Ketosis = State of being fueled by Ketones
When people ask me, this is how I describe ketosis:
Your body can only use one fuel source at a time.
Most people use glucose. Thus, your body is in "glucose burning mode."
Wheat (and other grains) become glucose as soon as they enter your body. Anything sugary has glucose. Fruits, too. Carbohydrates are sugar.
I use fat. Thus, my body is in "fat burning mode."
So, I burn fat, regardless of what I've eaten and what exercise I have (or haven't) done.
You can't burn fat if you are burning carbohydrates.
One more time: You can't burn fat if you are burning carbohydrates.
Digging a little deeper, it's not actually just fat that I'm using for energy. Because of low carbohydrates (less than 30g/day), my liver is magically producing ketones. I am fueled by ketones.
What is a ketone?
Imagine your body is a bonfire. It needs to keep burning.
Sure, you can throw plastic bags, crumpled-up newspapers, twigs, paint-chips, gasoline, and old clothes on the fire. It'll burn. But it'll burn big hot unpredictable flames, then die out quickly. Okay, quick throw something else on it, we gotta keep it going!
This is your body being fueled by carbohydrates. Mood and energy swings. Ugly looking fire.
Or, you can plan a little bit ahead of time. Build a nice foundation of proper charcoal and dried wood. It'll burn nice and warm. Leave it be for a while? The fire stays the same. Place some new charcoal on the hot coals, it slowly fuels the fire.
This is your body being fueled by fats. Consistent energy and mood. Looks perfect.
Bonus: If you throw the occasional plastic bag on the charcoal fire, it simply lights up briefly and disappears, barely affecting the overall fire (though it's still not so healthy for the fire.)
Ketosis Explained in a simple video.
Further reading: http://www.ketogenic-diet-resource.com/ketosis.html
Bonus: Think about this: your body is anywhere from 8 to 30 percent body fat. If you weight 170 pounds, that's 5 to 17 pounds of fat. That's a lot of stored energy, which is why (in my case) fasting for short periods of time is not only easy, but actually good for me.
#1 - Health: Introduction
#2 - Health: Food
#3 - Health: Exercise
#4 - Health: Information Sources
#5 - Health: Side-Effects
#6 - Health: Specific to Japan
#7 - Health: About Ketosis
#8 - Health: Book Recommendations
#9 - Health: Extra Thoughts
#10 - Health: "S" is for Success (Summary)