Using evidence to make nutrition decisions: a look at zinc

Evidence-based medicine provides the framework for decisions around clinical practice and treatment guidelines in HIV disease.

There is growing pressure in the field of nutrition to make recommendations, especially with regards to supplementation, using this rigorous method of evaluating the evidence. The strength of a recommendation, ranging from “should always be offered” to “should never be offered,” depends on the quality of evidence that is available. The gold standard is the randomised clinical trial, usually a double-blinded, placebo-controlled intervention study, which decreases bias and gives the most objective results. The weakest evidence is considered to be “expert opinion.”

In nutrition, there have been only a few randomised clinical trials, which makes it difficult to find proof of benefit or proof of cause and effect. Instead, we often rely on in vitro (test-tube) studies, epidemiological evidence (population studies), animal studies, and anecdotal evidence such as case reports and hearsay. As a result, expert opinion often serves to guide our decisions. Nutrients are hard to study with the usual scientific methods because there are complex interactions between the gut, immune system, viral replication and the nutrients. The body’s way of handling a systemic infection is called the acute phase response. When this occurs, the metabolism of micronutrients is altered, making it difficult to accurately assess deficiency.