Excerpt from Sugar Nation

Sugar Nation: The Hidden Truth Behind America's Deadliest Habit and the Simple Way to Beat It.
Jeff O'Connell

Just thought this was really interesting information (and this tells me fat is the preferred fuel, not carbs. If carbs were the preferred fuel then the human body would have unlimited carb storage, not unlimited fat storage):

Along with possessing an almost magical potency, insulin is ancient; it was found in organisms whose habitat was the cauldron of primitive life-forms known as primordial soup. Insulin allowed our own earliest ancestors to make a huge evolutionary leap. Their bodies could store fuel, which afforded them time for other pursuits. They could erect family structures, tell stories, and build languages now that didn’t have to hunt and scavenge all day for nourishment. Insulin helped make us human.
Insulin helps the body metabolize the sugar in the blood, which is called glucose. This blood sugar can come from the diet, but the liver and kidneys can also produce it. What isn’t needed for energy can also be stored in muscle tissue and the liver. This stored from is called glycogen. But because storage space is limited, at a certain point, the liver begins turning excess glucose into triglycerides, which very often become body fat. The human body has evolved such that it possesses a very low capacity to store carbs but a very high capacity to store fat. This phenomenon is evident in buffet lines across the heartland.
“That’s in a relatively healthy person,” says Jeff S. Volek, Ph.D., R.D., associate professor of kinesiology at the University of Connecticut. “Even before glycogen levels fill up, people with insulin resistance dispose of carbohydrates by converting the majority to fat.” That’s one reason why the heavy will still become heavier, even if they pass on the second helpings.
Nearly every cell in the body can take up and use glucose as fuel, and blood travels everywhere in the body, making it the ideal transporter of glucose to far-flung destinations. But how does the glucose know where to go? A messenger hormone called insulin escorts it. Certain tissues in the body attract insulin; their surface is lined with welcoming receptors. Receptors are proteins, but think of them more as magnets. Most of these insulin receptors are located in muscle tissue, a function of muscle’s large size and metabolic activity.
The system is designed to work so that after you eat a meal, the pancreas releases insulin in an amount proportional to whatever the glucose load happens to be. Insulin arrives at receptors and is recognized as such, and cells know what to do in response: absorb glucose from the bloodstream. So your blood glucose never shoots too high. As this process unfolds, a feedback loop signals the pancreas to produce less insulin, to keep the messengers home. So your blood glucose never falls too low, either. The normal blood sugar response to a meal is a slow rise flowed by a reasonable drop.
Insulin resistance occurs when insulin tries but fails to bind with receptors, and glucose is left stranded. Instead of taking five units of insulin to produce a certain amount of energy from glucose, it’s now taking your body, say, twenty. All the pancreas knows is that insulin isn’t doing its job, so it keeps secreting more and more, to little avail.
This creates an energy crisis for each cell, not to mention your entire body. To use a crude analogy: Imagine oil tankers sailing from port to port loaded with oil (glucose) that needs to be loaded onto small boats (insulin) for transport to shore. But once the oil has been loaded onto the smaller vessels, these boats bounce off the docks, unable to land. Thus the raw material never makes it to shore, and the factories in town sit idle. The crude oil can’t be delivered. Productivity halts.
Unfortunately the lifestyle choices causing insulin resistance – not exercising, indulging a sweet tooth, and eating too much in general [MY NOTE: I believe the overeating stems from the constant up and down blood sugars. When the insulin can’t push the glucose into the resistant cells it will convert it to fat and send it to storage. So you end up starved on a cellular level and your body signals hunger after only a couple of hours – and it’s looking for more carbs] – trigger a feedback loop. Particularly if you don’t exercise, those excess carbs will cause blood sugar to spike and then crash, at which point the body bellies up for another round of sugar.
Since your body is dumping glucose into boats that can’t land, it must find another fuel source. An alternative is fat, which can be burned for energy as long as oxygen and mitochondria, the parts of the cells that contain fat-burning enzymes, are present. Luckily, only a few places in the entire body lack oxygen, mitochondria, or both. Red blood cells don’t possess those tiny power plants, so it may no coincidence that glucose floats around in the blood. The lens of the eye and a remote area of the kidneys also depend solely on glucose. But that’s about it.
It should hardly come as a surprise, then, that diabetes consistently attack these parts of the body. The kidneys are one of only two organs capable of producing glucose from noncarb sources such as protein, the liver being the other.
So glucose is essential for life, and it usually comes from carbs. Wouldn’t we cease to function if we didn’t consume enough carbs? Consider: In the early 1900s, a pair of Arctic explorers, Vilhjalmur Stefansson and Rudolph M. Anderson, marveled at not only the carnivorous diets but also the robust health of Eskimos. So upon returning from their expedition, the two men embarked upon a meat-only diet. The resulting macronutrient ration amounted to 75 to 85 percent fat and 1 to 2 percent carbohydrates. Protein made up the balance. At the end of what was a yearlong experiment, they were alive and well, although perhaps a bit grumpy.
To find out how they survived, I spent a day at Dr. Westman’s Duke Clinic on my way back from the ADA conference in New Orleans. As befits someone who grew up in the cheese state of Wisconsin, the good doctor puts patients needing to shed extra pounds, manage diabetes, or both on a low-carb diet. To great effect, I might add. He’s fascinated by which organs actually need glucose – not which ones use it when it’s available. As I trail him into his office, my gaze is drawn to a homemade anatomy-chart-turned-schematic on one wall. The names of bodily organs are computer-printed on pieces of paper. This anatomy chart is proportional rather than representational; each cutout reflects the energy requirement of that organ, rather than its shape or size, I see that the liver sucks up as much glucose as the brain. “Pretty much everything can run on fat,” says the Stanford grad, noting the exceptions mentioned before – red blood cells, retina, and a remote region of the kidneys.
The assumption has been that dietary carbohydrates must provide 130g of glucose per day for the brain and central nervous system to function fully. But Dr. Westman insists that the liver and kidneys could produce more than enough glucose from protein to supply that amount, which explains why those Eskimos, and the explorers who found them, could live on only meat. No, I can’t imagine any sane non-Eskimo wanting to follow the Eskimo Diet, which is a product of their unique habitat. But the wall schematic is illuminating nonetheless. Everyone, from Gatorade and General Mills, to the corn lobby and dietetic organizations, keeps telling us that we need ALL these carbs, and that eating them gives us all this energy.
We’re being implored to eat them for reasons that have little to do with any sort of internal need. I bought into their sales pitch, and I write about this stuff for a living. The truth is, we don’t need all those carbs, and they don’t give us all that energy. In fact we don’t need nearly as many carbs as we are implored to consume by everything from government guidelines to television commercials. “The Western diet is far too high in carbohydrates,” says the IDF’s Raab. The metabolic system of the average human being was designed to run on some debatable fraction of that amount.
The solution to the Type 2 diabetes epidemic isn’t force-feeding the hard-core Atkins approach to everyone who’s either a diabetic or at risk of becoming one – although that approach, if followed, would produce better results than the approach we take now. But the solution isn’t the status quo approach of the diabetes industry, either. The evidence against that is prima facie. Just look at what amounts to an epidemiological study including the entire U.S. population, which makes the conventional wisdom look increasingly unwise.
Part of the solution for America’s obesity and diabetes epidemic is a diet lower in carbs – and less internal insulin production as a result – and a higher intake of protein and healthy fats. This will result in much better glucose control But you won’t hear that recommendation from most diabetes organizations and experts.