Diagnosing Alzheimer's with peanut butter - researchers caused a sensation with this study in 2013. It has since been regularly quoted by various media, including the Washington Post, which promoted the idea again just last year. But can the diagnosis of a still-incurable disease be so simple?

The peanut butter test

For the test, the patient has to smell peanut butter alternately with the left and right nostril while the other one is held closed. The patient starts sniffing at a distance of 30 centimetres. The distance is then reduced in one-centimetre steps until the patient is able to smell the product.

According to the 2013 study, Alzheimer's patients have a significantly poorer olfactory ability with their left nostril than with their right. The researchers attribute this to the fact that the left half of the frontal lobe of the brain is affected more by Alzheimer's disease. This area also contains the sense of smell.

But it is not that simple, says Richard Dodel, Professor for Geriatrics at the University of Duisburg-Essen, Germany.

"This study was carried out with too few test subjects and the procedure was not sufficiently standardised," he criticises. For example, the study, which had just 92 subjects, lacks information on which brand of peanut butter was used. "The composition of oils can make a big difference in perception," explains Dodel. There are also numerous other possible causes for a limited sense of smell. And in 2014 a second group of researchers tried to recreate and confirm the results, without success.

Read more: How mysterious smell memories overpower us

Diagnostic options for Alzheimer's disease

Alzheimer's disease can be diagnosed many years before the first symptoms become noticeable. Two imaging procedures and one invasive procedure dominate. According to Dodel, the so-called amyloid PET (positron emission tomography) can detect certain protein fragments, the so-called plaques, in the brain, 15 to 20 years before the first clinical symptoms.

In the second method, FDG-PET, the brain cells are examined to see how quickly they are able to degrade a specific sugar molecule. The brain areas that no longer process the molecule normally are already damaged, explains Dodel. The third method involves the examination of cerebrospinal fluid. Here, too, the doctor looks at the concentration of certain proteins.

When the first symptoms appear, the first three methods keep being an option. However, new neuropsychometric tests are being added. Using various questionnaires and examinations, the doctor puts the patient's brain to the test. One of the best-known tests is the clock test. The patient is asked to draw numbers from one to twelve onto a clock. The patient is then asked to enter the hands for a specific time. If this no longer works, or if the result is strangely shifted, this is a very clear indication of advanced dementia. Whether this is Alzheimer's must be tested with more detailed psychometric examinations.

Prevention is better than care

It is precisely because there is currently no cure for Alzheimer's disease that experts such as Richard Dodel are recommend preventive measures. "Education is a very important factor," says the physician. Although this is less a problem in Germany than in other countries, a good education in the first third of life can reduce the risk of developing Alzheimer's by up to eight percent.

With increasing age, further factors come into play. For example, it is very important to compensate for hearing and vision impairments with hearing aids and vision aids. If the brain is no longer used normally in these areas, the disease will advance.

"Excercise is also a major factor," says Dodel, who recommends dancing in particular. "But tango is better than waltzing. Because at some point you can do the waltz unconsciously, but with Tango you always have to think about complicated steps." Being overweight, diabetes and vascular diseases are also additional risk factors. Therefore, smoking, alcohol and an unbalanced diet can also increase the risk.

Last but not least, it is important to be in regular contact with other people. Loneliness and social isolation keep the brain idle. "If you can exclude all risk factors, you can reduce your risk by up to 35 percent," summarizes Dodel.