Low-Fat Diet May Improve Biomarker of Alzheimer’s Disease

The 42-amino-acid form of amyloid-beta protein in cerebrospinal fluid (CFS), known as CSF AB42, is considered to be a key biomarker of Alzheimer's disease risk, as some previous studies have reported that declines in CSF AB42 associate with worsening cognitive function and increased risk of Alzheimer's disease.  Suzanne Craft, from the VA Puget Sound Health Care System (Washington, USA), and colleagues recruited 29 patients with amnestic mild cognitive impairment and 20 cognitively normal controls, with the mean age in both groups at about 70 years, and randomly assigned each subject to either a low-fat diet (25% of calories from fat, with less than 7% from saturated fat and a glycemic index of less than 55), or high-fat diet (45% of calories from fat with saturated fat accounting for more than 25% of calories and a glycemic index of more than 70). In addition to CSF AB42, levels of other factors such as insulin, tau protein, and apolipoprotein E in CSF were measured, along with blood lipids and insulin.  In response to the low-fat diet, cognitively impaired patients had increases in CSF insulin and AB42, whereas decreases were seen in the healthy controls.   The high-fat diet seemed to affect the CSF biomarkers only in the normal controls. CSF insulin declined dramatically in controls with this diet but no mean change was seen in the patients. A similar pattern was seen for CSF levels of apolipoprotein E. Relative to those on the high-fat diet, those on the low-fat diet -- among both cognitively impaired patients and controls -- improved their performance on a test of delayed visual memory. Little change from baseline was seen in either group with the high-fat diet, but scores increased substantially from baseline in patients and controls.  The researchers conclude that:  “Our results suggest that diet may be a powerful environmental factor that modulates Alzheimer disease risk through its effects on central nervous system concentrations of A[beta]42, lipoproteins, oxidative stress, and insulin.”