Longer-term soy nut consumption improves cerebral blood flow and psychomotor speed: results of a randomized, controlled crossover trial in older men and women

Background Effects of soy foods on cerebral blood flow (CBF)-a marker of cerebrovascular function-may contribute to the beneficial effects of plant-based diets on cognitive performance. Objectives We aimed to investigate longer-term effects of soy nut consumption on CBF in older adults. Changes in 3 different domains of cognitive performance were also studied. Methods Twenty-three healthy participants (age: 60-70 y; BMI: 20-30 kg/m(2)) participated in a randomized, controlled, single-blinded crossover trial with an intervention (67 g/d of soy nuts providing similar to 25.5 g protein and 174 mg isoflavones) and control period (no nuts) of 16 wk, separated by an 8-wk washout period. Adults followed the Dutch food-based dietary guidelines. At the end of each period, CBF was assessed with arterial spin labeling MRI. Psychomotor speed, executive function, and memory were assessed using the Cambridge Neuropsychological Test Automated Battery (CANTAB). Results No serious adverse events were reported, and soy nut intake was well tolerated. Body weights remained stable during the study. Serum isoflavone concentrations increased (daidzein mean difference +/- SD: 128 +/- 113 ng/mL, P < 0.001; genistein: 454 +/- 256 ng/mL, P < 0.001), indicating excellent compliance. Regional CBF increased in 4 brain clusters located in the left occipital and temporal lobes (mean +/- SD increase: 11.1 +/- 12.4 mL center dot 100 g(-1) center dot min(-1), volume: 11,296 mm(3), P < 0.001), bilateral occipital lobe (12.1 +/- 15.0 mL center dot 100 g(-1) center dot min(-1), volume: 2632 mm(3), P = 0.002), right occipital and parietal lobes (12.7 +/- 14.3 mL center dot 100 g(-1) center dot min(-1), volume: 2280 mm(3), P = 0.005), and left frontal lobe (12.4 +/- 14.5 mL center dot 100 g(-1) center dot min(-1), volume: 2120 mm(3), P = 0.009) which is part of the ventral network. These 4 regions are involved in psychomotor speed performance, which improved as the movement time reduced by (mean +/- SD) 20 +/- 37 ms (P = 0.005). Executive function and memory did not change. Conclusions Longer-term soy nut consumption may improve cerebrovascular function of older adults, because regional CBF increased. Effects may underlie observed improvements in psychomotor speed. This trial was registered at clinicaltrials.gov as NCT03627637