effects of dietary fat and
    carbohydrate on plasma lipoproteins and cardiovascular disease. Am J Med
    2002;113(suppl 9B): s13-24.
    [CrossRef]
  5. Turpeinen
    O, Karvonen MJ, Pekkarinen M, Miettinen M, Elosuo R, Paavilainen E. Dietary
    prevention of coronary heart disease: The Finnish mental hospital study. Int
    J Epidemiol
    1979;8:99-118.
  6. Leren
    P. The effect of plasma cholesterol lowering diet in male survivors of
    myocardial infection. A controlled clinical trial. Acta Med Scand
    1966;(Suppl 466):1-92.
  7. Research
    committee to the Medical Research Council. Controlled trial of soya-bean oil
    in myocardial infarction. Lancet 1968;2: 693-700.
  8. Dayton 
    S, Pearce ML, Hashimoto S, Dixon WJ, Tomiyasu U. A controlled trial
    of a diet high in unsaturated fat in preventing complications of
    atherosclerosis.  Circulation 1969;40(suppl 2):1-63.
  9. Woodhill
    JM, Palmer AJ, Leelarthaepin B, McGilchrist C, Blacket RB. Low fat, low
    cholesterol diet in secondary prevention of coronary heart disease.
    Adv
    Exp Med Biol
    1978;109:317-330.
  10. Frantz
    ID Jr, Dawson EA, Ashman PL, Gatewood LC, Bartsch GE, Kuba K, Brewer ER.
    Test
    of effect of lipid lowering by diet on cardiovascular risk. The Minnesota
    Coronary Survey. Arteriosclerosis. 1989;9:129-35.
  11. Rose
    GA, Thomson WB, Williams RT. Corn oil in treatment of ischaemic heart
    disease. BMJ 1965;544:1531-3.
  12. Burr
    ML, Fehily AM, Gilbert JF, Rogers S, Holliday RM, Sweetnam PM, Elwood PC,
    Deadman NM. Effects of changes in fat, fish, and fibre intakes on death and
    myocardial reinfarction: diet and reinfarction trial (DART). Lancet.
    1989;2:757-61.
  13. Hooper
    L, Summerbell CD, Higgins JPT, Thompson R, Capps NE, Davey Smith G, et al.
    Dietary fat intake and prevention of cardiovascular disease: systematic
    review. BMJ 2001; 322: 757-763
    [Abstract/Free
    Full Text]
    .
  14. Ravnskov
    U. Cholesterol lowering trials in coronary
    heart disease: frequency of citation and outcome. BMJ 1992;305: 15-19. [Abstract]
  15. Ravnskov
    U. Quotation bias in reviews of the diet-heart idea.
    J
    Clin Epidemiol

    1995; 48: 713-9.
    [Abstract]
  16. Ravnskov
    U, Allan C, Atrens D, Enig MG, Groves B, Kaufman J, Kroneld R, Rosch PJ,
    Rosenman R, Werkö L, Nielsen JV, Wilske J, Worm N.
    Studies
    of dietary fat and heart disease. Science 2002; 295:1464-1465.
  17. He
    K, Merchant A, Rimm  EB, Rosner BA, Stampfer MJ, Willett WC, Ascherio
    A. Dietary fat intake and risk of stroke in male US healthcare professionals:
    14 year prospective cohort study. BMJ 2003 327: 777-782.
    [Abstract][Abridged
    text]
    [Full
    text]
     

Table. 
Total
mortality in eight cholesterol-lowering, controlled and randomised dietary
trials, where the only intervention was an exchange of saturated fats with
polyunsaturated fats.

 

Patients

(n)

T/C

SFA

(cal%)

T/C

PUFA

(cal%)

T/C

All
deaths

(n)

T/C

All
deaths

(%)

T/C

Relative

risk

(%)

Absolute

risk

(%)

Trials
cited by Sacks and Katan
4

Finnish
Mental Hospital*5

     1. period

     2. period



248/213

196/265



No data

No data



No data

No data



4/7

2/5



1.6/3.3

1.0/1.9



-52

-47



-1.7

-0.9

Oslo6

206/206

8.8/
?

20.7/
?

41/56

19.9/27.2

-27

-7.3

MRC
soy oil7

199/194

No
data

No
data

28/31

14/16

-12

-1.9

Los
Angeles8

424/422

8.3/18.5

16.1/4.1

174/177

41.0/41.9

-2

-0.9

Total

1273/1300

 

 

249/276

19.6/21.2

-8

-1.7

Trials
ignored by Sacks and Katan
4

Sydney
Diet Heart9

221/237

9.8/13.5

15.1/8.9

39/28

17.6/11.8

+49

+5.8

 Minnesota10

     men

     women



2197/2196

2344/2320



9.2/18.3

9.2/18.3



14.7/5.2

14.7/5.2



158/153

111/95



7.2/7.0

4.7/4.1



+3

+16



+0.2

+0.6

London11

     Olive oil

     Corn oil



26/26

28/**



No data

No data



No data

No data



3/1

5/**



11.5/3.8**

17.9/3.8**



+200

+365



+7.7

+14.0

DART12

1018/1015

11/15

9/7

111/113

10.9/11.1

-2

-0.2

Total

5834/5794

 

 

427/390

7.3/6.7

+9

+0.6

Grand
total

7107/7094 

 

 

676/666

9.5/9.4

+1

+0.1

*:
Not randomised

**: Only one control group

SFA: Saturated fatty acids

PUFA: Polyunsaturated fatty acids

Cal%:
Calories from fats in per cent of total calories

n: number

T: Treatment group

C: Control group

 

Competing interests:
None declared

Competing interests: No competing interests

08 December 2003
Uffe Ravnskov
Independent researcher
Magle Stora Kyrkogata 9, S-22350 Lund, Sweden
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