The health benefits of the so-called Mediterranean diet were first proposed in the 1950s. That’s when an American physiologist named Ancel Keys noticed something peculiar. Poor people in southern Italy were healthier than wealthy people in New York.
How could this be? To find out, Keys launched what was called the “Seven Countries Study,” which compared lifestyles, nutrition and heart disease in in Finland, Greece, Japan, the Netherlands, Italy, Yugoslavia and the United States. He found that people who ate little meat but lots of olive oil, bread, pasta, vegetables, herbs, garlic, red onions and other vegetable foods had low amounts of cholesterol in the blood and less heart disease. It wasn’t until the 1980s, however, that the diet, now named the “Mediterranean diet,” started to become popular. Since then it has been recommended by the American Heart Association and the American Diabetes Association. It’s defined as eating fish twice a week plus fruits, vegetables, whole grains, legumes, nuts and olive oil while reducing consumption of alcohol and red meat.
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The main benefits of the Mediterranean diet are generally said to be in the area of heart health, but a new study from researchers at the National Eye Institute (NEI) indicates that the diet can also lower the risk of cognitive impairment by as much as half. The research was based on analyses of two existing studies — the Age-Related Eye Disease Study (AREDS) and AREDS2. They were originally sponsored by the NEI in order to investigate risk factors in age-related macular degeneration (AMD) and cataracts and to learn more about how vitamins might affect these eye problems. AREDS included some 4,000 subjects, some with AMD and some without, while AREDS2 included about 4,000 participants with AMD. The new study, which was published in Alzheimer’s and Dementia, the journal of the Alzheimer’s Association, analyzed the data from both AREDS studies to investigate any possible relationship between food consumption and cognitive development, something that was regularly tested during the AREDS research. In the AREDS studies, the researchers at first assessed the subjects of both studies for diet; the AREDS study tested cognitive function at five years while AREDS2 tested it at the beginning and then two, four and ten years later. The AREDS researchers used standardized tests to rate cognitive function and evaluated diet with a questionnaire that asked participants their average consumption of each Mediterranean diet component over the previous year.
According to Emily Chew, MD, of the National Eye Institute and lead author of the new study, studies of the eye are valuable in assessing cognitive decline because the retina is an extension of the brain. As she explained, “A third of your brain functions for vision and the retina lines the eyeball and travels back via an optic nerve all the way to the brain.” The AREDS studies determined that people whose diets were high in fish and vegetables had less AMD. Because the retina is connected to the brain, the researchers surmised, these foods might also improve brain health.
After analyzing the AREDS research, the NEI researchers reported that subjects who most closely adhered to the Mediterranean diet showed the lowest risk of cognitive impairment. High fish and vegetable consumption appeared to have the greatest protective effect. In addition, those who ate the most fish had the slowest rate of cognitive decline. According to Dr. Chew, “People with the higher adherence to the Mediterranean diet had almost a 45% to 50% reduction in the risk of having an impaired cognitive function.” She added, however, that the Mediterranean diet in general didn’t seem to slow cognitive decline in subjects who had the ApoE gene, which significantly raises the risk for Alzheimer’s disease, but when the researchers investigated only fish consumption, they found eating fish twice a week did slow the decline in people who had the gene.
“We do not always pay attention to our diets,” commented Dr. Chew. “We need to explore how nutrition affects the brain and the eye. It’s a public health message. People need to eat well. It’s not like you have to get fresh fish. You can eat a can of tuna, for example.”