Feedback on the job

What we've constructed, by defining a 5 pound band for variation and a 10 pound range surrounded by brick walls, then prescribing the action to be taken when the trend is in each region, is a negative feedback system to replace the built-in one, shown on page , that misleads us into gaining weight.

By using the trend to adjust food intake, we have implemented a very different feedback system. As weight varies within the 5 pound band around the goal, 150 pounds here, it is subject to only a minor degree of feedback, applied by monthly adjustments to what you eat based on the slope of the trend line. If you choose not to bother with such small adjustments, the floor of the feedback curve from 147.5 to 152.5 pounds will be flat and your weight completely free to vary within that band.

Once the trend ends a month outside the 5 pound band but within the brick walls, calorie consumption is adjusted. The size of the adjustment is determined from the calorie excess or deficit indicated by the trend. Thus, when the trend strays outside the band it encounters negative feedback proportional to the calorie imbalance that caused it to diverge. This feedback, shown as a steeper line outside the 5 pound band, should normally return the trend to within the band in short order.

If, for whatever reason, the feedback invoked when the band is crossed doesn't have the intended effect, the trend will sooner or later hit the brick wall. When this happens, bang-bang negative feedback is triggered to ensure the trend is quickly reversed and brought back to the goal. Resuming a meal plan already proven effective for losing weight (or adding comparable calories if the trend hits the brick wall below the weight goal), provides absolute assurance the trend cannot slip out of control. This constitutes very strong negative feedback that kicks in when the brick wall is hit, shown by the steep rise in the feedback curve at that threshold.