High Intake of Some Dietary Fats May Double Risk

By Jeanie Davis
WebMD Medical News

Reviewed by Aman Shah, MD

Aug. 15, 2001 -- We've long known that some fats in processed foods can cause cardiovascular disease. A new study now shows that higher intake of some dietary fats, including vegetable, monounsaturated, polyunsaturated, and linoleic acid, could also cause age-related macular degeneration (AMD). The study, in the August issue of Archives of Ophthalmology, also showed that higher consumption of fish oils and omega-3 fatty acids combined with a low intake of linoleic acid reduced the risk of AMD.

Fats in such snacks foods as french fries, chocolate, potato chips, and cookies "caused a twofold increased risk of age-related macular degeneration," says lead author Johanna M. Seddon, MD, associate professor of ophthalmology at Harvard Medical School and director of the epidemiology unit at the Massachusetts Eye and Ear Infirmary, both in Boston.

"This is a significant finding," Seddon tells WebMD. "Age-related macular degeneration is a leading cause of blindness in people age 65 and over." There is no proven treatment for early and moderate forms of the disease, and therapies for advanced stages are limited, she says.

As with cardiovascular disease, some fats adversely affect blood vessels supplying the eye, she tells WebMD. "Such fats may also increase oxidative damage in the eye, since it is exposed to oxygen as well as light," she says.

Seddon's study -- the largest thus far to look at the connection between dietary fat and AMD -- involved 349 patients, aged 55-80 with advanced AMD, at five of the country's biggest ophthalmology centers and 504 controls. Patients were asked to fill out questionnaires regarding their diet in the past year.

People who ate more processed foods of any type on a daily basis -- foods high in vegetable, monounsaturated, and polyunsaturated fats -- were at high risk for AMD, she says. Those foods that were highest in linoleic acid -- found primarily in snack foods like potato chips -- seemed to put people at even higher risk.

And eating fish doesn't counteract the negative effects of a diet high in processed foods, says Seddon. Her study shows that "only if you have lower quantities of the highly processed foods, then the omega-3 fatty acids in fish are helpful," she tells WebMD.

Saturated fats did not seem to increase risk of macular degeneration, she says.

Bottom line, she says: "Physicians should counsel patients to eat a good healthy diet that includes fish and to have a low intake of these kinds of processed foods. They are not good for their heart or their eyes."

There's likely something to Seddon's findings, says Thomas Aaberg Sr., MD, director of the Emory Eye Center at Emory University in Atlanta. "I think very few ophthalmologists talk to patients about diet. I think this study shows that it is important. It's going to require some confirmatory papers to really show an association. It may be that the relationship is due to other factors in foods, as she says."

It's interesting, he says, that polyunsaturated fats are protective for cardiovascular disease but are bad for the eyes. "It's possible that high amounts of polyunsaturated fats increase lipids in the macula, increasing the oxidative damage. In the eye, you're getting light focused on the back of the eye, whereas the heart is deep inside the body. That's the major difference," says Aaberg. "If you have some fat elements that combine within the eye receptors, the light that is focused on this area causes oxidation, like rust on a gutter."

Macular degeneration is a 30-40 year process, and any dietary and lifestyle changes have to be made at an early age, says Aaberg. "People need to be eating leafy vegetables like spinach," he says. "If you're eating a lot of junk food, it's probably hurting you in many ways that [you] won't see effects of for many years."

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