Newsgroup: it.salute.alimentazione
Titolo: I grassi saturi prevengono gli ateromi?

Ho scovato un recente articolo dell'AJCN su un tema che in questi giorni è
molto dibattuto sul ng.
Non ho potuto leggerlo con particolare attenzione, per mancanza di tempo.
E' un po' complicato, ma magari leggendolo insieme riusciamo a capire
meglio il succo.
Faccio presente che è un editoriale in cui si commentano i risultati di
uno studio che appaiono nello stesso numero del giornale.
Eccolo di seguito,
Xlater
=======
Saturated fat prevents coronary artery disease? An American paradox1,2
(
http://www.ajcn.org/cgi/content/full/80/5/1102#FN2
) 
Robert H Knopp and Barbara M Retzlaff 
1 From the Northwest Lipid Research Clinic, University of Washington
School of Medicine, Seattle 
2 Address reprint requests to RH Knopp, Northwest Lipid Research Clinic,
University of Washington, School of Medicine, 325 9th Avenue, Seattle, WA
98104. E-mail: rhknopp~
u.washington.edu
. 
See corresponding article on page 1175
(
http://www.ajcn.org/cgi/lookup?lookupType=volpage&vol=80&fp=1175&view=short
).
It is an article of faith that saturated fat raises LDL cholesterol and
accelerates coronary artery disease, whereas unsaturated fatty acids have
the opposite effect (1
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R1
), 2
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R2)
). One of the earliest
and most convincing studies of the better efficacy of unsaturated than of
saturated fat in reducing cholesterol and heart disease is the Finnish
Mental Hospital Study conducted in the 12 y between 1959 and 1971. In this
study, the usual high-saturated-fat institutional diet was compared with
an equally high-fat diet in which the saturated fat in dairy products was
replaced with soybean oil and soft margarine and polyunsaturated fats were
used in cooking. Each diet was provided for 6 y and then the alternate
diet was provided for the next 6 y (3
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R3)
). After a comparison
of the effects of the 2 diets in both men and women, the incidence of
coronary artery disease was lower by 50% and 65% after the consumption of
polyunsaturated fat in the 2 hospitals. 
In this issue of the Journal, Mozaffarian et al (4
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R4
)) report the opposite
association. They found that a higher saturated fat intake is associated
with less progression of coronary artery disease according to quantitative
angiography. How can this paradox be explained? In food-frequency
questionnaires, saturated fat intake is more precisely estimated than is
total fat. If saturated fat is more precisely estimated, it will associate
more strongly in statistical analyses with the outcome variable, even
though other variables—such as total fat or carbohydrate—could be more
relevant physiologically. We believe that these possibilities deserve a
closer look. 
Unlike the diet used in the Finnish Mental Hospital Study, the diet
described by Mozaffarian et al was low in fat, averaging 25% of energy.
The study subjects were women with coronary artery disease: most were
hypertensive, many had diabetes (19–31%), their body mass index (kg/m2)
ranged from 29 to 30, and their lipid profile indicated combined
hyperlipidemia (triacylglycerol concentration:
http://www.ajcn.org/math/ap.gif200
 mg/dL; HDL-cholesterol concentration:
40–50 mg/dL; above-average LDL concentration: 135–141 mg/dL); these
characteristics are consistent with the metabolic syndrome. In addition,
two-thirds of these women were taking sex hormones. The importance of each
of these points is addressed below. 
What are the effects of a low-fat, high-carbohydrate diet in comparison
with those of a higher-fat, lower-carbohydrate diet? The response differs
by the 2 main types of hyperlipidemia: simple hypercholesterolemia and
combined hyperlipidemia. In our studies of simple hypercholesterolemia in
men, a fat intake <25% of energy and a carbohydrate intake >60% of energy
was associated with a sustained increase in triacylglycerol of 40%, a
decrease in HDL cholesterol of 3.5%, and no further decrease in LDL in
comparison with higher fat intakes (5
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R5)
). In contrast, a
low-fat diet in persons with combined hyperlipidemia caused no worsening
of triacylglycerol or HDL, but intakes of fat >40% of energy and of
carbohydrate <45% of energy for 2 y were associated with a lower
triacylglycerol concentration at a stable weight (6
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R6)
). In the subjects of
Mozaffarian et al, a greater saturated fat intake paralleled a total fat
intake, which ranged from 18% to 32% of energy in the first to fourth
quartiles. Modest favorable trends in triacylglycerol and HDL-cholesterol
concentrations were observed with higher fat intakes. 
