The Impact of Acute Soy Isoflavone Consumption on Cognition

1
The Impact of Acute Soy Isoflavone Consumption on
Cognition Among Healthy Young Adults David F.
Vanata1, Ph.D., R.D., L.D. Mitchell Metzger2,
Ph.D. 1Dept. of Family and Consumer Science
2Dept. of Psychology
INTRODUCTION Several potential health benefits
associated with soy-based food products have
previously been identified including reducing the
risk of coronary heart disease and some forms of
cancer, positively impacting bone density, and
improving cognitive function. While some
epidemiological and clinical data have implicated
a relationship between dietary soy consumption
and health, the evidence related to improvements
on cognitive function are less conclusive. Many
of the proposed health benefits obtained from
dietary intake of soy have been attributed to its
isoflavone content, primarily the aglycones
genistein and diadzein. Investigations
examining soys effect on cognition have mostly
focused on longitudinal consumption among adults,
and, specifically, pre- or post-menopausal women.
As there have been fewer studies examining the
impact of soy intake on younger populations, the
purpose of this study was to assess the effects
of an acute consumption of soy isoflavones,
genistein and diadzein, among a sample of healthy
young adults.
RESULTS The SOY and WHEY groups performed
similarly on all of the cognitive tests prior to
protein consumption, as the only difference
between the groups occurred on the first trial of
the VSM (F1,484.11, plt.05). As expected, group
means for both conditions improved across
repeated trials of the VSM task (F2,14757.37,
plt.01). For the word recall and recognition
tasks, regardless of which task was analyzed,
performance between participants in the SOY and
WHEY conditions were similar. Post-consumption
performance was similar to that prior to soy or
whey administration, as the groups performed
similarly on the VSM and verbal tasks. As with
the pre-consumption measures, performance did
improve over the three trials of the VSM
(F2,14737.76, plt.01). There were, however, no
differences between the groups on any of the VSM
trials, nor on the recall or recognition tasks
(for all comparisons, pgt.05).
Each participant indicated that they had fasted
for at least 8 hours prior to the experiment.
The sessions consisted of three phases (1)
Initial cognitive testing, (2) protein
consumption, and (3) subsequent cognitive
testing. During initial testing, subjects first
completed the VSM. Sixteen pictures were
projected on a 44 grid for ten seconds, followed
by a blank screen. Subjects were given a blank
44 grid and reproductions of each photograph,
and they were required to place the objects in
the correct locations on the grid. After the
first trial, two identical trials of the VSM were
completed (using the same objects in the same
location). After completion of the VSM, a verbal
task ensued. Twenty words were presented for 2
seconds each (with a 2 second ISI). A word
recall task followed, as subjects were given two
minutes to write down as many of the words that
they remembered from the list. A recognition
test occurred next, where participants identified
the words from a list of 40 items (20 original
and 20 new words). Immediately after the initial
cognitive testing session, participants consumed
the soy or whey protein shake (subjects were
blind to protein condition). The subsequent
testing session occurred approximately 1.75 hours
after protein consumption. The second testing
procedure was identical to that of the initial
testing, other than the stimuli for both tasks
were different from the first testing session.
METHODS Fifty college students (37 females and
13 males, M 19.9 years) participated. Protein
shakes consisting of soy protein (50 grams/shake)
containing 54 mg of isoflavones 38 grams total
aglycones (genistein and diadzein) and whey
protein (50 grams/shake) containing no
isoflavones, were formulated by diluting the
powders into 400ml of tap water. To increase the
palatability and visual appeal of the drinks,
three packets of Equal sweetener and several
drops of red food coloring were added. Stimulus
lists for word recall and recognition tests were
constructed using normed values determined by
Pavio et al. (1968). Photographs of common
objects used for the visual-spatial memory (VSM)
task were likewise standardized, and were taken
from the International Affective Picture System
(Lang et al., 1988). Stimuli were incorporated
into a PowerPoint slideshow, and projected onto a
screen via an LCD projector. Participants
penciled their responses onto prepared answer
sheets.
CONCLUSION Taken together, these results suggest
that an acute dose of soy protein, containing the
isoflavones genistein and diadzein, did not
positively impact memory in the young adult
sample tested here. These data do not permit us
to determine whether soy isoflavones,
administered to older adults and/or pre/post
menopausal women, would enhance memory. However,
it is clear that isoflavone administration, in
the doses administered here, was not effective in
enhancing performance on either the VSM task or
word recall/recognition procedures employed in
this experiment.