Amino Acid Found in Certain Food Could Increase Alzheimer's Risk

According to a study by researchers, a diet rich in methionine, an amino acid typically found in red meats, fish, beans, eggs, garlic, lentils, onions, yogurt and seeds, can possibly increase the risk of developing Alzheimer's disease.

"When methionine reaches too high a level, our body tries to protect itself by transforming it into a particular amino acid called homocysteine," said lead researcher Domenico Praticò. "The data from previous studies show, even in humans, when the level of homocysteine in the blood is high, there is a higher risk of developing dementia. We hypothesized that high levels of homocysteine in an animal model of Alzheimer's disease would accelerate the disease."

Using a seven-month old mouse model of Alzheimer's disease, they fed one group an eight-month diet of regular food and another group a diet high in methionine. The mice were then tested at 15 months of age, the equivalent of a 70-year-old human.

"We found that the mice with the normal diet had normal homocysteine levels, but the mice with the high methionine diet had significantly increased levels of homocysteine, very similar to human subjects with hyperhomocysteinemia," said Praticò. "The group with the high methionine diet also had up to 40 percent more amyloid plaque in their brains, which is a measurement of how much Alzheimer's disease has developed.

Image: A brain sample taken from mice used in a Temple University study on how a diet rich in the amino acid methionine may increase the risk of Alzheimer's disease. The dark spots are consistent with amyloid plaque, indicative of the progression of Alzheimer’s disease. Mice fed diets rich in methionine had an increased level of homocysteine and up to 40 percent more amyloid plaque in their brains.

The researchers also examined capacity to learn a new task and found it diminished in the group with the diet high in methionine.

Still, Praticò emphasized, methionine is an essential amino acid for the human body and "stopping one's intake of methionine won't prevent Alzheimer's disease. But people who have a diet high in red meat, for instance, could be more at risk because they are more likely to develop this high level of circulating homocysteine," he said.

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References:
1. Domenico Praticò, et al. Diet-induced hyperhomocysteinemia increases Amyloid-ß formation and deposition in a mouse model of Alzheimer's disease.Curr Alzheimer Res, 2009. PMID: 19939226