Ketosis This is my best way of describing it

Dragonwolf

Ketosis for a short period of time (couple of days) will do no harm what so ever. A prolonged period can lead to insulin resistance.

Not really true. There's a difference between insulin resistance and "physiological insulin resistance" (or peripheral insulin resistance) The first one is the diabetic/pre-diabetic state of not being able to process glucose and insulin effectively. The latter is a temporary state in which the body makes the muscles insulin resistant so that the available glucose can be used by the organs that have priority for using glucose (ie - the brain).

Ever watch Star Trek? Ever see any of the episodes where they have to route a whole bunch of energy to a particular thing? Where's the last place they pull energy from? Life support (specifically, life support on the bridge and engineering, and sick bay, just below that, as the system will allow life support in other areas to fail before letting those three fail). Why? Because those areas, and the crew in them, are vital to keeping the ship running over the long run.

It's the same idea when it comes to a lack of external sources of glucose - the brain is the body's "bridge" (and engineering), so when you're in ketosis, any glucose the body does get is reserved for the brain. The rest of the body can work just as well on fuel sources other than glucose. The fact that this is a non-permanent physiological adaptation is evident in the fact that if you eat a higher level of carbs for a period of time (the numbers I've seen mention about 4 days, as this is also a problem for keto people and glucose tolerance tests), then your body will make the muscles insulin-sensitive again.

Oh, and the big catch - the largely only happens in people who are already lean. In overweight people (and those who suffer from the pre-diabetic insulin resistance), the ketogenic state improves insulin sensitivity.

Mark Sisson has a good article on the topic of low carb and insulin sensitivity, including some links to studies on the matter - http://www.marksdailyapple.com/does-eating-low-carb-cause-insulin-resistance

tennisdude2004

Agreed physiological insulin resistance.