Polyunsaturated Vegetable Oils Cataracts, Research Suggests

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by Anthony Colpo

May 15, 2005

 

Last year, an Aussie doctor appeared on one of Australia's most

widely-viewed current affairs shows stating that refined vegetable

oils played a major role in causing macular degeneration.

 

His comments didn't exactly win him many friends in the powerful

vegetable oil industry, but newly published research by Boston

researchers further supports the contention that refined vegetable

oils can indeed be hazardous to your eyesight.

 

LA linked to cataracts in Boston

 

In their first study of women participating in a nearly-30-year-old

diet-and-health study, the researchers link the primary fat in many

popular vegetable oils, linoleic acid (LA), to incipient cataracts,

called opacities, in the lenses of the women's eyes. In this study,

this single fat accounted, on average, for roughly 5 percent of

calories consumed each day, and more than 85 percent of

polyunsaturated-fat intake.

 

Lens opacities are " a sensitive marker for the development of

cataracts " but don't initially cause vision loss, notes Paul F.

Jacques, director of nutritional epidemiology for the Agriculture

Department's Jean Mayer Human Nutrition Research Center on Aging at

Tufts University.

 

The second study by the same researchers included women who had

undergone surgery for removal of cataracts. Compared with

similarly-aged women who never had such a procedure, these women were

much less likely to have eaten omega-3 fatty acids, the type found in

fish oils. In this study, eating vegetable oils didn't appear to be

linked with cataracts, but eating mayonnaise and salad dressings did.

Refined vegetable oils are a primary ingredient of mayonnaise and

salad dressings.

 

The types and ratios of fatty acids we consume affect the flexibility

and permeability of cell membranes throughout the body. Cataracts are

associated with changes in lens-membrane structure and function and

could thus be affected by dietary fats.

 

You ought to be…saturated

 

In the April American Journal of Clinical Nutrition, the scientists

report that women whose diets were richest in polyunsaturated fats

were significantly more likely to have incipient nuclear cataracts,

while those whose diets were lowest in these fats were least likely. A

higher risk of early nuclear cataracts was also associated with diets

high in vegetable oils and trans fats.

 

Adding to the mountain of studies contradicting the prevailing

anti-saturated fat paranoia, no increased cataract risk was associated

with intake of saturate-rich animal fats.

 

When the researchers focused on the various types of polyunsaturated

fats, cataract risk appeared to be most associated with two fatty

acids: linoleic (LA) and alpha-linolenic (ALA).

 

LA is the primary fatty acid found in safflower, sunflower, corn,

soybean, and cottonseed oils. Although ALA is found in many plant

oils, its highest concentrations tend to be in flax, soy, walnuts, and

canola. Dietary trans fats, meanwhile, are most abundant in margarines

and shortenings. These are produced by subjecting unsaturated oils to

chemicals and special manufacturing technologies that make them solid

or semisolid at room temperature.

 

The researchers urge caution before indicting ALA for causing

cataracts. First, two previous studies by other researchers found

almost no alpha-linolenic in the eye's lens. Secondly, ALA occurs in

many of the same sources as LA does, but in smaller quantities, and

may simply serve as a marker for LA intake. Also, the body converts

some of its ALA into docosahexaenoic acid (DHA) and eicosapentaenoic

acid (EPA), two long-chain omega-3 fats found in fish oils.

 

Fishy findings

 

The second study by Jacques and his team encompassed dietary

information supplied by some 71,000 women between 1984 and 2000. To be

included for this analysis, a woman had to be free of cataracts,

cancer. During the study, over 4,000 women in the group had cataracts

diagnosed after age 45 and then had surgery. Roughly 60 percent of

these cases involved nuclear cataracts.

 

One finding stood out, Jacques notes: Women who developed cataracts

were far less likely to be big fish eaters. In contrast, women who

consumed dark-meat fish, such as salmon or tuna, at least once a week

had a 15 percent lower risk of cataracts than did women eating fish

less frequently. Dark-meat fish are the ones that tend to be

especially rich in DHA and EPA.

 

References

 

Lu M, et al. Prospective study of dietary fat and risk of cataract

extraction among U.S. women. American Journal of Epidemiology, May 15,

2005; 161: 948-959.

http://aje.oupjournals.org/cgi/content/abstract/161/10/948

 

Lu M, et al. Dietary fat intake and early age-related lens opacities.

American Journal of Clinical Nutrition, Apr 2005; 81: 773-779.

http://www.ajcn.org/cgi/content/abstract/81/4/773

 

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About the Author

Anthony Colpo is an independent researcher and certified fitness

consultant with 20 years' experience in the physical conditioning

arena. To contact: contact

 

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