Anybody can learn pretty quick to smell diabetics. Low blood sugar leaves one's breath bitter and metallic, high blood sugar causes fruity, sweet breath. It's extremely obvious if you're at all close to them.
On a ketogenic[diet] ... your body uses fat instead of carbohydrates for energy. This shift causes a major spike in ketones, the source of acetone breath. ... Sweet-smelling breath may be a short-term side effect of this type of diet.[0]
