Saturday, October 20, 2012

High-carb diet may impair brain function

Older people who load up their plates with carbohydrates have nearly four times the risk of developing mild cognitive impairment, a new study finds.

Sugars also played a role in the development of MCI, which is often a precursor to Alzheimer’s disease, says the report in the newest Journal of Alzheimer’s Disease. Eating more proteins and fats offers some protection from MCI.

Mayo Clinic researchers tracked 1,230 people ages 70 to 89 and asked them to provide information on what they ate the previous year. Among that group, only the 940 people who showed no signs of cognitive impairment were asked to return for follow-ups every 15 months.

By the study’s fourth year, 200 of the 940 were beginning to show mild cognitive impairment — problems with memory, language, thinking and judgment. Compared with people who rank in the bottom 20 percent for carbohydrate consumption, those in the highest 20 percent had a 3.68 times greater risk of MCI, the study found. Overall, about six in every 100 people develop MCI in their lifetime.

Not everyone with MCI develops Alzheimer’s disease, but many do, says lead author Rosebud Roberts, a professor in the department of epidemiology at the Mayo Clinic in Rochester, Minn. Alzheimer’s affects 5.2 million U.S. adults, numbers that are expected to triple by 2050.

“If we can stop people from developing MCI, we hope we can stop people from developing dementia. Once you hit the dementia stage, it’s irreversible,” says Roberts.

Among foods regarded as complex carbohydrates: rice, pasta, bread and cereals. The digestive system turns them into sugars. Fruits, vegetables and milk products are simple carbs.

“A high-carbohydrate intake could be bad for you because carbohydrates impact your glucose and insulin metabolism,” says Roberts. “Sugar fuels the brain, so moderate intake is good. However, high levels of sugar may actually prevent the brain from using the sugar — similar to what we see with type 2 diabetes.”

Roberts says high glucose levels might affect the brain’s blood vessels and play a role in the development of beta amyloid plaques, proteins toxic to brain health that are found in the brains of people with Alzheimer’s. Researchers don’t know what causes the disease, but they suspect the buildup of beta amyloid is a leading cause.

Also among the study’s findings:

Those whose diets were highest in fat (nuts, healthy oils) were 42 percent less likely to get cognitive impairment, while those who had the highest intake of protein (chicken, meat, fish) had a reduced risk of 21 percent.

Several popular diets, including the Mediterranean (fish, poultry-based protein; plenty of plant-based foods and healthy fats) and Atkins (low-carb, meat-lover’s diet), make pitches for the multiple health benefits from lowering carb intake, including reduced risk for heart disease and diabetes, and improved brain health.

Eric Westman of Duke University Health System, who is author of The New Atkins for a New You, called this “a provocative, preliminary study that suggests that we can add the loss of mental function in older age to the list of medical problems caused by excessive carbohydrate consumption. This is not proof that a low-carb diet will fix dementia, but it is a good argument for conducting studies to determine if it can.”

Roberts says the study offers hope because “it shows a modifiable way we can reduce risk for the disease. It is important to eat a balance of protein, carbohydrates and fat.”

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