Based on Steves posts it looks like it is actually possible to detect if a person is in a ketose state or not by analyzing that persons breath. But what are the signs of ketosis?
After doing some researching on Wikipedia I concluded that what we are looking for is acetone.
|Molar mass||58.08 g mol−1|
|Odor||Pungent, irritating, floral|
|Density||0.791 g cm−3|
|Melting point||-95–93 °C, 178-180 K, -139–136 °F|
|Boiling point||56-57 °C, 329-330 K, 133-134 °F|
|Vapor pressure||24.46–24.60 kPa (at 20 °C)|
|Refractive index (nD)||1.35900|
From the Wiki page about Ketone Bodies
Ketone bodies are three water-soluble compounds that are produced as by-products when fatty acids are broken down for energy in the liver. Two of the three are used as a source of energy in the heart and brain while the third (acetone) is a waste product excreted from the body. In the brain, they are a vital source of energy during fasting. Although termed ”bodies”, they are dissolved substances, not particles.
The three endogenous ketone bodies are acetone, acetoacetic acid, and beta-hydroxybutyric acid, although beta-hydroxybutyric acid is not technically a ketone but a carboxylic acid. Other ketone bodies such as beta-ketopentanoate and beta-hydroxypentanoate may be created as a result of the metabolism of synthetic triglycerides such as triheptanoin.d
Individuals who follow a low-carbohydrate diet will also develop ketosis, sometimes called nutritional ketosis, but the level of ketone body concentrations are on the order of 0.5-5 mM whereas the pathological ketoacidosis is 15-25 mM.