My deficit scale had never heard of my own settings

The calorie calendar in my Health Dashboard colours every day of the last 60 days by how good the deficit was. Green from 700 kcal, yellow from 300, red below that. I wrote those numbers down at some point and never touched them again.

I only noticed because almost every day came out yellow or red. My target deficit is set to 500 kcal, so a perfectly hit day was yellow by definition. The scale had no idea about the setting it was supposed to measure against.

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How much deficit is too much

The lower end was easy: green from the configured target deficit, red once you drop a third below it. The upper end I had no answer for. Too much deficit is as unhealthy as too little, but starting where?

I remembered a rule involving 20 percent and could not remember 20 percent of what. Turns out it exists in three versions, and they are nowhere near each other:

The CALERIE trial tested a 25 percent deficit off daily expenditure. With my 2,489 kcal that would be a whopping 622 kcal. The participants were of normal weight, though. At 118 kg the rule is absurdly strict and I would sit in the yellow zone permanently.

Alpert measured in 2005 how fast the body can pull energy out of its fat stores at all: 290 kJ per kg of fat mass per day. With my 37.6 kg of fat that comes to 2,600 kcal a day. That is the physiological ceiling, not a recommendation.

I went with the rule that obesity guidelines actually use: at most 1 percent of body weight per week. A kilo of fat is roughly 7,700 kcal, which as a daily figure gives:

0.01 * weight * 7700 / 7 = weight * 11

At 117.8 kg that is 1,295 kcal. Above it turns yellow, from 1.2 times that it turns red. The nice part is that the limit moves along with the weight. Every day in the calendar uses the weight that was on the scale that day.

I had guessed the wrong problem

After the rebuild I was convinced the colours would come out mostly green. They did not. Of 50 logged days, 17 are red and 19 yellow, and the reason is the opposite of what I assumed: 15 days sit above the upper limit, only 5 below my target. June 10th says 380 calories eaten and a deficit of 2,445.

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The reality check saves the balance anyway. From June 15th to July 28th it comes to 6.45 kg, so 1.03 kg per week. At 118 to 124 kg that is 0.85 percent, comfortably inside the rule. My average is 1,181 kcal, which lands in the green band. What is missing is consistency. The spread runs from minus 946 to plus 2,445.

The bar up top shows exactly that now. Hover a day and the marker jumps to that day's deficit and writes underneath why the colour is what it is. Move the mouse away and it goes back to the 60 day average.

One rule went straight back out

I had also built in a lower bound: eat less than 1,500 kcal and the day turns yellow, whatever the deficit says. Sounds sensible, but it says the same thing twice. At an expenditure of 2,500, eating 1,400 calories automatically produces a deficit of 1,100, and past 1,295 the upper limit kicks in anyway. The rule never caught anything the other one had not caught already. Four days jumped from yellow to green after I removed it, and rightly so.

All the thresholds now live in a single class. Before that, cell colour, legend and tooltip could have drifted apart independently, which is exactly how this started: a legend proudly claiming "deficit ≥ 700" while the settings said 500.