EFFECTS OF DIETARY SATURATED FATS AND SIMPLE CARBOHYDRATES ON CEREBRAL PERFUSION: A RANDOMIZED TRIAL

Abstract

Diets high in saturated fat and simple carbohydrates have been associated with an increased risk of Alzheimer's disease (AD) whereas low saturated/low simple carbohydrate diets are associated with lowered risk. In healthy midlife adults, consumption of high-saturated fat may prompt a cascade of inflammatory response and deleterious changes in vascular function that may promote AD pathological processes. The current study examined the impact of controlled diet intervention on cerebral perfusion as assessed with pseudocontinuous arterial spin labeling Magnetic Resonance Imaging (pcASLpMRI) in normal adults and adults with amnestic mild cognitive impairment (MCI), a presumed prodrome of AD. Fifty-three middle-aged adults with normal cognition (n=35, mean age 48 ±2.5 years) or MCI (n=18, mean age 52.5±3.5years) were randomized to receive one of two 4-week isocaloric experimental diets, a high saturated fat, high glycemic index, and high salt (HSF/HGI/HNa+) or a low saturated fat, low glycemic index, and low salt (LSF/LGI/LNa+). Prior to and after the completion of the experimental diet participants underwent pcASLpMRI. A whole-brain voxel-wise full factorial analysis was conducted in Statisical Parametric Mapping (SPM12) to examine diet group effects on pcASLpMRI. Regions were considered significant at p=0.005 with a voxel threshold of 50. A direct comparison of cerebral perfusion changes following 4 weeks of experimental diet intervention across diet groups revealed that the LSF/LGI/LNa+ group showed greater cerebral perfusion in several regions of the brain typically affected in AD. Regions of significance include the inferior frontal gyrus, middle and inferior temporal gyrus, postcentral gyrus, parahippocampal gyrus and the hippocampus. Similar patterns were observed for normal and MCI groups. Our findings suggest that diet influences cerebral blood flow such that consumption of foods high in saturated fats, simple carbohydrates, and sodium negatively affects cerebral perfusion particularly in brain regions that play integral role in memory and are also negatively affected by AD. Conversely, consumption of a low saturated fat, carbohydrate, and sodium diet promotes cerebral perfusion in these regions. Overall, the current study suggests that poor diet may confer risk for AD by reducing cerebral perfusion possibly through vasoconstriction and reduced capillary recruitment.