High-carb diet is linked to early Alzheimer's

• Balanced diet of protein, fat and carbs is best
• Carbs might be linked to buidup of toxic proteins in brain
• Diet might be a way to prevent Alzheimer's from starting

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

Sugars also played a role in the development of MCI, often a precursor to Alzheimer's disease, according to the report in the Journal of Alzheimer's Disease. Eating more proteins and fats offer 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 15-month follow-ups. By the study's fourth year, 200 of the 940 were beginning to show mild cognitive impairment, problems with memory, language, thinking and judgment.

Not everyone with MCI goes on to develop 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 adults in the nation, numbers that are expected to triple by 2050 as the Baby Boomers age.

"The research field is trying to find things that can help reduce risk factors for pre- dementia problems,'' says Roberts. "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."

Among the 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 also play a role in the development of beta amyloid plaques. Those proteins are toxic to brain health and 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% less likely to get cognitive impairment, while those who had the highest intake of protein (chicken, meat, fish) had a reduced risk of 21%.

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

"This (study) is consistent with what we've seen in past published research on how a lower carbohydrate diet can help to reduce the risk of Alzheimer's,'' says Colette Heimowitz, vice president of Nutrition and Education for Atkins Nutritionals Inc.

The authors write that unsaturated fats and proteins might be important to the brain by maintaining insulin sensitivity, the integrity of the neuron structure and the successful firing of neurotransmitters.

There is no treatment for Alzheimer's disease, only drugs to treat symptoms. 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."