Not only animals, but also people can estimate a person's age by smell.
The Japanese are especially concerned about this, and they have a special word for the smell of old age - kareishu. And if a person does not distinguish between young and middle age, but the old people determine confidently [1].
This has been shown to be due to a special substance called 2-nonenal, which results from the peroxidation of fats in the skin from omega-7 fatty acids [2]. It smells like dark beer and buckwheat. Actually the odor itself is not unpleasant, its perception is probably related to the cultural context.
Interestingly, before the age of 40 this substance is not detected at all, but after 40 its levels start to rise higher and higher [3], in parallel with the increase in these omega-7 acids and lipid oxidation. Recall, too, that the risk of chronic disease begins to double every 8 years after 40.
Of course, it is likely that improved health will also affect the smell, and the Japanese offer special cosmetics based on green tea and persimmons, but no guarantees. One study found that regular mushrooms improve body odor, and the effect is dose-dependent! [4]
When it comes to mushrooms, their health benefits don't end there. Many of us ignore this food group, but for nothing. Mushrooms contain chitin and beta-glucan, these dietary fibers improve intestinal function and reduce the risk of constipation.
Consuming mushrooms three times a week reduces the risk of dementia and diabetes. Interestingly, the effect on carbohydrate metabolism is indirect, through the microbiome. Mushrooms increase the proportion of Prevotella bacteria, and those already in turn affect metabolism.
There are many other useful compounds in mushrooms, such as mushroom sugar trehalose (1% of the population - intolerance).
Immunomodulatory properties of mushrooms deserve special attention, but they are specific to their individual species.
Notes
[1] (The Smell of Age: Perception and Discrimination of Body Odors of Different Ages". PLOS ONE. 7(5): e38110. 2012 )
[2] (2-Nonenal Newly Found in Human Body Odor Tends to Increase with Aging". Journal of Investigative Dermatology. 2001 116 (4): 520–4.)
[3] (Odor Associated with Aging Anti-Aging Medicine 7 (6) : 60-65, 2010)
[4] (Effects of 4-week continuous ingestion of champignon extract on halitosis and body and fecal odor Journal of Traditional and Complementary Medicine Volume 7, Issue 1, January 2017, Pages 110-116)
