Are Polyunsaturated Fats really safe?

[Guest guest]

I have comes across a number of studies against polyunsaturated

fats, in relation to immune system and cancer. A good selection

are listed in the article below (whole article can be got here:

http://www.second-opinions.co.uk/fats_and_cancer.html. And I don't

want to start up the saturated fat debate again.

But I would like to know how we can gamble reducing LDL via

increasing poly fats to lower CHD risk when there is the potential

life threatening condition of cancer as the alternative.

Personally having now looked at many studies using the statistical P

value I think that all assumptions made using that statistical

equation are not worth the paper they are written upon, it is, to

me, all really shoddy science open to massive coincidence,

manipulation and failing to factor in various dietary disease risks

that have yet to be discovered.

But Rodney and Tony have both mentioned polyunsaturated fats in a

good light recently so I think this balances the perspective a

little. Personally I don't have a clue was going on, so will just

stick to 5% calories from poly fats for now.

...

Dietary fat patterns

The total amount of fats in our diet today, according to the MAFF

National Food Survey, is almost the same as it was at the beginning

of this century. What has changed, to some extent, is the types of

fats eaten. At the turn of the century we ate mainly animal fats

that are largely saturated and monounsaturated. Now we are tending

to eat more polyunsaturated fats – it's what we are advised to do.

In 1991, two studies, from USA (4) and Canada, (5) found that

linoleic acid, the major polyunsaturated fatty acid found in

vegetable oils, increased the risk of breast tumours. This, it

seems, was responsible for the rise in the cancers noted in previous

studies. Experiments with a variety of fats showed that saturated

fats did not cause tumours but, when small amounts of

polyunsaturated vegetable oil or linoleic acid itself was added,

this greatly increased the promotion of breast cancer.

Body cell walls are made of cholesterol, protein and fats. The graph

below demonstrates that the human body's fat make-up is largely of

saturated and monounsaturated fatty acids. We contain very little

polyunsaturated fat. Cell walls have to allow the various nutrients

that body cells need from the blood, but stop harmful pathogens.

They must be stable. An intake of large quantities of

polyunsaturated fatty acids changes the constituency of cholesterol

and body fat. Cell walls become softer and more unstable.

Polyunsaturated fats suppress the immune system

Polyunsaturated fats (PUFs) are greatly immunosuppressive, and

anything that suppresses the immune system is likely to cause

cancer. The first person to suggest that polyunsaturated fats cause

cancer was Dr R A Newsholme of Oxford University, England. (6) What

Newsholme wrote was that when our bodies get sufficient nutrition,

our diet includes immunosuppressive PUFs which make us prone to

infection by bacteria and viruses. When we are starved, however, our

body stores of PUFs are depleted. This allows our bodies' immune

systems to recover which, in turn, allows us to fight existing

infection and prevent other infections. He was making the point that

the immunosuppressive effects of PUFs in sunflower seeds are useful

in treating autoimmune diseases such as multiple sclerosis, (7) and

that the same fatty acids could be used to suppress the immune

system to prevent rejection of kidney transplants.

It was during the early days of kidney transplantation that doctors

first encountered the problem of tissue rejection as their patients'

bodies destroyed the alien transplanted kidneys. If transplantation

were to be a success, they had to find a way to suppress the immune

system. Newsholme had said that there was no better way to

immunosuppress a renal patient than with sunflower seed oil. So

kidney transplant doctors fed their patients linoleic acid. (8)

(Linoleic acid is the major polyunsaturated fatty acid in vegetable

oils.) But the transplant doctors were then astonished to see how

quickly their patients developed cancers: some cancers were up to

twenty times as frequent as was expected.

This was in line with heart trials using diets that were high in

PUFs which, reported an excess of cancer deaths from as early as

1971. (9)

By the early 1980s, we were being exhorted by doctors and

nutritionists to eat more PUFs because they were 'good for us'

despite the fact that Oncology Times carried a paper in January 1980

from the University of California at that mice fet PUFs were

more prone to develop melanoma. In May 1980, the same publication

carried a similar report from Oregon State University which said

that PUFs fed to cancer-prone mice increased the numbers of cancers

formed.

In 1989 there was a report of a ten-year trial at a Veterans'

Administration Hospital in Los Angeles. In this trial half the

patients were fed a diet which had double the amount of PUFs as

compared to saturated fats. In the half of the patients on the high

PUF diet there was a fifteen percent increase in cancer deaths

compared to the saturated fat group. (10)The authors of the report

said that the PUFs had been the cause of the increase in cancer

deaths. The British Medical Journal carried an editorial in its 6

October 1973 issue which asked if PUFs were carcinogenic. It came to

the conclusion that they were.

