Dexter deceived

Examining Dexter's weight chart and diary evokes memories of similar times of triumph and days of despair in anybody who has dieted. Dexter exulted with each new low on the scale, while fearing it wouldn't last. He grew depressed as weight plateaus extended from days into weeks. His spirits rose and fell with the daily readings on the scale. When a month's progress was seemingly erased in a single day, a part of Dexter's joy in life withered and died.

  Yet despite the ups and downs of the scale and the emotional battering they administered to Dexter, his diet worked perfectly, achieving precisely the result he intended in the anticipated time. Dexter was deceived by his scale. It didn't measure what he cared about: pounds of fat. Instead, the changes in daily weight reflected primarily what happened to be in the rubber bag at the instant it was weighed.

The detailed picture of what goes in and out of the rubber bag on page explains why daily weight measurements have so little to do with how fat you really are. Dexter went on a two month diet to lose 10 pounds. And yet every single day, on average, a total of 13.5 pounds of food, air, and water went into Dexter's rubber bag, and a comparable amount went out. His daily weight loss during the diet was less than one fifth of a pound per day, yet each and every day almost 80 times that weight passed through his body!

If the body consumed and disposed of these substances on a rigid schedule, maintaining a precise balance at all times, weight would be consistent from day to day. But that is not the way of biological systems. A few salty potato chips are enough to cause the body to crave, drink, and retain a much larger amount of water to dilute the extra salt. The body's internal water balance varies widely over the day and from day to day. Since water accounts for three quarters of everything that goes into and out of the rubber bag, it dominates all other components of weight on the scale.

Every morning, when Dexter stepped on the scale, it's as if he carried, unknowingly, a water tank filled to an unknowable level by a mischievous elf, put there to confound his attempt to track the progress of his diet. If Dexter's scale had been able to disregard the extraneous day to day changes in weight, it would have produced a graph like this.

Shortly after Dexter began his diet, he started to lose weight. He continued to lose until he declared the diet successful in the third week of August, after which his weight leveled off at the goal of 145 pounds. Imagine how calm and confident Dexter's diary would have been if he'd plotted this curve instead of daily weight.

By relying solely on daily weights from his scale, Dexter endured two months of unnecessary suffering. His diet worked, as was inevitable from a simple calculation based on the rubber bag, but the day to day weight readings obscured his steady progress. An eat watch would have assured Dexter he was on the right course and making steady progress toward the goal. The scale seems, by comparison, a modern instrument of psychological torture, an engine of confusion and despair. Can it be made to tell the truth?