Omega-6 and omega-3 fatty acids reduce incidence of CVD

[Guest guest]

Al brought to our attention an issue of J Cardiovasc Med (Hagerstown).

2007 Sep;8 Suppl 1 ( http://tinyurl.com/2arzcc ) that has several

important papers about essential dietary fatty acids. This one had

some interesting comments about the proportion of the fatty acids:

Willett WC.

The role of dietary n-6 fatty acids in the prevention of cardiovascular

disease.

J Cardiovasc Med (Hagerstown). 2007 Sep;8 Suppl 1:S42-5.

PMID: 17876199

Abstract

n-6 Fatty acids, like n-3 fatty acids, play essential roles in many

biological functions. Because n-6 fatty acids are the precursors of

proinflammatory eicosanoids, higher intakes have been suggested to be

detrimental, and the ratio of n-6 to n-3 fatty acids has been

suggested by

some to be particularly important. However, this hypothesis is based on

minimal evidence, and in humans higher intakes of n-6 fatty acids have

not

been associated with elevated levels of inflammatory markers.

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n-6 Fatty acids have long been known to reduce serum total and

low-density

lipoprotein cholesterol, and increases in polyunsaturated fat intake,

mostly

as n-6 fatty acids, were a cornerstone of dietary advice during the 1960s

and 1970s. In the United States, for example, intake of n-6 fatty acids

doubled and coronary heart disease (CHD) mortality fell by 50% over a

period

of several decades. In a series of relatively small, older randomized

trials, in which intakes of polyunsaturated fat were increased (even

up to

20% of calories), rates of CHD were generally reduced. In a more recent

detailed examination of fatty acid intake within the Nurses' Health

Study,

greater intake of linoleic acid, up to about 8% of energy, has been

strongly

related to lower incidence of myocardial infarction or CHD death. Because

n-3 fatty acids were also related inversely to risk of CHD, the ratio was

unrelated to risk. n-6 Fatty acids reduce insulin resistance, probably by

acting as a ligand for peroxisome proliferator-activated

receptors-[gamma],

and intakes have been inversely related to risk of type 2 diabetes.

Adequate intakes of both n-6 and n-3 fatty acids are essential for good

health and low rates of cardiovascular disease and type 2 diabetes,

but the

ratio of these fatty acids is not useful. Reductions of linoleic acid to

" improve " this ratio would likely increase rates of cardiovascular

disease

and diabetes.

....

Effects of linoleic acid on blood lipids

The role of polyunsaturated fat (which is primarily LA) in reducing blood

total cholesterol levels became well recognized in the 1960s. This effect

was documented in dozens of controlled feeding studies that were

summarized

by the Keys and Hegsted equations [4,5]. These equations demonstrated

nearly

identical results, with saturated fat positively related to serum

cholesterol and polyunsaturated fat inversely related to serum

cholesterol.

Primarily on the basis of the Keys and Hegsted equations, dietary

recommendations in the United States and other western countries

between the

1960s and early 1980s included advice to replace saturated fat with

polyunsaturated fat, because this would have a double benefit in reducing

total serum cholesterol. As a result of these recommendations,

consumption

of polyunsaturated fat (primarily LA) in the United States increased from

~3% of energy in the 1950s to ~6-7% of energy by the late 1980s [6,7].

This

dietary change was confirmed by large increases in the LA content of

adipose

samples; concentrations increased from about 8.5% in 1962 and about

10% in

1966 [8] to 17% to 19% in the 1980s [9-11].

More recently, using data from 61 controlled feeding studies, Mensink

et al.

[12] assessed the effects of dietary fats on not only blood total

cholesterol, but also low-density lipoprotein (LDL) cholesterol,

high-density lipoprotein (HDL) cholesterol, and triglycerides. This

analysis

demonstrated that compared to carbohydrate, polyunsaturated fat

reduces LDL

cholesterol, increases HDL cholesterol, and reduces triglycerides

[12]; each

of these effects favors lower risk of CHD. Indeed, compared to all other

classes of fatty acids, LA produces the most favorable lipid changes, as

reflected by the lowest ratio of LDL to HDL cholesterol.