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Dietary Fat and AMD
The July issue of Archives of Ophthalmology contained important information on dietary fat and the risk of AMD. Chua et al. reported results of the large Blue Mountains Eye Study in Australia.
People who had the lowest quintile, (lowest 20%), of dietary fat consumption had a 70% increase of early AMD compared to those who had a moderate intake. That means a very low fat diet is not good for you if you’re at risk for AMD. Those who ate fish at least once a week had a 42% risk reduction in early AMD and a 56% reduction in late AMD compared to those who ate fish less than once per month.
Those who ate fish three times a week had a 75% reduction in late AMD compared to those who ate fish once a month.
The consumption or lack of consumption of butter, margarine, and nuts seemed to have little effect.Seddon,
George, and Rosner, in this same issue, reported the results of a dietary survey on elderly male twins who had served in the United States armed forces.
They found that those who ate at least two servings of fish a week had a 32% reduction in the risk of AMD compared to those who ate less than one serving per week. Those in the top 25% of dietary intake of omega-3 fatty acids had a 44% decrease in the risk of AMD compared to those in the lowest 25%. This protective effect was wiped out however, in people who also had a high dietary intake of omega-6 fatty acids or linoleic acid. Linoleic acid is found in beef, pork, lamb, and processed foods cooked in vegetable oils.
So, if you are at risk for AMD, you should not limit your fat intake.
But you should increase your intake of omega-3 fatty acids and decrease your intake of omega-6. The ideal ratio of omega-6 to omega 3 is 3:1 or 4:1 not the 10:1 or even 50:1 ratio found in some American diets. That means you should eat more fish, walnuts, flaxseeds and tofu. Eat less beef, pork, lamb, processed foods, trans-fats, and vegetable oils. The best oils to use are canola, olive, and flaxseed. The worst oils are corn, peanut, safflower, and sunflower.
I found this site helpful for the content of various oils: http://math.ucsd.edu/~ebender/Health%20&%20Nutrition/Nutrition/oil_good.html (or http://tinyurl.com/ed2d3).
References:
1. Chua B, Flood V, Rochtchina E, Wang JJ, Smith W, Mitchell P. Dietary fatty acids and the 5-year incidence of age-related maculopathy. Arch Ophthalmol. 2006 Jul;124(7):981-6.
2. Seddon JM, George S, Rosner B. Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration: the US Twin Study of Age-Related Macular Degeneration.
Arch Ophthalmol. 2006 Jul;124(7):995-1001.
Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration: the US Twin Study of Age-Related Macular Degeneration.
Seddon JM, George S, Rosner B.
Massachusetts Eye and Ear Infirmary and Channing Laboratory, Harvard Medical School, 243 Charles Street, Boston, MA, USA. johanna_seddon@meei.harvard.edu
OBJECTIVE: To evaluate modifiable risk and protective factors for age-related macular degeneration (AMD) among elderly twins.
METHODS: The US Twin Study of Age-Related Macular Degeneration comprises elderly male twins from the National Academy of Sciences-National Research Council World War II Veteran Twin Registry. To determine genetic and environmental risk factors for AMD, twins were surveyed for a prior diagnosis of AMD and underwent an eye examination, fundus photography, and food frequency and risk factor questionnaires. This environmental component of the study includes 681 twins: 222 twins with AMD (intermediate or late stages) and 459 twins with no maculopathy or early signs. Risk for AMD according to cigarette smoking and dietary fat intake was estimated using logistic regression analyses.
RESULTS: Current smokers had a 1.9-fold increased risk (95% confidence interval, 0.99-3.68, P = .06) of AMD while past smokers had about a 1.7-fold increased risk (95% confidence interval, 1.2-2.6, P = .009). Increased intake of fish reduced risk of AMD, particularly for 2 or more servings per week (P trend = .04). Dietary omega-3 fatty intake was inversely associated with AMD (odds ratio, 0.55; 95% confidence interval, 0.32-0.95) comparing the highest vs lowest quartile. Reduction in risk of AMD with higher intake of omega-3 fatty acids was seen primarily among subjects with low levels (below median) of linoleic acid intake, an omega-6 fatty acid (P trend<.001). The attributable risk percentage was 32% for smoking and the preventive fraction was 22% for higher omega-3 intake.
CONCLUSIONS: This study of twins provides further evidence that cigarette smoking increases risk while fish consumption and omega-3 fatty acid intake reduce risk of AMD.