[legitsource]

Ketosis is an alternative method of using fats for energy in the absence of normal process using glucose. The presence of ketones on your breath makes a "fruity" smell that can range from minor to fairly unpleasant. It may make your mouth taste "metallic".

When your body is breaking down protein for energy, you will smell like ammonia, which is significantly different smelling than ketones like acetone.

[foobarbazqux]

Okay, so ketosis (ketogenesis?) is one step before breaking down proteins, i.e. first you smell like ketones, then you smell like ammonia?

[legitsource]

Basically, you don't have to enter ketosis on the way to burning proteins for energy.

If you stop eating entirely, you will enter ketosis and also be breaking down some protein for energy as soon as your blood glucose and your liver glycogen is depleted (your brain still needs about 20 grams of glucose a day even in ketosis, so gluconeogenesis will occur turning protein into glucose). You probably won't even smell the ammonia at this rate, since it's pretty low.

After being in ketosis for a while (a few weeks) your body gets better at producing ketones on demand instead of just supplying them all the time and the acetone smell decreases substantially, but you still shouldn't be breaking down protein unless you are low body fat and not eating enough fat for the calories you need.

I never smell like ammonia unless I'm working out really hard and in ketosis.

If you aren't lazy, you can work hard enough to smell like ammonia no matter what you eat if you are pushing yourself really hard in an anaerobic exercise set.

[foobarbazqux]

Wow, that was an awesome explanation. Thanks.

[legitsource]

Not a problem at all.