Nutrition experts have long advised against eating a sugar-rich diet high in saturated fats because it can lead to obesity, diabetes and heart disease, all risk factors for Alzheimer’s disease. Now a new study shows why such a diet may be bad for the brain.
Researchers found that eating a high-fat, sugary diet, even for a short time, robs the brain of a substance that helps clear the brain of beta-amyloid. In its toxic form, beta-amyloid can build up and form the gummy plaques that are a hallmark of Alzheimer’s disease.
For the study, the researchers looked at 20 seniors with no signs of Alzheimer’s disease, and 27 older adults with mild cognitive impairment, a form of memory loss that can lead to Alzheimer’s disease. The study participants were also tested to see if they carried the APOE-E4 gene, which raises the risk of developing Alzheimer’s disease (though many carrying the gene do not get Alzheimer’s).
Half were randomly assigned to a diet high in saturated fat and with a high glycemic index. Foods with a high glycemic index quickly turn to sugar (glucose) in the blood, and include carbohydrate-rich foods like white bread, pasta, and sugar-rich baked goods. The diet consisted of more than 25 percent saturated fat (the kind found in meats and butter), 35 to 40 percent sugary carbohydrates, and 15 to 20 percent protein. They followed the diet for four weeks.
The other half ate a diet low in saturated fat and with a low glycemic index, though they ate the same number of calories. Foods with a low glycemic index include fiber-rich vegetables and whole grains. The diet consisted of less than 7 percent saturated fat, 55 to 60 percent low-glycemic carbohydrates, and 15 to 20 percent protein.
Over the four-week course of the study, diet seemed to alter levels of toxic beta-amyloid in the spinal fluid. Those who ate the low glycemic, low saturated fat diet tended to have lower levels of toxic beta-amyloid, while those who ate the high glycemic, high saturated fat diet had high levels of the toxic protein.
Normally, beta-amyloid binds to a chemical called apolipoprotein E, or ApoE, which then shuttles it out of the brain. But in those consuming the high-fat, high-sugar diet, ApoE levels were diminished, so more beta-amyloid was left in a free form, which might lead to plaque formation. The free beta-amyloid was also in a form that proves particularly toxic to brain cells. The findings were published in the journal JAMA Neurology.
The study does not prove that a high-fat sugary diet leads to Alzheimer’s. Diet is just one of many factors that may be involved in the disease. But it does show how diet can adversely affect the brain, even after just a few weeks.
“The important lesson from the study is that dietary intervention can change brain amyloid chemistry in largely consistent and apparently meaningful ways – in a short period of time,” wrote Dr. Deborah Blacker, director of the Gerontology Research Unit at Massachusetts General Hospital in Boston in an editorial accompanying the study. “Does this change clinical practice for those advising patients who want to avoid dementia? Probably not, but it adds another small piece to the growing evidence that taking good care of your heart is probably good for your brain too.”
Source: Angela J. Hanson MD, Jennifer L. Bayer-Carter PhD, et al: “Effect of Apolipoprotein E Genotype and Diet on Apolipoprotein E Lipidation and Amyloid Peptides: Randomized Clinical Trial.” JAMA Neurology, Vol. 70 (No. 6), 2013. doi:10.1001/jamaneurol.2013.396