One thing I have learned along the way is that carbs don't really matter in the grand scheme of things. Well, they matter. But not as much as we've been led to believe over the past several years.
We all know protein is super important. In truth, it is second only to water. Protein builds and maintains muscle. Muscle, in turn, burns fat. So, the more muscle you have, the more fat burning potential you have. That part is easy to understand and most people don't have a hard time with this. Also, protein will make you feel full, longer.
Carbs are often thought of as the "evil macronutrient". But in truth, they are the fuel we need to move. Our bodies simply can not turn protein into energy. Protein is the building blocks, carbs is the gas to get the hunk of blocks moving. The simple truth is, most of your calories tend to come from carbs. Our bodies are programed to want carbs, because we want energy. Enter in 20th and 21st century and we have evolved to not be required to run after our food and harvest our grain. In essence, we are lazy. That means we need less energy, less carbs, than we did 100 years ago. Or, we need to pick up exercise. The reason low carb diets work isn't because we don't need carbs. It works because we have grown lazy over the years and are not using our resources as they were intended. Tri-athletes eat upwards of 300 carbs a day. And they are rail thin most of the time. It isn't genetics, not entirely. It's that they use carbs efficently, something a good many of us don't do. It's still the old cliche, calories in versus calories out. And most our calories tends to come from carbs...so it is easy to eliminate extra calories by cutting back on our allowed carbs. Well, easy in theory. In practice, it kinda sucks sometimes.
And fats...did you know that the only way to burn old fat is to take in new fat? If you aren't taking in new sources of fat, your body gets scared and holds on to every ounce you have. On the other hand, if you take in moderate, healthy amounts (such as what WS recommends), your body will go ahead and get rid of that extra fat when you are dieting because it knows it is getting a very important nutrient all the time.
But you asked about ketosis. It depends on your own body and the way it metabolises. Some people hit it at 150g. Some at 90g. Others have to go all the way to 20g. For me, I hit it at 72g. And I HATED the way I felt in ketosis. Some people claim to have more energy and be in a better mood. Not me. I slept all the time. I was crabby. The only good thing is I didn't carve junk.
The headache the first day is a carb withdrawl. The first couple days suck. Day three was the worst for me. After that, it wasn't so hard, except I was tired all the time. But that was my fault (I didn't eat the fruit, the starch, or the milk at first.)
And FWIW, consistently high-protein diet could lead to joint pain as a result of a loss of calcium, dehydration, gout, or arthritis-like symptoms. That's why doctors recommend against long term
high protein diets.