Nutrition Science and Everyday Application - beta v 0.1

92 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
a Mediterranean diet might also be the same kind of people who exercise more, sleep
more, have higher income (fish and nuts can be expensive!), or be less stressed. These are
called confounding factors; they’re factors that can affect the outcome in question (i.e., heart
disease) and also vary with the factor being studied (i.e., Mediterranean diet).
INTERVENTION STUDIES
Intervention studies, also sometimes called experimental studies or clinical trials,
include some type of treatment or change imposed by the researcher. Examples of
interventions in nutrition research include asking participants to change their diet, take
a supplement, or change the time of day that they eat. Unlike observational studies,
intervention studies can provide evidence of cause and effect, so they are higher in the
hierarchy of evidence pyramid.
The gold standard for intervention studies is the randomized controlled trial (RCT). In an
RCT, study subjects are recruited to participate in the study. They are then randomly
assigned into one of at least two groups, one of which is a control group (this is what
makes the study controlled). In an RCT to study the effects of the Mediterranean diet
on cardiovascular disease development, researchers might ask the control group to follow
a low-fat diet (typically recommended for heart disease prevention) and the intervention
group to eat a Mediterrean diet. The study would continue for a defined period of time
(usually years to study an outcome like heart disease), at which point the researchers would
analyze their data to see if more people in the control or Mediterranean diet had heart
attacks or strokes. Because the treatment and control groups were randomly assigned,
they should be alike in every other way except for diet, so differences in heart disease
could be attributed to the diet. This eliminates the problem of confounding factors found
in observational research, and it’s why RCTs can provide evidence of causation, not just
correlation.
Imagine for a moment what would happen if the two groups weren’t randomly assigned.
What if the researchers let study participants choose which diet they’d like to adopt for
the study? They might, for whatever reason, end up with more overweight people who
smoke and have high blood pressure in the low-fat diet group, and more people who
exercised regularly and had already been eating lots of olive oil and nuts for years in the
Mediterranean diet group. If they found that the Mediterranean diet group had fewer heart
attacks by the end of the study, they would have no way of knowing if this was because
of the diet or because of the underlying differences in the groups. In other words, without
randomization, their results would be compromised by confounding factors, with many of
the same limitations as observational studies.
In an RCT of a supplement, the control group would receive a placebo—a “fake”
treatment that contains no active ingredients, such as a sugar pill. The use of a placebo
is necessary in medical research because of a phenomenon known as the placebo effect. The
placebo effect results in a beneficial effect because of a subject’s belief in the treatment, even
though there is no treatment actually being administered.
For example, imagine an athlete who consumes a sports drink and then runs 100 meters
in 11.0 seconds. On a different day, under the exact same conditions, the athlete is given a
Super Duper Sports Drink and again runs 100 meters, this time in 10.5 seconds. But what
the athlete didn’t know was that the Super Duper Sports Drink was the same as the regular
sports drink—it just had a bit of food coloring added. There was nothing different between