Intervention intensity was the most important factor
for differences in effect size among different trials.
However, the effects of counseling intensity could not
be fully disentangled from the risk among the populations
studied. Although trials in populations with
known traditional cardiovascular risk factors or risk
equivalents were excluded, many of the medium- to
high- intensity interventions were conducted in participants
selected for suboptimal lifestyle behaviors or factors
associated with increased cardiovascular disease
(Table 2). In multivariate meta-regression, both intervention
intensity and risk in the population predicted
larger effects. In addition, some participant populations
were volunteers. Exploratory meta-regressions suggested
that use of volunteer participants was also predictive of
larger effect sizes, although in multivariate analyses this
was significant only for dietary fat intake. Almost all of
the effective medium- to high-intensity interventions
were delivered by specially trained health educators or
nurses, counselors or psychologists, dietitians or nutritionists,
or exercise instructors or physiologists; very few
involved the primary care provider (Table 2). Many of
the high-intensity interventions used 12 or more sessions
and therefore required resources that may not
be available or paid for in the current health care system
(in addition to raising issues of real-world patient
adherence).