With less carbs your body switches to burning more fat. When you become more efficient at burning fat you can go for longer periods without eating and you typically don't experience hypoglycemic symptoms (wooziness, lack of energy, etc). That's the simple explanation at least.

It's amazing to be able to go 16 hours non stop on two eggs,a can of tuna, and some butter tea.Did my first beach hike this year(5 miles) completely fasted, and didn't get the least bit weak.It's got to be the blood sugar being regulated,because killing sugar/grains is all I did.

Same here! I would never leave the house without a big breakfast, and then a few hours later had to eat something again. I would never even dream of exercising on empty stomach! And when I was hungry, I felt sick. I had to eat NOW.

enters paleo... :) now I can fast, I can workout after 16h of fast and I have energy and feel great. It's quite amazing!

This is an almost unanimous result. The more modern crap you eat, the more you feel like grazing all day. Basically everybody who goes "paleo" finds that out of nowhere they can go a whole day without eating, fast and be fine, skip breakfast and feel excellent, go 3 days without eating and still have energy, etc. The tendency is to skip meals, feel awesome, and go many many hours without eating. I constantly go 20+ hours without eating, doing tons of hard exercise along the way, feeling light and powerful. And that trend will only increase.

When you're paleo, you don't need to eat as MUCH, and you don't need to eat as OFTEN. Normal people have to graze all day long or they'll start feeling "woozy" or dizzy or or something. Paleo people find the opposite. Often they feel BETTER when they don't eat. Of course you need to eat SOMETIME, but all the old rules stop applying. Don't feel bad about skipping breakfast. It doesn't matter if you only eat one meal per day. Whatever. Just follow your hunger. Forget about all the conventional wisdom like "eat a bunch of small meals evenly spaced throughout the day". NORMAL people came up with those rules; they needn't apply in OUR world.

I agree, I feel much better even when not eating. It's difficult for me to ignore the conventional wisdom we've had drummed into us sometimes though - I often eat for the sake of three square a day, rather than hunger necessarily - but thanks to this I'll actually listen to my body (novel concept eh? :D)

EDIT: I totally read the thread title wrong, so this info doesn't really answer your question. In case you were wondering about exercise blood sugar regulation, well, here you go!

My guess:

-- Biochemistry alert :( --

When on SAD, you are insulin insensitive. Circulating at any given time, especially after insulinogenic meals, is an unusually high concentration of insulin. Insulin leads to glycogen synthesis and uptake of free blood glucose. This is a normal parasympathetic process, a "resting" process. Insulin binds to receptors on most cells of the body that leads to a signal to take in sugar from the blood. Insulin binds to cells in the liver to tell it to form glycogen from the liver for storage.

When on Paleo, you are insulin sensitive. While exercising, glucagon and norepinephrine/noradrenaline are present in much greater quantities than when at rest. These hormones bind liver cells and signal glycogenolysis, a process that digests glycogen into glucose and releases the free glucose into the blood where hungry, worked-out cells can take in the glucose and metabolize it for energy (I'm looking at you, slow-twitch muscle fibers). This is a normal sympathetic process, a "fight or flight" process.

Both insulin and glucagon/norepinephrine bind to different, antagonistic receptors on the same liver cell type. SAD dieting increases base insulin levels relative to glucagon/norepi levels. Paleo dieting reduces base insulin levels relative to glucagon/norepi levels. In the case of SAD, insulin's signal to the liver may be so strong relative to that of glucagon/norepi that the glycogenolysis process that would otherwise feed your hungry muscles is instead being antagonized by the glycogen synthesis signal from insulin. Paleo, on the other hand, prevents this antagonism by attenuating insulin levels and allowing the glucagon/norepi signal to transmit to the liver.

Net effect of SAD: Too strong base insulin signal -> insufficient glycogenolysis -> low active blood sugar -> insufficient sugar supply to muscles and brain -> muscular and mental fatigue

Net effect of Paleo: Relatively weak insulin signal -> proper transduction of glucagon/norepi signal -> glycogenolysis -> increased blood sugar -> sufficient sugar supply to muscles and brain -> maximally efficient muscles and neuromuscular pathways -> bulging muscles -> hot new girlfriend