In summary, the omni group allowed for the examination of what would
occur via minimal intervention with no recommendation to limit food groups
(i.e., usual diet).
Although only vegan diets require supplementary vitamin B12 [1], to control
for supplement intake across groups, all participants were required to purchase
and take a multivitamin or other form of vitamin B12 daily. After the 2-mo main
intervention was completed, all participants (including the omni group) were
offered monthly meetings to assist with dietary maintenance. Participants were
also provided with a private Facebook group for their diet group after the 2-mo
mark to provide social support in between monthly meetings (joining was
optional). After the 2-mo intensive intervention phase, participants were
encouraged to continue following their assigned diet and meet with their diet
group each month. Participants were told they could make alterations to the diet
if they needed to but were encouraged to maintain their dietary changes. Participants
received handouts and recipes related to the session topic for every
meeting during the 6-mo study. Topic sessions for all the group meetings were
informed by the Diabetes Prevention Program [18] and were grounded in social
cognitive theory [19]. Each class included food samples or a cooking demonstration.
All group sessions covered identical topics among the five groups with
the only difference being the type of diet discussed. The first eight topic sessions
for all groups were as follow: