MONDAY, June 13, 2011 (HealthDay News) — The low-fat, low-glycemic diet often promoted for general health and well-being may lower the risk of developing Alzheimer's disease if adopted early in life, researchers say. 

But starting such an eating plan after symptoms surface doesn't seem to help prevent deterioration of brain function, according to new research published online June 13 in Archives of Neurology. 

"This is not the first time this concept has emerged, that things you do in midlife or earlier on may have effects later on," said Dr. Marc L. Gordon, chief of neurology at Zucker Hillside Hospital and an Alzheimer's researcher at the Feinstein Institute for Medical Research in Manhasset, N.Y. 

"For example, we know that midlife obesity is associated epidemiologically with a higher risk of late-life dementia," he continued. "Whether that's causal or an effect of the disease is open to speculation, but it suggests that there may be periods of vulnerability that are different in different times in the life span." 

Although numerous studies have probed connections between lifestyle factors and cognitive ability, no solid proof yet exists that diet (or much else) can prevent Alzheimer's, the most common form of dementia among the elderly. 

A low-glycemic diet, which focuses on eating fruits and vegetables, whole grains and lean meats, avoids spikes in blood sugar and is said to promote feelings of fullness. 

A U.S. National Institutes of Health conference convened last spring concluded that, for now, older age is the leading known risk factor for Alzheimer's disease. A gene variation is also tied to increased risk for the brain disorder, the NIH review said. Experts at the conference stressed that the general public should still focus on avoiding behaviors already linked to other chronic diseases. 

This new study looked at the effect of different diets on biomarkers associated with Alzheimer's, such as blood sugar levels, cholesterol and blood lipid levels. The researchers also tested memory after participants followed the assigned diets. 

Twenty healthy adults and 29 with mild memory problems that could be predictive of Alzheimer's followed either a high-fat, high simple-carbohydrate diet ("HIGH" diet) or a diet lower in fat and simple carbohydrates ("LOW" diet). 

After four weeks, healthy participants on the LOW diet had changes in biomarkers, including insulin and lipid levels in the blood, which were moving away from those normally associated with dementia. 

In participants with mild cognitive impairment, this diet had the opposite effect. 

Commenting on the study, Dr. Suzanne de la Monte, professor of neurosurgery and pathology at Brown University and Rhode Island Hospital in Providence, said it remains to be seen if the changes noted in this study actually translate, over the longer term, into differences in risk for developing Alzheimer's disease. 

The bottom line, though, is the same as it's been for eons: A healthy diet lowers your risk of type 2 diabetes, heart disease, cancer and maybe even Alzheimer's. 

That means staying away as much as possible from processed foods, de la Monte advised. 

A second study, in the same issue of the journal, also looked at biomarkers and found that different levels were associated with different measures of cognitive function associated with Alzheimer's disease. 

This finding could help improve diagnosis of Alzheimer's, which now relies mostly on clinical observation.