Organic chemistry's an intricate subject. Media chatter about wellness, though, is an action movie, where "good" molecules (like Omega-3 fatty acids) battle "bad" ones (like LDL cholesterol). If they could, Americans would gladly take LDL cholesterol out and lynch it, before it twirls its mustache again and kills some more of us. Marketers and PR people love this kind of clarity, because it really sells their message. Like Wile E. Coyote chasing the Road Runner, they want to pin down ever-moving, uncatchable science, and cook it down to tasty little bits.

Beep-beep! The clarity of marketers and PR people is a false light. No molecule is entirely bad, not even "bad" cholesterol. Case in point: Low levels of cholesterol have been linked in a number of studies to depression, violence and, especially, suicide.

Not everyone agrees that the effect is real, or strong enough to raise concerns about the effects of crash diets. (This review concluded that doctors should only worry about lowering the cholesterol of a vulnerable minority of people with psychiatric problems.) Moreover, the association doesn't say anything about cause and effect. Low cholesterol levels and "suicidality" could be parallel symptoms of some other underlying problem. Speculation runs free because no one has found a precise physiological pathway that connects cholesterol levels in the blood to thoughts about suicide in the mind.

Still, in this study in the January Journal of Affective Disorders, Aleksandra Lalovic of McGill University and her colleagues suggest a place to look for such a pathway. They examined the brains of 22 men who had committed suicide and found that three genes involved in both fat metabolism and immune function were much less active in the frontal cortex regions of the suicides' brains than in those of 13 other men used for comparison. If low cholesterol levels change the metabolism of brain regions involved in conscious thought and planning, there might be a cause-and-effect relationship after all. Not exactly material for a simple health message. Just a reminder that simple health messages always come short of life's complexity.