The reason it's so tough to start a diet follows directly from our understanding of the rubber bag, how fat cells store and release calories, and the relationship between calorie intake, weight gain or loss, and hunger as shown by the chart on page 81. Regardless of the shape of your own feedback curve, if you tend to overweight it's certain the left side of the curve, the hunger signal when you eat too little, looks much like the one in that graph.
In order to lose weight, you have to reduce your calories sufficiently to move beyond the flat part of the curve where your body compensates by adjusting metabolism into the downslope at the left where you're actually losing weight. This follows from understanding the simple world of a fat cell. There's no central control in your body that tells cells what to do metabolically. You can think all the right thoughts for as long as you want, but the only thing that's going to cause your fat cells to start tapping their reserves is lowering blood sugar, the ultimate product of the food you eat, below a given level. As the fat cells, one by one, detect low blood sugar, they cease banking excess calories or sitting on the sidelines and begin breaking down fat and releasing energy into the bloodstream. This is what's happening as you move from the flat part of the curve onto the downslope: the fat cells are beginning to make up the shortage of food and, as they do, your weight begins to fall.
Once that happens, you're in "burn mode." Part of your daily need for calories is now being met by breaking down fat, and as long as that continues your blood sugar won't drop to the very low levels that trigger severe hunger. Unfortunately, first you have to get into that mode, and that's what makes the start of a diet so trying. To begin losing weight, you have to cut back substantially on calories, enough to move beyond what metabolism can adjust for, to trigger the fat cells to make up the shortage. But, as you can see from the feedback chart, that requires going well into the region where hunger urges you to eat more. Further, there's a delay between the time you reduce your calorie intake and when blood sugar falls low enough for the fat cells to react. Even more time elapses before substantial calories from breaking down fat reach the bloodstream. Unfortunately, hunger has no such delay.
This explains the rocky start every dieter must endure. There is a delay, usually between 48 and 72 hours, between the time you cut back on calories and when fat burning begins in earnest. In those hours, you will experience the most severe shortage of nutrition in the entire course of your diet. You'll feel cold, weak, irritable, tired yet prone to sleep poorly, and a constant, gnawing hunger that urges you toward the refrigerator and implores you to rethink your resolve to lose weight. Yes, it really is that bad, and I'm not going to try to sugar coat it as many diet books do; better to face it squarely and know what you're in for and that it's worth enduring.
First, some perspective: the first two or three days of a diet are rough but, all in all, you won't feel anything close to as miserable as when you catch a winter cold, nor will you suffer as long or feel the lingering effects of a cold. A cold makes you feel really awful and leaves you in worse shape. Starting a diet makes you feel less miserable for fewer days than a cold and it's the first step toward much better health. Only the fact that it's self-inflicted makes it harder to live through. After all, you don't voluntarily catch a cold and you don't have the option of ending it at will. I view what must be endured in the first few days of a diet as an investment that will pay off in reduced suffering later on. As I mentioned in conjunction with exercise, it's worth comparing the undeniable aggravation of dieting with the inestimably less enjoyable sequel® of excess weight: heart attacks, strokes, and premature death. If you think of a balance sheet with three days of hunger on one side and six weeks of recuperation from a coronary on the other, it's a lot easier to get through the first days into the long haul where dieting becomes at most a nuisance to be tolerated.
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