A HOUSE OF PROTEINS 39with disease rates in 1990, then observe whether any changes in disease
rates correspond to dietary changes.
In addition to observing what already exists, we might do an experi-
ment and intentionally intervene with a hypothetical treatment to see
what happens. We intervene, for example, when testing for the safety
and efficacy of drugs. One group of people is given the drug and a sec-
ond group a placebo (an inactive look-alike substance to please the
patient). Intervening with diet, however, is far more difficult, especially
if people aren't confined to a clinical setting, because then we must rely
on everyone to faithfully use the specified diets.
As we do observational and interventional research, we begin to amass
the findings and weigh the evidence for or against a certain hypothesis.
When the weight of the evidence favors an idea so strongly that it can no
longer be plausibly denied, we advance the idea as a likely truth. It is in
this way that I am advancing an argument for a whole foods, plant-based
diet. As you continue reading, realize that those seeking absolute proof
of optimal nutrition in one or two studies will be disappointed and con-
fused. However, I am confident that those seeking the truth regarding diet
and health by surveying the weight of the evidence from the variety of
available studies will be amazed and enlightened. There are several ideas
to keep in mind when determining the weight of the evidence, including
the following ideas.CORRELATION VERSUS CAUSATION
In many studies, you will find that the words correlation and association
are used to describe a relationship between two factors, perhaps even in-
dicating a cause-and-effect relationship. This idea is featured prominently
in the China Study: We observed whether there were patterns of associa-
tions for different dietary, lifestyle and disease characteristics within the
survey of 65 counties, 130 villages and 6,500 adults and their families.
If protein consumption, for example, is higher among populations that
have a high incidence of liver cancer, we can say that protein is positively
correlated or associated with liver cancer incidence; as one goes up, the
other goes up. If protein intake is higher among populations that have a
low incidence of liver cancer, we can say that protein is inversely associ-
ated with liver cancer incidence. In other words, the two factors go in the
opposite direction; as one goes up, the other goes down.
In our hypothetical example, if protein is correlated with liver can-
cer incidence, this does not prove that protein causes or prevents liver