And measurement of urinary metabolites - small molecules produced from foods, drinks, drugs, environmental contaminants, bodily waste products and bacterial by-products -
is key to the analysis.
We applied this approach to an elusive condition that has always evaded diagnosis: socially and psychologically distressing odors that occur without a known or apparent cause.
The figure below summarizes preliminary results of metabolic profiling performed by Dr. Wishart's research group, using direct Flow Injection Mass Spectrometry (DI-MS).
No measurement differed from normal population values - individuals that never complained of any unusual odor problems or other notable medical issues) - even for the "smelliest" compounds such as Putrescine (rotting fish smell) or Spermidine (sperm-like or bleach-like smell). Moreover, average values for these metabolites were actually lower in our cohort, as were values for selected aminoacids, although some aminoacids, biogenic amines and lipids were slightly higher than averages for normal population. So there were definitely significant albeit subtle differences in metabolism between the control and test group, as well as among the participants.
We combined results for all 95 metabolites using a uniform standard scale. A statistical technique, Principal Component Analysis (PCA), uncovered combinations that best differentiated the participants. The figure shows that there are at least two or three different types of profiles. Is there something in common between participants in each group?
Our questionnaire shows that there is, and it is not the diet!
Participants from the first group (green dots) had very different diets ranging from plant-based, low choline, low carb and Paleo diets to standard American and junk food diets. They seemed to be more tolerant to sugar than other groups, but more sensitive to dairy/lactose. All participants reported exhibiting sour odors including vinegar, ammonia, fishy and urine-like odors. When the usual odor was less sour (but nonetheless unpleasant), it became more sour with lower blood sugar (for example, with alpha lipoic acid supplements). Chlorophyll supplements led to a grass- or weed-like smell. This group was similar to the "sour" group from our earlier study in UK (NCT02692495, discussed in this video).
The second group (purple dots) was similar to the "sweet" group from the earlier UK study. Participants seemed to be more sensitive to sugar and carbohydrates, and to environmental triggers. Main odors experienced ranged from fecal, sewage, cheese-like, rubber, burning, tobacco smoke (participants were non-smoking), barn, rotten eggs and mold. Dairy could make odors "cheesier".
The third group was also sensitive to sugar, but the main difference with first and second groups was structural gastrointestinal issues. This group had a different diet from other groups too, it was 98-100% vegan. But further testing is needed before any conclusions can be drawn.
We observed a few other interesting patterns but will wait before commenting on them until more data is collected.
Meanwhile, if you have never experienced any unpleasant odors in your life, or experienced some that did not affect your social life, you can contribute to our analysis of the human metabolism by participating in this anonymous survey.