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Calories and weight

To fully understand the difference between Skinny Stable Sam and ourselves, it's necessary to consider the rubber bag again. Sam's feedback system connects calories eaten to appetite. It does not connect weight to appetite. Failing to appreciate this distinction has led millions of dieters to fail. Remember the rubber bag. For the most part it doesn't matter how much you weigh; whether you gain or lose weight depends only on the balance between calories eaten and calories burned.

One encouraging conclusion can be drawn from this: you won't be any more hungry at your optimal weight than at any weight above it. The rubber bag cares only about the difference between what goes in and what goes out. So don't assume that being thin dooms you to a life of endless hunger. You now understand enough of what's going on to see what utter, discouraging bilge that suggestion is.

Consider how Sam's body reacts when it gets too much or too little food. Assume Sam's normal weight is 150 pounds.


Here the horizontal axis represents the number of calories eaten per day, with the centre point, ``Ideal calorie intake,'' the amount Sam burns per day. The rubber bag, like most models, doesn't precisely represent the underlying reality: the human body. It isn't necessary to exactly balance calories eaten with calories burned. If you eat a little too much, the body cranks up the burn rate a little: you feel warmer and more inclined to run up a flight of stairs rather than walk. If you eat a tad less than ideal, you may feel chilly and inclined to curl up with a book under the blankets and get a little extra sleep.

This is the lowest level of proportional weight control, and it works for all of us. It means that there's no need to become obsessed with matching calories eaten and burned; it's only when the balance shifts decisively and consistently to one side or the other of the ideal calorie intake that we get into trouble.

The vertical axis makes it clear what that trouble amounts to. The rubber bag expands or shrinks: we gain or lose weight. Once what goes into the rubber bag exceeds your capacity to crank up the heat, the excess starts showing up as fat. Similarly, to achieve weight loss, you have to reduce what goes in below your capacity to adjust by banking the metabolic fires, forcing your body to tap its reserves: to burn fat and thereby shrink the rubber bag.

To complete our understanding of how feedback keeps Sam's weight under control, let's overlay the graph that shows how calories affect weight and the chart of feedback from calorie consumption to appetite.


The feedback, neatly centred around the ideal calorie intake, keeps the calories eaten within the region that changes in metabolism can adapt to. Since feedback balances what goes into the rubber bag with what's burned, weight remains constant. When Sam eats a bit too much or too little his metabolism adjusts, as does ours. But, if he goes beyond that point, his appetite begins to tell him to eat more or less before the shortfall or excess shows up on the scale or the waistline.

Ahhhh, Sam..., if you only knew the thoughts that run through our minds. Sam's got it made. But for those of us who don't the real question is what it is Sam has that we're lacking. And that's now clear: a built in eat watch--a proportional negative feedback system that adjusts what he eats, by controlling appetite, to equal what his body burns. We're missing that negative feedback system. Should we begrudge Sam his genetic advantage and accustom ourselves to overweight, or just fix the system? Fix it, of course! But first, let's consider what happens when it's broken.

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By John Walker