**The Effect of Whey and Soy Protein Isolates on Cognitive Function in Older Australians with Low Vitamin B12: A Randomised Controlled Crossover Trial**

#### **Ian T. Zajac \*, Danielle Herreen, Kathryn Bastiaans, Varinderpal S. Dhillon and Michael Fenech**

Health & Biosecurity, Commonwealth Scientific and Industrial Research Organisation (CSIRO), 5000 Adelaide, South Australia, Australia

**\*** Correspondence: ian.zajac@csiro.au; Tel.: +61-8-8303-8875

Received: 29 November 2018; Accepted: 17 December 2018; Published: 21 December 2018

**Abstract:** Whey protein isolate (WPI) is high in vitamin B12 and folate. These and other related markers (holotranscobalamin, methylmalonic acid and homocysteine) have been linked with cognitive health. This study explored the efficacy of WPI for improving cognitive function via delivery of vitamin B12. Moderately vitamin B12-deficient participants aged between 45 and 75 years (*n* = 56) were recruited into this randomised controlled crossover trial. Participants (55% female) consumed 50 g whey (WPI; active) or soy protein isolate (SPI; control) for eight weeks. Following a 16-week washout phase, they consumed the alternative supplement. Consumption of WPI significantly improved active B12 and folate status but did not result in direct improvements in cognitive function. However, there was evidence of improvement in reaction time (*p* = 0.02) and reasoning speed (*p* = 0.04) in the SPI condition for females. Additional analyses showed that changes in active B12, HcY and folate measures during WPI treatment correlated with improvements in cognitive function (all *p* < 0.05). Results indicate that WPI itself did not result in improved cognitive function but some evidence of benefit of SPI for females was found. However, consistent with previous research, we present further evidence of a role for active B12, HcY and folate in supporting cognitive improvement in adults with low B vitamin status.

**Keywords:** whey protein isolate; dairy; cognitive function; cobalamin; vitamin B12
