Smells Like Satiety

The NYT Well Blog recently covered a fascinating study out of TUM* in Munich, Germany: olive oil may cause you to feel satiated faster and eat less food. Apparently, study volunteers fed yogurt with olive oil mixed in showed a spike in serotonin levels, and ate about 175 calories less each day than experimental groups given different fats (rapeseed, butterfat, or lard).

But was it the fat, or was it the flavor? The researchers isolated aroma compounds from the olive oil, specifically hexanal and 2E-hexenal, and mixed them in with yogurt. Same effects! In the press release, Prof. Peter Schieberle comments "Our findings show that aroma is capable of regulating satiety."

Smells rule neurochemistry. It wasn't that long ago, really, that Axel and Buck won the 
Nobel Prize for their research into olfactory organization. Two years later, another unsolved mystery, that of "blood smell," came to light in ACIEE. Turns out, both blood smell and the new research on olive oil aroma depend partially on medium-chain aldehydes (hexanal-decanal) and unsaturated ketones. You can even smell ketosis, an alternative metabolism found in diabetic crises and Atkins dieters, by the tangy, astringent odor on the breath. 

Amazing how sensitive the human nose is for volatile carbonyls! Perhaps this harks back to a rather strange notion of odotopes, or "weak-shape" theory. This suggests that, rather than the "lock-and-key" model observed for enzymatic binding, smell may result from a collection of weak interactions with multiple receptors, based predominantly on molecular shape. 

*Bonus note: I knew I recognized the TUM group from somewhere! Remember this abstract, from J. Agric. Food Chem. last year? Based on my (single, not to be repeated) experience with durian fruit candy, I do wonder how they convinced this poor scientist to be the GC smell-port 'volunteer.'

You couldn't pay me enough.
Source: Steinhaus, TUM | J. Agric. Food Chem 2012