Triacylglycerol and HDL-cholesterol concentrations are stronger predictors
of coronary artery disease in women, whereas the LDL-cholesterol
concentration is a stronger predictor in men (7
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R7)
). Because VLDL
triacylglycerol secretion and removal rates in healthy women are double
those of men (8 (
http://www.ajcn.org/cgi/content/full/80/5/1102#R8)
),
conditions impairing lipoprotein removal would be expected to exaggerate
the hyperlipidemic response in women as compared with that in men (9
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R9)
). This sex difference
is seen with the development of diabetes. The increment in lipids is
greater in women than in men and is associated with a greater increment in
coronary artery disease risk in women than in men (9
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R9)
). Similarly, the
development of insulin resistance and obesity is associated with a greater
lipoprotein increment in women than in men (10
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R10)
). The exaggerated
decreases in HDL- and HDL2-cholesterol concentrations observed with the
consumption of a low-fat Step II diet in women but not in men appear to be
another facet of this effect (11
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R11)
). 
The failure of female sex hormones to prevent coronary artery disease has
been a great disappointment (9
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R9)
). This effect might
also be due to an estrogen-induced increase in lipoprotein entry against a
fixed or impaired rate of lipoprotein removal, as might be expected in
women with the metabolic syndrome and coronary artery disease. 
Would saturated fat still be bad for anyone? Not necessarily. The effect
of saturated fat and cholesterol ingestion in the form of 4 eggs/d for 1
mo in obese, insulin-resistant subjects is
http://www.ajcn.org/math/ap.gif33%
 of that seen in lean, insulin-sensitive
subjects, likely because of diminished cholesterol absorption (12
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R12)
). Thus, the classic
effects of saturated fat as compared with those of unsaturated fat seen in
the Finnish Mental Hospital Study are likely blunted in the subjects of
Mozaffarian et al, whereas the effects of low fat and high carbohydrate
intakes on triacylglycerol and HDL-cholesterol concentrations appear to be
exaggerated by the interactions of female sex, exogenous sex hormones, and
the metabolic syndrome. A major effect on cardiovascular disease risk
would be the result of hypertriglyceridemia and low HDL-cholesterol
concentrations, which are attenuated by an increase in saturated fat
intake itself or in total fat intake, for which saturated fat is a more
statistically stable surrogate (4
(
http://www.ajcn.org/cgi/content/full/80/5/1102#R4)
). 
In conclusion, the hypothesis-generating report of Mozaffarian et al draws
attention to the different effects of diet on lipoprotein physiology and
cardiovascular disease risk. These effects include the paradox that a
high-fat, high–saturated fat diet is associated with diminished coronary
artery disease progression in women with the metabolic syndrome, a
condition that is epidemic in the United States. This paradox presents a
challenge to differentiate the effects of dietary fat on lipoproteins and
cardiovascular disease risk in men and women, in the different lipid
disorders, and in the metabolic syndrome. 
