[throwaway286]

It absolutely does happen. If you stop eating carbs for several days, you will go into ketosis. You can tell because your glycogen will be depleted, temporarily dropping your weight by a few pounds in a short time period. Also, your breath and urine will start to smell. If this isn't ketosis, then what is it?

[bscphil]

There's a little bit of a disconnect on the definitions people use. Usually when people talk about ketosis, they are implying the body has some kind of "fat burning" mode where you will burn the fat you have stored, and that you can trigger this mode without changing the number of calories you eat just by getting rid of carbs. This is for all intents and purposes a myth.

Of course you're right, in the other sense, that if you don't eat any carbs your body will be burning the fat you ingest instead, and that this will show up in your bloodstream. You also won't burn any weight this way unless you have a calorie deficit (as you note, it's "temporary").

Note that when OP said that "it doesn't happen", they didn't mean ketosis doesn't happen. They meant that meat-heavy diets don't result in weight loss because of ketosis.

[ulisesrmzroche]

It’s not a myth. Do you lift weights? Do you know about calorie partitioning and glycogen restoration?