Longer-Term Soy Consumption Improves Cerebral Blood Flow and Psychomotor Speed: Results of a Randomized, Controlled Cross-Over Trial in Older Males and Females

Abstract

ObjectivesEffects of plant-based diets on cerebral blood flow (CBF), which is a physiological marker of cerebrovascular function, have hardly been studied and may contribute to the beneficial effects of these diets on cognitive performance. Therefore, the primary objective of this study was to investigate longer-term effects of soy nut consumption on CBF in older men and women. Changes in cognitive performance were also studied. MethodsA randomized, controlled, cross-over trial was performed with a sixteen-week intervention period, separated by a wash-out period of eight weeks. Twenty-three males and females, aged 64 ± 3 (mean ± SD) years and with a BMI of 25.9 ± 2.7 kg/m2, started with the soy intervention period (67 g of soy nuts daily providing 25.5 g soy protein) or control period (no nuts). The two periods were separated by a wash-out period of eight weeks. At the end of each period, CBF was assessed with arterial spin labeling magnetic resonance imaging. Cognitive performance was assessed in the main cognitive domains using well-validated CANTAB tests. ResultsSerum isoflavone concentrations significantly increased after the soy intervention (daidzein Δ 133 ± 113 ng/mL, P < 0.001; genistein Δ 456 ± 256 ng/mL, P < 0.001), indicating good compliance. Regional increases in CBF were observed in four brain regions that are involved in object recognition, visual information processing and target reorientation. These brain clusters were located in the (1) left occipital and temporal lobe (Δ 36%, volume 11,296 mm3, P < 0.001), (2) bilateral occipital lobe (Δ 32%, volume 2632 mm3, P = 0.002), (3) right occipital and parietal lobe (Δ 47%, volume 2280 mm3, P = 0.005). The fourth cluster was located in the left frontal lobe (Δ 43%, volume 2120 mm3, P = 0.009), and is part of the ventral network, which is involved in task-relevant stimuli. Movement time during the psychomotor speed test was reduced by 7% (P = 0.005), while no changes were observed in executive function or memory. ConclusionsA longer-term soy nut intervention improved cerebrovascular function in older adults, as regional CBF increased. These effects may underlie observed beneficial effects on cognitive performance in the psychomotor speed domain. Funding SourcesThis research was supported by a grant from the Alpro Foundation.