Wayne likes to tell a story which suggests just how cancer-

causing are PUFs. In 1930 in the USA, eighty percent of men smoked

cigarettes and the tar content of cigarettes was much higher than it

is today. The death rate at that time from lung cancer was very low.

In 1955 doctors decided that PUFs were good in terms of heart

disease protection. After this lung cancer deaths increased so

dramatically. By 1980 although the number of American men who smoked

had dropped to only thirty percent, three times as much PUF was

being eaten – and there were sixty times as many lung cancer

deaths. (11)

In 1990, called Newsholme's Oxford University office but by

then Newsholme had retired. spoke to his successor to find

that they were still treating autoimmune diseases with PUFs. By then

they were using fish oil. The doctor said the reason for the fish

oil was that the degree of immunosuppression increased with the

degree of unsaturation and fish oil was much more unsaturated than

sunflower oil. asked the doctor why they were not talking

about PUFs causing cancer. The doctor replied that if he did that he

would be run out of Oxford.

Carcinogens – background radiation, ultraviolet radiation from the

sun, particles in the air we breathe and the food we eat –

continually attack us all. Normally, the immune system deals with

any small focus of cancer cells so formed and that is the end of it.

But linoleic acid suppresses the immune system. With a high intake

of margarine, therefore, a tumour may grow too rapidly for the

weakened immune system to cope thus increasing our risk of a cancer.

Polyunsaturated fats cause cancer

Since 1974, the increase of polyunsaturated fats has been blamed for

the alarming increase in malignant melanoma (skin cancer) in

Australia. (12) We are all told that the sun causes it. Are

Australians going out in the sun any more now than they were fifty

years ago? They are certainly eating more polyunsaturated oils: in

Australia in 1995 I saw that even the cream on milk was removed and

replaced with vegetable oil. Victims of the disease have been found

to have polyunsaturated oils in their skin cells. Polyunsaturated

oils are oxidised readily by ultra-violet radiation from the sun and

form harmful 'free radicals'. These are known to damage the cell's

DNA and this can lead to the deregulation we call cancer. Saturated

fats are stable. They do not oxidise and form free radicals.

Malignant melanoma is also said to be increasing in this country.

Does the sun cause this? In Britain the number of sufferers is so

small as to be relatively insignificant. Even so, it is not likely

that the sun is to blame since all the significant increase is in

the over-seventy-five-year-olds. People in this age group tend to

get very little sun.

That the sun is not to blame is confirmed by other findings:

· Melanoma occurs ten times as often in Orkney and Shetland

than it does on Mediterranean islands.

· It also occurs more frequently on areas that are not exposed

to the sun.

· In Scotland, for example, there are five times as many

melanomas on the feet as on the hands;

· and in Japan, forty per cent of pedal melanomas are on the

soles of the feet . (13)

Polyunsaturated fats promote cancer

Many laboratories have shown that diets high in polyunsaturated

fatty acids promote tumours. Cancer promotion is not the same as

cancer causing. The subject is complex; suffice to say here that

promoters are substances that help to speed up reproduction of

existing cancer cells.

It has been known since the early 1970s that it is linoleic acid

that is the major culprit. As Professor Kearney of Sydney

University put it in 1987: 'Many laboratories have shown that a

greater proportion of polyunsaturated fats are superior to diets

rich in saturated fats in promoting the yield of experimental

mammary tumours. In such studies, omega-6 linoleic acid appeared to

be the crucial fatty acid . . .' and 'Vegetable oils (eg Corn oil

and sunflower oil) which are rich in linoleic acid are potent

promoters of tumour growth.' (14)

Polyunsaturated fats and breast cancer

A study of 61,471 women aged forty to seventy-six, conducted in

Sweden, looked into the relation of different fats and breast

cancer. The results were published in January 1998. This study found

an inverse association with monounsaturated fat and a positive

association with polyunsaturated fat. In other words,

monounsaturated fats protected against breast cancer and

polyunsaturated fats increased the risk. Saturated fats were

neutral. (15)

Flora margarine, the brand leader, is thirty-nine percent linoleic

acid; Vitalite and other 'own brand' polyunsaturated margarines are

similar. Of cooking oils, sunflower oil is fifty percent and

safflower oil seventy-two percent linoleic acid. Butter, on the

other hand, has only a mere two percent and lard is just nine

percent linoleic acid. Linoleic acid is one of the essential fatty

acids. We must eat some to live, but we do not need much. The amount

in animal fats is quite sufficient.