REFERENCES 
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Balch HE. Effect of vegetable fat on hypercholesterolemia and
hyperphospholipidemia: observations on diabetic and nondiabetic subjects
given diets high in vegetable fat and protein. Diabetes
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(
http://www.ajcn.org/cgi/external_ref?access_num=13161731&link_type=MED
)
<LI value=2>Grundy SM, Denke MA. Dietary influences on serum lipids and
lipoproteins. J Lipid Res 1990;31:1149-72.[Abstract]
(
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)
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E. Effect of cholesterol-lowering diet on mortality from coronary
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women. Lancet 1972;2:835-8.[Medline]
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)
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Text]
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)
<LI value=5>Knopp RH, Walden CE, Retzlaff BM, et al. Long-term
cholesterol-lowering effects of 4 fat-restricted diets in
hypercholesterolemic and combined hyperlipidemic men. The Dietary
Alternatives Study. JAMA 1997;278:1509-15.[Abstract]
(
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)
<LI value=6>Retzlaff BM, Walden CE, Dowdy AA, McCann BS, Anderson KV,
Knopp RH. Changes in plasma triacylglycerol concentrations among
free-living hyperlipidemic men adopting different carbohydrate intakes
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(
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)
<LI value=7>Knopp RH, Zhu X, Bonet B. Effects of estrogens on lipoprotein
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)
<LI value=8>Mittendorfer B, Patterson BW, Klein S. Effect of sex and
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)
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)
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Wallick S, McCann BS, Knopp RH. Differential effect of the National
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)
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)
http://www.ajcn.org/cgi/content/full/80/5/1102
--------------------------------------------------------------------------------
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 uno studio che appaiono nello stesso numero del giornale.
A. Colpo (the ominivore) commenta l'articolo di cui parli qui:
http://www.theomnivore.com/Sat%20Fat_Less%20CAD.html
Ciao!
Gianni

 syndrome.
questo è il messaggio generale importante da cogliere, oltre al fatto 
che non bisogna demonizzare i grassi saturi sempre e comunque ( anche se 
chi ha studiato un po' più approfonditamente la fisiologia umana questo 
concetto già lo conosceva).
Ovviamente ora mi aspetterò che questo studio venga sbandierato dalle
industrie dei grassi saturi come la ratifica scientifica delle loro 
ragioni : " ingurgitate grassi saturi perchè così prevenite addirittura 
le malattie coronariche ".
-- 
    ______________________________________
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         Profumo di fiori di pruno:
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                        (M.Basho)
    ______________________________________

 le malattie coronariche ".
Non mi risulta che esitano "industrie dei grassi saturi". Ci sono
piuttosto i grassi di origine animale, che non sono particolarmente amati
dall'industria. Per una ragione molto semplice: costano di più. A parità
di grasso ottenuto costa molto di più allevare bovini che coltivare mais e
girasoli.
Se ti capita di entrare in un supermercato, vai al reparto dei biscotti, e
prova a vedere quante industrie utilizzano ancora eroicamente il sano e
costoso burro, e quante invece non meglio precisati "oli e grassi
vegetali". Qualcuno addirittura smercia questa surrogazione per incremento
della salubrità del prodotto, facendoselo addirittura pagare di più perchè
"senza colesterolo", "bassi grassi saturi" o "100% vegetale".
Prova a pensare quanto costa produrre una fettina di manzo vera, e quanto
costa invece mettere insieme una polpetta di soia, infarcita di aromi. Chi
comprerebbe mai quest'ultima ad un prezzo paragonabile, se non ci fosse
chi ti fa credere che è salutare perchè "senza grassi saturi" "senza
colesterolo" e "vegetale", sorvolando allegramente sugli effetti
ampiamente documentati dei fitoestrogeni sulla funzionalità della tiroide
e sull'apparato riproduttivo maschile e femminile.
No, fidati. All'industria alimentare va benissimo così. E te lo dimostra
il fatto che sebbene come dici tu "chi ha studiato un po' più
approfonditamente la fisiologia umana" sapeva bene che la demonizzazione
dei saturi tout court non era giustificata da nulla, la percezione che è
trapelata verso la massa è che i grassi saturi sono il male peggiore
immaginabile.
E lo si nota dalle reazioni sorprese di tante persone bene informate
quando qualcuno prova a mettere in dubbio questo concetto.
Xlater


 "senza colesterolo", "bassi grassi saturi" o "100% vegetale".
hai ragione, ho generalizzato, comunque intendevo proprio questo.
ps: grazie per la segnalazione dello studio che ha aggiunto un tassello 
importante per le conoscenze che mi sto costruendo.
