My Clinical Nutrition professor is one passionate guy. He gets really worked up over stupid nutrition theories that people have that aren't supported by research nor basic scientific common sense. It's a good thing he's entertaining: the class is five hours long, we need it to be interesting!
The main concept he drove home during Thursday's class was the concept of biomarkers. To summarize, have you ever heard in the media, read in a health magazine or book, or hear someone quote some obscure molecule that prevents cancer? Here is an example: "Sodium kills! Research has shown that diets high in sodium predispose people to heart attacks." Well the truth is that sodium doesn't directly kill people or cause heart attacks. In these research studies, sodium is used to measure the effect of processed foods on heart attacks. Researchers aren't able to measure the effect of a particular food on a biological level. So, they instead chose a molecule that is high abundance in the food they are studying and measure that. Then they publish their research saying that their biomarker (the molecule they are measuring to determine the effect of the whole food on the body) causes or prevents X, Y, and Z. THEN the media takes hold of the study and gets everybody worked up over the biomarker and forget the actual food the researchers were really trying to study. The problem isn't really salt, but processed foods which happen to have a lot of salt in them.
A few other examples of biomarkers include flavonoids and vitamin C (markers of fruit and vegetable consumption), reversatol (marker of red wine consumption), and omega-3s (marker of fish consumption).
The big problem with the media and general public obsessing over biomarkers is that they forget about the big picture and think that a simple tablet of vitamin C or an expensive reversatol supplement will make them healthier and will prevent disease, when the truth is that whole, healthy foods are what make people healthy and disease-free.
To summarize, beware of health claims that promote a single molecule cure or culprit.