Because of the heart disease risk from trans-fats in margarines, in

1994 the manufacturers of Flora changed its formula to cut out the

trans fats and other manufacturers have since followed. But that

still leaves the linoleic acid.

The anti-cancer fat

Linoleic acid is one of the essential fatty acids that our bodies

need but cannot synthesise. We must eat some to survive. Fortunately

there is one form of linoleic acid that is beneficial. Conjugated

linoleic acid (CLA) differs from the normal form of linoleic acid

only in the position of two of the bonds that join its atoms. But

this small difference has been shown to give it powerful anti-cancer

properties. Scientists at the Department of Surgical Oncology,

Roswell Park Cancer Institute, New York (16) and the Department of

Biochemistry and Molecular Biology, New Jersey Medical School, (17)

showed that even at concentrations of less than one percent, CLA in

the diet is protective against several cancers including breast

cancer, colorectal cancer and malignant melanoma.

Conjugated linoleic acid has one other difference from the usual

form – it is not found in vegetables but in the fat of ruminant

animals. The best sources are dairy products and the fat on red

meat, principally beef. (18)

It has been suggested that the consumption of red meat increases the

risk of colon cancer, yet in Britain there is no evidence to support

this. (19) It is interesting that all the evidence implicating red

meat in cancer comes from the USA – where they cut the fat off.

Conclusions

Saturated fats and animal fats are usually blamed for all manner of

diseases in Western society. But look at the facts:

· In the 19th-century, when animal fats were all that was

available, cancers were rare (as was heart disease).

· Polyunsaturated fats and oils are used to suppress the

immune system, such immunosuppression is known to cause cancers to

start and promote cancer.

· In this last century there has been a change in favour of

polyunsaturated fats and oils – and cancer rates have soared.

Unfortunately, as polyunsaturated fatty acids are also essential to

the body; we must have some. So a proper balance must be struck.

Whether the dramatic increase in the numbers of cancers in the last

century was as a result of a similarly dramatic rise in our intake

of polyunsaturated vegetable oils is not known – but the evidence

strongly favours such a conclusion.

Under the circumstances, it seems prudent to get what linoleic acid

we need from animal sources. Or to restrict polyunsaturated oil

consumption so that linoleic acid is no more than three percent of

the total fat intake.

References

1. Gofman, J W, et al. The role of lipids and lipoproteins in

atherosclerosis. Science 1950; 111: 166-181, 186

2. Keys A. Atherosclerosis: a problem in newer public health. J Mt

Sinai Hosp 1953; 20: 118-139.

3. Mann G V. Diet-heart: End of an Era. New Eng J Med . 1977; 297:

644.

4. Carroll K K. Dietary fats and cancer. Am J Clin Nutr 1991; 53:

1064S.

5. France T, Brown P. Test-tube cancers raise doubts over fats. New

Scientist , 7 December 1991, p 12.

6. Newsholme E A. Mechanism for starvation suppression and refeeding

activity of infection. Lancet 1977; i: 654.

7. JD, et al. Br Med J 1973; i: 765.

8. Uldall PR, et al . Lancet 1974; ii: 514.

9. Pearce M L, Dayton S. Incidence of cancer in men on a diet high

in polyunsaturated fat. Lancet 1971; i: 464.

10. American Heart Association Monograph, No 25. 1969.

11. Nauts HC. Cancer Research Institute Monograph No 18. 1984, p 91.

12. Mackie BS. Med J Austr 1974; 1: 810.

13. Karnauchow PN. Melanoma and sun exposure. Lancet 1995; 346: 915.

14. Kearney R. Promotion and prevention of tumour growth – effects

of endotoxin, inflammation and dietary lipids. Int Clin Nutr Rev

1987; 7: 157.

15. Wolk A, et al. A Prospective Study of Association of

Monounsaturated Fat and Other Types of Fat With Risk of Breast

Cancer. Arch Intern Med . 1998; 158: 41-45

16. Ip C, Scimeca J A, H J. Conjugated linoleic acid. A

powerful anticarcinogen from animal fat sources. Cancer 1994; 74(3

Suppl): 1050-4.

17. Shultz T D, Chew B P, Seaman W R, Luedecke L O. Inhibitory

effect of conjugated dienoic derivatives of linoleic acid and beta-

carotene on the in vitro growth of human cancer cells. Cancer

Letters 1992; 63: 125-133.

18. Lin H, Boylston TD, Chang MJ, Luedecke LO, Schultz TD. Survey of

the conjugated linoleic acid contents of dairy products. J Dairy

Sci . 1995; 78: 2358-65.

19. BD, Whichelow MJ. Frequent consumption of red meat is not a

risk factor for cancer. Br Med J 1997; 315: 1018.