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

[Guest guest]

It's difficult to gauge from your post whether the studies refer to

the effects of increasing the *proportion* of Omega-6 relative to

some canonical fat consumption profile (made up of various types of

fat, including many types), or whether it's a more absolute statement

about increasing Omega-6 regardless of one's current total fat intake?

Thanks, -Dave

>

> 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.

> =================================

> 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.

>