but the message will be that insulin drives fat storage in the context of the elevated blood sugar that comes with either eating a carb-rich meal or type 2 diabetes.* (Location 1363)
High blood glucose elicits the release of insulin, which speeds the uptake of glucose by tissues and favors the storage of fuels as glycogen and triacylglycerols while inhibiting fatty acid mobilization in adipose tissue. (Location 1367)
High blood sugar, which you can have when you either are diabetic or have eaten a carb-rich meal, will prompt your pancreas to secrete insulin, which in turn will prompt you to burn the carbohydrates for fuel, store glucose as glycogen and fat, and prompt your fat cells to store the fat you’ve eaten and the fat made from glucose and hold on to the fat it already has. (Location 1370)
As you can see, everywhere the fat tissue is taking up fat, it’s insulin that’s promoting it—“Insulin +” as it’s labeled. When the fat tissue is mobilizing fat, getting fat out of the cells and into the circulation where it can be used for fuel, it’s insulin that’s inhibiting it (“insulin –”) and other hormones (adrenaline, noradrenaline, and ANP in the diagram) that are doing the promoting. (Location 1384)
One obvious implication of this basic human physiology is that if we want to get fat out of our fat cells in any biologically efficient way, we have to keep the insulin levels in our circulation low. We have to create that negative stimulus of insulin deficiency, which means not eating carbohydrates. (Location 1396)
Ketones are molecules that are synthesized in liver cells when those cells are burning fat for fuel. They are created from the by-products of this fat burning (oxidation), either from the fat in your diet or from the fat you store when insulin is low enough that the fat is mobilized. (Location 1466)
For Atkins, ketones and ketosis were his patent claim, to use Gladwell’s phrase, that set his diet apart from the every-woman-knows conventional wisdom. Rather than merely noting that carbohydrates are fattening, and that diets that restrict them but not calories (hence replacing the carbohydrate calories with fat) seem to be a biologically appropriate means to reduce excess weight, he couched his eating plan as a revolutionary diet. (Location 1471)
Continue to fast for more than several days, and you’ll be at 5 to 10 mmol/l.† On an Atkins diet—aka nutritional ketosis—your ketones might be as high as 2 or 3 mmol/l. After exercise on the same diet, when insulin is very low, you might even hit 5 mmol/l, all relatively low numbers compared to those in diabetic ketoacidosis, the state that so justifiably worries physicians and diabetes specialists. (Location 1514)
First, we all respond to carbohydrates differently. Enormous variation exists from person to person. That’s one very good reason why, given the same foods to eat, some of us will grow up to be built like fashion models and some of us will be extremely obese. (Location 1537)
Moreover, different cells and tissues even in the same individual respond differently to insulin. Here, too, there’s enormous variation. When tissues and cells become resistant to insulin, they do so at different rates and different levels of insulin in the circulation. For this reason, as Berson and Yalow cautioned, “it is desirable wherever possible, to distinguish generalized resistance of all tissues from resistance of only individual tissues.” (Location 1538)
In other words, as Yalow and Berson pointed out, if you’re actually getting fatter, your fat cells must be responding to insulin regardless of what is happening elsewhere in your body. Your fat cells must still be insulin sensitive. It seems to be a precondition of the fattening process. (Location 1546)
Fat cells, in particular, tend to be “exquisitely sensitive” to insulin. (Location 1548)
It means that fat cells sense and respond to the presence of insulin in the circulation at levels so low that other cells and tissues don’t even know it’s there, and fat cells continue to respond to insulin long after those other cells and tissues become resistant. (Location 1550)
When we’re almost below it, our livers may or may not be synthesizing ketones in large numbers, but we are certainly burning fat for fuel. If we are synthesizing considerable ketones and so are in ketosis, we’re certainly below the threshold, and the more time we spend below this threshold—day in and day out—the more time we spend burning fat, and the less fat we’re storing. (Location 1592)
Authorities like to say that glucose—blood sugar—is your brain’s preferred fuel, but that, again, is because your brain burns glucose for fuel when you’re eating a carb-rich diet. It’s conceivable that our bodies decided, figuratively speaking, that since our brains use up so much of the energy we generate—around 20 percent—having our brains burn glucose would be necessary to control blood sugar in a high-carb world, even if ketones were somehow a better source, like a higher-octane fuel for your car. (Location 1607)
Worth noting is that ketones themselves stimulate some insulin secretion, and the insulin secretion in turn inhibits ketone synthesis. This is a naturally occurring negative feedback loop that prevents ketone levels from getting pathologically high merely from changing our diets. (Location 1617)
If you’re insulin resistant, these dynamics still hold true. But now you have more insulin circulating through your body than is ideal, and the amount of insulin will remain high for longer than ideal. This means you’ll spend that much more time above the threshold, with the switch on, storing fat. (Location 1629)
In short, when insulin is above the threshold, when the switch is on, your body is running on carbohydrates. They are your fuel. So it makes sense that you’ll hunger for carbohydrate-rich foods. This is likely why you may not be able to imagine life worth living without your morning bagel, or your sweets, or your pasta. (For me, it was fresh-squeezed orange juice at breakfast.) Ultimately, as we’ll discuss, these carbohydrate-rich foods become your favorites. A likely reason is that your brain has learned to respond to these foods by rewarding you with pleasure when you eat them. (Location 1636)
When insulin is below the threshold, when the switch is in the off position, your body is burning the fat you’ve stored. It will continue to burn fat as long as you remain below the threshold. Now your body has access to plenty of fuel. Twenty pounds of body fat provides fuel for well over two months. (Location 1640)
Your body is being constantly fed on this supply of stored fat, so it’s satisfied. Your appetite will be blunted. The brain has no reason to think more food is necessary. Your body has no need to ingest more food, hence there’s little or no urge to do so. You experience weight loss—the burning of your stored body fat—without hunger. (Location 1644)
Above the insulin threshold, you have to replenish frequently. You have a limited supply of carbohydrates, and insulin works to keep the carbohydrates you’ve stored (a maximum of about two thousand calories of glycogen) locked away as well. As your blood sugar drops, you’ll get hungry. And because carbohydrates are your fuel above the threshold, you’ll hunger for carbohydrate-rich foods. (Location 1646)