On Mon, 13 Jul 1998, Gregg Carter wrote:

> I am drawn to nuts/seeds--as well as seafood--because of
> the research correlating omega 3 (fish/walnuts) and the unsaturated fats
> in nuts/seeds with a lowering of blood pressure (which tends to be on the
> high side, and which I am trying to reduce).

But see the following two studies, which suggest the the
effectiveness of the omega-3 fats depends upon the presence of
saturated fats as well:

J Nutr Sci Vitaminol (Tokyo) 1988 Feb;34(1):117-129

Effects of various combinations of omega 3 and omega 6
polyunsaturated fats with saturated fat on serum lipid levels and
eicosanoid production in rats.

Lee JH, Sugano M, Ide T

Laboratory of Nutrition Chemistry, Kyushu University
School of Agriculture, Fukuoka, Japan.

The effects of varying the ratio of polyunsaturated/saturated
fatty acids (P/S) and omega 3/omega 6 polyunsaturated fatty acids
(PUFA) of dietary fats on lipid metabolism were studied in rats
using safflower oil (SFO), linseed oil (LSO), palm oil (PLO), and
a 1:1 combination of these oils. The hypocholesterolemic and
hypotriglyceridemic effects depended on the P/S ratio of dietary
fats, LSO (omega 3 PUFA) being more effective than SFO (omega 6
PUFA). A similar pattern of the response was observed on liver
cholesterol and triglyceride. The liver cholesterol-lowering
effect of LSO, but not SFO, remained even when they were combined
with PLO. The activity of liver delta 6-desaturase tended to be
higher while that of liver phospholipase A2 was significantly
lower in the LSO group than in the SFO or PLO groups. The aortic
PGI2 production and the production by platelets of thromboxane A2
were significantly low in rats fed LSO accompanying a distinct
reduction of arachidonate in tissue phospholipids. The depressing
effect of LSO disappeared when it was combined with SFO but not
with PLO. There were no significant differences in enzyme
activities and eicosanoid production between SFO and PLO in spite
of a large difference in their P/S ratio. Thus, lipid parameters
examined were complicatedly regulated by the ratios of omega
3/omega 6 as well as P/S, suggesting an existence of an
appropriate ratio for these variables.


J Lipid Res 1990 Feb;31(2):271-277

Interactions of saturated, n-6 and n-3 polyunsaturated fatty
acids to modulate arachidonic acid metabolism.

Garg ML, Thomson AB, Clandinin MT

Nutrition and Metabolism Research Group, University of Alberta,
Edmonton, Canada.

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed
to be due to their ability to reduce arachidonic acid levels.
Therefore, weanling rats were fed n-3 acids in the form of
linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and
22:6n-3) in diets containing high levels of either saturated
fatty acids (hydrogenated beef tallow) or high levels of linoleic
acid (safflower oil) for 4 weeks. The effect of diet on the
rate-limiting enzyme of arachidonic acid biosynthesis (delta
6-desaturase) and on the lipid composition of hepatic microsomal
membrane was determined. Both linseed oil- or fish oil-containing
diets inhibited conversion of linoleic acid to gamma-linolenic
acid. Inhibition was greater with fish oil than with linseed oil,
only when fed with saturated fat. delta 6-Desaturase activity was
not affected when n-3 fatty acids were fed with high levels of
n-6 fatty acids. Arachidonic acid content of serum lipids and
hepatic microsomal phospholipids was lower when n-3 fatty acids
were fed in combination with beef tallow but not when fed with
safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3,
22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3
fatty acids were fed with beef tallow than with safflower oil.
These observations indicate that the efficacy of n-3 fatty acids
in reducing arachidonic acid level is dependent on the linoleic
acid to saturated fatty acid ratio of the diet consumed.