Can you define "fat adaptation"? We all burn fat, no matter what our macronutrient intake is, unless we eat every couple hours even when sleeping. Fat is the primary fuel of resting or slow activity.

Most people generate ketones at about 50 grams of carb or under. I personally feel an even energy level eating anywhere from 10-100 grams of carbs, perhaps due to infrequent and low amplitude insulin/sugar bumps.

There are different levels of ketosis, depending on your daily carbohydrate intake:

• @ 0g: your brain is burning about 25g of glucose, all of which is manufactured from gluconeogensis, with the rest of its energy coming from ketones (most of your other cells are fuelled by free fatty acids)
• @ 25g your brain is burning about 25g of glucose, which comes from dietary carbohydrate with the rest of it's energy coming from ketones (most of your other cells are fuelled by free fatty acids).(most of your other cells are fuelled by free fatty acids).
• @100g+ your brain in burning 100g of glucose which comes from dietart carbohydrate, with any excess being stored (and used) in your muscles and liver.

So technically, if you are eating less than 100g of carb a day, you are in ketosis to some degree.

The difficult area is what happens in the 25g to 100g range where your brain is burning some glucose and some ketones.

When people talk about being "kicked out of ketosis", I think they usually mean "no longer show any purple on ketostix", which usually occurs for most people if they eat more than 30-50g a day.

I personally aim for about 30g, because it seems closer to a physical limit (25g) than 50g, which just seems a bit arbitrary.

I think this is definitely one of those "everybody is different" because every body is different. My threshold is very, very low. Some are very high. I'm kicked out of ketosis at about 40g carbs. I rarely eat starch but even the smallest bit like half a small sweet potato does me in. I am hugely metabolically challenged though so hopefully your threshold will be much higher. You just have to play with it and see what your body's tolerance for starch and carbohydrate is.

I dont think its wise to be "fat adapted" for long periods. Maybe a few days a month but remember the brain needs carbs.

Basically a carb is a carb. Simple sugar or complex it all breaks down to glucose fuel. Your question regarding fructose is interesting. Although it is metabolised differently I am not sure if there is a "net" carb effect from that or if a carb is a carb. Fructose is typically stored as fat and nor burned like glucose. I have not myself come across any science on fructose having a distict carb value but I am betting the storage as fat is a reason it is often recommended to eat very little of it.

keto-adapted and primarily/preferentially using fat for fuel after 2-6 week adaptation stage is different than "some" fat burning- now and then-here and there.

what shows on keto stix is excess unburned ketones during the adaptation stage. If you are showing ketones in urine you are not fully keto-adapted.

I agree <30 g CHO is VLC 50-100 LC

In agreement with those who say it is an individual thing above 30-50g CHO. I did quite well around 70 or so on a broader diet-problem is you tend to just add this here and that there and before you know you are way over and out.

Here's a good article on metabolic flexibility:

http://www.gnolls.org/1984/the-science-behind-the-low-carb-flu-and-how-to-regain-your-metabolic-flexibility/

Basically, we all can and do switch between burning fat and burning sugar. Some of us are better at it than others. As long as you're not eating lots of carbs all day long which would cause chronically high insulin, I wouldn't worry about it. If you've been paleo for a while and have things mostly dialed in, then you can trust your body and just go by how you look, feel, and perform. So just add carbs as long as you keep feeling good.

Just an heads up: ketosis is not simply a game resuting from carbs in carbs out equations. For example, the shot chain fatty acids present in Coconut oil, have the potencial to "deepen" the ketone body formation, even on the presence of carbs. The same goes for some aminoacids, such as lysine and leucine. Supplementing with both and introducing coconut oil can often induce a more ketogenic state even in the presence of a higher carb threshold.

If you personally get kicked out of ketosis when go higher than 50gr, if the same level of CHO is assumed but incorporate coconut or leucine, you would be producing the same ketone bodies.