A new diagnostic test for Alzheimer's involves peanut butter.

The "peanut butter test" is based on research showing that the ability to smell involves parts of the brain first affected in cognitive decline, and for some reason, the left nostril becomes more impaired than the right in Alzheimer's.

The test involves capping one nostril and measuring the distance at which a patient can smell peanut butter. For Alzheimer's, the left nostril has about 10 centimeters less range than the right.

Some doctors say the peanut butter test could be an inexpensive, non-invasive early warning system for the disease. 

--Rob Archer